12.5:1 compression on pump gas???

[Project69]

I remember reading through a magazine, not sure which one it was, but it said it was possible to run 12.5:1 Compression on pump gas. It gave information about Cylinder head combustion chamber shape, it explained about what quench is, the total cc's above the piston at TDC etc. I lost the Article but if anyone has information on this that would be really helpfull

Thanks.

[Project69]

Never mind is 12:1 compression, and i found the article here.

http://www.popularhotrodding.com/tech/0606phr_understanding_compression_ratio/

Any insight on this theory? Is it actually possible?

I also see that David Vizard is the Author of this theory so it must be true then?

[silver69camaro]

It's absolutely possible. It all depends on how much cylinder pressure is bleed off by the intake valve. Big cams = lots of pressure bleed.

Having all the details correct, like Vizard points out, can make or break the scenario as well.

Or, use direct injection. IIRC, Audi was running 12:1 on their 3.XL V6. And that's a production engine.

[6'9"Witha69]

I had a buddy with 14:1 in a 302 sbc '68 Camaro. HUGE cam really bled off pressure. Loped like an sob as well.

[68sixspeed]

Well, I'm up there on the cam end of things (.700 lift, 262/268 duration @ .050), and at 11:1, I think it's close to maxed with 93 octane. The heads were massaged too on top of the cnc work- no sharp edges, etc. At times I have to add some booster to keep it from diesel-ing on shutoff, etc.

For some of these pump gas shootout motors with high compression - they are ok at WOT with the propper tune, but I wonder how they are under real-world conditions? (i.e. part throttle loads, shutting off without diesel-ing, etc.) just my 2cents

[Project69]

So im guessing that inorder to run high compression with 93 pump gas, you'll need a huge cam to bleed off cylinder pressure. If thats the case would there be a way to tell how much pressure there will be with a given combonation of parts? Im trying to rebuild my 350 to the best that I possibly can, and if i can some how fully understand this i bet it would be one hell of a motor.

So what heads, and cam would you use on a 357 sbc with 12:1 compression to run on 93 octane?

[badbu68]

I think it's very inefficient to run a bunch of compression and then bleed it off with a cam or retard the timing. I'd want to use an appropiate amount of compression with an appropriate cam for the octane you're planning on using. For a street vehicle, it means you'll have to run a big stall or bring the revs up for it to start going. Just seems like a waste to me.

68sixspeed: with that cam and what I assume aluminum heads, even with the appropiate timing (34-6), as long as you have the amount of added timing by vacuum limited, I think you'd be fine with 93 especially in a lite camaro.

[Project69]

So there would be no benefit from running a high compression cam on pump gas with a huge cam?

[68sixspeed]

badbu68 - thanks- yes, aluminum heads, even aluminum block (big old heat sink!); and about 3500 miles on it so far, no vacuum advance, I've had mixed results with that on aggressive motors, so go without. If you think about it, the diesel-ing is not timing related- that is on shut-down, it is pre-igniting on poor fuel and it keeps the motor running.

[MarkM66]

So there would be no benefit from running a high compression cam on pump gas with a huge cam?

For a controlled dyno only engine. Yes.

For a real world, multiple conditions in car engine. Not worth the gamble IMO.

[wendell]

Folks are refering you to the concept of Dynamic Compresion Ratio. If your valvles closed at BDC, your cylinder presure would be wholely determined by your compression ratio. In reality the intake valve closes some time after BDC. The formula for DCR attempts to acount for this. If you subscribe to this theory, you're looking to find a combination of static compression and cam duration that yeilds around 8.2:1 DCR for pump 93. A google search should give you all the information you'd ever want.

My $0.02, don't ask the internet for head and cam advise. Especially with out pertinant details like: weight, rear end gear, transmission, torque converter, intended use, AL or steel.... Build a relationship with a professional engine builder and ask them.

[hotrdblder]

11-1 max on a steel block, alum header motor, 11.5-1 with all alum are starting point numbers

[ITLBTU]

I used to have a dieseling issue on an old engine that had high compression. I found a throttle solenoid that I think was used from the factory to up the idle speed when the AC kicked on. I had it set to idle speed when energized, but when the ign. was shut off it closed the carb. Worked great.

[68Formula]

If you're going that high you're going to want to have the intake and exhaust valves thermal coated as well. I'd all also consider an oil cooler.

[Project69]

11-1 max on a steel block, alum header motor, 11.5-1 with all alum are starting point numbers

Would i need a huge cam, to bleed of some compression or would i be safe without one? And by huge cam what are they talking about? Long duration, Max lift or both?

[68sixspeed]

I used to have a dieseling issue on an old engine that had high compression. I found a throttle solenoid that I think was used from the factory to up the idle speed when the AC kicked on. I had it set to idle speed when energized, but when the ign. was shut off it closed the carb. Worked great.

That's a very cool idea-- I think I have the holley kit around too - I was going to use it as a high idle for warming the car up.

Rob- on the cam front; for ref- the 358 I have in the for sale area, steel block, flat top pistons w/2 valve reliefs (coated), aluminum heads, 10.4:1 compression, also ran well on pump 93 - occasionally dieseled on shutdown on poor fuel too, probably acted about the same as 11:1 on the aluminum motor I now have (same basic cam spec, I think the LSA is 112 vs 108) 260/268 duration, .634 lift on the 358.

[hotrdblder]

get a dcr calxculator and figure head cc,head gasket cc, compression ratio, and cam specs, like wendeall said 8.1-1 dynamic compression is maqx on pump gas, which basically equates to 11-1 with iron block,alum head(with 10.8-1 being better max, or 11.5-1 all alum,

[MonzaRacer]

Ok guys forget the static compression and go for the dynamic cranking compression.
If you get an engine over 200 psi its gonna need some serious octane.
Now the best idea is to use a decent compression for the engine design.
Figure old style sbc w/iron heads (ie stockers modified) you will push it with high 9s, aluminums you can push as far as 11 to 1 if you choose the cam right.
LSx engines are more tollerant.
For best power production, I prefer to massage a set of medium sized heads, keep my valves moderate, and be frugal with cam selection as too much will hamper the port velocity.
I took a set of 991 truck heads and rebuilt them as 194/150, I throated the bowls under the valves, I raised the guide height 5/32 and throated righ to that.My throats were the same size as the inside diameter of the valve face.
This engine had a split lift/split duration cam that was computer friendly, as it was designed by John Lingenfelter for the Accell SuperRam FI kit.
I built this engien as a 355 with flat tops down in the hole 018, steel shim head gaskets 015 and the chambers were something like 78 or 79 cc and this thing was MEAN and it would only run on 94 Sunoco Ultra or 93 Super.
I ran a 600 AFB, old Edelbrock Scorpion intake, HEI, HOOKER Monza Headers, 2 1/2 pipes to rear axle and a set of Flowtech Afterburners.
This BIOTCH ran and hard, I used a TCI saturday Night special converter in a TCI th350, and 3.42 rear gears.
I prefer to keep my street engines in the 180 to 190 range or you have knock issues, generally.
Now that engine had some AWESOME prot velocity,,, a friend of mine had me do another set of those heads, and he was getting some serious port velocity from them and told me that it was within the 10 percent or so of raching the Hemholts resonance point, but he never had my intake and I bet it would have hit it.
That is where the speed of the air coming in has reached the speed at which the mass of the air molecules are going so fast as to liken them to a car going over a long tall steep hill, thier weight actually has them accelrating to a degree.
I wish I had those heads back now.
Lee

[Project69]

Yea ive heard something about if you keep the cranking pressure around 180-185 your safe with your fuel.


Say i want to run 11:1 or a little more compression with my iron head small block, could i get away with using 93 octane if i have a big enough cam to bleed of compression?

[wendell]

Read the posts above and start researching DRC. There's more to it than static compression and cam duration. Take inititive and figure it out.

[68sixspeed]

Rob- as a general answer, probably not for street use, or at least it would be on the edge- unless you had a very well thought our system. Especially given your location - low altitude and humid (I'd asume based on Florida!) Back it down to 10:1-10.5:1 IMO - the 1.5% in hp you are giving up by the 1/2 pt of compression are not worth risking bigger problems if you plan on driving this a bunch. - Dan

[Project69]

thanks 68 you helped out alot.

[pdq67]

Mr. Ray T. Bohacz wrote two back to back tech articles years ago for onna the mag's about a Trade School's Shop Class that took a new 502 and installed the late Mr. Fueling's aluminumTorque Truck heads that had about 80 or so cc peanut shaped, centrally located sparkplug, almost 100 percent flat little-bitty valved chambers and dinky ports in them and the kids got it to run on 87 octane gasoline using a SMALL cam!! Mr. Bohacz said that they thought that a cam as big as a 230 at .050" lift could be used fine..

Engine had right at 12.1 to 1 CR. and created 660 T at like 3500 rpm!! The kids were shooting for 700 T on 87 octane!!

The article went on to say that Mr. Fueling's heads were sized right for a 454 which is what he made them for and that they were almost too small for the 502!! Mr. Fueling created his heads to be used on stock, 454 P/U engines and that they raised T right at 100 pound foot at 3400 rpm!!! AND that they ARE NOT race heads at all... WORK MOTOR heads..

The gist of the story is that you need to use as small a chamber that you can buy/create along w/ true flat-top notched pistons and long rods so that you can create a very fast-burn chamber so that detonation can't raise it's ugly head!!

11 to 1 w/ cast-iron heads is pretty easy if you really get your combination rght and I'm talking about using 87 octane and a MILD torque RV-type cam, not a big-timed, bleed-down, race cam!!

This stuff fascinate's the heck out of me b/c it is a way of either making MORE power OR using less fuel to increase my gas mileage so think about this..

I figure that the Jaguar "May" chambered head as well as the early MOPAR 318 poly chambered head, the real early closed chamber BB head and the 50 cc SB wedge head can be used to do this EASY if you get the combination right!!

I'd love to do two things!! First, put a set of 409 "W" engine heads on a peanut dished pistoned 454 engine to prove Mr. Fuelings theories!

And second, install a complete LS- top-end on the old L-48 350 cast-iron block just to prove that GM obsoleted the GREATEST SB engine made when they went to the newer LS- design...

pdq67

[Project69]

Very useful information thanks.

[jerome]

http://www.snowperformance.net/product.php?pk=7

something like this might help

[rocketman]

PHR had a good article on this awhile back, I have run acouple high comp motors on pg, but it's a pain, by the time it's detuned it's lazy and not worth it. I always planned 150-200 mile round trips on fuel, or I found to 2 bottles of booster in pg is close to race fuel.

[ITLBTU]

According to an online compression program I'm running around 12.3:1. I do mix 5 gal of 110 race fuel per tank and have my timiing set at 38 deg of total advance. I have a decent cam so I'm sure some is bled off at low RPM, but I have around 235 psi dynamic compression pressure. I need the race gas for it not to ping though.

[badbu68]

badbu68 - thanks- yes, aluminum heads, even aluminum block (big old heat sink!); and about 3500 miles on it so far, no vacuum advance, I've had mixed results with that on aggressive motors, so go without. If you think about it, the diesel-ing is not timing related- that is on shut-down, it is pre-igniting on poor fuel and it keeps the motor running.

I'm wondering then how your cam was degreed. Cause something doesn't seem right about that.

[68sixspeed]

Straight up according to comp's cam card; keep in mind it's a carb'd motor that idles around 1200rpm; there is a lot of fuel at idle, and once the gas sits a couple weeks or you get a bad tank, it will diesel; if it were fuel injected - the fuel supply is just cut off, one several reason LS motors can get away with a 11:1 on lower octane. (combustion chamber temps, other things also play in.)

Also worth noting though, I've never had problems with detonation under load; it's more of a side topic on lots of compression and dieseling.

[LS6 Tommy]

Rob- as a general answer, probably not for street use, or at least it would be on the edge- unless you had a very well thought our system. Especially given your location - low altitude and humid (I'd asume based on Florida!) Back it down to 10:1-10.5:1 IMO - the 1.5% in hp you are giving up by the 1/2 pt of compression are not worth risking bigger problems if you plan on driving this a bunch. - Dan

I agree. A rough rule of thumb is dropping 1 full point of compression is worth somewhere just shy of 4% loss in horsepower. People (especially some "Old Schoolers" or those with magazine ad "educations") always seem to equate high compression with high horsepower. On the flip side, just adding 1 point of compression to a 550 hp engine isn't going to be an instant increase of 22 hp without the combo being optimized for that higher compression ratio.

Tommy

[pdq67]

TTT..

Anybody ever find a link to Mr. Ray T. Bohacz's two back to back mag. tech article's???

Excellent info on this!!

And a link to Mr. Fuelings heads??

pdq67

[Lowend]

I gotta stir the pot a little
2007 Audi RS4 Road Test
The 4.2-liter V-8 is completely new. Direct fuel injection, which Audi calls FSI, squirts fuel into each combustion chamber. More accurate fuel metering, plus the cooling effect of the directly injected fuel, enabled Audi engineers to raise the engine’s compression ratio to 12.5 to 1 . Audi also enabled this engine to have an 8,250-rpm maximum redline, which is quite high for a production V-8. Audi said the RS 4 accelerates to 60 miles per hour in 4.8 seconds and has an electronically limited top track speed of 155 mph.

[Lowend]

It passes smog, runs on pump gas, and has a warranty!
https://static1.pt-content.com/images/pt/2007/12/Enginemd-1.jpg

[SDMAN]

Let me get this straight. You add compression to gain power. The result of adding the compression is higher cylinder pressures. Since the fuel you want to use wont support the higher cylinder pressures, you add way to much camshaft to bleed the pressure off (down low...eventually, as the RPM's increase into the cams power range, the cylinder pressures will rise and youre back to the original problem). And, with the huge cam, the motor is a PIG down low, where you spend 95% of your driving.

I dont get it? Makes no sense. Unless all youre really after is a car to idle around the car show in that sounds tuff, but really isnt.

[Project69]

Well thats why they make stalls. So you leave at the bottom of you range. Besides i was just wondering if was possible.

[MonzaRacer]

The big problem with Audis are they are junk, ex boss's duaghter had aA4 Quatro and it lost its 3rd trans while she owned it.
$4200 for a used trans and $6900 for reman. Forget it.
Besides the stupid car has had so many Audi issues it is pathetic.
Now if you have several million dollars to fund a design group to "figure it ou" go for the high compression engine on 87 octane.
too bad its unfeasible for anything over debate.
A lot people keep tryig to make those wierd combos work.
when you can take an older 454 with peanut port oval port heads and make 660 hp why worry about it.
Take same engine(short block) and add some well preped AFR aluminum heads and a decent but not to large cam and make even more power.
I put an AFR headed 427 together and we go it to turn 640 hp and 698 lb ft of torque,,, it took 3 trys to get a converter to hold up behind it.
The engine ran on 89 octane and was running 11.8 to one compression.
The big trick in any engine is the dynamic compression, thats the cylinder pressure created buy the engine. Too high too fast and you will get preignition. Thats uncontrolled premature ignition of the air/fuel mixture.
Now if you get a hot spot that will cause fuel to ignite worng and the noise you hear there is detonation.
Either are destructive.
The best way to build power and torque is to keep your port volumes in reason and your port velocities can be made to force extra mixture into your combustion chamber.
If you read up on Hemholdts Resonance you can understand the theory.
Getting mixture velocities and you then also get mixture motion, this is the same technology use on Vortec heads and the new LSx engines.
Much more productive and useful.
Fuelings heads are good but quite pricey for the power produced.

[Fuelie Fan]

I don't think either of you understand what a Helmholtz resonance is, much less how to spell it. Any volume can act as a helmholtz resonator given the proper forcing function. Also, it has no relevance to average port velocity WHATSOEVER.


a friend of mine had me do another set of those heads, and he was getting some serious port velocity from them and told me that it was within the 10 percent or so of raching the Hemholts resonance point, but he never had my intake and I bet it would have hit it.
That is where the speed of the air coming in has reached the speed at which the mass of the air molecules are going so fast as to liken them to a car going over a long tall steep hill, thier weight actually has them accelrating to a degree.
I wish I had those heads back now.
Lee

[MonzaRacer]

Hey fulie fan Just because I cant spell something doesnt mean what I am try to point out wrong.
IF you create a port that allows the volume of air and fuel to accelerate and all factors are right it can allow the port charge to actually pack the cylinder harder.
I built a set of heads and teamed it up with a reasonable sized intake, not too large or small. and I found the perfect cam it seems. while the engine had 78cc heads, 030 pistons,018"in the hole, 015" steel shim head gaskets. The engine came in the 8.5 range if i remember but it would run a dynamic cylinder pressure of 235 and woul only run on 94 /93 octane.
We had afriend who wanted to try to build similar setup, he had cam ground same as mine, built different heads(too large of ports) and his never made anything near what mine did.
WE had a portable flow velocity probe in the intake (ran through a custom base plate under carb) int each port and the figures showed that my set up was getting up over the 100% VE and we had some strange readings from another probe and the guy doing the figureing on some of the data told me I had some how stumbled on a near perfect setup and the resonate frequency, velocities and everything. It was probably the best running engine I ever scratch built for little dollars.
I Always wondered if the "noise" under hood was something going wrong but it was the resonate frequency I was hearing.
Here is one factor that I never could understand, the intake bolts would back out if I drove it hard, till I used aircraft grade locktite on them.
The responce I got for my issues to the bolts backing out AFTER we started testing the setup was the term Helmholtz resonance.
Ifthe guy who was helping us test it and decipher the information used a wrong term so be it.
BUT I do know that if you desgn/build a proper port you DO get a "supercharger effect" from the velocity accerlerating to a speed where the inertia of the charge basicly get out of control as I was told.
Similar stock parts are now sold using charge velocity taloring and even use it to induce mixture motion.
If I had my choice I would prefer to use a well designed port that will give you enough fill with mixture motion over trying to "crutch" the high compression/87octane design.
Properly done, and using a properly dialed in EGR setup would allow a person to keep something like my old engine from "rattling".
So ANYONE wanna come after me better disprove what I have already build and drove.

[Fuelie Fan]

My points are:

1) EVERY intake system has a resonant frequency. Actually, it has a series of them.

2) This resonant frequency is a product of the entire system: Heads, runners, plenum, and (if attached) any pre-throttle intake ducting

So, the idea that just tweaking a head port will turn your engine into the magic tuning fork of power is a little far fetched. You did not DRASTICALLY alter the port length, port volume, or average cross sectional area enough to change tuning frequency.

PLEASE READ and don't get me wrong here: The difference between a good port job and and a bad port job is NIGHT AND DAY. I am not discounting that you may have done excellent porting on that engine and made awesome power. I am also not discounting the high importance of pressure wave tuning or cam selection. I do agree, in fact, that your cam selection as mentioned in your second post (you didn't bring up that point in your first) is a huge component as well. In fact, it is the matching of cam to intake that allows you take advantage of the pressure waves in your intake. So, if anything, pat yourself on the back for cam choice. My overall point is that it is your SYSTEM that made for good power.

I also will say that I agree with your next to last statement regarding the "crutch" approach to trying to run huge compression.

[pdq67]

Back again.

Try here for some interesting reading on the Miller Cycle Engine!

http://en.wikipedia.org/wiki/Miller_cycle

Mazda has had one for a while.

And Smokey was working on something like this years and years ago w/ his hot-air engine!!

Anybody catch the latest copy of CC's article on stroking a 409 "W" engine. You will see what I mean about a flat-chambered BB head that is a whole bunch like Mr. Fuelings chamber except he uses peanut dished pistons in a 454 vs the 16 degree deck slant the 409 uses.

pdq67

[Project69]

So i can get away with 11:1 compression with aluminum 64cc heads if i built a motor?

[SatisTraction]

I built a 12.5:1 438w for my old mustang. tonight ithe new owner ran a 9.63 on motor on 93 octane pump gas. so it can be done. now if the tank would have been full of 110 he would have bumped the timing and ran some 9.30's

[Grandpa Ronsy]

Hey Lowend,
All that Audi high tech stuff is fine until the repairs come up. We have a 6 year old A4 4 cyl all wheel drive in our shop at the moment that has a transmission fault when it's hot. It has a C.V.T.with the computer in the oil pan and here in Australia there are no parts available. Audi's answer is a replacement unit at $19k plus fitting and it has expensive oil too. Cant see why the engine would be any different.(Ouch) :smashcomp

Long live build yourself engine combos. It is affordable fun and even if the Audi wins they dont have the style of the old muscle cars.

Merry Christmas car dudes and I hope to have the old 68 camaro going in '08
Grandpa Ronsy

[Grandpa Ronsy]

Lowend,
I forgot to add
The mileage indicated was 137.000k's which is about 80.000miles near enough. The average guy in our country probably afford to replace/recondition the engine if it lost coolant!!

Anyway loves you all

[funcars]

Another important consideration besides the cam timing is the combustion chamber design, both the head and in the piston. Some of the more sophisticated head designs have a much lower inital timing requirement and these would be a good place to start since they need less timing lead to begin with. I have some CHI heads for my Ford motor that require less advance (29 is absolute max) and help me to run more CR.

It's hard to find the perfect combination that does everything great and 12.5 CR with the target rpm range and gearing you are willing to run might be a challenge.



Good luck

[monzilla]

back in the day, i ran a destroked 327 (302, just gotta love that engine) with 12.5 to one compression, a small cam (.480 lift), 192 casting heads, and an old edelbrock tunnel ram that looked like a shoebox on amoco 93 day in, day out with never a bit of trouble. it was in a 75 monza so it bay have helped being in a reletively light car, but i always attributed it to a smaller displacement engine. always seemed to me that any of the big blocks i ran were more finicky about compression and cubic inches.
just my 2 cents
good luck and happy building
mike d

[SatisTraction]

here is a little vid of the 438 red coupe making a mid 9 second pass on 93 octane and 12.5:1 compression.

https://static1.pt-content.com/images/pt/2007/12/th_TrackDayDec162007010-1.jpg (http://s219.photobucket.com/albums/cc307/camoyota86/?action=view&current=TrackDayDec162007010.flv)

[MonzaRacer]

With aluminum heads you can get away with 1 to 1.5 points higher compression.
I have found that using Evan NPG+/NPG-R coolant can let it run even better with lower octane.
BUT the big ticket for which octane to run is the dynamic compression (take a good compression tester, remove the check valve that makes it hold pressure, then screw it in and start the engine and watch the needle the high pressure is the one you have to tun for. My rules have been for the last 15 yrs is 190psi and lower 91/92/93/ anything over 200psi you better have 93 and octane boost, 94 Octane Sunoco Ultra or 100 octane "race" unleaded.
My engine I was bragging about had a cam that my buddy had ,it was an old hyd split lift/split duration designed by Lingenfelter for the Accel Super Ram, i used an older Edelbrock Scorpion intake, Carter 600 AFB, and old 991 truck heads, I rebuilt them with 1.94 intakes and 150 ex and throated the ports to the inside of the valve face(s) both intake and exhaust and I have always raised guides (spotted them) up 5/32(fun thing I do on a head machine used for installing guides and seats, I would zero on the stock guide then use the cutter stop and a 5/32 drill bit nad spotted the guide in the port.
Trust me I have done hundreds of heads this way to clean up the flow of stock heads. and so far have never had any issues with excessive guide wear.
honestly the rought stone I used I contoured on the seat grinding stone truer and just contoured them to a smooth radius.
The fact that the engine just plain made torque like no other throw together engine (it was from my 71 Monte that had broke a cam and damaged 2 rods/pistons. 2 new pistons (cast) new molly rings and some new rod bearings, Oil pump out of corner with new drive and pickup, and new timing chain as at one time I would get tripple key way timing sets from autozone cheap.
With Monza headers ,2 1/2 " duals and Flowtech Afterburner mufflers it all just worked.
sold it with out the intake,carb,headers. New owner used a eppoxid Performer RPM air gap and a 750 holley I set up and it went into his Gbody and was teamed with same trans/converter I had TCI/Sat SPCL and 373a posi and it still rips from what I heard.
The real trick is cooling, no dome to interupt mixture motion, and some quench area to induce mixture motion if ports dont do enough.
Lots of factors are critical and if you dont have dyno with knock microphones/sensors and some smart tuners you can trash an engine on one of those high compression low octane setup very quickly and never rune Hypertech pistons in something like this, Forged, ,heck nitrous spec pistons are the strongest.

[pdq67]

I think some of the guys are realizing that hypers can turn ta aluminum gravel under detonation!

pdq67

[65protourgto]

This whole compression thinng brings up motorcycles for me. My old triumph daytona 650 had 12.65 to 1 compression and the honda cbr600rr = 13 to 1 , etc


I dont even want to go into explaining compression and theory. I do advise that if your really wanting to know pick up a race engie building book at borders. I didn't go that route, I just read a hell of a lot off the net and built my own engine with some of the top guys in northern california. I urge all of you that are interested to just ask questions.

[steinepstein]

This is a great piece...2 things.
1. I recall an article by hot rod or car craft on rod ratios on compression, basically they were getting 12:1 compression with a mild cam on 87 pump gas.
2. I went to school for mech eng and had a professor named Dean Hill that was a famous hot rodder in the 60s, anyway, he had a basically stock engine that was running 16:1 compression on 87 gas. Of course the manifold was about 5 feet tall and had to do something with the atomization of fuel. That was about 8-10 years ago, you would think some people have advanced on this.

[BulldawgMusclecars]

I'm running 12.3:1 in my 97 Camaro SS (run 93 octane), and it works fine...of course, it has an LT1 (reverse cooled),ported factory heads, and a really good cooling system. I'm running 236/242 duration. Nothing unusual for an LT1, and honestly one of their few redeeming factors now that LSx parts have become so plentiful, and come down so much.

[MonzaRacer]

Two of the tricks to get high compression and low octane to live together is mixture motion(ie a more homogenous (re even) mixture and also peak cylinder pressures
If you get to high cylinder pressure it will knock, kill the cyl pressure down to the 180-190,, maybe 200psi if you use good (ie hi octane) the engine willive, aluminum heads loose heat much faster and help so you may even get to push it.
I just havent seen that much in an increase in engine out put by the compression increase so drastic. If you build it right and keep it properly cooled, maybe even add on a water injection (just run winshield washer solvent as the plain blue stuff is water and methanol) for when you cant get good fuel and drive.
Honestly I see so many people who want to run garbage a$$ crap 87 octane and just F--K up every thing trying to "dial" it in.
Got a fella who has a 72 Continental with a factory 460/4bbl made to run on 91 LEADED which comes out to about a 93 or 94 octane unleaded.
Idiot keeps letting other people work on his cars and they took pefectly fine factory carb off engine, (trying to diag a dead plug I think) and put on a 600 Edelbrock electric choke. The Edelbrock works fine, but the factory carb was rated BY FORD at 600 CFM, but not by the same specs as aftermarket carbs and it had a (by aftermarket specs) a 735cfm carb.
But they had the tranny kick down bent, the throttle cable wont fit straight(had to mod the cable bracket more) lots of stupid stuff.
Oh did get to change all the freeze plugs IN CAR too.
I try to make people understand 1 point will make in the range of 4% to 6% but isnt worth the hassle and expense.
If you have a reasonable cranking compression dont raise it, if its low (like below 180psi to 190 psi) try a thinner head gasket or advance the cam.
Peak torque is made best at the highest cam advance without going the other way or getting it too far off from the grind numbers.
Any cam can be advanced for best cranking compression number and will produce the best peak torque.
Aluminum heads can add 1 to 1.5 points in the compression dept. with no bad effects.
Use the Evans Cooling NPG+ or NPGR and you can gain a little more leeway.
Iron heads hold heat more and wont take the numbers.
The smaller the combustion chamber and no dome makes a better more detonation resistant end product, add in some good mixture motion and you will have a great running hard to beat detonation resistant combo.
Oh and you may never hear any of the knocks and still break things.

[pdq67]

Anybody have any real world experience using Singh's grooved head theory?

http://somender-singh.com/content/view/7/31/

I know there's somebody that is doing something about like it, only to the piston top. I think they dimple it and it's top is also swirl ramped, but I can't find where they are made??

I even handled one out at SEMA, the year I went.

pdq67

[My427stang]

DCR is one thing, I use it, and I run a 489 inch FE with .048 quench, 8.33 DCR, and 10.7:1 static compression ratio

Its happy as a clam on premium and will even run mid grade if I am just cruising.

However, remember that as RPM increases, the more overlap you have, the more efficient the overlap period gets at pulling in more a/f mixture.

That means that despite a low DCR, at RPM cyl pressure still skyrockets

Bottom line, quench distance and a turbulent chamber are great for detonation resistance, go for it, but you cant just go with a monster cam and run 12+:1 compression, eventually it turns into a pig down low, with unmanageable cylinder pressure and a timing curve forced to be very slow. (Doesnt sound too impressive huh)

In other words, tighten up that quench and use a turbulent, small chamber with some sort of reverse chamber piston, thats a good thing, but if the cam choice doesnt seem to match, its probably wrong. Dont pick a cam that kills compression, pick one that matches the RPM range and then pick a compression ratio to match

[nastee383]

I have an 11:1 383 sbc in my S15 Jimmy. It has aluminum heads(65cc), 242/[email protected] cam, 8.19 DCR, .042 quench (.039 gasket+.003 deck). I use 93 octane and I've had no problems at all even in the heat of the Florida Summer.

[Mkelcy]

I have an 11:1 383 sbc in my S15 Jimmy. It has aluminum heads(65cc), 242/[email protected] cam, 8.19 DCR, .042 quench (.039 gasket+.003 deck). I use 93 octane and I've had no problems at all even in the heat of the Florida Summer.

Pretty much the same engine in my '68 Camaro: 11:1 383, 232/242 @ 0.050", 0.040 quench, Dart Pro Ones, 6" rods, about 8.2 DCR running just fine on California's 91 octane.

That said, there seemed to be a lot of mis-information in this thread.

[jerome]

me 3
383 SBC
11:1 pistons
AFR 75cc 195's
236° / 242° @ 0.05 hydraulic roller

hoping to run on 89 octane, will use water/methanol injection if necessary. engine has never been fired though.