Chevelle69

2002 LQ4 bored out 20 thou to 4.02
Speed Pro h1129cpa .50mm flat top pistons sitting .007 below the deck
Felpro 26192PT Bore: 4.100 Compressed thickness .048 Head gaskets
Comp cam 54-414-11 XR269HR 216/220 Duration @ .050 inch, .525 inch/.532 inch Lift, 114 Lobe Separation


So thats my set up going into a 1969 Chevelle 5 speed manual with 3:55 rear gears. Just undecided on the heads, thinking about 243 heads. With this set up I calculated a Static Compression Ratio of 10.93 and a Dynamic Compression ratio of 9.32. Looking for longevity and be able to run on 93 pump gas.

Should I reconsider this set up?

Che70velle

iTrader: (6)

The setup is fine, but I don’t like the headgasket. The 4.100 bore will lead to too much crevice volume. Cometic recommends a headgasket that is .030 larger than the bore, which is .015 on either side. Of course chamber dimensions come into play here. You never want the gasket encroaching into the chamber which isn’t an issue with a 243 head. I’d go with a C5751-040 gasket personally. It will minimize crevice volume and give you a better quench, while also getting you a little more compression. I didn’t do the math to see the compression numbers here, but if your going to run 93 octane exclusively, you can run just north of 12:1 without issues with a good tune. I’m 12.4 on 93 with my 434. I’d suspect you’d see 11.2ish with this gasket just guessing.

Chevelle69

That's good to know its just when I calculated the DCR came out to 9.32:1 . It spooked me a little was reading you should try to keep it around 8.5:1 for a street engine. Don't want any detonation issues.
https://www.gofastmath.com/Compressi...tio-Calculator

Thanks for the tip on the headgasket. I haven't bought it yet just what the Fel pro guys recommended over the phone.

RonSSNova

iTrader: (3)

If worried about DCR, maybe pick a different cam? I bet Summit has something nice.

243 heads will work well. My LS1 was 11.4:1, 226/230 114 .600 cam.

Couldn't get away with much more than 21 degrees timing below 4800, but you dial that while tuning. Run the fuel a bit fat helps too. Car ran excellent, and we only get 92 here in Oregon.

Chevelle69

Already bought the cam but not the heads yet. Could always go with some 317s I suppose if I really had to ah decisions decision...

JF74chevelle

My set up that I swapped into my Chevelle was a LQ4 long block stock, 799 heads I had surfaced with a summit 8707 cam. 226/238 .600/.600 lift. With stock GM performance .051 thick head gaskets, I think it was around 10.8:1 compression something like that.

00pooterSS

iTrader: (40)

That's kinda doing it backwards. I'd run the 243's and choose the right cam. Dropping SCR to suit DCR isn't the best way to do it. And I agree with Che70velle about the gaskets. And if you don't wanna go custom you could run LS3 gaskets.

jlangley

iTrader: (8)

You should try using the Wallace racing calculator instead.

http://www.wallaceracing.com/Calculators.html

I got a significantly higher dcr using the calculator you linked than I did with the Wallace one. Not sure which is more accurate but I'm thinking the Wallace as it uses the .006 intake closing.

Chevelle69

I agree mistakes were made. I'd followed the recommendation of a local machine shop, they picked out this package for me. Not knowing an better I followed their advice. I've since fired them for other issues but this is what I have to work with now.

rpturbo

iTrader: (47)

Personally, I'd get your plan together and re-execute. Worst case, sell the cam and buy exactly what you need. The sting of loosing at most $200 is much easier to swallow than the regret and performance you think you should or could have by not having the setup you want.