I need to know what head gaskets I should run with my new set up. It will be a 383 with 6" rods and 5cc dish pistons that combination motorsports sells. They are JE/SRP. My heads are stock castings that Lloyd did. And i guess they were just cleaned up. My block has not been milled. I want to go with the .029 Impala gaskets but I wanna make sure im not going to have to much compression. Thanks guys.

 

Just rebuilt my similar 383. Used Fel-Pro 1074.

Emil DUsek:93Z,383,Vortech,NOS

 

Any other opinions?

 

I'm running Cometics MLS (Multi-Layer Steel) series...Phil @ Advanced Induction can hook you up. They're pretty $$$ though...

 

So nobody knows if the Impy gaskets will be ok on this setup? How many CCs are the combustions chambers on stock LT1 heads? How much compression can an LT1 have and still only run 93 octane? If i know these things, i can figure it out on the compression calculator.

 

If you wnat to know what compresion you can run on 93 then you need to know dynamic not static CR and it has as much to do with your cam as the static CR. I know of people running 12.5:1 with no problems on pump gas.

 

Still dont know if i can use the Impala Head gaskets.

 

Stock chambers for an aluminum LT1 head are 54.4 (give or take a little - and I mean a little). Your going to need to know how far your pistons are down in the holes to figure the compression though. I don't know how far the stockers sit down in there, I never bothered to check.

OBTW, I'm one of those with 12.5 compression with no troubles. I DO run an MSD timing box to pull about 6 degrees across the board for pump gas though. It sure beats having to flash the computer at the track when I put "good" fuel in it though I'm sure you could setup the computer to not be quite as aggressive as I have mine set for and get good performace and not have to mess with it at all. Just might have to give up a couple degrees of timing here and there...

As for the impy gaskets, just plug in the numbers and see what you get.

Anyone else wanna chime in for the factory installed height on the pistons in a stocker LT1


Oh yeah.. I'm using the Fel-pro 1074's with ARP Studs. No issues to report.

Dave C.

 

stock height is usually between .025-.030 I believe.


yes the imp. head gaskets will work, thats what i have. you WILL have pretty high static compression though. I milled my block .015", and my pistons are in the hole about .008". but I have the -16cc srp's to keep the static just under 11:1. the prob. with the higher static #s are that the tune has to be pretty spot on to avoid knock. I drive mine alot on the street, so for me it was worth the few HP that I would have gained by goin lower with the SCR. if you havent figured out wich cam to get yet, you can get a good match between the SCR and the cam to allow you to have a high SCR

 

I just want something that I can drive on my PCMforless mail order tune without knocking. On the automotive compression calculator on here it is breaking down like this.

Cylinder Head volume : 54.4CC
Piston Top Volume : 5CC
Cylinder Bore : 4.030"
Stroke : 3.75"
Deck Height: .030
( Impala) Head Gasket Thickness: .029

Compression Ratio: 11.9 to 1

Is this static or dynamic?
Will this run ok on a Mail order tune untill I can get it Dyno Tuned?

 

well, thats exactly the same boat I was in. notice that doesnt leave you ANY room to clean up the deck of the block or heads if you need it. so I erred on the side of caution. IMHO, thats too high on a mail order tune. maybe with great gas, and a real good DYNO tune it'd be fine. but I think youre really askin alot from a mailorder tune. at best a mail order tune is a good guess. it will get you close, but in no way is it the best it can be. (FYI, I have a madwolf tune, and its great sofar) you can always put a .050 felpro or cometic gasket in there to help lower that somewhere in between. the eng. builders I spoke to all told me that the diff. in 12:1 and 11:1 is pretty slim. not really noticable on the street anyways. I think I read somewhere that 1 point raise in compression is like 3-4% increase in power. so at best your looking at a diff. of about 12 HP. to me, thats not worth the hassle of fuel additives, or race fuel, or worrying about my tune if its good enough. but thats just me and I can certainly understand some people wanting to take all the horesepower they can get. another great affect of higher Static Compression Ratio is great throttle response. also nitrous loves compression.

oh yeah, and were still talking about static compression ratio. dynamic is figured out using the static ratio and the cam specs.

 

I would seriously consider changing my piston choice if I were you. If you want to have a little lower compression ( IE <11.5), then your going to want to go with something with a little more dish in it. Say an off the shelf SRP 16 cc dish for a 4.030 bore. With that choice, you could zero the deck for good quench, run the impy gasket, and still get about 11.25 static ( about 10.9 comp ratio on the fel-pro 1074 @ .039). Thats PLENTY low to run pump gas in an LT1. What you DON'T want to do is run the pistons 30 down in the holes, AND use a .050 gasket. Your quench (@ .080) is going to suck with that setup, and might actually be MORE prone to detonation than the same thing with slightly HIGHER compression. Quench has a lot to do with an engines resistance to detonation. It's not just the static ratio. Quench and the chamber design.

Also, don't forget that the cam you choose really dictates what static compression you build into a particular combination. A long duration cam is going to pull a lot of that static compression out of the equation, and if you don't have ENOUGH static compression, the final dynamic compression number can make the engine "lazy" until you hit very high RPM's.

Dave C.

 

You need to know your adv duration and intake closing point.Get on line and search for a dynamic comp caluclator and enter the numbers.If you are running any kind of cam at all you are way low on static comp now. Can't guess at how deep the piston is in the hole and get good numbers or valve relief's.
You can run a 8.9-9.0 dcr and be safe on 92 octane,but it will have to have a dyno tune to take advantage of it.
When you get that high with dcr things have to be figured exactly to make it work.

 

[QUOTE=CCCCCYA]What you DON'T want to do is run the pistons 30 down in the holes, AND use a .050 gasket. Your quench (@ .080) is going to suck with that setup, and might actually be MORE prone to detonation than the same thing with slightly HIGHER compression. Quench has a lot to do with an engines resistance to detonation. It's not just the static ratio. Quench and the chamber design.


Dave C.[/QUOTE


good point. that was another factor in my reasoning to use the bigger dish and shorter deck height.

 

You can run a .0 deck height,flat tops with 4CC valve reliefs(2 eyebrow),56CC heads and .039 Fell Pro head gasket,with a intake closing point around 74* and be safe on pump gas. This is a fairly good set up. You still need to figure up your dcr as this leaves some on the table.