Port Volume and Chamber Volume (from old site)

toofun
Registered User
Posts: 264
(6/4/04 8:23 am)
Reply PORT VOLUME? CHAMBER VOLUME?
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Ok,

I am trying to understand some specs on heads before making a choice. I see a lot of talk about port volume and chamber volume. What do these numbers mean and how do they affect the characteristics of the heads? Bigger is not always better correct? I see specs that say that port volumes of 215 and up are better for all out street performance and race applications(3500 rpms and up) while 190 port volumes are better for street manners and low to mid range torque. Also there are some head comparisons out there that measure all of the specs with the TAIL PIPE FLOW in cfm's. With all other parts being equal at a certain lift, wouldnt this ultimately determine how well the components are working? Any light that can be shed to better educate me would be greatly appreciated.

Thanks
Mark

XcYZ
Registered User
Posts: 1202
(6/4/04 10:55 am)
Reply
Re: PORT VOLUME? CHAMBER VOLUME?
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Mark, I'll throw a little out here to get started, but heads are only part of the whole equation. Everything must work together to make the system reach full potential. There are a lot of dynamics involved.

Chamber volume is simply the area of the head that houses the valves. Larger chamber volume, the lower the compression.

Port volume in cc's is the intake runner size. The problem with running large intake runners is that you lose port velocity. When port velocity goes does, the cylinder doesn't get filled as well, and torque goes down. Torque is representative of cylinder pressure. Peak torque is where the cylinder is filled the most effectively. Another problem with large intake runners is that fuel can drop out of the intake charge and puddle in the runners. There are also harmonics involved, port reversions, just a ton of dynamics. Engineers make a career out of this very subject.

This is just an simple overview. I'm sure others that know a lot more than me will chime in.
Scott
My 69
Lateral-g.net


toofun
Registered User
Posts: 266
(6/5/04 7:30 am)
Reply thanks so....
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If larger intake runners hurt torque and you are trying to build something that will be more torque orientated, would it be safe to say that you would want to stay with a smaller intake runner and smaller chamber size?

BADVELLE
Registered User
Posts: 13
(6/6/04 1:08 pm)
Reply Re: thanks so....
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I believe Scott made a very good explaination of this subject. There are trade-offs regarding your selection, but if you know what application you are shooting for, then I would say that you will want to stay with a shorter/smaller runner size and smaller chamber size. Now, your chamber size could be larger, then in order for you to get that number down, then you could use a larger dome piston. If you go this route, then the piston-valve clearance becomes even that much more critical. Just my thoughts.... Later.

JustBringIt
Registered User
Posts: 287
(6/7/04 8:04 am)
Reply How many cubes?
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XcYZ is correct. I will add a little. How many cubes is something important to know, for example, 215s are pretty big for a 355, but just right for a 421, 427 or 434 street motor with a big hydraulic cam. Cams work the same way, what is huge for a 355, is only big for a 434.
tell us how many cubes, and what you are trying to achieve and we can help.

Frank

toofun
Registered User
Posts: 270
(6/7/04 10:52 am)
Reply GOODWRENCH 350
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Thanks for the input. I am running a bone stock gm goodwrench 350 with dog dish pistons and all. I read an article a while ago on how chevy high performance used bolt on parts to make a goodwrench engine run over 430 hp with just out of the box bolt on parts. I dont want to race the car since it is a convertible and it runs excellent. Just want some extra umph in it. I have a chance to buy a set of dart iron eagle heads wth 215 intake runners complete brand new for around 600 bucks, but dont want to spend the money if they are not going to yield me some favorable results that justify the expense. Other options I was considering were the trick flow 23 degree heads as used in the CHP article or the AFR 190 heads. I dont want to tear into the lower end of the motor just want some bolt ons to boost me up. One note, I LOVE TORQUE!! Always been a big fan of the low to mid torque since it is something you can feel.

JustBringIt
Registered User
Posts: 288
(6/7/04 4:06 pm)
Reply AFRs would be perfect
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I love the AFRs. I have not used the trick Flows, but do not hear much great stuff. Dart Pro 1s come in 200s, that would work great also, I did some real world back to back testing with some 200CC Pro 1s replacing some good double humps. Edelbrock Performers are a budget choice in aluminum, but my least favorite. Some 200CC Pro 1s with 2.02 / 1.60 valves and 64cc or so chambers would ease the compression up, I would get around 10 to 1 if possible. Check E bay for Pro 1s.
Iron eagles are basically iron Pro 1s, but the 215 Iron Eagles would make your car a stone under 4000RPM, and you would really need to see 7000RPMs to see the benefit of these heads.

Frank

toofun
Registered User
Posts: 272
(6/10/04 3:47 am)
Reply yea know what you mean
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I know what you mean about the 215 iron eagles. I had a set on a 408 in my last car with a big full roller cam. Sounded hairy as hell but you couldnt get the car to move out of its own way unless you stalled it over 3500 rpms, but once it did, wow it would take you for one hell of a ride. I just dont like high revving motors. Hearing an engine scream at 7500 rpms just makes my blood curl. Inevitable at some point to hear that god aweful kabooming of the motor. I like TORQUE, Right down low where you can feel it in the seat of your pants. Think that is why I have always been partial to big blocks. Even a mild built big block has gobs of torque down low.

streetfytr68
Registered User
Posts: 1029
(6/10/04 5:39 am)
Reply Know it all pain in the Arse
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A little more info.
First I put 11 years in at a prominent aftermarket cyl head manufacturer, so anyone who disagrees with me can kiss my hairy greek...well you know. :rotfl:

Everything said so far is almost entirely correct so I am--for the most part--just filling in a few details and misconceptions.

First some lingo correction:
"Port" is a two diemnsional value: length times width. Intake gaskets intake manifolds and cylinder heads all have ports but the gaskets do not have runners. Runners define the three dimensional tracts that connect the intake and exhaust ports to the valve seats. Just want to clarify that because I will be using the term "runner" not "port" from here on out.
Everything said so far about size is essentially true. But keep in mind that runner shape is just as important. You had better believe that Warren Johnson has engineered significant velocity into his giant 400cc-plus runners.

Those AFR 190's have higher flow AND velocity than Edelbrock Performer RPMS which have 170cc intake runners. So smaller does not automatically mean more velocity or more torque. The manufacturers who only make small heads would like you to believe otherwise. World, Brodix, Dart, AFR all offer a wide range of cylinder heads and will back up my logic.

Let's keep going. Hype about fuel coming out of suspension in cylinder heads is largely just that: hype (Sorry Scott) The logic is mistakenly carried over from intake manifold science. Most of that breakdown occurs in the intake manifold. Intakes and heads are two very different animals. Cylinder heads have pistons sucking directly on one end. Furthermore, intake manifolds have to deal with a sometimes 90 degree change in direction of the fuel air mixture. And of course carbureted intake manifolds have runners that can be twice as long as cylinder head runners.
What this means is that a larger cylinder head, say 190 to 200cc, may not be such a bad thing depending on your application. As Frank has stated, a 215 on an essentially stock 355 is crossing the line though.
Chambers: What has been stated with chamber size is 100% accurate. All other things equal, smaller chambers will yield higher compression than larger chambers. But again, when shopping--look for chamber shape. The design of the chamber is critical. You want to get the a/f in there, burn it efficiently, and push it out--all as fast as possible. So look for heads with nice tight "fast burn" shapes. The old school heads with big open "D" shaped chambers will not work as well as the shapes that look light hearts or kidney beans. Look for heads that locate the spark plugs close to the valves--more towards the center of the chamber and pointed towards the exhaust valve. You can now go back to everyone's websites and compare chamber shapes.

Toofun,
Will you eventually be modifying your short block? Will you eventually slide a different short under your new heads? If so, get the AFR 190's and tune them down with the right intake and headers. That's another thing about "size isn't everything". Same motor with 190's will behave differently with "one-step-up" intake/headers than it will with "one-step-down" intake/headers. You can move the power around the rpm range by tuning the tract. Then, you can further tune it with cam and carb selection.
If this engine will never be torn into--and torque/budget are king, you CAN go with the right small heads (170cc) such as GM's Vortecs-- a very modern efficient (and cheap) design or World Products 170cc S/R Torquer. The World design is not as efficient and the price is not as low. I used to work for World so my loyalties are there--but I would suggest the Vortecs--especially if you can score a set of fast burns (better chamber design).

And Trick Flow? Trick Flow is owned by a mail order company. When I go to the supermarket, I get the spaghetti sauce with the italian guy's name on the jar--not the one with the supermarket's private label name on the jar. Maybe it's the same with cylinder heads? :lmao:
/Steevo

www.lateral-g.net

toofun
Registered User
Posts: 273
(6/10/04 11:34 am)
Reply Thanks for the input
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Thanks for the input. I really appreciate it. I wont ever tear into the lower portion of the engine. Just looking for some extra umph past the gm goodwrench stocker motor. So hypothically, if I go with the stock lower end, bolt on a set of fast burn vortec heads with a dual plane airgap intake, 750 dp carb. Which size cam would you recommend to compliment what I am trying to acheive and what thickness head gasket? Dont want a high reving street machine just a seat of the pants stop light runner . Also, what could I expect to see HP and torque wise?

Thanks
Mark
TOOFUN

streetfytr68
Registered User
Posts: 1033
(6/10/04 1:03 pm)
Reply Re: Thanks for the input
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Toofun,
Gmachinz is probably the best person to recommend a cam for Vortecs--and he may be set up to provide you with the parts as well.
Best for you to describe the tops of your pistons if you don't know the exact volume. Dish? flat top? How many valve notches 0, 2, or 4? is the dish "d" shaped or a full circle? How deep is the dish?
Good luck
/Steevo

www.lateral-g.net

pdq67
Registered User
Posts: 290
(6/20/04 6:16 pm)
Reply xx
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Always got to be a ringer in stuff so I'm gonna throw this out too..

Short rod motors like the 400 can use slightly larger ports/runners, (-whatever-), when compared to longer rod motors like all the rest of the SB family b/c the shorter rod gets the "suck" started harder/quicker b/c the short rod moves the piston away from TDC some faster then a long rod does..


BUT, AND I do mean BUT, all this stuff to really show up making better power over just more stock stuff HAS to be a matched carb, intake system and cam as well as headers b/c just part of it alone won't do much, imho....

This goes into what I call building a "balls-out" motor where you want that last little bit of MAX. POWER!!!

pdq67