Cammed VE SS not making the power it should

[Jimbosa]

Hi guys first post, So I have a VE manual UTE with a L77 and its just been cammed with a VCM OTR, REX triple step headers and a 3 inch hurricane exhaust and its making 420rwhp but this cam is supposed to make at least 460rwhp if not more. these are the cam specs:
HTP02 cam:
233/233 @-050
598/598 Lift
113 LSA
Power from approx. 2600-6800 rpm
The place that did the job is blaming the headers cause they normally use pacemaker or xforce and the headers are the only odd thing in the build.
They are saying that they think the headers dont have enough back pressure so it is loosing top end power.
I'm not sure I buy that being as back pressure doesn't even have anything to do with power and the correct thing to bring up would be exhaust velocity.
I called GM motorsport who makes the headers to ask them what they think is going on and they have said they dont think the headers should be causing this issue.
What do you guys think? Where should I start if not changing the headers to find the cause of the low dyno figures?
Honestly pretty bummed about this whole thing.

 

[ZX14RVFSS]

Dynos all read different - ask to see some other car runs, they may be running low. Even a tiny bit of drag or a poor operator with inaccurate correction values on the software and you aren’t making advertised power or same power as others.
It’s more important to check the curve AND the AFR. If the AFR is spot on, then generally (absent timing changes) you will not get much more additional power without more mods.

That being said - I used to have a VE 6.0L manual ute as well, I cannot recall exact cam specs, it had all the usual mods, and was close to underivable under 1500 rpm’s due to cam, so it’s a safe bet to say it was similar specs / timed to your specs.
.
That Ute spent almost a week being tuned, to get it running as good as it possibly could, simply because it was being a pig / hard to drive, and eventually it managed 325 rear wheel kilowatts. 325 x 1.34 = 436 rear horsepower.
I don’t know re latest tech but 460 plus rear hp from a cam? - no idea… maybe they were advertising engine power rather than rear wheel (approx 22% difference).

I now have a VF with a LOT more mods - obviously a 6.2, full 3” mantra, OTR, new flowed heads, ported valves, upgraded springs, crow cam, increase comp, etc - even that was “only” tuned at 360 rear kws. 360kw x 1.34 = 483 rear hp….

 

[losh1971]

320RWKW is probably about right. It is what it is. I have about 440hp at the wheels. It's not all about power it's also torque.

 

[J_D 2.0]

I’d be happy with 420. 69% of people agree with me!

In all seriousness though wheel dynos aren’t all that accurate and the only valid figures from them are before and after figures on the same car using the same dyno to see what your difference gained is. Hub dynos are more accurate but not used that often.

Was the engine tuned after all the work was done (I assume so but your post doesn’t mention it)? If it was tuned by a competent tuner then it is what it is.

If your basing your hp figure off of some advertising material then take it with a pinch of salt. They always want to advertise the highest horsepower figure so will always publish the best attainable figure rather than the average or lowest expected figure.

 

[MrBags]

Like all say every dyno is different and really should only look at the before and after comparisons to see net gains.
460 may be in the ballpark with the addition of cnc heads on the L77 but those numbers don’t seem too unexpected from the norm to me. So many potential variables.

 

[losh1971]

Dynos all read different - ask to see some other car runs, they may be running low.

Yep, agree there are happy dynos and unhappy dynos. A good tuner will air on the side of caution and claim a few kw less than the reading on the chart. It could also be a safe tune.

Ute spent almost a week being tuned, to get it running as good as it possibly could, simply because it was being a pig / hard to drive, and eventually it managed 325 rear wheel kilowatts. 325 x 1.34 = 436 rear horsepower.

This would be my next question, how long was it in for? A good tune can't be done in one or two days, it takes 3-4 days on a VE SS.

 

[Immortality]

They are saying that they think the headers dont have enough back pressure so it is loosing top end power.

Find a different tuner. People who say engines need back pressure need to find work in a different industry.

I'd try and find some other cars with similar engine combo's and see what they made but as mentioned above, there will be great variations between dyno places and even different power readings day to day depending on the prevailing conditions.

 

[Drawnnite]

Ask them to adjust the straps that hold the car down?

I had a 70rwkw difference between 3 different dynos. 1 was the original tune, 1 was a well known shop I won't go back to, the other is another very respected shop who was straight down the line.
All 3 had different torque figures.
1 explained how and why and what could be done and a whole bunch of other nuances.

It's a tuning tool that's in a controlled environment. Using references at that particular time as known values that then get corrected to a reference.

The quoted figures are a guide only. As has been mentioned by others.

 

[Jimbosa]

Yep, agree there are happy dynos and unhappy dynos. A good tuner will air on the side of caution and claim a few kw less than the reading on the chart. It could also be a safe tune.

This would be my next question, how long was it in for? A good tune can't be done in one or two days, it takes 3-4 days on a VE SS.

yeah honestly I recon the problem might be a shitty tune because I have become aware the place that did the build has a dyno but they get a guy to come in every Friday to tune a bunch of cars at once so NO ******* WAY it was as thorough a tune as it could of been. I'll be taking the car somewhere else for a better tune asap.

 

[Jimbosa]

Ask them to adjust the straps that hold the car down?

I had a 70rwkw difference between 3 different dynos. 1 was the original tune, 1 was a well known shop I won't go back to, the other is another very respected shop who was straight down the line.
All 3 had different torque figures.
1 explained how and why and what could be done and a whole bunch of other nuances.

It's a tuning tool that's in a controlled environment. Using references at that particular time as known values that then get corrected to a reference.

The quoted figures are a guide only. As has been mentioned by others.

bro I think they said the dont even strap the car down it just rides on top of the roller