More cam/less compression or less cam/more compression??
 

Hey Everyone! I've been silently reading through this forum and others over the last couple months, since I started getting parts together for my ls3 top end swap. This is a common build with plenty of reading but I haven't been able to find the answer to my dilemma and the thing that has my build on hold.

My builder and my cam suppliers tech (at Brian Tooley) are saying two different things. One is saying leave the LS3 head unmilled and run a larger cam, the other is saying to mill them. I do not want to flycut.

The problem: Do I leave the heads unmilled and go with a larger cam or do I mill them and run a smaller cam? I cant seem to get a good answer for the combo I ideally want (milled with a max street effort cam).

The car is NOT daily driven but it is a street car. I'm looking for a sort of max power effort build that is streetable. Along the lines of what a stage 4 ls3 btr cam would be on an ls3.
2006 M6 GTO
Mods: 25% ATI udp
Kooks 1 3/4" LTs
Corsa Sport Catback (high flow cats)
BER ported L76 intake and TB
CAI
3.91 gears

And of course finalizing the LS3 heads and cam combo.

Looking to make 480+ whp.

Heylp please!

I think you will find answers supporting both scenarios. Neither of which is "wrong", but a matter of what your expectations are.

The lower compression bigger cam will most likely have less low end torque (below 4K) and either make more HP at the peak or extend the peak HP a little further.

The smaller cam with more compression will have more torque under the peak and most likely better drivability.

So it all comes down to what you prefer. I doubt you would be disappointed with either choice in all reality because it will be better than what you had. Also, you have a 3.91 gear, so I would favor the larger cam choice. But, understand that the street manners are going to suffer with the larger cam.

Thank you for this response. This is actually pretty helpful. Based off of what you said, I've decided to take the following steps.

Based on the BTR Stage IV LS3 cam (233/250 .619"/.595" 113+5)
I'll probably have the builder measure PTV clearance with the heads unmilled. If I have the clearance or room to grow, I will mill the heads/modify head gasket thickness to tighten up compression as much as possible. That's assuming the cam will fit.

If I cannot run that cam, even with unmilled heads then I will have to back track a bit and change strategy altogether.

Does it make sense to try to maximize the build around a cam in this way?

Absolutely. If you are certain that the cam you chose is what you MUST have to get to your goals, then yes. If you can live with a little comprimise and find out that you don't have enough piston to valve or what ever, then you can make the decision at that point. Change the cam, change where you degree the cam in at (advance gives more exhaust PtoV clearance and retarded gives more intake PtoV clearance) don't mill the heads, fly cut the pistons, etc. There are lots of options.

I pretty much did the same thing. I had a cam that was given to me for free that wasn't exactly ideal, but it was in the ball park and I was willing to give it a try.

I wasn't able to mill the heads any more than .005" just to clean them up so my compression ended up at 10.5:1 instead or the 11:1 I was hoping for. I already had the bottom end together and didn't want to fly cut the pistons so it is what it is.

I'm still happy with my compromise because it's 1,000x faster than it was stock, but it isn't EXACTLY what I had my mind set on.

I like your way of thinking.

Good luck with your build.

Thank you gentlemen. I will update here in this thread as the build continues

Hendrick Head = Wide C/L + Compression
 

Hi EJ2, the Hendrick head you have chosen LOVES a WIDE C/L camshaft 116+ AND this head loves compression.

I would fit your "medium" cam duration of 236/250 on a 116 C/L or greater C/L. (GOOD for P/V)
I too would run a .032"-.035" Squish Distance.

The "Big Cam" with Low Compression is a DISASTER choice.

I am able to calculate your P/V if you post your valve drop.

Lance

Ya might wanna just get a heads/cam/piston/head gasket combo that'll get you a dynamic compression ratio in the 9:1 range.

Hard to go wrong with that......

KW

Thank you for the advice!
I won't have measurement for a another week or so. Still waiting on parts.

is it still an LS2 6.0 ? Or ls3?

If ls2 I would NOT run Square port heads, I would run Cathedrals. your 480 rwhp goal is probably not going t0 happen with stock squares, stock compression and a shelf cam on a 4" bore

Just my $.02.

Hey everyone! Thanks for sharing all the information! The BTR Stage 4 was put in. I received a call from the shop telling me the car should be ready for pick up tomorrow.

I was told it dynoed at 465whp. Which is admittedly a little disappointing considering the max effort approach I took with this build. I had my suspicions with the cam specs but ultimately left it in the hands of a very competent shop. My car is also geared.

There are many factors that affect dyno numbers and I am not so naive to think humidity, heat, clutch slip, a stingy dyno or any other host of variables could affect the overall number, but I was hoping for more.

If you are looking for LS2 Parts and some other things...ill be selling parts soon in the for sale section! PM's are welcome, too!

Electric water pump will put you over 480 and greatly improve your throttle response as well.

Is an electric water pump really worth that much?

15 HP to the wheels? Yep.....right about that much.

KW

I had read some older threads on here that some people picked up a little and others said they didn't have any noticeable gains. But a true 15whp is very enticing :nod:

Water Pump Dyno = Drake Pump
 

Hi EJ2, I was the one who made the Data Logger for John Drake when he patented his version of the engine water pump.
The water pump does not require that AMOUNT of HP to operate. (20+ HP ?)
Then there is the Belt Drive HP ABILITY of ???

SO I ASK, if the reported gains are true, where did the HP increase come from ?

MY Guess is LOWER Jacket Temperature AND a viable cause or various reports !

I will add my art of a "balanced" coolant flow, by pump output restriction, required to keep HEAD TEMPS EVEN. (side/side)

Lance

I could not find any conclusive evidence that an electric pump provided substantial gains. I opted for a new factory pump. Perhaps later down the road I'll give it a shot.

I picked up the car today. I gained a little more info on the tune as well. It was put on a speed density tune which I understand to mean that the MAF is bypassed for a sensor built into the intake manifold itself. The tuner found that there is some restriction based on vacuum near redline. He suspects it to be from my throttle body, intake, old maf sensor (left for the sake of iat sensor) or combination of the 3. He suspects that with a different intake setup pre-manifold that another 15-20whp is in the car as is.

The car sounds great and pulls super hard past 4k. It does like to buck around 1500rpm in certain gears but this is a minor thing that I will adjust to.

I will say, I would not want to DD this car with this setup. Its pretty aggressive for my taste in a daily but considering that I have a Forester for that, this is EXACTLY what I was looking for. I like its occasional bad manners thus far.

That idle, and that smell on cold starts.......

On mine, i did find the maf itself was a restriction. And it was 100mm. Same evidence - I was getting vacuum at WOT on a fast 102 and on a MSD. Ditched the maf, rewired for the standalone IAT, got better WOT pressure at the manifold. If you are flowing that much and you down't have enough air filter surface area, that can also be part of the issue. There was another guy on here a while back who lost power right at WOT and it turned out his intake tubing was collapsing.

Cam that big is going to chop. sometimes you can tame it with timing and mixture in the part throttle ranges, but for the mixture changes to stick, you have to run open loop or the fuel trims will bring you right back every time.

Hey Darth
Thanks for the reply. This definitely helps. My tuner says that I can replace the IAT without retuning as long as the new IAT is calibrated the same as the factory one. Which one are you running? And is it possible to get a better temperature sensor (that works better/faster) and still have factory calibration?

I use the F body stock IAT sensor. Any different sensor is likely to require a different calibration.