12.5:1 compression on pump gas???

[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!

[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