Questons about cams, flow, and velocity
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Joined: Apr 2003
Posts: 1,591
From: PA
Re: Questons about cams, flow, and velocity
Originally Posted by jrg77
It seems that almost all of the heads work if you know what you are doing. The challenge is I don't. To make up for that I've tried to learn through the books and internet (and magazines) what to pick and what to walk by.
Every article or or internet build-up I've seen that has had AFR heads in them for a 383 or bigger has "shown" 500 hp on them. Getting them would be a no-brainer, as my 408 would give me 25 more cubic inches to work with to get there. The challenge is I don't want to wait 2-6 months for them. The next closest I've seen is with Victor jr aluminum heads and a matching single plane intake. Definitely magazine stuff, but may not really be workable because they don't start "making power" until 3500 rpm. Thanks to this website I now know why. I would sure like to know what they are like at part throttle, or if EFI could smooth out the low rpm stuff...
If I run a 64cc chamber that puts me at 11.59:1 combustion. From what I've read that is too much for 91 octane gas even with aluminum pistons. I've read a bit about dynmaic compression ratios and using a lager cam to bleed off some of the compression, but I don't know if that is just compensating for poor design, or just the way this all works. Unless informed otherwise that excludes the fastburns and the vortecs or any other GM head. If I could do it with heads for less than $1000 believe me I would. If the calculator is correct I need a chamber 70cc or bigger to get under 11:1.
Every article or or internet build-up I've seen that has had AFR heads in them for a 383 or bigger has "shown" 500 hp on them. Getting them would be a no-brainer, as my 408 would give me 25 more cubic inches to work with to get there. The challenge is I don't want to wait 2-6 months for them. The next closest I've seen is with Victor jr aluminum heads and a matching single plane intake. Definitely magazine stuff, but may not really be workable because they don't start "making power" until 3500 rpm. Thanks to this website I now know why. I would sure like to know what they are like at part throttle, or if EFI could smooth out the low rpm stuff...
If I run a 64cc chamber that puts me at 11.59:1 combustion. From what I've read that is too much for 91 octane gas even with aluminum pistons. I've read a bit about dynmaic compression ratios and using a lager cam to bleed off some of the compression, but I don't know if that is just compensating for poor design, or just the way this all works. Unless informed otherwise that excludes the fastburns and the vortecs or any other GM head. If I could do it with heads for less than $1000 believe me I would. If the calculator is correct I need a chamber 70cc or bigger to get under 11:1.
Your approaching your compression all wrong.
1. Pick your bore and stroke.
2. Then pick a head(and intake) with flow and port volume to support that bottom end in the rpm range you decided on.
3. Then pick your cam (or pay someone else to, it'll be worth it
) to match the heads, rpm range, cubic inches, and intake you picked. 4. After all that, THEN you can start thinking about milling your heads and or selecting pistons so that your arbitrary static compression ratio gives you a good dynamic compression ratio close to but definitly below 9:1.
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Joined: Nov 2003
Posts: 67
Re: Questons about cams, flow, and velocity
So I should pick the pistons last?!
Well I guess I better get the digital camera out to sell these on ebay.
Which is better - small chamber with dish pistons, or larger chamber with flat pistons? I understand the chamber does not make the power, but it affects the compression ratio a lot. With dish pistons can you get more lift out of the chamber? Doesn't that throw the quench away?
Well I guess I better get the digital camera out to sell these on ebay.
Which is better - small chamber with dish pistons, or larger chamber with flat pistons? I understand the chamber does not make the power, but it affects the compression ratio a lot. With dish pistons can you get more lift out of the chamber? Doesn't that throw the quench away?
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