Sprockett

OK,
The other night I was entering the freeway right in back of a modified Pontiac Grand Prix GTP. He took off from the entrance ramp, and I was close behind him. I was with him through fourth, and was up to 145 mph, but when I shifted into fifth, there was absolutely no accelleration. After the shift I was at 5000rpm, and it just stayed there. Is this normal for anyone else? I was pretty pissed that I was winning all that way, then lost in 5th.

JspecFD

iTrader: (2)

what was your boost reading while in 5th?

Sprockett

I don't have a boost guage yet. Do you think a boost controller set at a higher PSI would help get rid of this problem?

Talek

Get a boost gauge, you probably have a vacuum leak somewhere and upping the boost will not help. If everything is running properly you should have plenty of accelleration in 5th, it's better to fix whats wrong before trying to up the performance other ways.

rynberg

NO! First of all, all you would do is hit fuel-cut. And you think you can't accelerate now....

Apart from your acceleration problem, you definitely need to spend more time learning about how to mod your car. Read through Robinette's and Steve's sites (and this one).

Your issue could be a simple boost leak causing you to make less horsepower than you should. When you go into 5th, your engine simply might not be making enough power to make the car go faster.

If you don't want to spend the money for a boost gauge right now, go buy a $20 vacuum/boost gauge from the auto parts store. Run some vacuum tubing (about 8') from the gauge to the nipple on the upper intake extension. Run a couple of WOT runs to see what your boost is doing. This is a quick, easy, and cheap way to check your boost conditions.

Sprockett

Ok, thanks for the suggestions - I just have one more question. Let's say I do have a vacuum leak somewhere. How would I go about finding where it is, and once I locate it, how would I fix it? Could this problem be caused by a broken hose going into the airbox? I say this because a while ago the hose on the top right (looking from the front of the car) of the airbox broke away from the airbox. I haven't had the money I need to replace it (I'm going to get the HKS intake upgrade). Could this be the problem?

Snook

iTrader: (12)

when I shift into 5th I'm at about 125 (not sure exactly I like to keep my eyes on the road)

I thought that if we all had the same gears since his is 5 speed and mine is 5 speed that in every gear at a certain rpm you would have to be at the same speed.
How could his car be at 145 when he shifts into 5th and mine be at 125?

I think you may have shifted into 5th too early and looked down a few seconds later and seen it at 145 and not felt the acceleration because you didn't use 4th totally up.

I dunno please no flaming I'm also trying to understand what happened like he is.

Snook

rynberg

snook: actually, 4th redlines at about 140 mph. Do you have non-stock size rear wheels/tires? Even if you do, there must be something else going on.

disturbd: get the boost gauge and do a couple of runs in 3rd and 4th gear and let us know what the results are. We can go from there.

Talek

If you have a disconnected hose from your airbox then that wouldn't decrease boost, in fact it would increase flow because you wouldn't be restricted by the stock intake. However, you're breathing hot air from the engine/intercooler which can make your car run slower and hotter, plus it's unfiltered air which can cause problems if you get any debris in your intake manifold..

Snook

iTrader: (12)

rynberg yes I have 245/45/16 all around
I think that is very close to stock
they have more width but the aspect ratio is less so I think that makes up for it.

Is that enough or is there another problem for sure? I know I wasn't going 140 and I shifted at 7k into 5th gear. It could have been 130 tops.

maybe my gauges need to be reset?

rynberg

snook: you say you shifted at 7k? That's your problem right there. Redline that sucker at 8k! Actually, it is painfully obvious when running out 4th gear that the power drops off dramatically after 7300 rpm or so. With a close to stock FD anyway. If I was in a serious race, I would shift into 5th a little bit before 7500 rpm.

BTW, yes with 245/45 you have maintained the stock wheel+tire diameter.

Snook

iTrader: (12)

I'm scared to shift at anything higher than 7
I thought 7 was the point where you really need to shift or you could be hurting your car.
I do have intake, dp, catback, mild streetport and pettit unlimited boost ecu. Midpipe and fuel pump in a week or 2 and the boost set to 13 psi max.

I heard that a streetport shifts your power higher so for me at the track or in a race I should shift higher in every gear? When should I start losing power and what is a good safe rpm to shift at when I want to run my fastest a few times a year at the track or in a good race?

rynberg I also know that you know a lot about tire sizes from other posts. Can I fit any wider tires on the back on the x 8 wheels? Even 255s would be better maybe 265? I know 265s go on x 9 perfect.

thanks and sorry for the length of the post I have lots and lots of questions about my car this is just a little one.
Snook

poss

iTrader: (5)

245's were the widest i could find in a 16 inch rim and still maintain roughly the stock overall diameter.