Let's Talk Compression
Thread Starter
Burning Brakes
Joined: Jan 2011
Posts: 819
Likes: 130
From: San Antonio TX
Let's Talk Compression
I am rebuilding a LS2 for a TVS2300. I am going to keep the stock crank with forged pistons and rods. I don't have high hp goals, and I probably wouldn't have even bothered with a rebuild had it not been for a stripped crank bolt. I found another stock crank that I plan to polish and use. I really don't want to deal with high IATs and spinning the blower for higher psi with lower compression i.e.9-9.5:1.
Are there any issues that I may not be aware of with staying in the 10.5:1 range (maybe a bit less with the LS9 gaskets) and keeping the psi lower. I know the tuning window is narrower with higher compression, but with a goal of mid 600's rwhp on 93 I think that I am well in the safe zone at that compression with forged slugs and rods. Reliability is key for me. Pat G will be doing the tune, so no worries there.
Should I drop to 10 and add some more psi or roll with the 10.5?
Engine has TSP heads, mild PD cam, and headers.
Are there any issues that I may not be aware of with staying in the 10.5:1 range (maybe a bit less with the LS9 gaskets) and keeping the psi lower. I know the tuning window is narrower with higher compression, but with a goal of mid 600's rwhp on 93 I think that I am well in the safe zone at that compression with forged slugs and rods. Reliability is key for me. Pat G will be doing the tune, so no worries there.
Should I drop to 10 and add some more psi or roll with the 10.5?
Engine has TSP heads, mild PD cam, and headers.
Racer
Joined: Oct 2018
Posts: 466
Likes: 158
From: ATX
On straight 93 lower compression is always a plus because you have more timing adjustability for knock where you cant remove compression. With that said a stock LS3's compression is 10:7:1 and tons of people making 600's with no issues on 93. Id go with 10:5:1.
Your compression is not going to effect you IATS. IATS are effected by the air coming in (where its pulling front and what heat is getting to it), the intercooler bricks and rotors in your setup. Things that will help your IATS on that setup is a good blower cooling system ie, bigger tank, pump, heat exchanger with fans... the best thing would be something like the INNERCHILLER. The ecu will pull timing for high iats so getting those under control will keep everything happy.
Your compression is not going to effect you IATS. IATS are effected by the air coming in (where its pulling front and what heat is getting to it), the intercooler bricks and rotors in your setup. Things that will help your IATS on that setup is a good blower cooling system ie, bigger tank, pump, heat exchanger with fans... the best thing would be something like the INNERCHILLER. The ecu will pull timing for high iats so getting those under control will keep everything happy.
Thread Starter
Burning Brakes
Joined: Jan 2011
Posts: 819
Likes: 130
From: San Antonio TX
On straight 93 lower compression is always a plus because you have more timing adjustability for knock where you cant remove compression. With that said a stock LS3's compression is 10:7:1 and tons of people making 600's with no issues on 93. Id go with 10:5:1.
Your compression is not going to effect you IATS. IATS are effected by the air coming in (where its pulling front and what heat is getting to it), the intercooler bricks and rotors in your setup. Things that will help your IATS on that setup is a good blower cooling system ie, bigger tank, pump, heat exchanger with fans... the best thing would be something like the INNERCHILLER. The ecu will pull timing for high iats so getting those under control will keep everything happy.
Your compression is not going to effect you IATS. IATS are effected by the air coming in (where its pulling front and what heat is getting to it), the intercooler bricks and rotors in your setup. Things that will help your IATS on that setup is a good blower cooling system ie, bigger tank, pump, heat exchanger with fans... the best thing would be something like the INNERCHILLER. The ecu will pull timing for high iats so getting those under control will keep everything happy.
Racer
Joined: Oct 2018
Posts: 466
Likes: 158
From: ATX
I am looking at the interchiler with spacers/blanket and have reached out to some people regarding the install. I haven't got a definitive answer on the how much freon needs to be added over stock to accommodate the increased demand and capacity. Being in Texas, I won't compromise cabin A/C for performance since this is just a cruising car.
Thread Starter
Burning Brakes
Joined: Jan 2011
Posts: 819
Likes: 130
From: San Antonio TX
What I was driving at is that higher compression will make more power at the same psi than lower compression, thus requiring less blower psi to hit x goal thus lower IATs. The more the motor is making the less the SC has to work. The flipside is that higher compression equals higher cylinder temps/pressures resulting in a smaller tuning window margin of error before things go boom. I think we are saying the same thing.
Racer
Joined: Oct 2018
Posts: 466
Likes: 158
From: ATX
What I was driving at is that higher compression will make more power at the same psi than lower compression, thus requiring less blower psi to hit x goal thus lower IATs. The more the motor is making the less the SC has to work. The flipside is that higher compression equals higher cylinder temps/pressures resulting in a smaller tuning window margin of error before things go boom. I think we are saying the same thing.
Le Mans Master
Joined: Dec 2005
Posts: 7,002
Likes: 1,688
From: Southeast TX
I've had two TVS2300 blown LS3's. Both running stock LS3 10.7:1 compression ratio. The first one was a jackshaft model running a 3.3" front pulley and 1:1 rear pulleys. It had a 219/231 115 lsa blower cam and long tubes. At about 8.5psi, it did 640 at the wheels. No issues on 93 octane.
The second one had a Heartbeat blower with 3.2" front pulley. It had a 224/234 116+2 cam along with headers. It showed 9.5psi and did 660 at the wheels. That one had meth which I think is a waste of money on a TVS blower unless you figure out a way to inject it evenly post blower.
I'd definitely upgrade your cooling system as mentioned above. I ran a Dewitts radiator along with a 160* stat. It actually ran too cool in anything but really hot weather. If I had a do over on that one, I would use a 185* stat.
Said all that to say my vote would be to run 10.5:1 static CR.
The second one had a Heartbeat blower with 3.2" front pulley. It had a 224/234 116+2 cam along with headers. It showed 9.5psi and did 660 at the wheels. That one had meth which I think is a waste of money on a TVS blower unless you figure out a way to inject it evenly post blower.
I'd definitely upgrade your cooling system as mentioned above. I ran a Dewitts radiator along with a 160* stat. It actually ran too cool in anything but really hot weather. If I had a do over on that one, I would use a 185* stat.
Said all that to say my vote would be to run 10.5:1 static CR.
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Le Mans Master
Joined: Dec 2005
Posts: 7,002
Likes: 1,688
From: Southeast TX
I'd run this past Pat G. Your dynamic compression ratio is probably more important than the static CR. Static CR and cam timing both effect dynamic compression ratio. You didn't mention cam specs. Most blower cams specced for PD blowers have wide LSA's and not much advance. Both tend to lower DCR's and allow more timing and boost before reaching octane limits.
Le Mans Master
Joined: Dec 2005
Posts: 7,002
Likes: 1,688
From: Southeast TX
Good choice.
Pat G has specced several PD blower cams for me over the years. All created a DCR of 8:1 in an otherwise stock LS engine. Your DCR, with a static CR of 10.5:1 checks in at 7.85:1. That's a good thing. If you didn't have access to quality 93 octane, you might consider a lower static. I've run Vettes and trucks with PD blowers for years. Never had one tank of fuel with low octane in any my blown LS engines. That covers several hundred thousand miles. Did have one in my N/A LS3 last year. It's 11.3:1 static with a DCR of 8.5:1. A can of octane booster from my local parts store cured that.
Pat G has specced several PD blower cams for me over the years. All created a DCR of 8:1 in an otherwise stock LS engine. Your DCR, with a static CR of 10.5:1 checks in at 7.85:1. That's a good thing. If you didn't have access to quality 93 octane, you might consider a lower static. I've run Vettes and trucks with PD blowers for years. Never had one tank of fuel with low octane in any my blown LS engines. That covers several hundred thousand miles. Did have one in my N/A LS3 last year. It's 11.3:1 static with a DCR of 8.5:1. A can of octane booster from my local parts store cured that.
Le Mans Master
Joined: Dec 2005
Posts: 7,002
Likes: 1,688
From: Southeast TX
The only time you'll have IAT issues is when you make back-to-back runs. Recovery is pretty quick as long as you have decent air going through the heat exchanger. More pump and a higher volume tank definitely helps. I've heard that the Edelbrock HE that comes in the EForce kits is really good. The ZR1 guys see it as an upgrade over the dual pass HE that comes on the ZR1. Might be worth considering.