bouncedcheque

I may be narrowing this build down. If I were to use AFR heads, 195 street with 68cc, and JE dished forged pistons, 28 cc, and the H-272 -2 crane cam, will I be able to run on regular gas without sacrificing the power I"m looking for? Is there a more aggressive cam that can/should be used? Those dished pistons are rated at 8.7:1 compression at 64 cc. Is there any rationale for going to the AFR 210 street head? Thanks again for your help.

traviss

what are the specs for that camshaft?

i am up at the lake and all my notes are at home, ca't help ya much

ursus

CR with 68cc will be 8.4:1 seems a little low to me

The H-272-2 is 216/228 on 112 .454/.480

rmbuilder

The CR of 8.4 would be with a .020 gasket and a .025 deck (.039 gasket yields 8.16). Given the IC angle of 67* with the H-272-2 that nets a DCR of 6.7. That combination of low static compression and the relatively late intake closing angle will result in low cylinder pressures and disappointing performance. If you reduce the dish to 16 cc your numbers are 9.38 SCR and 7.43 DCR with the H-272-2. This will work fine with pump gas and deliver much improved performance.
Question. Do you have a specific reason for going with a flat tappet cam? There is a substantial performance gain to be had by going roller.
Is there any rationale for going to the AFR 210 street head?
No.
Hope this helps,
Bob

bouncedcheque

I'm trying to find the optimal power package that will allow me to run on 87 octane gas. I've reviewed other threads and am yet to find one that uses the AFR heads with regular gas. I found some interesting dynoed 383 packages at www.ryanscarpage.50megs.com. Package #11 puts out 440 hp at just 5000 rpm with 470 lbs of torque at just 3500 rpm. Compression ratio is said to be 9:1. I like those numbers! The compression ratio on my stock 350 mag mpi is 9:4 to 1 and I run on 87 octane all day. The cam in the #11 combo is described as an AFR hydraulic, 218/223, .46/.47. I don't think AFR makes cams? Anyway, any suggestions you might have re: an appropriate "marine" roller cam would be appreciated. In reviewing old posts I saw that the H-272-2 was recommended, but I know it depends on all of the other variables; I don't have the experience/knowledge to know how they all affect one another. In the end, I want to get as close as possible to my ideal: high hp and torque and the ability to run on regular gas. Thanks again.

ursus

The compcams extreme marine XM270hr is pretty close 218/224 on 112 .495/.503 to the cam you mentioned there. The Crane HR-276-2s-12 IG is is 214/222 on 112 .488/.509. The H-272-2 is 216/228 on 112 .454/.480 but it is a flat tappet hydraulic not a hydralic roller cam. Either of the rollers there would be a great choice, I would think peak hp would be closer to 5500 rpm tho with those heads.

9:1 is a good comp ratio to target for 87 pump gas

rmbuilder

bouncedcheque,
A word of caution about the dyno numbers listed on that site. Most are reprints from adverts or magazine articles, both of which have a leaning toward the high side of real world figures. HP, torque, and test cell conditions of the tests conducted will vary by dyno and location. Additionally they are automotive applications, not marine.
Bob

robyw1

You're gonna have to get that compression up unless you want to supercharge this thing. Now you are off to a good start if you are looking for a dependable engine that will run 4800 to 5200 RPM. That's all this cam will give you with this compression ratio. I would also pull that cam in 4 degrees early at least. Yes you could run fine on 87 pump gas with no problem as long as your timing is set right.

Roby

bouncedcheque

Thanks for all the input. It's a great help. How much performance (hp) is sacrificed by staying with 87 octane versus 91? Any guess?

robyw1

With the compression advertised here you might be surprised to know that you might get more power with 87 octane then with 93 or higher.

Roby