427 help
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From: visalia california
427 help I am runing a 427 in a 4500 (with driver) 73 blazer. it is a 69 block with the heads that would of came with it stock. the story is that it is out of a vett I do know thats it a 2 bolt main so i know its not to special. anyway I have the large oval, closed chamber heads on it. when I re-did the motor I did it right, with it balcened, heads and block decked, line bored, etc. it put 219 int. and 188 exh. valves. it has 10.1 now with all comp cam valve train and pro magnem roller rockers, I have big headers and an old edelbrock performer 2.0(from the 80's with capped off egr). the cam is comp cam 515 520 lift and 224 and 230 duration at .50. anyway it runs ok now 13.8 103 (3.73 gears and 2200-2400 stall) off the 125 shot. but you know you always want more. I was thinking of going with a comp cam with 574 578 lift and 240 246 duation at .50 (when I did the motor I set the heads up to go 600 lift) and going with an air gap intake. do you think my heads can support that cam (I know I could go bigger but I like the power band on that cam 2300-6500) what do you think my 1/4 improvment will be?
It depends on what your compression ratio is. And thats with everything cc'd, not guessed at. Usually going with a cam made for higher rpm requires longer duration, longer duration requires more compression.
You should read up on dynamic compression, then pick a combination that will give you around 8:1 to 8.5:1 dynamic compression.
I'm building a 468 right now. First I chose the rpm range I wanted, then the cam that will get it there, then the pistons that will give it enough dynamic compression to run there. What it's ending up at is 11.1:1 static compression and 8.2:1 dynamic.
This engine is going to replace a 427 based 438 that was running 11.4:1 SCR with a big solid cam to give it 7.6:1 DCR. This engine would run 11's on pump gas and rev close to 8000 rpm.
You should read up on dynamic compression, then pick a combination that will give you around 8:1 to 8.5:1 dynamic compression.
I'm building a 468 right now. First I chose the rpm range I wanted, then the cam that will get it there, then the pistons that will give it enough dynamic compression to run there. What it's ending up at is 11.1:1 static compression and 8.2:1 dynamic.
This engine is going to replace a 427 based 438 that was running 11.4:1 SCR with a big solid cam to give it 7.6:1 DCR. This engine would run 11's on pump gas and rev close to 8000 rpm.
Staging Lane
Joined: Jun 2006
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Originally Posted by orangefun
how to you calculate dynamic compression?I know i have 10:1 static right now. thanks for the great info!
Yea check piston to valve clearance too. The piston below is a forged 427 piston. Had good clearance with a .595 lift cam, then I put in a .567/.590 with a long duration and didn't check. It had .000 clearance on the intake. This happened about 500 miles after installing the cam, going down the highway at 5000 rpm. It also bent the rod, put a hole in the head, cracked the cylinder wall. I had the block sleeved, and used an 'in the head' piston fly cutter when I built it back up.
Last edited by 8a8mfh; Jan 10, 2008 at 07:37 PM.
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Staging Lane
Joined: Jun 2006
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[QUOTE=8a8mfh]Yea check piston to valve clearance too. The piston below is a forged 427 piston. Had good clearance with a .595 lift cam, then I put in a .567/.590 with a long duration and didn't check. It had .000 clearance on the intake. This happened about 500 miles after installing the cam, going down the highway at 5000 rpm. It also bent the rod, put a hole in the head, cracked the cylinder wall. I had the block sleeved, and used an 'in the head' piston fly cutter when I built it back up.[/QUOTE
The method we use is with the deg wheel is while turning it in a clockwise direction at 4* to 15* dependes on your cam the valve will be at its closest to the piston the intake is going away from the piston --- but the exhaust is coming twards the piston .100 is the spec jz
The method we use is with the deg wheel is while turning it in a clockwise direction at 4* to 15* dependes on your cam the valve will be at its closest to the piston the intake is going away from the piston --- but the exhaust is coming twards the piston .100 is the spec jz
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Verdad Gallardo Thats what my engine was doing, as the piston went down the intake would open quick and hit it for only about 1 degree. And that picture is the result. It ran great up to the point the valve head broke off. I'd rather it just slammed the valves and bent them all than to have this happen.
Staging Lane
Joined: Jun 2006
Posts: 60
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Originally Posted by 8a8mfh
Thats what my engine was doing, as the piston went down the intake would open quick and hit it for only about 1 degree. And that picture is the result. It ran great up to the point the valve head broke off. I'd rather it just slammed the valves and bent them all than to have this happen.
stock valves brake off all the time stainless will some times only bend you understand how to check it now jz
Originally Posted by johnjzjz
stock valves brake off all the time stainless will some times only bend you understand how to check it now jz
I'm going to use stronger springs with a comp cams .595 lift solid cam. The stock valves should be alright as long as there is no contact right?
Staging Lane
Joined: Jun 2006
Posts: 60
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Originally Posted by 8a8mfh
Well these were stainless valves. But you got my attention now. I'm building a 468 right now and was planning on using the stock valves in the 781 heads for now.
I'm going to use stronger springs with a comp cams .595 lift solid cam. The stock valves should be alright as long as there is no contact right?
I'm going to use stronger springs with a comp cams .595 lift solid cam. The stock valves should be alright as long as there is no contact right?
https://ls1tech.com/forums/eastern-members/517917-super-comp-super-street-bbc-cars-shop-today-pics-vids.html
Staging Lane
Joined: Jun 2006
Posts: 63
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From: New Lenox, Il.
I have a cam recomendation for you. Comp Cams #11-568-4. Its a nitrousHP cam that has .575/.595 lift. We put it in an 396 with ported and polished closed chamber heads with 10.5:1 compression and it was amazing. Big lopey idle, incredible throtle response and it pulled all the way to 7000 in an otherwise stock 396.
