Hey all, I am a new member here but no stranger to wrenching. I have a 97 lt1 and I am planning to clean up the heads and replace the head gaskets with .015" fel-pro 1094's. I hear from a lot of people that 9:1 is the limit for pump gas but I figure that is on an engine with a good VE. My heads will be cleaned up which I doubt will affect flow numbers much so my VE won't be as high in my application. On another forum someone mentioned VE is much more important than the simple 9:1 figure when determining what an engine can tolerate. I am going for ~9:1 perhaps a little lower. I even heard that on a car with stock flowing heads you can even run higher than 9:1 with no problems because VE is lower (not much higher I imagine). Don't think I'm going to try that though unless I see proof of no knock.

My static compression I think will be around 11:1 but I am unsure because I have not measured. Anyone have a clue what the valve reliefs are on the pistons? I will measure beforehand though-I am not doing this blind. What does everyone think about the above? I know cooling is needed and a tune. I have a 160* thermostat and a fan switch might get some purple ice. Anyone think I will have problems with knock?

 

What pistons do you have? That would help.

There are no thinner gaskets for the LT1 than the Mr Gasket ones at .0026", the Fel Pro's you are talking about are probably for a SBC and will not work.

Bret

 

WOW! I must say...this is one of the best questions I think I have seen posted in a long while...someone that actually thinks trapped VE plays a role in DCR!! HURRAY!

I hope this turns into a killer thread. Allot of info to be shared for sure.

Will post info when tooth-picks aren't holding my eyes open...But I think Bret's got your back for now...

Dennis

 

Dennis,

Unfortuneatly I don't think he can trap enough in there with his heads where it would skew the traditional thinking on DCR.

Bret

 

I certainly agree that it is no where as critical on his application. I was still hoping to see some activity on the thread .... I can dream can't I

Dennis

 

Yeah, it would be a good thread. The problem is that these guys will want a definate number in which to hang their hat on.... I don't know how to give that to them! Way to many variables on determining VE or cylinder pressures!

BTW you get me a CAD file of that chamber yet? **** is getting antsy about pistons!

bret

 

:subscribe:

Cool question.

 

Tell the ****, if he would make his mind up...we would of had this **** already to you!

 

I am using the stock lt1 pistons (for now). I am going to cc them but was trying to get an idea for the dcr calculator.

The head gaskets are at summit. http://store.summitracing.com/partde...5&autoview=sku

I was told by a friend that these will work but you have to modify the coolant passages in the gaskets (open them up). He made it seem like it was easy to do and only a few needed modification. I guess I will find out since these are the smallest gaskets I can find without going cutom cometics (not even sure they offer around a .010 which is what I would get). These just seem more cost efficient at 40 a pair.

From what I have found VE does play a bigger role in DCR vs. just the standard 9:1 is the limit. In fact I met a few people running .030 milled unported stock heads and thin custom gaskets and stock pistons they were around 11.5 static with baby cam specs so I imagine the ivc had to be early and dcr had to be up there they all had 160* tstats and various additives but apparantly no knock. Conversely, I think the better your heads flow the less dcr an engine can tolerate. RPM also plays a role here too. I would like to see this turn into an informative thread. I will try to scrounge up some more info. Post away

 

Try -4cc. I have not measured for myself, but was told by another engine builder to use that.

 

LOL agreed! I've told him that! Now the LS2 block is getting here and I'm collecting parts before vacation.

Cometic can only get you down to .030" and a 4.040" bore.

You are right that the VE% has a lot to do with it. I'm working on a LT1 now that is for road racing that's only going to be 8.25:1 DCR but it will be slightly on the safe side with a little timing taken out since the motor will be hot all the time and the thing should make 1.45 ft lbs per cube, which takes some very good VE% for a street motor. Even with good quench (under .040") and reverse cooling, 160 deg thermo and paying attention to DCR the setup should be iffy when the motor temps get over 250 degs on the track with 92 octane. This motor will start off with a stock intake that is less efficent compared to the one that is going on it later (Dennis this is the CNC intake we were talking about) and it will have ZERO problems with knock, but later on it might be on the edge, but i'm trying to play it really safe (for me).

Most times even if you are making some good VE% 8.3:1 DCR is good. I know racerdude wants more than that, but I'd rather have the timing the motor needs in it than dialing it back to get the thing not to knock on pump gas. I've done some 9:1 DCR stuff that I've fed the timing too and listened to them rattle just a tad without issues but thats on stuff I can tear down and fix if need be!! Not stuff going states away that has to be bulletproof.

Bret

 

I personally know people who are running 9.5/6 on the street on pump gas. One is in an IMPY in Vegas and it gets hot there too.
MG and several others have done the 9.0/1 thing with no ill effects and made plenty of power.
One person on this board is/was running 9.1 with stock timing so 9.0 if figured CORRECTLY will NOT hurt ya. If ya got GOOD cooling that doesn't let the engine run over 180* then it is OK.
If it runs 250* ya are out to lunch. There is NO reason to set up/run an engine that hot. It doesn't have to be over 180* with GOOD cooling.

 

Depends on what the motor does all day long. A street motor or a drag motor that gets time to cool off in the pits is a different animal from a road race motor, even with a oil cooler and a Griffen radiator those puppies are going to run over 200*. Now match that up with uphill west coast gas and you could have a issue. Over 100% VE, with 210 deg motor temps, 80+ deg intake air temps and cylinder pressures above 1250psi it can get a little dicey. Remember this is more like designing a OEM motor, than a drag race motor. A LT head and chamber, tight quench and a long rod are all part of this as well, that extra dwell time isin't helping the detonation but it does help the forces on the crank with the lighter weight stuff. It's all a comprimise.

Bret

 

The Impy I spoke of runs 170/80 on the street with the air on in 'Vegas. Mine (what little it ran) didn't get over 180* so the rad and Evans and the fans are doing their job.

 

Bret, when you refer to engine temps (210, 250, etc), are you referring to coolant temperature measured at the thermostat, or something else?