Dyno Graph
I had my car on a mustang II dyno this weekend with some disappointing results. I’m hoping someone here can help point me in the right direction for fixing it. Texas speed shortblock, aluminum 5.3 sleeeved and bored to 4.125”. 4” stroke, wiseco -2.8cc pistons, 0.051” head gasket, 11.5:1 compression. LS7 heads ported by Texas speed 265cc intake, and milled to 69cc chamber, PAC 660 springs, factory intake valves and hollow stem exhaust valves. MSD intake, ported with 102mm TB. 1-7/8” headers. Cam is a Pat G. Stage 2 LS7 cam with 240/252 duration 112 LSA 108 ICL, when I degrees the cam it showed 106 degree ICL. Johnson 2110r lifters, Texas speed 7.825” pushrods, it has .040” preload on the intake and .030” on the exhaust. Yella terra rocker arms. TKX trans with 3.73 rear gears. It runs and drives great, quiet valve train. No misfires on the dyno. I’m really scratching my head here and hoping someone has some insight as to what may be wrong.

 

So first thing's first.. It is just a dyno, so numbers mean nothing. My c5z on my friends mustang dyno made 440 whp, and on another friends dynojet (same area, weather, etc) made 510 whp.

The setup looks fine aside from the yella terra rockers (touch on that in a second), so you could say it would possibly make somewhere in the 550whp range on a dynojet.

The graph drops off pretty hard at 6100. Did the dyno operator let off at that point or was he still on the throttle? If he was still in it, then something caused that thing to fall off a cliff, and it is safe to say it would have revved out to at least 6600-6800 before flattening out... Probably would have been in the 510-520 whp range on that dyno if so just based on the curve.

Peak torque seems a bit early on this, was the cam installed dot to dot? Or was it advanced at all?

 

No he stayed in it. The graph looks nothing like it feels driving it. It pulls cleanly and hard to 7000 RPM when driving it. I installed the cam dot to dot, when i checked it with a degree wheel, it showed it was advanced two degrees. It is running a holley terminator x ECU. I attached a data log from the dyno graph, if anyone wants to look at that.

 

Did you verify timing with a light?

 

No I haven't, I didn't realize you needed to on an LS. Would i add timing tape to the balancer to do that?

 

What balancer is on it?

 

If it is an ati then it will have timing marks, just need a pointer. If it doesn't, then you will need to find tdc and mark the balancer.

Was the reluctor wheel on the crank welded? Or just pressed on?

 

The reluctor was welded on. The balancer is a holley balancer that comes with the mid mount kit. I have a piston stop, so i can determine TDC and add timing tape.

 

Something isn't happy up top. That combo should never peak and fall off hard at that low of rpm. With no datalog it's hard to say. Could be fueling, ignition, or valvetrain.

 

I added a data log from the dyno run, post 3. I agree, the fall off at 6200 seems valvetrain related. But I feel like the overall torque curve is low too. Ignition and fuel looked good in the data log. No audible misfires on the dyno run. I figured I would hear it if the valve train was unhappy.

 

What does the map kpa look like up in the rpms ? On my wife's current setup with the MSD we ran into a intake restriction and power was falling off pretty hard.

 

Did PatG sell you this cam? If you purchased it from him I'd recommend asking him for advice. He should know what the torque curve should look like. Odd behavior down low I'm not sure if I'd expect the first torque peak to be higher than the second.

I have a couple instances where I've seen Holley EFI's have been seen retarding ~3.5 degrees by high rpm on my engines. You can run a custom ignition profile and add inductive delay, but it made for a hard start condition for me. I run the normal 58X ignition scheme, and just add more timing up top. ~1 degree extra at 3000 and ramp up to 3 degrees extra by redline. A timing check would be great. My engine I can't fit a timing pointer and accessories on at the same time - I had to check timing with the accessories off and the engine running, and then put it all back together.

Questions from the datalog:

What do you have for an intake tract, and what throttle body? MAP sensor shows it is starving for air. You're all the way down at 92kPA at high rpm. Baro was at 99.1kPA so you're seeing > 7% restriction in the intake manifold and it drops all the way through the run as RPM climbs.

Fuel pressure - where are you measuring it, and how are you regulating it? It is moving around during the pull a little strangely

Was this the final run? The closed loop fueling is doing weird things. It goes from +5% at 3400, to -2% at 4400, to +6% at 5000. This window overlaps the weird double torque peak you have going.

MAT (IAT) - your IAT sensor was cooked. 129* at start of run and 140* IAT at the end. Closed hood? Insufficient fans in front of the dyno?

Timing - I'd need to see a timing graph. Very notable, right at 6000 rpm it appears that something changed with how timing was being commanded. Leading up to 6000, it was scribbly with timing wiggling .1* here and there. At 6000 it went to a smooth line, and started pulling timing. I think this may be due to the MAP falling enough that it fell into a different timing row potentially?

I'm guessing your tuner has a V shape timing curve in here, but some modifier kicked in at 6000 rpm and pulled timing. V shape - High at low RPM, minimum at toruqe peak (peak VE), and high at redline. Especially if you have any timing skew going on due to inductive lag on the Holley system, you could be down at 18 degrees or so by 6500 rpm.

Did he ever try more timing? I've had best power on LS7 stuff way higher than 20-22*, but I know other combos do max out in the low 20's.

 

I have a short radius elbow on the throttle body to a 4" intake tube with a cone filter element. The MAT is on the bottom of the intake tube. The hood was open during the dyno run. I attached the tune and some pictures. I hadn't heard of the inductive loss on Holley's, so it needs more commanded timing in higher RPM bands? I'm measuring fuel pressure at the end of the fuel rail. I'm using the Holley ECU to control a ZL1 fuel pump with a PWM signal through a C6 fan controller. Thank you for the help and insight.

 

Run it all by Pat he tunes too.

How much timing advance?

Load / Mustang dyno will show lower number than a Dynojet, not sure about hub dynos.

I made 475rwhp on a Mustang dyno and my heavy car trapped 125mph, 3800 r/w. I'm guessing your camaro is about 3500 r/w.

 

22 degrees at WOT. I've never weighed the camaro, so I'm not sure how heavy it is. I emailed Pat G to see if he has any advice.

 

First off, nice car!

Do not treat my comments about the Holley timing dropping as a rule - however, I have seen 3 different Holley computers on 2 different engines do the same thing. This was with OEM crankshaft and reluctor. They all retarded timing with RPM. I would not feed more timing into it unless you have a timing light on it to verify, or it is on a dyno and you can see the power output.

I'm surprised to see such a bad restriction at WOT even for a 427. I would not be surprised to see ~96 kpa, but 92 kpa is really bad. That short radius bend on the TB is not doing you any favors.

Stupid question, but have you verified that you're getting WOT. I know your TPS says WOT in the log, but is there a chance the blade isn't all the way open?

It would be nice to see a front feed intake tube sticking out the hood as a test, but I don't think you'd be able to get one on there with the radiator and fans right there.

The timing table isn't bad. I don't like the drop timing from 6000 to redline, especially if there's any timing drop happening outside of the tables. At the least, I want to see timing held flat from 6000 to 7000. Probably best would be to feed another 1-2 degrees in. As RPM climbs, especially if MAP is dropping, you can typically add more timing.

I would also be curious to know if he added timing until he found best power, or just stopped at 21-23 because it is an LS7.

Will you have a chance to get back on a dyno for additional tuning or was this one and done?

It is hard to know if the drop in power from 6000 is mechanical or tune related. Yella Terra rockers do stand out. You might need a beefier spring like PAC 1207X. It would be interesting to see it back on the dyno with 1207X without any tune changes and overlay the curves. Then start playing with timing to see if it has more in it. I would also imagine that PatG could offer feedback on this cam + valvetrain combo.

 

Thanks, Spanks. Yes we verified it was actually WOT. That was one of the first things we checked. I'm going to verify timing with a light to make sure it is accurate in the car. I can get back on the dyno, but we stopped at 21-23, expecially with the big drop off at 6200. He was worried the valve train may have issues, which is possible. I'll look into the valve springs as well, I thought the PAC 660 would be good.

 

I had another build, was a 422 with cathedral heads. It was ~12.2:1 and I had the timing at WOT at 25 degrees.

For that other engine I mentioned it was lower compression but we ran it at 28 degrees.

I think 22 is low. You could if you dyno it again put fresh plugs in it and after a dyno pull take a plug out and see where the timing mark is on the strap. You could just replace that plug after each pull to see if it likes more timing. Sounds like the dyno operator was playing it kinda safe.

Having a swapped 1st gen myself, I don't think you have many options regarding the air intake, might be the best you can do.

What power were you hoping to make?

 

I was hoping it would be solidly in the 500s.

 

100% should've been.