For those who know what they are talking about. I am one of the people that have blown the motor and is the process of rebuilding. I have to a couple of quick questions regarding rebuild and boost applications. Before I start if you plan on flamming or start post wars please leave the thread. Here is my sitiuation last winter installed 2.2L cometic headgasket instead of the 2.0L because at the time the 2.0L was not in production and purchased head studs. Well now the motor shot due to whatever the flaws are, pistons, fuel starvation, heat etc.... I ordered new pistons. Went with 10:1 because of the headgasket dropping the compression down to 9.5:1 which brings it back to stock compression. Right now I am trying to decide which route to go far as pulley setup:
1.keep the headgasket which is perfectly fine and go with a whatever pulley that will work to maximize the power
2.get the 2.0L headgasket which will raise the compression to 10:1 and run a larger pulley

Any thoughts or comments in general regarding builds for the LSJ. I would like this thread to be an informative and useful resource for people that are the same position or will be in the same position down the road.

Thought I would bring this thread back to life. I would also like to know. I always felt that low compression pistons would work great with the LSJ. Maybe go as far as 8:1 so you can run even more boost. Maybe just keeping the stock compression would also work nice since its strengthing everything. What is this talk about compression changing with head gasket?

from what I have read is that since the 2.2L headgasket is thicker than the 2.0L it lowers the compression about a .5 So theoreticaly by having a 2.2L headgasket would drop stock down to 9:1 instead of maintaining 9.5:1. Therefore the 10:1 pistons I bought now should have a compression ratio of 9.5:1 with that headgasket. I only went with the 2.2L because that was the only headgasket available at the time when I wanted to switch it out asap because people at the time were starting to blow the stock headgaskets with 20lb of boost or more. After I installed it then they released the 2.0L and I wasnt about to tear the motor back apart again to change it lol since the only difference is the thickness.

Well basically a higher compression ratio helps improve off boost performance. Since an Eaton supercharged makes boost almost instaneously, I would run a lower compression ratio and help make up the difference with more airflow.

9:1 sounds like a good comfortable number to run.

The thicker head gasket will effectively increase your combustion chamber volume which in turn will lower your static compression ratio.You did not mention what piston manufacturer you will use so I'm unsure if your pistons will have a dome or not.I am not a fan of thicker head gaskets especilly stock compositin types as they tend to blow easier.If your pistons have a dome I would have your local machine shop shave them the desired amount to produce a combustion chamber volume,including deck height and compressed gasket thickness to give you the desired 9.5 compression ratio using the LSJ gasket.You also didn't mention what you plan to use for camshafts.If you are grinding something custom the amount of overlap comes into play as a lot of overlap will bleed off cylinder pressure.Depending on your budget,my choice would be to use the GMPP cylinder head that is cut for O-Rings and the gasket set that goes with it.
Just my opinion of course,good luck on the build keep us posted

Stock compression is perfect for this motor. Ever wonder why no one makes low compression pistons for the LSJ? The ecotec is an extremly knock resistant motor, meaning you can run it with lots of boost and heat, and still get minimal if any detonaton. In my experience this motor gets less detonation than almost any other motor I've worked with. The head design is very good and the combustion chamber does a good job of eliminating hot spots.

Go with the 10:1 and the cometic gasket for the lsj. The problem with the m62 is when you run a 2.5 pulley you are over spinning it and it looses efficency. Bump up the compression and run a 2.7 pulley cooler IAT 2's more timing less blower drag on the engine.=More power.
Side note: The top fuel dragsters blowers take 300 hp to turn.

from what I have read is that since the 2.2L headgasket is thicker than the 2.0L it lowers the compression about a .5

By the way, the gasket difference is only .014" different resulting in approximately 0.3 loss in compression ratio. You would really be at 9.204449920485652.:cssNET:

thanks for correction

Go with the 10:1 and the cometic gasket for the lsj. The problem with the m62 is when you run a 2.5 pulley you are over spinning it and it looses efficency. Bump up the compression and run a 2.7 pulley cooler IAT 2's more timing less blower drag on the engine.=More power.
Side note: The top fuel dragsters blowers take 300 hp to turn.

What he said, a 2.7 would be ideal, its right in the middle, or you can run even bigger and work around the blower, i.e. build it up like you are get a h/e, run meth, make the blower more efficient.

What he said, a 2.7 would be ideal, its right in the middle, or you can run even bigger and work around the blower, i.e. build it up like you are get a h/e, run meth, make the blower more efficient.

I got every cooling mod except the meth injection

thanks for correction

Eh, I had nothing else to do right now.:lol: But I would listen to Blown4banger he is just starting his rebuild, and knows what he is talkin about.

Top fuel dragsters=7000 hp - 900 to turn the blower.

Go with the 10:1 and the cometic gasket for the lsj. The problem with the m62 is when you run a 2.5 pulley you are over spinning it and it looses efficency. Bump up the compression and run a 2.7 pulley cooler IAT 2's more timing less blower drag on the engine.=More power.
Side note: The top fuel dragsters blowers take 300 hp to turn.

I agree. A lot of people here on the forum are afraid to run compression over 9.5:1. Theres nothing wrong with it as long as you have the mods to support it. Like ARP Head Studs and a nice head gasket. The higher compression and lower blower speeds is going to make you soo much more efficient. On top of that, do some cam work and you will be golden.

I agree. Higher compression, supporting mods, larger pulley, and cam work will make you a lot more efficient and greatly cut down on the heat problem. Remember, the cooler your charge, the denser the air. Meaning you can move more air mass with a lower volume (and thous lower psi), with less risk of blow ups from heat. Plus you won't heat soak near as easy and the car will cruise easier since it will be making more power while not under boost.

The blower looses efficiency not with speed, but with boost. The more boost, the less efficient. If you could spin the blower with a 2.6" pulley and only make 15-16 psi the blower would be back in its efficiency range but with the CFM of a 2.6". Thats why I'm doing extensive head work on mine, my goal is less than 17 psi with a 2.6" pulley, if I could get it down to 15 psi the heat would almost not be an issue with all the cooling mods I have.

The blower looses efficiency not with speed, but with boost. The more boost, the less efficient. If you could spin the blower with a 2.6" pulley and only make 15-16 psi the blower would be back in its efficiency range but with the CFM of a 2.6". Thats why I'm doing extensive head work on mine, my goal is less than 17 psi with a 2.6" pulley, if I could get it down to 15 psi the heat would almost not be an issue with all the cooling mods I have.

Dumb question.... when you mean "make 15-16psi" with a 2.6, do you mean at redline or WOT? Because I'm seeing around 15psi with my 2.6 I may be wrong at where I'm seeing it though? I'm sure I sound like a complete tard, sorry

Dumb question.... when you mean "make 15-16psi" with a 2.6, do you mean at redline or WOT? Because I'm seeing around 15psi with my 2.6 I may be wrong at where I'm seeing it though? I'm sure I sound like a complete tard, sorry

Well, I don't know what to tell you. Whats your elevation? When I said 15-16 psi, I mean to make the head flow so much air, that the blower will have trouble keeping up, meaning it makes less boost, but flows the same amount of air.

Top fuel dragsters=7000 hp - 900 to turn the blower.

They take 200-300 hp to turn the blower depending on the track.

Well, I don't know what to tell you. Whats your elevation? When I said 15-16 psi, I mean to make the head flow so much air, that the blower will have trouble keeping up, meaning it makes less boost, but flows the same amount of air.

650ft above sea level

15-16psi is still high for a roots blower. 12psi would be what I would be shooting for.

im hoping porting my blower will drop my boost levels enough unfortunetly head work, is august for me, when my spare head gets done, god i hate long line ups for head work sometimes but its worth it

Porting your blower won't really reduce your psi that much. Without reducing the amount of air your shoving into the engine, the only ways to reduce the psi are:
1) Cool the air
2) Increase engine flow
3) Enlarge compression chamber size

1 & 2 are the way you want to go. 3 will just mean you'll hit the high point psi a little later in the rpm band.

anyone know the smallest pulley that would be safe to run on 10.0 compression without having to run race gas?

I'd say 2.8" or 2.9" Anything more and your looking at too much combustion chamber heat for pump gas.

I'd say 2.8" or 2.9" Anything more and your looking at too much combustion chamber heat for pump gas.

thanks I will run the 2.8 then, how will that compare to running 2.6 with 9.5:1 far as power wise, I know there will be less heat generated.

Dumb question.... when you mean "make 15-16psi" with a 2.6, do you mean at redline or WOT? Because I'm seeing around 15psi with my 2.6 I may be wrong at where I'm seeing it though? I'm sure I sound like a complete tard, sorry

I too see only 15-16psi with a 2.7" so you sound similar. My car runs fine and is FAST, that's all that matters.

i dont know if it was said or not but the stock compression on the 2.0 is 9.5 to 1 not 10 to 1.

When did we say it was 10:1??? I'm pretty sure everyone knows it 9.5:1. Hell I even know that the combustion chambers are 52 cc :lol: (CC'd the combustion chamber at work today)

am i understanding this correctly? upping the compression and dropping the boost produces similar power to high boost and low compression? that would seem like a good idea to me since i wont overspin the blower........

Non of us are over spinning the blower. The blowers max constant RPM is 16000, and short burst is 20000. At 7000 rpm and a 2.5" pulley the blower is spinning at 16,500 rpm.

do you happen to know the power difference say 9.5:1 runnign a 2.6 and 10:1 running a 2.8? Are they going to be similar in power wise?

IMO you gonna be better off running more boost and less compression. Why? Because with lower compression pump gas is much more accepted by the motor. 10:1 compression with boost is kinda iffy with pump gas (at least in AZ).

is it because of the heat out in AZ?

That plus the shittiest bottom of the barrel 91 SHITane gas in the country :thumbsdow

well thats sucks on the gas, well i will probably do the 2.8 and hopefully next weekend get it dynoed tuned, and crossing fingers it will not blow up on the dyno like it did last time. I pretty nervous about it going on the dyno.

The blower looses efficiency not with speed, but with boost. The more boost, the less efficient. If you could spin the blower with a 2.6" pulley and only make 15-16 psi the blower would be back in its efficiency range but with the CFM of a 2.6". Thats why I'm doing extensive head work on mine, my goal is less than 17 psi with a 2.6" pulley, if I could get it down to 15 psi the heat would almost not be an issue with all the cooling mods I have.



That sounds like a good plan!