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

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Old 04-17-2018, 01:34 PM
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Default 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!
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Old 04-17-2018, 02:50 PM
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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.
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Old 04-17-2018, 03:41 PM
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Originally Posted by ColeGTO View Post
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?
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Old 04-17-2018, 03:56 PM
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Originally Posted by EJ2King View Post
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.
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Old 04-17-2018, 04:42 PM
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Originally Posted by EJ2King View Post
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?

I like your way of thinking.

Good luck with your build.
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Old 04-18-2018, 10:59 AM
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Thank you gentlemen. I will update here in this thread as the build continues
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Old 04-18-2018, 11:24 AM
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Default 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
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Old Yesterday, 02:55 AM
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Originally Posted by EJ2King View Post
.......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).......
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
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Old Yesterday, 08:46 AM
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Originally Posted by Pantera EFI View Post
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
Thank you for the advice!
I won't have measurement for a another week or so. Still waiting on parts.
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Old Yesterday, 10:04 AM
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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.
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