Whats holding it back, view power graph
Thread Starter
10 Second Club
Joined: Nov 2007
Posts: 458
Likes: 2
From: Birmingham UK
Whats holding it back, view power graph I took this to the Dyno yesterday, it is crank not RWHP, my suspicions are that the LS2 ported manifold is restrictive, and/or the cam is not radical enough? I am happy with the power really, but i would like a few more revs.
What tuning software are you using? Can you provide info on Timing?
The LS2 manifold is not the best but still shouldn't be causing your engine to sign off so early.
Sidenote: Do you have any pics of your Cerbera and any TVR Cerbera Speed 12 pics? I've looked all over good high res shots.
The LS2 manifold is not the best but still shouldn't be causing your engine to sign off so early.
Sidenote: Do you have any pics of your Cerbera and any TVR Cerbera Speed 12 pics? I've looked all over good high res shots.
Thread Starter
10 Second Club
Joined: Nov 2007
Posts: 458
Likes: 2
From: Birmingham UK
I am not using knock sensors, the timing is mapped by simply going through the load sites and holding on the brake and trimming the timing up and down. Where it makes more power is where it gets set. The timing trigger is external and is roughly 90 degrees before TDC, but it could be a couple of degrees one way or the other, because the bracket is fabricated. But the way the timing is done it should not really matter, its just a number, as i say the bracket could be out.
i have no cats.
Valve springs are Dual Extreme Gold.
The injectors are at 100% but the AFR is ok.
My Dyno operator thinks there is a restriction, in the fact that air flow is being restricted somewhere, it might be the exhaust manifolds even?
My friends 427 made 684bhp earlier in the day, and hung on until 6500rpm but peaked at 6000rpm, like i say it hung on making useful power till 6.5K. He is on the same bore as me but 4.125 crank. Bigger exhaust manifolds, that in all fairness look alot nicer flow wise because he has alot more room, they are also 1 7/8 mine 1 3/4, he has a fast manifold, and is on the off the shelf comp cam 238/240. He has some Very nice heads also, RHS?? that have bigger valves. Like i say i'm not necessarily chasing bigger numbers, just more rev range. Cheers.
i have no cats.
Valve springs are Dual Extreme Gold.
The injectors are at 100% but the AFR is ok.
My Dyno operator thinks there is a restriction, in the fact that air flow is being restricted somewhere, it might be the exhaust manifolds even?
My friends 427 made 684bhp earlier in the day, and hung on until 6500rpm but peaked at 6000rpm, like i say it hung on making useful power till 6.5K. He is on the same bore as me but 4.125 crank. Bigger exhaust manifolds, that in all fairness look alot nicer flow wise because he has alot more room, they are also 1 7/8 mine 1 3/4, he has a fast manifold, and is on the off the shelf comp cam 238/240. He has some Very nice heads also, RHS?? that have bigger valves. Like i say i'm not necessarily chasing bigger numbers, just more rev range. Cheers.
Could be a couple of things. One is a restriction either going in or coming out. The other is possible valve float/valve train instability since you're using 1.85 rockers on a cam with some lift to start with. Doesn't look like a timing or KR issue to me.
My $.02
My $.02
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I think the valvetrain would be stuttering more than that. My guess is a combo of small cam and restrictive intake. Put a fast 90 on there and see what it does, then cam it, that cam has no duration.
The cam is not too small. That particular cam would be like a 222/226 cam in a 346. I suspect valve control issues are making your power sign off early. Is that cam lift in your signature calculated with the 1.85 rockers? If so, then you'll just need to make sure that your installed height of your springs are corect. If that is 1.7 ratio lift and you have 1.85 rockers on top of that, then you may have exceeded the design of those springs. I suspect the former. Make sure your pushrods are the correct length and make sure your springs are between .050-.100" from coil bind (preferably closer to 50 thou).
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2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
2013 Corvette Grand Sport A6 LME forged 416, Greg Good ported TFS 255 LS3 heads, 222/242 .629"/.604" 121LSA Pat G blower cam, ARH 1 7/8" headers, ESC Novi 1500 Supercharger w/8 rib direct drive conversion, 747rwhp/709rwtq on 93 octane, 801rwhp/735rwtq on race fuel, 10.1 @ 147.25mph 1/4 mile, 174.7mph Half Mile.
2016 Corvette Z51 M7 Magnuson Heartbeat 2300 supercharger, TSP LT headers, Pat G tuned, 667rwhp, 662rwtq, 191mph TX Mile.
2009.5 Pontiac G8 GT 6.0L, A6, AFR 230v2 heads. 506rwhp/442rwtq. 11.413 @ 121.29mph 1/4 mile, 168.7mph TX Mile
2000 Pewter Ram Air Trans Am M6 heads/cam 508 rwhp/445 rwtq SAE, 183.092 TX Mile
2022 Cadillac Escalade 6.2L A10 S&B CAI, Corsa catback.
2023 Corvette 3LT Z51 soon to be modified.
Custom LSX tuning in person or via email press here.
Thread Starter
10 Second Club
Joined: Nov 2007
Posts: 458
Likes: 2
From: Birmingham UK
Hi Guys, thanks for the replies. Here is a before the block swap and an after. The differences are Ls3 block swapped from LS1, comp ratio up from 11.2 to 11.5. The wobbly areas on the graph i think are due to rollers being too small for the power we are making on his dyno. Patrick the lift i have in my profile is taking into account of the 1.85 rockers...in fact somebody not far from THAT seat you are sitting in specced it for me 
, however it was my 383 you did it for! also i opened the chambers out to match the 4.070 bore and cc'd the chambers from 62cc to 65cc to get the comp ratio i desired.
, however it was my 383 you did it for! also i opened the chambers out to match the 4.070 bore and cc'd the chambers from 62cc to 65cc to get the comp ratio i desired. 
id say swap your buddies fast intake and see what happens , youll only be out a couple hours worth of work
and if it works then youll atleast know that is part of why
the LS2 intakes seam to fall on a stock size LS2 , so anything bigger id think it would start falling off a little sooner even ported
and if it works then youll atleast know that is part of why
the LS2 intakes seam to fall on a stock size LS2 , so anything bigger id think it would start falling off a little sooner even ported
i have no cats.
Valve springs are Dual Extreme Gold.
The injectors are at 100% but the AFR is ok.
Bigger exhaust manifolds, that in all fairness look alot nicer flow wise because he has alot more room, they are also 1 7/8 mine 1 3/4, he has a fast manifold, and is on the off the shelf comp cam 238/240. He has some Very nice heads also, RHS?? that have bigger valves. Like i say i'm not necessarily chasing bigger numbers, just more rev range. Cheers.
Valve springs are Dual Extreme Gold.
The injectors are at 100% but the AFR is ok.
Bigger exhaust manifolds, that in all fairness look alot nicer flow wise because he has alot more room, they are also 1 7/8 mine 1 3/4, he has a fast manifold, and is on the off the shelf comp cam 238/240. He has some Very nice heads also, RHS?? that have bigger valves. Like i say i'm not necessarily chasing bigger numbers, just more rev range. Cheers.
What is your injector rated at?
Fuel Pump flow?
Are you running some style of block hugger exhaust?
Are the springs set to within .050 of coil bind as Patrick G mentioned?
Are you seeing a good sweep pattern on your valvestem tips?
Just for kicks at is max timing currently at?
A well designed 1 3/4 can carry an engine the size of yours beyond this RPM. Look at LG Pro Long Tubes on the myriad of Vettes with 400+in engines.
Your AFR is a little leaner than I would prefer. The graph appears to be in the 13:1+ range. I generally tune for 12.4-12.7:1 NA.
An injector @100% is always an issue. That means it's open constantly. Not ony this this detrimental to the injector it's possibly endangering your engine.
A hot tune + injectors on the ragged edge = an engine thats an atmospheric change away from meltdown.
Thread Starter
10 Second Club
Joined: Nov 2007
Posts: 458
Likes: 2
From: Birmingham UK
Injectors are stock LS2.
I am Really limited on exhaust design, i'll post some pics later so you can see what i'm talking about. The valve springs are at stock height also. But i really dont think its a valve control issue, it revs on the road to past 6500 without hitting say, a brick wall just its not as convincing as i'm sure its potential could be.
I am Really limited on exhaust design, i'll post some pics later so you can see what i'm talking about. The valve springs are at stock height also. But i really dont think its a valve control issue, it revs on the road to past 6500 without hitting say, a brick wall just its not as convincing as i'm sure its potential could be.
TECH Fanatic
Joined: Aug 2005
Posts: 1,691
Likes: 1
From: Sunny London, UK
Might be a combo of things. Whats your manifold pressure at WOT? Does it drop much below barrometric? That will tell you if its an intake restriction. Exhaust you probably should have 1.75" long tubes with dual 3" pipes. Anything less is going to cost you some lost power.
I think the fast will help too. I gained a lot with the fast on my H/C 346 over the LS6.
I think the fast will help too. I gained a lot with the fast on my H/C 346 over the LS6.
Thread Starter
10 Second Club
Joined: Nov 2007
Posts: 458
Likes: 2
From: Birmingham UK
id say swap your buddies fast intake and see what happens , youll only be out a couple hours worth of work
and if it works then youll atleast know that is part of why
the LS2 intakes seam to fall on a stock size LS2 , so anything bigger id think it would start falling off a little sooner even ported
and if it works then youll atleast know that is part of why
the LS2 intakes seam to fall on a stock size LS2 , so anything bigger id think it would start falling off a little sooner even ported