Best Compression Ratio

criket

criket

Blue Ridge 4x4
Joined
Aug 18, 2010
Location
Dobson, NC
Currently I'm in the middle of building a Chevy 355 and now I need to buy some heads but I'm wondering which compression ratio would be best.

After doing the math for the heads I've chose (Eldebrock E Street) if I get the 64cc heads, my ratio will be around 10.3:1 to 10.5:1. If I get the 70cc heads, it'll probably be around 9.6:1 to 9.8:1. I'm not afriad to run a higher octane gas either. So which would be best?


FWIW, motor specs:
-chevy 355 bore 4.030, stroke 3.48
-stock crank
-stock rods and bolts
-flat top hypertuetic pistons 4 valve relief, (new)
-this motor will eventually go into a chevy truck and be used partially for a DD and weekend show truck.

Thanks guys.
 
need a little more information-what cam are you planning on? higher duration cams can live with higher compression due to overlap. are you planning on towing anything? a high compression motor is fun, but they tend to run hot when lugged down. running the aluminum heads does make high compression more doable without detonation setting in, if you're not towing heavy, the 64 cc should work well. fwiw, i just got a deal on a set of Dart SHP 200 heads that make way healthy power for a reasonable price.(to me, edelbrock seems to spend more on advertising than product development-there's alot of great deals out there right now on really good SBC aftermarket heads)
 
flatblackzj said:
need a little more information-what cam are you planning on? higher duration cams can live with higher compression due to overlap. are you planning on towing anything? a high compression motor is fun, but they tend to run hot when lugged down. running the aluminum heads does make high compression more doable without detonation setting in, if you're not towing heavy, the 64 cc should work well. fwiw, i just got a deal on a set of Dart SHP 200 heads that make way healthy power for a reasonable price.(to me, edelbrock seems to spend more on advertising than product development-there's alot of great deals out there right now on really good SBC aftermarket heads)
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x2 about the edelbrock heads, much better heads can be found for the same or less.
 
Compression is a naturally aspirated motor's best friend. 10-10.5 in a pretty good range to be in without much worry. I'm running 10.4:1 in the 6.0 I just built for my Silverado.
 
look into a set of L31 vortec heads...
fwiw, just got out my notes on sbc cylinder head flow to compare-in comparison to a set of factory L31 vortec heads, the e-street performed equally or better at lifts above 0.500 to 0.600, at lifts 0.400 and below, the vortec heads blew the edelbrock out of the water.
from past experience, the factory vortec heads generate alot of low lift flow from exceptional air velocity through the port. in english, this means you will have a motor with very good bottom to midrange torque with the vortecs. the only place you may lose out is high rpm power(over 5500), since vortecs don't respond as well to cams with lift above 0.500. Cost wise there is no comparison between the edelbrock at $800+ to the vortec which you can buy new from GM for around $600/pr or find them stock on a 96-99 5.7L pickup, tahoe, suburban, or yukon and pay junkyard prices($300 should just about cover it)
 
@flatblackzj, thanks for the responses. The cam I have is a Comp Cams Xtreme energy. The max lift I think is .475, I can't remember but I do knwo that it is below .500. I went with one below .500 because I'm not building a high horse motor. This is my first motor build and I wanted a reliable daily motor. I have looked at the vortec heads really hard and I may go that way. Since you said and I have read that vortec makes power better on the low end than the high end and that it will be going in a truck (little to no towing) and not a drag car, I think that the vortec heads would be better.

@Croatan Kid, thanks. I've been following your motor build. It's sweet. My motor will be naturally aspirated and I don't plan on a blower or nothing fo rit in the future. I'll build another motor with all that stuff on down the road.

Thanks for the responses guys. I'll finish my build thread on this motor once it runs, LOL.
 
If you ever decide to go LSx, you'll never go back :D Really easy to work on and get damn good power out of compared to the old school small blocks. Did I mention they bolt up to old style transmissions too? :driver:
 
After reading up on the vortecs, jegs website says max lift .475 and summit racing website doesn't have it listed anywhere. My cam is .477 max lift. So I guess I cna't run this head unless I get different springs?????
 
for .477, factory vortec springs should be good, the .475 limit is where the retainer will hit the factory valve seal, for that cam, you have two options with vortec heads, the first and cheapest/easiest is to swap the factory valve seals for umbrella seals, the heads should be good for up to .495 lift. the second is to clearance cut/grind the valve guides and use the factory style valve guide seals.
 
flatblackzj said:
for .477, factory vortec springs should be good, the .475 limit is where the retainer will hit the factory valve seal, for that cam, you have two options with vortec heads, the first and cheapest/easiest is to swap the factory valve seals for umbrella seals, the heads should be good for up to .495 lift. the second is to clearance cut/grind the valve guides and use the factory style valve guide seals.
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Thank you sir.
 
Ok bringing this back up.

I purchased the vortec heads and I decided to get the comp cams beehive springs to replace the stock vortec springs. I probably didn't have to with my .477 max lift comp cam but I may want to upgrade my cam in the future and well I'd rather have the beehives now than buy later.

So i've been searching the internet for about a month or so to find that you can swap these beehives over and it doesn't require maching of the head. According to car craft article, all they did was swap in the beehive spring and the steel retainer from comp cams and bam, the head can handle around a .525-.550 lift.

One guys build thread on these vortecs on his own website, he said that after he installed the beehives and the steel retainers that he would need to add shims to the spring to get it back to the stock spec valve height.

Why didnt' the car craft article cover this and why have I only found 1 person that has mentioned this? (I've searched probably 15 different vortec head builds) Can someone explain OR guide me to a engine builder forum to where I can research this to see if adding these shims is necessary?

Thanks.
 
what part number springs and retainers are you going after? there's two main clearances to worry about with the beehive swap-the first being the spring installed height(most aftermarket springs rated at 1.80"), since the beehive springs tend to have alot lower spring pressure on the seat, you would want to use the shims to acheive the proper installed height and get sufficient seat pressure. This is also dependent upon the retainers being used to figure the installed height.
The second clearance to worry about is between the retainer and valve guide/seal when at full open lift, the retainers and valve seals being used will have alot to do with how much lift you can safely run.
 
Springs are Comp Camd Beehive 26915 and the retainers are 774.

My cam is max lift .477 and I believe that the vortec springs can handle ~.475 so I should be able to run these safely since the specs are close to begin with.

Thanks for the help.
 
according to the comp website, for 350 vortec heads, a 26981 spring with a 787 retainer should be good for .525 lift, the 26915's are a ls or lt1 spring setup which will work as well with the 787 retainer.i'm not for sure on the 774 retainers, they are a direct fit on ls motors, but to be safe, give comp a call directly and they should be happy to help you out.
 
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flatblackzj said:
according to the comp website, for 350 vortec heads, a 26981 spring with a 787 retainer should be good for .525 lift, the 26915's are a ls or lt1 spring setup which will work as well with the 787 retainer.i'm not for sure on the 774 retainers, they are a direct fit on ls motors, but to be safe, give comp a call directly and they should be happy to help you out.
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I might do that. BTW, I found a fourm, nastyz28 dot com, and there was a thread about 60 pages going in depth with the vortec heads. That thread answered all my questions. It took me a while to find it and read it but it did help.

And thanks for your help flatblackzj !!!

I need a better valve spring compressor. Those beehive springs wore me out! LOL
 
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