350 LT1 compression...Lower it?

[TDW]

I took the engine from my 70 Z28 to the machine shop. It needs .030 over pistons. I bought a set a while back. TRW, GM replacement pistons. The engine builder wants to cut the pistons compression ratio down to 9.3 to 9.5. I don't drive the car too much,so I am thinking about leaving them at 11.1 and running a Crane Blueprint Series factory spec LT1 cam. Any thoughts are welcome. What have you guys with this engine done at rebuild time? Engine builder says it won't run on 93 octane, but my L78 and my 302 both run good on 93 pump gas.

[Chevy454]

Follow *your* gut, Tony...I'll betcha a barley pop those TRW pistons would spec out too short [as is] and you'd be low on compression, especially if you haven't gone hog wild with decking the block...tell him to leave the pistons as is, cc everything, and I bet you'll see 10 to 10.5:1 *max*...also, that Crane cam is the way to go...

[COPO PETE]

I'll bet on it being 10:1 tops. If your really concerned, cc your head to see how close it really is to spec.
Peter

[Salvatore]

I agree with both these gentlemen. My 302 came out to 10.4:1 with TRW's and the head work. I used the Crane blueprint cam also. Never have problems with gas or heat. Sam

[TDW]

Thanks guys. That is excatley what I wanted to hear!

[YENKO DEUCE REGISTRY]

I used the TRW's with a .030 overbore, I know it's not 11.0:1 - and it will run ok on 93 octane, it likes a little more, but will dawdle around on 93. Don't go with 9.x's http://www.yenko.net/ubbthreads/images/graemlins/shocked.gif

[olredalert]

------Every point of compression is worth somewhere around 50 to 75 horsepower so let the emasculation begin!!! Dont let him talk you into the drop. The little amount of time we spend in these cars these days, its worth finding a bit of racing gas if you do have a slight ping problem. The sound is different as well. Its like putting a hydraulic cam in a solid lift motor, just doesnt sound right. Half of the heart of these cars we are interested in is the sound.....Bill S

[BUIZILLA]

What head gaskets are you using ?? there is a HUGE difference right there.... the stockers were .020 compressed, you can use the .039 FelPro gasket and be just fine with the stock pistons, 93 gas, and 34* total timing..set the initial at 14* and put 10 basic in the distributor curve and that'll give ya 34* total. It'll run perfect.... my LT-1 is 14.95-1 and I kinda like that myself...

JH

[olredalert]

------WOW!!!!!! Jim,,,,That thing has got to crackle. Anybody indexing plugs down there???......Bill S

[Keith Tedford]

Our L78 runs fine on 91-93 gas as does our '70 455 Pontiac. I think the key is a curve as mentioned above and possibly run slightly rich. 40 degrees was fine for 102 grade gas. These cams bleed off quite a bit of cylincer pressure. More cam would help the situation more.

[YENKO DEUCE REGISTRY]

Jim, when you say the 'stockers were .020 compressed' were you referring to the steel shim gaskets? I reinstalled the steel shim gaskets on mine, I think they were .018'ish ??

I think Keith is right, these cams bleed off a lot of the cylinder pressure so pinging is not too big of a problem - especially if you turn the timing back a little. I found that running 93 and turning the timing back a bit significantly altered the 'seat of the pants' performance, but... could've been in my head http://www.yenko.net/ubbthreads/images/graemlins/grin.gif

[Donnie]

Tony,
my .30 over 11:1 LT1 ran just fine on 93

[Chevy454]

Granted this pertains to BBC's, but going from memory the AMA specs list the head gasket [steel shim] at .018"-.020"...

[BUIZILLA]

I don't think they ever got to .018 unless it was an early editions...
indexing plugs??? uhhhh, hell yeah, usually takes me 20 to get 8 to line up right, so I buy 50 at a time to get maybe 3 sets..
crackle ??? yeah, it's got a tad of a pop to it http://www.yenko.net/ubbthreads/images/graemlins/smile.gif at 7400 it doesn't crackle, but dammmmmmmm does it sound good....there is no better music than an x pipe exhaust and a small block at 7400...

[bilede]

Hell no, I don't quite understand why everyone lowers the compression and yet is so worried about the car being 100% original, numbers matching, as rolled off the assembly line. we like them because they were hi compression, great sounding, running, and a little crazy at times.. don't lower it is my vote!

[TDW]

Thanks everyone. I will not have them cut. I ordered the cam from Crane. Should be good to go now.