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377tk 09-18-2012 05:31 PM

427 build
I am building a 427 +30 based on a mid 70's 454 block I currently have 11 to 1 forged TRW domes forged rods and forged oem crank. Assembly has been balanced at machine shop. Have the heads and intake are at the machine shop having port work done and the intake port matched. The heads are 781's and intake is an RPM. Issue is looking at cams. Money isnt allowing me to run a roller but am looking at the 294s and 11-606-5 comp cams. Prefer staying with solid flat tappet and other suggestions would be appreciated. It will be going in a 80 malibu, currently has a 3500 stall and gears will be changed out to 3.73's and am running mt 29x10.5 rears. Car is licensed but not worried about streetability and I know compression is a limiting factor. Wanting to be running 11.5 or better in the 1/4mi. with out power adders

vinniekq2 09-18-2012 06:03 PM

something like
122142-12 NA 285 295 250 260 .595 .629 112 108 .022 .022 1
3000-6800 Fair idle, excellent Bracket cam. Increased CR required.
and an OPEN intake. My 80 Camaro picked up 4/10 going from rpm to vic jr oval port. I used basically a stock ls5 with a z-55 isky cam vic jr,oval port and 830 annular will want a little more for parts and/or lighter car. I ran 11,9s.....

454C10 09-19-2012 05:02 AM

Sounds like a good cam choice.

I doubt you will get 11:1 with a 427 and 781 heads. Those pistons are most likely rated at 11:1 with 100cc or maybe 110cc heads, not 120cc 781 heads.

For a BBC on pump gas and that cam (294S), I would try to get 10:1.

Your leaving 100hp and 100ftlb on the table by not building a 496.

377tk 09-19-2012 02:19 PM

I appreciate the info on both responses, the pistons are TRW's L2239N's what is a close guess on compression with 781's, not having chambers reworked unless they do not work with the pistons I have.

454C10 09-20-2012 04:23 AM

I found a 43cc rating on the dome for those pistons. however not sure that is right. but if so the cr should be 10.75:1

887cc/cylinder (433 cid)
120cc heads
10cc head gasket (0.040")
4 cc piston under deck (-0.015")
+43cc piston

(887 + 120 + 10 + 4 -43)/ (120 + 10 + 4 - 43) = (887 + 91) / 91 = 10.75

You don't need to machine the chambers as these are big open chamber heads. However, if you want to, you can have the pistons cut down to reduce compression a little.

1971BB427 09-20-2012 11:12 AM

That's a pretty high rpm cam, with a very close LSA at 108, and should be OK for drag racing, but not too good for the street with it's 3,500-6,500 rated power range.
I like the old 427 format, as it's a little less torque, but higher rpm engine. Less hp/torque than the trendy 496-572 engines, but a nice little big block.

cdminter59 09-20-2012 01:13 PM

427 build
It is good to see you are having your rotating balanced. I was wondering if you talked to a machinist about using closed chamber pistons with the open chambered heads. I have heard it reduces flame travel so try and keep your quench as close to .040 as possible. If your block has not been decked then the pistons are .020-.025 in the hole at TDC. This makes having a quench of 040 impossible. On my 454 block I had it decked to .005 and use .036 head gaskets. The Comp Cam you chose should work just fine. Don't forget to check your valve to piston clearance.

vinniekq2 09-20-2012 01:26 PM

both of the above camshafts will likely need more space.The cam I mentioned might idle slightly smoother. 112 lda and 108 icl Vs square. I use a square cam in my street car,sounds mean at idle,which is 900-950 rpm

377tk 09-20-2012 06:01 PM

The engine builder I got the rotating assembly from said it will work good with the 781 heads. I am not to worried about the compression or idle. I believe the overlap will take some of the compression out, probably not much and from there I'll see what I need. My current engine is an old circle track engine flat top 350 solid 292 cam with 540 lift 210 runner heads a 2925 super vic intake and a 750 hp with a 3500 stall. Idle is 1400 in park and 1200 in gear with a hell of a lope. I enjoy borderline streetability, dont drive on the street much but it gets looks and runs well. I thought about having the 294s ground on a 108 instead of a 110 any suggestions? I have a cam grinder that will grind any cam I want for $40 plus shipping as long as he has a compatable core then he has it hardened before sending it out hes just hard to reach. thanks for your input

vinniekq2 09-20-2012 06:13 PM

whats your question?

377tk 09-20-2012 09:49 PM

with a 427bbc is the 108 lobe center or 110 going to be better if I go with the 294s cam or do you think it should be wider

vinniekq2 09-20-2012 09:57 PM

Pick an RPM range you want to operate.If a cam is only slightly different,the engine will only behave slightly different.You said you want to go mid 11s,,,either cam will do that if the car is reasonable weight and hooks well. The 427 can rev to 7k and make good power.
close your eyes and pick a cam thats close to what has been mentioned.You want more? go 1 size up,you want less?,,,,
I have a comp cam in my engine,works great,makes good power,similar specs but in a small block, roller though

454C10 09-21-2012 04:11 AM

fyi, overlap doesn't reduce compression ratio or reduce cylinder pressure. The engine isn't trying to make pressure at that point in the combustion cycle.

What lowers cylinder pressure is the intake closing point. The later the intake closes the lower the pressure will be.

Use a dynamic compression calculator and it will ask you for the intake closing point. As after the intake closes is when the engine starts to make pressure.

377tk 09-25-2012 08:26 PM

I purchased a solid flat tappet ultradyne cam this week, it is a 288/298 255/265 615/630 lift ground on a 112. According to the specs on this cam I think it should work well with my set up. May need to change intake and carb set up or single plane and larger carb.

vinniekq2 09-25-2012 08:47 PM

thats a fairly big cam. same as what I use in my 434 small block,except my lda is 108 and icl.My engine peaks at 6500,yours will be higher

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