I am in the proccess of building a F.I. LT1 355 that is projected see about 8-10 lbs of boost (Vortec V-1). Based on my calculations, the SCR came in at 9.7:1 based on the following:

52cc head chambers (clean-up cut/ 2.00 & 1.60 valves using stock seats)
4.030 bore
.039 fel-pro 1074s (4.125 hole)
-20cc wisecos
5.7 rod
3.48 stroke
deck hieght of .015 (assumed based on factory spec;I will doulbe-check how far the piston sits in the hole once the s.b. is assembled)

Accepted theory is that this CR is too high for a F.I. motor. Is DCR more important than SCR? I am researching how to reduce CR without raplacing the pistons. Here's what i've theorized thus far:

-The original valve seats were used, if I have larger seats installed to drop the valves deeper into the chamber, would that significantly increase the chamber volume enough?

-The Fel-Pros are .039 thick. Is there a thicker gasket on the market that will hold up to this moderate amount of boost?

-Can a significant amount of head chamber material be removed on the LT1 heads to reduce SCR?

This is my first F.I. build and I definatley chose the wrong pistons. -20cc was not enough to get to my target 9:1 cr, but replacing them isn't an option. If i'm stuck with this CR, then i'll just have to reduce the boost accordingly and have it tuned accordingly.

Any insight/advice would be greatly apprecieated.

Cheers,
John

 

DCR is more important. Ya don't want to increase the quinch area with a thicker gasket ya want to try to keep it at .035-.040. Ya can change pistons and come up with most any static ratio.
Going deaper with the valves won't help much on compression but it sure will hurt flow.Ya can take the smog knot out of it and gain a pretty good bit.

 

Confirming your SCR- I get 9.65:1, but that's becuase I know that a compressed fel pro .039" gasket is 9cc (not an estimate based on bore and thickness).

Maybe on a reverse-cooled LT-1 you can get away with this much compression with that much (intercooled) boost, but on an earlier gen-1 engine you'd probably be flirting with problems using pump premium.

If in doubt, drop the compression. It's a lot easier to dial in another pound of boost than to dig into the motor to drop the compression another half a point.

 

I ran 6 lbs (non-intercooled) on the stock LT1 set-up without any issues. The factory pistons were perfect and sparkplugs were fine. I never noticed any detonation issues either; that was at 10.4 to 1. Combination Motorsports can supply me with a set of Cometic .051 thick MLS set for $130 if I absolutely need to go that route.

I am attempting to research the effects of DCR, SCR, quench and boost to figure out what the best approach will be. I am a novice at this and am learning groups of info daily.

With my cam profile (listed below)I got 8.7 to 1 DCR and 9.58 SCR using an online calculator (assumed .020 deck height):

LT1 3314/ 3316 HR115+3

lift- .502/ .520 (@1.5)

Valve timing @.50- open close
int: 0 btdc 44 abdc
exh: 56 bbdc 0 atdc

The specs are for cam installed @112 ICL
Dur- 224/ 236 (@1.5)

Lobe seperation 115 + 3 degress adv. ground in

Since I have no idea how to read a compressor map, I cannot deduce the cfm I am producing with my v-1 S trim Vortech (a 3.33" supercharger and 6.00" crank pulley). Therefore, I assume that the DCR calculators are for NA motors; how would I calculate for a F.I. application? Should I even be concerned?

 

9.7:1 isin't that bad.... a later IVC point will help, but the most help is a colder intake charge.

Race motors run a lot higher SCR than what you have.

Bret

 

Thanks for the advice and insight. A wise friend once told me that it's very easy to spend others money on the internet; keeping within your budget and maintaining realistic expectations is the key to a succesful project.

With the mild boost, i'm going to focus my research on quench, keep the motor healthy and maintain a slightly conservative approach.

 

Are there any pics of a finished LT1 head with the smog knot removed? About how many CCs would this equate to?

 

The computer and knock sensors do wonderful things in these later gen motors. They will pull/give as much timing is needed without issue. And there never is an issue with altitude density. Bryan will be performing my tune; he is pretty confident I'll see at the least high 400ish hp figure to the wheels.

 

Ya can take 5-6CC's out.
No pictures---top secret
Any porter knows how to do it, if you try it, be prepared to ruin a set of heads as ya will hit water quick.