I am looking to upgrade my stock heads on my 355 small block.

I know that I need 62~64 CC chambers, but how do I determine waht intake runner volume is best.

Is a smaller intake volume better for low end torque and larger runners better for high RPM output?

I will have 9.8-1 compression with an automatic, and will drive mostly on the street with some trips to the dragstrip.

Thanks for the help.



White 77 coupe, 350HP crate motor, headman headers, true duals, comp 234@50 cam. Edelbrock carb and intake.

 

Here's more information than you will probably need, but a good place to start researching heads. Joe

http://chevyhiperformance.com/techarticles/41598/

 

FOr the money, you can't bet Vortec heads. You will need a Vortec style intake. Generally speaking, smaller ports increase torque and larger ports allow for higher RPM breathing. Getting into the nuts and bolts, it is not the port size, but the amoutn of air it flows. If you have two cylinder heads, both with 170 cc ports, but one flows more, you want that one.

 

180cc to 200cc and you can not go wrong. The 200cc would be better if you ever decide to go bigger. 180cc might give you better bottom end but the difference is small enough that it will not make you unhappy either way IMHO. The 180's are larger than any factory SB head.

I put Dart Iron Eagle 64cc/200cc heads on my L-82 and would not do it differently if given the opportunity. Runs like a Vette should run. If I ever decide to stroke it to 383 the heads will still be a good match.

-Mark.

 

For the money they cost, the vortec's are hard to beat. The flow numbers on the intake side are really good. They are designed for good flow up to around .500 and after that they don't increase with more lift. The maximum lift cam you can use is around .480", due to the springs, which makes sense. It seems GM installed springs to match where the heads flow best. It is up the user to pick an cam that works with these limitations. Some sellers such as Pace will install different springs which will allow the use of higher lift cams. Besides having to change to a vortec style intake, you'll also need self aligning rockers(which come with the head) and center bolt valve covers.
The decesion you will have to make is what cam you want to run before deciding if these low cost performance heads are the right choice.

 

I've still got a few bugs to work out but I just put a Vortec engine in my car & I'm Impressed!!! She Flies!!!! ALOT more power than I expected.... Just ask my neighbors
I'll be posting a thread in the next few day's with pictures.

 

Vortec is good if you want to go iron, but at your compression, I would plan on aluminum, and the protopline lightening 180s are pretty nice.

 

From my understanding 10-1 compression with Vortec heads should not be a problem. In fact I read somewhere that at even 10.5-1 compression with a higher duration /higher performance cam the engine should run on premium pump gas. Voctec heads supposedly allow about .5 bump in compression ratio without the valve pinging.

 

In my book, John Lingenfelter on Modifying Small-Block Chevy Engines, he states "...will further increase compression up to around 9.5:1 which is the maximum for iron head street engines on 92 octane fuel. Later he says "I typically will add a full point of compression for aluminum heads over an iron head on a carbureted engine."
This all comes from Mr. Lingenfelter himself, and as such is beyond contestation.

 

The rule of thumb was that aluminum heads would allow an extra point of compression. This is accepted by many people not only John Lingenfelter. When someone states the compression it is normally being referred to the static compression. I am not sure of the exact term they use, but for the sake of this post I use the term dynamic compression. During the compression stroke the intake vavle in open. The engine does not make compression while the valve is open. A higher duration cam or advancing the cam will have an effect, lowering the dynamic compression. This is one of the reasons why you'll see higher duration camshafts recommending a higher static compression. If you start with 9.5 compression and have a long duration cam, then do a compression test; don't be surprised that the cylinders are lower in pressure than anticipated.
Head design as well as the material will also have an effect on the maximum compression that the engine can have before denotation. The combustion chamber of the Vortec supposedly allows for a bump, .5, in compression in comparison to older technology cast iron heads. If you take the 9.5 and add 0.5 to it, then 10 to 1 is realistic. These are the little details that large compaines such as GM hire engineers to figure out. Smaller professional engine builders more than likely have this figured out as well. They may have calculated what compression pistons to use with a certain cam and head, or they may have learned by trial and error. Other engine builders will just bolt on parts and assume they built a great engine.

 

good book. He also says he tries to keep things around 10.2 : 1 compression with aluminum heads.

 

I agree. The dynamic compression ratio is calculated like the static compression ratio but is based on the amount of mixture trapped at the exact time the intake valve closes. The recomendations taken from it come from empirical evidence, not science. Using DCR and typical aftermarket cam designs will give you good guidelines to shoot for in optimizing the combination for pump gas. GM cams typicaly have different ramp rates and lobe designs as opposed to the aftermarket cams so the stock cams would use different recomended DCR's than what is shown on the web page. I have used the program a bit and it seems to be fairly accurate for typical aftermarket cams. This is a very good tool to use when selecting either a cam or a static compression ratio which ever way you are trying to shoot for.

Here is a page you can check out. It has a downloadable file for you to use to determine if your DCR is in the ballpark or not.

http://cochise.uia.net/pkelley2/DynamicCR.html

Remember not to use the actual intake valve closing figures, not the .050" figures or other such numbers. They will throw you way off.

-Mark.

 

I wanted to look this up to be sure before I posted.
GM states the Vortec 350 "R" engine is rated at 9.4:1 cr and Uses 89 octane fuel or better.

 

Looks like if a bump in the grade of gas to premium, 92/93 octane, then hitting 10:1 is realistic. My Acura TL owner's manual states to run 91 octane in it. Although I hate to spend the extra money at the pump, I am starting to get used to it.

 

Thanks for all of the help.

I still am tossed up between the Vortek Heads or aluminum aftermarket heads.

Guess I will keep investigating unless a great deal on either shows up.

Beardface

 

I am running TF 23* 64cc heads with Fel-Pro 1010 head gaskets and stock dished L-48 pistons. I run 89 octane without a hint of pinging. Timing is about 18* initial, 37* total, mechanical + initial. Plan to run about 10.4 C.R. on new 383 motor with same heads and flat top pistons.