Raising compression on LS1 and other C5 mods over winter

[DriveHard]

Mods I am considering...

Changing to a 4.10 rear end...this is my highest priority mod for AutoX. 1st is too low, and 2nd is too high, I think this would make the car much more engaging to drive on the street as well. With a 0.5:1 6th gear, it will still be plenty tall enough for good highway mileage.

Increase compression ratio...considering milling the heads 0.040" - that should bring me to about 11.1-11.2:1. I always run 93 octane...and have seen reports of many folks streeting this high of a ratio...thoughts? (head cleaning, crack check and valve job brings it to ~$400 total at a very reputable shop).

Considering going to full roller rocker arms and increased ratio to 1.8:1...should increase lift and duration of the stock cam.

-Will the combo of milled heads and slightly more lift cause piston/Valve interference if I keep the stock cam?

Engine has ~100k miles, and purrs like a kitty. Burns or leaks zero fluids. All stock internals AFAIK

Thoughts?
-I am NOT changing the cam...I want to keep that stock.
-I am NOT going forced induction for now...or most likely ever. I already have long tube headers and CAI.
-These seem to be really good choices for a low budget boost in hp and driving fun.
-New heads are most likely out of budget...but could I get new heads that would out perform the increase in CR and rocker arm combo for just a small $$$ increase? (new heads, but no spending on rocker arms, and head machining)
-I have no desire to raise the redline...would like good power below 6k rpm

 

[Cujet]

You can easily calculate the CR increase in HP. 1 point will be 3% in this case. Likewise, the increased lift of higher ratio roller rockers will provide a few percent in mid range and top end HP. Heck, even a good 3 angle valve job and simple port cleanup has some HP value. Since you already have headers, your engine will be well optimized with these changes. And you can probably then benefit from higher octane fuel, for considerably less timing retard.

Check the forums for whether any of these engines have interference issues with the suggested mods. I'm guessing not.

My thoughts on the final drive ratio are along these lines. Mod the engine exactly the way you want it first, then determine whats needed for ratio. Let's say you make enough changes to add 50HP, which would take more than your plans. You'd then find that 2nd might be just right.

 

[Tman220]

What heads do you have now? 241's? I would consider looking for some 243's and leaving the deck alone other than a cleanup job. If I recall the LS6 243's will get you to 10.5 to 10.8-1 by themselves as well as more flow.

I would look into some thinner head gaskets, there's a few choices out there that will raise compression without cutting that much off the heads.

Also consider this, taking .040" off the heads will require cutting on the intake flange to maintain the proper width/location of the ports for the intake manifold. Also take into account and budget for new pushrods since you will likely require shorter pushrods if you cut that much off the heads and go with higher ratio rockers.

Do you have HP tuners for tuning? You may be leaving power on the table right now if you have access to 93 octane gas. A couple degrees in timing might give you a boost in low to midrange torque as well. You would also be shooting yourself in the foot if you made all those changes and didn't take advantage of them through tuning afterwords.

 

[DriveHard]

What heads do you have now? 241's? I would consider looking for some 243's and leaving the deck alone other than a cleanup job. If I recall the LS6 243's will get you to 10.5 to 10.8-1 by themselves as well as more flow.

I would look into some thinner head gaskets, there's a few choices out there that will raise compression without cutting that much off the heads.

Also consider this, taking .040" off the heads will require cutting on the intake flange to maintain the proper width/location of the ports for the intake manifold. Also take into account and budget for new pushrods since you will likely require shorter pushrods if you cut that much off the heads and go with higher ratio rockers.

Do you have HP tuners for tuning? You may be leaving power on the table right now if you have access to 93 octane gas. A couple degrees in timing might give you a boost in low to midrange torque as well. You would also be shooting yourself in the foot if you made all those changes and didn't take advantage of them through tuning afterwords.

Yes, I realize new pushrods will be needed as well as most likely valve springs...I have an email to Texas Speed right now asking their guidance.
I do have 241 heads...not easy to find 243's around here at a decent price, but I will keep looking.
I have found accounts of several people taking 0.050" off and using stock intakes with no mods. Also Lingenfelter engineering says max safe with no mods is 0.050"
Was already going to use a 0.041" head gasket to help with CR
My neighbor owns this race shop, and will most likely do final tuning.
https://offthelineperformance.com/?...GYHpBWhRQaL2dt6rNFRhf6lf-o_kOfvMaAlgvEALw_wcB

 

[AdmiralYoda]

When you start to consider milling the head and replacing the valve springs...with 100k on the heads you might want to consider a new valve job and new guides and seals. Or go one step further and purchase CNC ported 241 or 243 heads that come with upgraded valves and springs. They will flow much better than stock, but still not as good as aftermarket ones...but waaaaay cheaper. They can mill the heads too.

There are a number of companies that port and upgrade Gen 3/4 LS heads.

 

[DriveHard]

When you start to consider milling the head and replacing the valve springs...with 100k on the heads you might want to consider a new valve job and new guides and seals. Or go one step further and purchase CNC ported 241 or 243 heads that come with upgraded valves and springs. They will flow much better than stock, but still not as good as aftermarket ones...but waaaaay cheaper. They can mill the heads too.

There are a number of companies that port and upgrade Gen 3/4 LS heads.

The $400 cost I stated above included cleaning/crack checking/complete valve job as well as the milling on my current heads.

 

[DriveHard]

...thinking of trying my hand at a mild port and polish job. I've never done that before, and it looks simple enough.

 

[redhat]

Pull some 243 heads off of some Gen IV 5.3s, LS4s or aluminum Gen III 5.3s at a local u pull it junkyard. Around me, a head is $35.

 

[thastinger]

Mods I am considering...

Changing to a 4.10 rear end...this is my highest priority mod for AutoX. 1st is too low, and 2nd is too high, I think this would make the car much more engaging to drive on the street as well. With a 0.5:1 6th gear, it will still be plenty tall enough for good highway mileage.

Increase compression ratio...considering milling the heads 0.040" - that should bring me to about 11.1-11.2:1. I always run 93 octane...and have seen reports of many folks streeting this high of a ratio...thoughts? (head cleaning, crack check and valve job brings it to ~$400 total at a very reputable shop).

Considering going to full roller rocker arms and increased ratio to 1.8:1...should increase lift and duration of the stock cam.

-Will the combo of milled heads and slightly more lift cause piston/Valve interference if I keep the stock cam?

Engine has ~100k miles, and purrs like a kitty. Burns or leaks zero fluids. All stock internals AFAIK

Thoughts?
-I am NOT changing the cam...I want to keep that stock.
-I am NOT going forced induction for now...or most likely ever. I already have long tube headers and CAI.
-These seem to be really good choices for a low budget boost in hp and driving fun.
-New heads are most likely out of budget...but could I get new heads that would out perform the increase in CR and rocker arm combo for just a small $$$ increase? (new heads, but no spending on rocker arms, and head machining)
-I have no desire to raise the redline...would like good power below 6k rpm

I wouldn't push the static compression up if you are depending on 93 octane, especially with the stock cam. I would put a set of trickflow heads on it and keep the safety margin for the premium unleaded fuel.

Boostane works though if you decide to go the compression route.

 

[DriveHard]

I wouldn't push the static compression up if you are depending on 93 octane, especially with the stock cam. I would put a set of trickflow heads on it and keep the safety margin for the premium unleaded fuel.

Boostane works though if you decide to go the compression route.

Any additional input on why? Being in Iowa I can also up the ethanol content...I used to run split tanks of E85 and Premium to get a higher octane blend. The alcohol also helps cool the intake charge.

 

[thastinger]

Any additional input on why? Being in Iowa I can also up the ethanol content...I used to run split tanks of E85 and Premium to get a higher octane blend. The alcohol also helps cool the intake charge.

I understood your original post to say "I always run 93 octane" I took that to mean that you ONLY run 93 octane.
If E85 is on the table then you could go with that for the added compression but E85 comes with its own set of problems with needing to upsize the fuel delivery system, needing a different tune for it, being hygroscopic, inconsistency of gas station pump % etc.
E85 octane is about 100-104 depending on actual %, the pump can legally dispense E51 and it be sold as E85. I would personally never depend on pump E85 unless I could test every tank and had a tune for E60, one for E70 etc, then you could load the tune to match what the pump put in your tank.

For me, I run 93 octane and I put .42 ounces per gallon of Marine Boostane in with it, brings the octane to 99 but running any of the actual octane boosters will make it impossible to read spark plugs because it leaves the orange residue (MMT) on the plug.

 

[DriveHard]

I understood your original post to say "I always run 93 octane" I took that to mean that you ONLY run 93 octane.
If E85 is on the table then you could go with that for the added compression but E85 comes with its own set of problems with needing to upsize the fuel delivery system, needing a different tune for it, being hygroscopic, inconsistency of gas station pump % etc.
E85 octane is about 100-104 depending on actual %, the pump can legally dispense E51 and it be sold as E85. I would personally never depend on pump E85 unless I could test every tank and had a tune for E60, one for E70 etc, then you could load the tune to match what the pump put in your tank.

For me, I run 93 octane and I put .42 ounces per gallon of Marine Boostane in with it, brings the octane to 99 but running any of the actual octane boosters will make it impossible to read spark plugs because it leaves the orange residue (MMT) on the plug.

In Iowa I believe the lower legal limit for E85 is E70 by law, with I believe a minimum of 105 octane.
The 93 sold here is already E10. I figure about 3 gallons of E85 in my tank gets me up to at least a 95 octane and still under E20.
Also planned on lowering the fan temps and thermostat as well.

 

[AdmiralYoda]

If $400 gets you a valve job, inspection, cleaning, decked, etc...I need to move to IOWA!!!! In MA the prices are ridiculous. The same head job with new OEM equivalent springs, valves and hardware is going to be $1k easy. Around here unless you are restoring something of value it just makes sense to go aftermarket.

 

[DriveHard]

If $400 gets you a valve job, inspection, cleaning, decked, etc...I need to move to IOWA!!!! In MA the prices are ridiculous. The same head job with new OEM equivalent springs, valves and hardware is going to be $1k easy. Around here unless you are restoring something of value it just makes sense to go aftermarket.

I am assuming that is keeping the springs and valves the head came in with, just lapping them (assumption) and new seals.

 

[SubieRubyRoo]

The $400 cost I stated above included cleaning/crack checking/complete valve job as well as the milling on my current heads.

Make sure the shop you use knows how to mill the heads at the correct angles. Depending on how far you’re going, they will need to offset/correct the angle on the intake flange as well, that way you’re not leaving possible areas that the gasket is not sealing properly.

In reality, you’d probably pick up more power and torque (and better drivability), and not have to have any guesses about part quality/durability by picking up a set of AFR heads… or see if you can get your stock heads into Tony Mamo or Brian Tooley. Any local shop is simply not going to have the expertise those guys do in LS-specific stuff unless you’re local to Tony Bischoff…

Getting the rocker running conversion kits from Comp Cams is always a good upgrade, but to upgrade to 1.8s you don’t gain any duration per se, just lift.

...thinking of trying my hand at a mild port and polish job. I've never done that before, and it looks simple enough.

Don’t. It may look “simple enough” but you can easily ruin a good port with one ham-fisted move. Leave port & polish to the CNCs & pros; port velocity (and in the right places) is way more important than biggest size. Also, the final finish on the port wall surface is critical as well; most DIYers do too much of the “polish” aspect and slick port walls are terrible at maintaining boundary turbulence, and keeping the fuel in suspension in the air suffers, and you’ll actually make less power than a stock head.

The 404-cube LS2/3 hybrid my brother and I built about 2006 or so had CNC matched, cut 66cc chamber LS3 heads, a custom Erson cam (244/[email protected]”, .621/.621” lift, 113+0 ICL), stock but port-matched LS3 intake, and ported TB with full exhaust made 568HP@6600rpm on a DynoJet and was set up for a 250HP TB plate kit. At just over 4100lbs with driver, it ran a 10.07@137 with low 1.3 sec 60’ on motor and I got kicked off the track because we didn’t have a chute. That’s in a full stock interior 2001 Camaro SS with 10pt cage and a 9” Ford rearend.

Believe me, you want the port shape and velocity to be spot on, more than overall flow, especially if you’re running auto-X events!

 

[DriveHard]

Getting the rocker running conversion kits from Comp Cams is always a good upgrade, but to upgrade to 1.8s you don’t gain any duration per se, just lift.

It doesn't change seat to seat duration, but it does increase 0.050" to 0.050" duration...up to 4 degrees.

 

[SubieRubyRoo]

It doesn't change seat to seat duration, but it does increase 0.050" to 0.050" duration...up to 4 degrees.

It doesn’t truly increase duration as that is ground into the cam. But it increases the area under the curve because the valve is lifted off the seat slightly earlier and held off slightly later. It does not give the same effect as actual added duration as a lobe change would do.

Sure, it’s a modification, but now you’re changing where the rocker contacts the valve tip, and pushrods will change, and for all the added cost there, in keeping with your other fairly low-buck and low-complexity mods you’d be better served with the trunnion kit and keeping the stock ratio. It’s pretty well proven that LS rockers are well-designed and strong for a factory offering, and that the headaches induced by changing ratios are much greater than the minimal performance benefit.

 

[Cujet]

OP, while off topic, in the normally aspirated world, the old claim that there is no replacement for displacement, still holds true. It is often difficult to get significantly more torque from a specific engine that is already well tuned. A huge increase in HP requires RPM and airflow.

I'm reading between the lines and it seems that you want considerably more than the 20HP you'll gain with your planned mods.

With that in mind, why disassemble the engine at all? Just install a supercharger and enjoy the powa!

 

[clinebarger]

OP, while off topic, in the normally aspirated world, the old claim that there is no replacement for displacement, still holds true. It is often difficult to get significantly more torque from a specific engine that is already well tuned. A huge increase in HP requires RPM and airflow.

I'm reading between the lines and it seems that you want considerably more than the 20HP you'll gain with your planned mods.

With that in mind, why disassemble the engine at all? Just install a supercharger and enjoy the powa!

I agree.

 

[jhs914]

I haven't autocrossed in years but for autocross the best bang for your buck is tires and suspension. Getting the gearing right might be worthwhile but the little bit of HP you will gain from your proposed mods will not improve your times that much. If you are modifying your car you are no longer in a stock class so an improved suspension set up and sticky tires should be allowed. I don't know your proficiency level but you should also consider some driving instruction from a pro. That can really knock your times down.