Ls2 403 with L92 heads looking for improvement - LS1TECH - Camaro and Firebird Forum Discussion



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Ls2 403 with L92 heads looking for improvement

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Old 08-31-2016, 02:31 AM   #1
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Well, I finally got my 403 build done and tuned back in May. After driving it for a few months I'm fairly happy with it but I came far short of my goal of at least 500whp. I've attached the Dyno sheet below. Car made 467 434 on a know to be stingy mustang Dyno. The car just doesn't feel very torquey to me and seems to run out of steam faster than I'd like. I spoke with btr where I bought my cam and they are insisting 1 7/8 headers will really open this setup up, but I'm a little skeptical of this. I kind of feel maybe the cam is leaving some on the table. With all the voodoo floating around out there on cam selection for rectangle port heads I'm not sure now if I made the right choice. Looking for suggestions as to what I could do to improve this setup and gain some hp and torque. Looking to keep it n/a. My current setup is listed below. Car is tuned on speed density. Thanks for the help

2006 GTO 6speed manual Ls2 block -Full Manley 403 rotating assembly with -4cc flat tops with reliefs -Rings gapped for N/a - Johnson 2110 lifters @ .035 preload -stock rockers with trunion upgrade -Stock L92 heads with btr .660 springs -Stock LS3 .051 thick head gaskets -static compression 10.9:1 -Btr N/a stroker cam Cam specs are 239/254 .624"/.595" 114+3. -Fast 102 lsxr manifold with NW102 throttle body -Pacesetter 1 3/4 headers with catless mids to custom 3in exhaust -stock ls3 injectors currently at 92% duty cycle. New 70Lb injectors and dw265 fuel pump waiting to go in. Ls2 403 with L92 heads looking for improvement-image-1477982946.jpg
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Old 08-31-2016, 05:15 AM   #2
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The torque seems low for a 400ci engine with almost 11:1, even for a mustang dyno I would check to make sure there isn't something wrong, like a dead cylinder or the cam installed on the wrong centerlines.

The cam doesn't really seem like it's way out in left field or anything. You could advance it and see if that picks up any low end torque. You could mill the the heads some more to get the compression ratio up as well.
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Old 08-31-2016, 05:32 AM   #3
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The torque seems low for a 400ci engine with almost 11:1, even for a mustang dyno I would check to make sure there isn't something wrong, like a dead cylinder or the cam installed on the wrong centerlines. The cam doesn't really seem like it's way out in left field or anything. You could advance it and see if that picks up any low end torque. You could mill the the heads some more to get the compression ratio up as well.
Funny that you mention, dead cylinder, I'm having a drivability issue with bucking between 1500-2000rpm under steady throttle. The tuner has attempted several revisions and it hasn't gotten better. I'll run a compression check tonight.

As far as cam timing I'm 900% sure it went in straight up. Verified it with a degree wheel 3 times so I could calm my ocd lol
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Old 08-31-2016, 02:34 PM   #4
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It's a long shot but I would confirm the TB blade is opening all the way as part of the trouble shooting.
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Old 08-31-2016, 04:22 PM   #5
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It's a long shot but I would confirm the TB blade is opening all the way as part of the trouble shooting.
I thought only the first run of nick Williams 102's had this issue?
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Old 09-01-2016, 05:15 AM   #6
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I'm sure that's that probably the case but my experience has been it's best to check or have some one check rather than assume an item is set up correctly. That's based on getting a set of cylinder heads that were "ready to bolt on" that had metal shavings in the intake ports, a new carb that had part of the link installed backwards that would lock the secondaries open at wide open throttle, a couple of new but defective Accel ignition modules, buying a new crate motor that had a half dozen issues that should have been caught by the builder and so on. Just a few lessons I learned about trusting parts to be correct.
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Old 09-01-2016, 07:15 AM   #7
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Funny that you mention, dead cylinder, I'm having a drivability issue with bucking between 1500-2000rpm under steady throttle. The tuner has attempted several revisions and it hasn't gotten better. I'll run a compression check tonight.
That's due to the cam's 19* of overlap. No amount of tuning is going to fix that issue. The larger LS3/L92 intake valve just doesn't play well with a lot of overlap and intake reversion starts to occur in that RPM range. The only way to fix it is to install a camshaft with less overlap.

Trust me. Been there. Done that. I went from 20* of overlap to 5*. I lost 10 peak HP, gained 50 ft lbs on the bottom end, and the car drives so much nicer.


What intake and MAF are you using?

Last edited by MuhThugga; 09-01-2016 at 07:28 AM.
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Old 09-01-2016, 07:19 AM   #8
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The Ls3 head is VERY picky on cam choice due to the big *** valves in those heads.... hard to tune also from what I hear espically with the a/c on.
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Old 09-01-2016, 04:29 PM   #9
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That's due to the cam's 19* of overlap. No amount of tuning is going to fix that issue........

.......Trust me. Been there. Done that. I went from 20* of overlap to 5*. I lost 10 peak HP, gained 50 ft lbs on the bottom end, and the car drives so much nicer......
Agreed. I have 18* of overlap and I'm gonna swap my cam as well. My car does a good bit of bucking and surging....my new cam will have right about 7* overlap.

Also.....are your pistons in of out of the cylinders at TDC? A .051" head gasket is kinda thick and not optimal for good quench if the piston is in the hole.

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Old 09-01-2016, 05:11 PM   #10
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My .02
Smaller Cam something like ~ 231*/243* 114*+3* same lifts.
(12* E split good for stock LS3 heads up to ~ 6500 rpm NA)
1 7/8" LTs Definetely!
.030 Head Gaskets, up to 11.5:1 Comp.
Since you have the fast 102 already get the mid length runners
Easy enough to swap out. Should pump 12-15+ @ Peak +300-500 RPM
and carry 300-500 beyond peak with little fall off compared to
Stock runners, might be 30-45+ HP @ 7000 compared to now.
No expert, worth what you paid for it LOL.
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Old 09-01-2016, 05:37 PM   #11
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I'm betting there's an easy 10-15rwhp in those headers, going to a 1 7/8
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Old 09-01-2016, 08:34 PM   #12
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Quote:
Originally Posted by MuhThugga View Post
That's due to the cam's 19* of overlap. No amount of tuning is going to fix that issue. The larger LS3/L92 intake valve just doesn't play well with a lot of overlap and intake reversion starts to occur in that RPM range. The only way to fix it is to install a camshaft with less overlap. Trust me. Been there. Done that. I went from 20* of overlap to 5*. I lost 10 peak HP, gained 50 ft lbs on the bottom end, and the car drives so much nicer. What intake and MAF are you using?
I'm speed density tuned with an over the rad style intake.
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Old 09-01-2016, 08:38 PM   #13
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Agreed. I have 18* of overlap and I'm gonna swap my cam as well. My car does a good bit of bucking and surging....my new cam will have right about 7* overlap. Also.....are your pistons in of out of the cylinders at TDC? A .051" head gasket is kinda thick and not optimal for good quench if the piston is in the hole. KW
My Pistons were in the hole. Forget by how much. I agree. I'm thinking quench is a big part of this
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Old 09-02-2016, 06:53 AM   #14
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If your pistons are in the hole, then you are looking at .051" + below deck for a quench. So, you probably have somewhere around .060" of quench. That's huge. Try getting the quench between .035" and .045", and you should see significant gains with timing adjustments.
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Old 09-07-2016, 02:42 PM   #15
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Well did the compression check. All cylinders at between 195 and 200. I did find two plugs with the porcelain cracked as well as one not threaded in all the way. Guess I should have supervised better when my buddies were helping me finish it up.

Any way I'm probably going to pop the heads off when I'm home again and switch to a .030 compressed thickness gasket to get the quench back down. I've been looking at cometic's site as well as Google trying to find a LS 4.085 bore head gasket with .030 compressed thickness but have had no luck. Would the 4.060 bore gaskets work ok on an l92 head?
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Old 09-07-2016, 03:34 PM   #16
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Quote:
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Well did the compression check. All cylinders at between 195 and 200. I did find two plugs with the porcelain cracked as well as one not threaded in all the way. Guess I should have supervised better when my buddies were helping me finish it up.

Any way I'm probably going to pop the heads off when I'm home again and switch to a .030 compressed thickness gasket to get the quench back down. I've been looking at cometic's site as well as Google trying to find a LS 4.085 bore head gasket with .030 compressed thickness but have had no luck. Would the 4.060 bore gaskets work ok on an l92 head?
Yes they will work just fine. Your actually cylinders are less than 4.060 bore
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Old 09-07-2016, 04:07 PM   #17
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Yes they will work just fine. Your actually cylinders are less than 4.060 bore
i always thought you were supposed to base your gasket bore off the head chamber bore
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Old 09-07-2016, 05:36 PM   #18
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Quote:
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i always thought you were supposed to base your gasket bore off the head chamber bore
Well it needs to be bigger than your cylinder bore or your pistons could hit.
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Old 09-08-2016, 02:38 PM   #19
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Piston bore or head chamber bore; whichever is bigger.
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Old 09-08-2016, 02:41 PM   #20
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Definitely the head chamber in my case.
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