Need help guys, engine gurus PLEASE!

[VintageMusclecar]

Mark;

Is the current converter a GER, or the 3500 you plan on purchasing? If you're planning on purchasing a GER, please PM me first!

Do you know what the "list" number is on your 1050? There are several different 1050's available, some can be made to work well on the street while others can't.

As Rob stated above, those 990 heads have pretty big chambers to begin with. Unless they've been whittled down, they should have around 119-121 c.c chambers. Any chance you have the spec/build sheet from the engine builder?

The reason I ask is, the last 461 BBC I built for a customer had SRP pistons in it that were rated at something like 12.4 with a 119 c.c. head (been a while since I built that, but those #'s should be pretty close). I didn't have to flycut the pistons to clear the cam. With the pistons roughly .010 down in the hole, a .041 gasket and 121 c.c. chambers in the heads, the actual measured compression ratio came out to roughly 11.8. You can't always go by what the catalog says. Just a few c.c's either way can make a notable difference in actual compression ratio.

As far as the cam/compression deal, running too much static compression with a cam that's too small will build too much cylinder pressure and can lead to detonation problems. That's why it's really important to know the actual compression ratio when choosing a cam. At roughly 12-1, you still have room to step the cam down w/o running into this problem.

If your compression actually is 12-1 or slightly above, I'd look into something like the Crane roller p.n. 138121, which is .663-.638 lift (gross), 260-270 at .050 and has a 110 LSA. The duration is 14* smaller at .050 and you're losing roughly .074" lift on the intake and .088" on the exhaust. This will still have enough duration to work with your compression, but the reduced lift will dramatically improve valvetrain life. Power loss would be mild.

If you'd rather go with a solid flat tappet cam, look at something like the Crane 134691 or 131311 (256*-266* @ .050, .580-.600 and 256*-264* @ .050 and .618-.638 respectively) The 691 cam makes great power from about 4000 up and has a nice thumpy idle. The 311 cam makes great power from about 3600 up and has an absolutely wicked idle. Both are "streetable" cams, but they can be pretty choppy unless you've got the carb dialed in for part throttle cruising.

Sorry for being so long-winded, just trying to cover as many bases as I can.

Eric

[Chevy454]

One of our L-72s came in at a lowly 10.2:1 (11:1-11.25:1 according to published info!), even after taking a couple thou off the heads. I've even heard of some rebuilt L-72s (all stock, no milling/decking) only having a CR in the high 9:1s!! If you have it torn down, cc everything so you know exactly where you're at.

[VintageMusclecar]

Rob;

Just out of curiosity, did it come in at 10.2 with OEM style steel shim head gaskets or composition styles? What did the heads c.c at? How far were the pistons down in the hole?

I agree with you 100000% about checking everything if/when the engine comes apart. If I had $1.00 for every "13.1" motor I've torn down only to find actual compression at 12-1 or less....well, I'd have a lotta dollars.

Eric

[Chevy454]

Nope, that was the only variation from an "as delivered" L-72...I wanted to see exactly what someone would have gotten had they ordered an L-72 car back in '69. Instead of the .018"-.020" shim I used the .038" Fel-Pro composite, but did take a bit off the heads. The heads were around a 112cc average (I believe they're supposed to be 107cc), the piston domes (TRW) were around 28cc (supposed to be 34cc), and the slugs were somewhere around .015" in the hole (can't remember that spec exactly). Not exactly the specs I expected to find!

But, that engine still hit 425hp on the engine dyno through stock exhaust manifolds/head pipes with the factory L-72 cam, and pushed our 3800lb. Camaro to a 12.79@108+, all on Polyglass tires...and it was bracket car consistent to boot.

We blue-printed our latest L-72 and picked up about 55hp at the flywheel...

[Pantera]

With his back problems I was recomending he drop it back to near stock L-72 or LS-6 spec's just to not cause any problems with his back.

Those stock motors are no slouch on the street. Since I am familar with traffic in Dallas I was also considering the mess that can cause.

I was just thinking of a less radical cam and compression for his condition.

[WANNA BE SYC]

Eric & Rob I'm going to have to pull engine down to see pistons and head gskts and maybe cc size.your help is completly what i expected from this site. you guys are great.I can't get anyone to talk to me down here.the car did go at motorplex 12.189 @118 mph off the foot brake spinning slightly and lifting front wheels 3.5 to 4.0" with 29x11 hoosiers.I go about 325lbs. All steel except 6"glass hood.w/full int.and 8 point mild steel cage.picture to follow thanks again i'll definitly be in touch.thanks mark b.

[WANNA BE SYC]

Heres a shot of engine

[WANNA BE SYC]

conv.in car is 5000 trans king out of houston.3500 conv is GER.brand new in box from friend for free he owes me.thanks to pantera as well my back is ok its my neck but it's fused nicely.no problems now.just cant race off the trans brake or garuntee no accidents to doctor. Mark B.

[VintageMusclecar]

Mark;

Looks like a sweet ride!

Here's a couple of shots of my "endless money pit" `67 Chevelle.

[VintageMusclecar]

572" motor, +/- 800 HP on pump gas. Eventually will get Big Cheif heads, shooting for +/- 900 HP next time around.