Blacker2000SS

I am totally stumped. Here it goes:
Ever since I put the motor back in my car this spring, the motor totally falls on its face at 6400 RPMs. This motor easily revved over 7000 RPMs last year. The things I changed this winter were: Comp 987 valve springs(replaced the Edel. Sure Seat 5767's), Milodin 7 quart oil pan, and a heavily built GN 2004-R and a Vigilante 3200 stall. I really wanted to know what the problem was, so I took the car to the chassis dyno I ran on last year. To my surprise, the car easily revved to 7300 RPMs on the dyno.. The motor ran very strong and made 357 HP @ 6100 RPMs on the dyno with a beautiful fuel curve. After I left, I tried it on the road and it totally flattened out at 6400 again. My first thought was a possible dry fuel pickup problem with acceleration. I filled the tank to the brim and had the same problem. Second thought was a problem with venting in the tank. I vented the gas cap and same problem. Third thought was possibly too much oil in the pan. I took a couple quarts out to no avail..... Someone mentioned a possible transmission problem, but I dont understand how it could not do it on the dyno. In motion the car does it, stationary it doesnt... I'm stumped. Any thoughts would be greatly appreciated. Sorry for the long post.

irocz8957

im not really sure what it could be but im pretty sure it doesnt have anything to do with your transmission!!

92BLKL98

What about the difference in overall vehicle operating conditions on the road vs. the dyno on the road you have the rolling resistance of the tires on the road plus two more tires you're pushing plus aerodynamics of the car loading up the powertrain. These operating dynamics are something I don't believe the dyno compensates for. What about differences in tach readings. Are you using your factory tach vs. the dyno tach, your factory tach could be off. If hp peaks at 6100 rpm why worry about 7300 rpm that sounds like 1200 wasted rpm which is wasted time on the track. JMHO but I have a hard time trusting chassis dynos anyway, my car runs 9.0 1/8 mi the dyno says it puts out 213 hp and 345 tq to the rear wheels those numbers don't jive none of them. I reallize that I'm HP/RPM limited with TPI but my Tq/HP doesn't add up to 9.0 1/8 mi times .

Mike

Blacker2000SS

I understand where you are coming from. The problem is I dont know if whatever is hurting me uptop could be affecting it at other times as well. I have an AutoMeter sport comp tach in the car. I thought of the road resistance thing too, but when I'm wide open in first gear at 30-35 MPH(max) the front tires are light as a feather, and wind resistance isnt anything. This car would still cut out with a tailwind. Stumped is the word of the day.

92BLKL98

Yeah but you still have rolling resistance, until you get to 100+ mph you still have a lot of weight on your front tires and what kind of tail wind are ya talking about we don't normally have continuously high tail winds of this magnitude so I believe wind is still a factor. for the vehicle dynamics involved I don't believe a 900 rpm loss is that bad you would really need to talk with someone with a lot of racing experience and who deals with this kind of thing every day. I'm not knocking this board you get a lot of good info here but my experience is there is not much professional experience here.

TheGreatJ

Overfill your tranny fluid a little and try it again. If inertia is puching the fluid to the back of the pan then the filter may be picking up air pockets. It seems likely since the problem occurs just after you pass your peak HP (hardest acceleration.)