mikew968

I just had the race car dynoed today on a dyno jet 248 and rwhp is at 196 and 202 T. I seem to have an issue where the HP drops about 12-15hp between 5500-5800 rpm and then returns to it's previous level. Any ideas why? I have dyno runs from 2008 on the same dyno and don't see this drop.

Thanks,

odurandina

1. ****ty aftermarket exhaust.






































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odurandina

2. ****ty stock exhaust with cat well past it's prime.

mbardeen

Isn't 5500 RPM when the variocam system kicks on/off? Sounds rather suspiciously related to that.

ramius665

Yes, 5500 RPM is where the variocam advances timing again. It's also that way from idle-1500 RPM. Unfortunately I don't think the dyno chart will give any usable information on the lower RPM range.

mikew968

No cats, no resonator and pretty basic muffler

Dyno shows steep climb in torque from 3900 to 4300( 165T to 200T) then relatively flat until 5250 and then it falls off

Lemming

Can you post an image of the dyno chart?

Lemming

Mike sent me the dyno and asked me to post, see below.

Mike, I am guessing that your timing belt is off by one tooth. This happened to me after a rebuild a few years ago and the dyno chart is very similar. After dealing with the misalignment, that 10+ hp dip went away. I'm pretty sure that I posted that dyno on this forum, but I don't have time to search at the moment.

ramius665

Well, that would explain the HP dip then, as the timing advances from the variocam the DME is compensating for the timing off by 6* or so... For a bone-stock 968 I would expect to see ~200hp at the wheels.

Lemming

Mike, here is what I consider a "normal" 968 dyno on the same dyno model. This is from back in 2008. Car was chipped, with header and mostly open pipe.

Lemming

Mike, I may have been hasty on my "1 tooth off" diagnosis. When I got home I found the dyno (mustang, so lower numbers) that shows the effect of being 1 tooth off. As you can see, the effect on the HP and torque curves is much longer lasting.

Lemming

Here is an example of my old engine #2. As you can see, it has a dip at nearly the same rpm range as yours. We never determined why this occurred, but I'm guessing that it was timing, just not one tooth off.

93 FireHawk 968

I had my 968 tuned a couple of years ago and as much as peak hp is important I was told the delivery of max hp to max torque was equally if not more important.

Dougs951

I would expect a 968 engine to be more than 196, I just did my S2 and put down 191hp/188tq.

mikew968

We have never really "tuned" the engine for max hp/t. I am in a hp/weight class and at these level i will be about 40lbs heavy. If the power comes up some I should be right at my min weight. All dyno's are different and my last dyno was about 207t and 200 hp just 1 month ago.