SleeperX

Finally got my car dyno tested.
I think it might be running a little low on HP.
VRUS, or anyone else, any suggestions of what it might be by looking at the chart.

Mods:
Renntech ECU
Renntech Pulley
Renntech headers
Renntech airbox (stock filter)

Grumpy666

Upon first glance, the curves look fairly typical, except for the region above 5000 PM. In that area, th HP curve flattens out. It should continue to rise to just past 6000 RPM, where it would begin to taper off. The top two reasons that come to my mind is a rich A/F ratio or S/C belt slippage. Can you post the A/F curve? If the curve wasn't flattening out, I would expect your HP to be in the 460-470 range, maybe about 20 HP shy of where you should be with your mods. Your peak torque looks to be a little low, too. How's your IC cooling circuit performing? Any idea of IAT during the pulls?

SleeperX

Hopefully this image is better.

BTW, I also have the Kleemann I/C pump upgrade.

SleeperX

Unfortunately the A/F measure wasn't working properly at the shop, so they couldn't give me a A/F curve. I was thinking that My A/F might be too high and that is why I took it to the dyno in the first place.

I have attached Renntech's dynograph from their website for a car with my upgrades.

BTW, would the A/F ratio affect my torque. It seems like my car is putting out more torque than was advertised by Renntech. Any thoughts.

rflow306

I would recommend a data logger before your next dyno. With our cars, i believe it's a must.

Choson1

what is the average drivetrain loss % for the E55?

Grumpy666

IMO, A/F ratio is part & parcel to dyno testing. You should go back and request another pull when their's is working properly - at their expense.

In that RPM range, I would expect your ratio to be too low, not too high. Probably somewhere around 9:1-10:1.

My comment about your torque being low was based on an average pre-mod dyno. The Renntech dyno plot shows a car that I would consider to be at the low end of the range. If I'm not mistaken, an average stock E55 puts out closer to 410 rwhp and 460 rwt. I think your post-mods torque should be closer to 520 lb-ft at the wheels.

GTA23109a

MB_Steve: My dyno plots look nearly identical to yours and I'm using the Renntech parts as well (minus the airbox). My a/f was about right on but the HP was leveling off on top. Shortly thereafter (i.e as soon as we got home) we noticed that the SC belt was shredding. It's my belief that we need some sort of additional belt-retention either in the form of a secondary idler pulley or a backup to the stock tensioner (preferably both). Also, my car was way higher on TQ than expected as well, but down a few HP. Very interesting to see that I wasn't the only one . . .

Grumpy666

19% seems to be the accepted value.

jangy

I thought it was between 16%-20%? Dunno, but it looks like most stage 2 cars are putting about 475 to the rears. Is that what most K2, EVO2, and Renn2s are seeing?

SleeperX

In the first run it put out 524 Ib-ft at the wheel. How does the A/F ratio impact torque?

Choson1

thanks. that's pretty damn efficient for a torque converter.

dragonAMG

Both the torque and horsepower seem a bit low. K2's are doing roughly 460-480rwhp and 530-550 rwtq. We don't have a 4k carbon airbox... just chip, pulley, and headers.

SleeperX

However, K2s have no cats. I still have my cats in place.
Kleemann headers are much larger than Renntech headers. Much larger. If there was a way to keep my primary cats with those headers, I would have bought them in a second. (in hindsight, the Evosport headers might have been a better option). I believe Kleemann states that their headers add about 40hp whereas Renntech claims that their headers add 20hp. (In reality, I think the difference between the 2 is greater than 20hp) My airbox is only suppose to add 15hp, so I do not think that is a fair comparison. In addition, I am running factory air filters. Does your K2 figures stated above assume factory air filters?

As for K2 putting out 460-480hp vs. my Renntech stage 4's 449hp, I do not think my car is testing properly. Take a look at the dyno for yourself. As Grumpy666 pointed out, my dyno graph is flattening out at 5K rpm as opposed to 6K rpm. Something is clearly wrong. I would be that my belt is slipping. Do you have a K2 dyno chart. I would be curious to see how much HP they put out at 5K rpm for a true comparison.

SleeperX

I think we really need to look into this. If my/our SC belts are slipping I think this is a huge problem. I was planning on getting the Renntech throttle body installed in a few weeks, but now that I am under the assumption that my SC belt is slipping I am having second thoughts. That may only exacerbate
my problem.

Has anyone, Kleemann, Renntech, Evosport, Brabus looked into a tensioner for the SC belt?

Grumpy666

My bad - that was supposed to say 540, not 520. I was looking at your graph at 520 and thought to myself, that needs to be 540 - so I wrote 520. Had a mild case of Rectal Cranium Inversion. All better now.

I wasn't trying to imply that your torque peak is low due to the A/F ratio - especially w/o knowing what the ratio is. I think it's more likely that it's related to heat. I think the torque at the HP peak is probably due to a low A/F ratio.

But, to answer your question, dynos measure torque, not HP. If the A/F ratio is not near optimum, the fuel that is burned during the combustion process does not release as much energy as it would at the optimum ratio. This reduces torque output, and hence, horsepower. It's just easier to see it in the curve at the HP peak, since it has an expected shape.

SleeperX

So would you say that my problem is too rich of a A/F ratio, potential S/C belt slippage, heat soak, or maybe all 3.

dragonAMG

I see... I didn't know that about Renntech headers. That explains the difference.

As requested...

SleeperX

Very nice dyno. What is the X=6.31 for in the bottom right corner

Grumpy666

Your curves indicate that you may have some S/C belt slippage occurring. At 4400 RPM, the two curves start to diverge, with the second run being higher than the first. So it's not likely a heat-related issue. If you look closely at the A/F ratio curves at 5200 RPM, you'll see that the first run is dipping lower than the second. This is probably due to less air being available for the first run compared to the second. This could be caused by belt slippage. If it were caused by ECU programming, I would expect both curves to be the same.

The good news is you have the best A/F curves I've seen posted on this forum. Someone really nailed your ECU programming for fuel tables.

Vadim @ FD

It is bypass valve opening and closing.

It is not belt slippage, I actually verified this using shaft-speed strobe reader.

vader

hmmm....there was some talk about this by-pass valve in Vrus' 80mm. thread. What exactly is the purpose of this valve ? Is anyone playing with it to see if it can be de-activated when needed ?

jangy

Please explain this for the rest of us that have no clue.

Grumpy666

Looking at the smooth, consistent difference between the two torque curves, that makes sense. If it were belt slippage, I would expect the curve to be a little more erratic.

You were researching this valve with one of ECU programmers about 6 or 7 months ago. Did you guys ever figure out how to control it?

vrus

Everyone has already pointed out the issues and recommendations. A dyno chart without the A/F is useless. You shouldnt even accept it from the dyno shop that way.

Invest $250 in a datalogger like rflow mentioned because it is an invaluable tool. It will give you a good indication of whether your car has a problem or not.

Get the dyno shop to redyno the car and put up the chart with A/F showing.