I though I would post my base dyno runs. I haven't dynoed the downpipes yet; the shop was busy. I am scheduled for the dyno on Sept. 1st and will post my results then.

Car is a 99 XJR 4.0 SC 370 hp 387 tq. factory numbers. I never dynoed it completely stock.
My only mods are a Macleod II X-pipe exhaust and my own intake.
It was nearly 100 deg. F that day. With 20% drive train losses, it comes out to 400-412 hp, not bad for just exhaust and intake and considering how hot it was.

The first two runs are in 3rd gear, because it kept downshifting, even though I unhooked the kickdown switch. 3rd run got botched. 4th and 5th runs were in 4th gear; they started these runs at a higher rpm to prevent downshifting.

1st and 2nd runs




4th run





5th run






4th and 5th together with AFR

 

Here is the first dyno I ever did on my car, it was bone stock back then.

The engine power has been calculated (about 17% drive train loss), it is of course the wheel power you should look at. But I need to add that the 17% drivetrain loss used is more to the truth than 20%.

The rwhp came to 327.9 uncorrected, and the din correction for the day was about 1.03 so acutally 337 rwhp (they only corrected the rule Power with this, and it was 86 degrees).

Dont' want to hyjack this thread either, only want to show you that my 4.0 engine (very similar to yours, though with some small differences as it is a AJ27 versus the AJ26) also has had a high output and without any modifications at the time. This doesn't mean that the modifications you have haven't brought you anything, as maybe your initial power output could have been lower.

 

hi steve, do you have some pics of your wheels ?

 

I don't know what exact drivetrain loss is; could be 17%. Although that does seem low for an automatic. It's not only the transmission loss, but everything else as well: driveshaft couplings, differential, axles, etc. Like you said, only the wheel hp really matters.

As you should know, comparing numbers from different types of dynos is not accurate since they read differently. What is definitive are the numbers I ran at the 1/4 mile dragstrip: 12.996 @ 107.05 mph. This shows that I have even more power than the dyno showed. That was with the same mods as the base dyno; only exhaust and intake. Stock numbers are high 13's. The fastest stock time I have seen was 13.6something. Generally, one tenth of a second improvement equals 10 horsepower.

 

You mean the wheels or the car?

 

I know of one person that had the engine out also on an engine bench, and he came with this figure, it also does seem to fit nicely with other experiences/values I have seen.


I am very aware of many different types of dynos that WIL give different readings even if you were able to keep the circumstances similar, which is why I usually mention numbers with the word about, and always want to know on what type of dyno a run is done when I want to compare. You can compare values, but not as exact figures, purely as indication, as when knowing the dyno type and how the run was made you can interpret the results pretty well.

Have never done a ¼ mile (uncommon here to do, so not many places that offer this), so would probably even with a high powered car not even get good times, maybe when I chose a nice cold day it could help ;-).


I just do not believe (just like that without creditable dynos) that a larger bore exhaust will give significant extra horses (with the tenths counted you are suggesting here now more then 60 extra). It will probably give some which I can imagine and will instanly believe, but even with my high powered car now I didn’t see a significant difference, which is 1 of the reasons I sold my larger exhaust and put back on my stock exhaust.


Made my point I guess, and am looking forward to see what the straight pipes will do now that you have some base runs, or as you say a ¼.

 

I don't think the exhaust added much power either. No way am I suggesting the exhaust alone added 60hp. My intake with the exhaust added about 30-40hp. The additional power came mostly from when I added my intake, in conjunction to the exhaust. I should have did a base dyno with 100% stock car.

 

Well, I had the downpipes dynoed Wed. They did add some power.

The conditions were almost exactly the same. Temperatures were in the 90's again. Fuel from the same gas station and same amount, same tire pressures; everything was pretty much identical.

We did three pulls; 1st run downshifted to 3rd gear again, so we have two good pulls in 4th gear.


Here are the graphs. Last two runs of round two compared to last two runs of the base runs.



Round 2 run 2 compared to base run 4



Run 2: 92.06 deg. F. 29.63 in-Hg, Humidity: 25% SAE 1.02


Round 2 run 3 compared to base run 5



Run 3: 93.53 deg. F, 29.64 in-Hg, Humidity: 23% SAE 1.02

 

Thanks for sharing your experience, and it does seem to make a difference (although small). Not sure why a/f ratio is .25 to .5 richer, it might have given a slight advantage, still not bad. Where these the pipes without catalyst or the sports catalysts?

 

Yeah, the gains are less than I was expecting; only because other vendors that sell high flow cats for these cars claim 20-25 hp. Since these down pipes don't have cats at all, I was expecting that much at least. I'm still pleased with the downpipes, they're still a decent bang for the buck, very well made, well fitting, and much lighter.

The AFR is richer probably because there's no cats to lean out the mixture reading. I would think the richer AFR would be a disadvantage, since leaner makes more power?

I guess companies that claim 22-25 hp gain (Paramount Performance), for sport cats are full of it, according to only my data.

Next is get some runs at the drag strip to see how they perform when the weather is similar to the last time I went.

 

It fits with my experiences also that there isn't that much to be gained and I have yet to see any creditable dyno slips from the manufacturers that prove what they claim. Knowing how easy they pump up the expected values has made me very skeptical, and it is so easy for them to say afterwards that hp would depend on the condition of the car if you would complain.
The gains (or lower than expected gains) are also hard to prove, not many people will go thru the trouble to get comparable dyno runs, so a free run for the sellers... Last but not least, the extra noises will give you the sensation that you have more power, and that is on its own already worth something, just not so much for those who do like more actual power.
Still about 10 hp isn't that bad I would say, it's another 10 extra for not much.

 

Well, I went to the drag strip Oct. 1st. I wasn't able to beat my previous fastest time, but I did beat my fastest trap speed; which is the better indicator of power. Had trouble launching all night.

Using this horsepower calculator http://www.wallaceracing.com/et-correction.php shows I gained 15 hp.

Previous Fastest trap speed run:
60' 2.105
1/4 13.037
mph 107.65
temp. 51 F
humid. 43%
weight 4000lbs
elevation 900ft elev. 900ft

Current Fastest trap speed run:
60' 2.286
1/4 13.200
mph 108.57
temp. 57 F
humid. 62%
weight 3960lbs

 

Great results Shane thanks for posting this info, just found it via the cat thread..

 

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