Picked up 5.5 mph with a cutout

I

INTMD8

Member
Joined
Jun 24, 2001
I bought a bone stock 87 GN with 124k on it about a week ago. So far I have done-

K&N filter
Adj regulator
welded drivers manifold
threaded wastegate rod for adjustment
walbro intank fuel pump
exhaust cutout

I tuned it on the dyno with the adj regulator and through the midas exhaust system it put down 258rwhp and 378rwtq with 16psi and 93 octane.

Just opening the cutout made the boost go up to 19psi and it was breaking up on the top end but it made 263rwhp and 399rwtq.

I ran it at the track today and mixed in some 110 octane fuel, opened the cutout, and had 30 psi in my 215 60 15 BFG Radial T/A's. It ran

1.823 60ft

12.993 1/4

103.73 1/4 mph

I then capped up the exhaust, and through the midas system it ran

1.962 60ft

13.72 1/4

98.23 1/4 mph

I was very happy with the track times I got for the work that was done to the car, but I'm suprised I picked up 5.5 mph with a cutout.

If I installed a good aftermarket exhaust could I run 103mph through the exhaust, or would I still gain hp with a cutout even with a good exhaust?
 
see the difference between a good and a bad exhaust system?? With a good system you should be within 1-2 tenths MAX of open exhaust..
This is good info.. thanks..
 
Hooker makes a good reasonable price 2.5 inch mandrel bend dual cat back exhaust. You can get it for around $300 or less from Jegs, Summit, Postons, etc. If your car is cutting out on the top end, most likely the timing is being retarded from detonation. Do you have a scantool? If not, it is one of the best investments you can make.
 
How could he have a catalytic convertor if he has an exhaust cutout in place of it?

If you have a good free-flowing exhaust (like ATR), you will see within about .1 difference. I went .08 faster with the cutout open.
 
Well, a Jersey DP has a cat and a dump, but I don't think this gentleman has one...

OK, if you were running 19 PSI on a dyno on pump gas be very thankful you still have a motor. Maybe you should drop the oil and look for metal? Oh, and listen for strange noises for the next little while?

If you've got a crap exhaust, and it sounds like you have, when you open the dump, the boost increases perhaps 2-4 PSI. So, when you say you saw a 5.5 MPH increase with the dump open, it was b-o-o-s-t related. What I'm trying to say is - you're comparing apples to oranges. The question is, what MPH would the car have run had you increased the boost 2-4 PSI and not opened the dump?

Comprendez?

:D
 
Or just open the dump and keep the boost the same as it was before it went up 2-4psi.

AintGoinSlo you and I are thinking of a different type of cutout I think. I was assuming on the DP
 
dump pipe vs Hooker...

I had the stock exhaust and a cut out pipe long ago, opened the cap when i raced , boost went up 4 LBs more boost. When i put the Hooker exhaust on, i raced it, came back to pits and took off dump cap.......... no difference in boost with next run.........so the Hooker flowed just as good with the dump pipe capped vs stock system uncapped ... :eek: alan
 
My car has always seemd to pick up a little with the dump open but the biggest difference I have noticed is better spooling of the turbo while staging.
 
LOL, you guys act like I entered the silver state classic with 40 pounds of boost and 87 octane.

I was testing on the dyno and when I uncorced the exhaust the boost went up to 19psi and it started breaking up so I shut it down. I ran it with 16psi/closed exhaust until I mixed in some 110 octane. With the good gas it was running very good.

I realize that the increase in trap speed was due to the increase in boost. My question was, will a good aftermarket exhaust flow as well as a cutout. It seems the answer is yes.

I also couldn't believe it was pulling 1.8 60's on those puny tires. It definitely was hooking better at the track then it does on the street.
 
Re: dump pipe vs Hooker...

Originally posted by ACME RACING
When i put the Hooker exhaust on, i raced it, came back to pits and took off dump cap.......... no difference in boost with next run.........so the Hooker flowed just as good with the dump pipe capped vs stock system uncapped ... :eek: alan
Click to expand...

I have seen that exact same thing in person.

A buddy and I were testing at the track last year. Just for S & G's we both opened up the dumps, he has the Hooker System, I have the ATR 2 1/2" system.

We both slowed down by a hair with the dumps open. Capped them back up for the next pass and both went a hair quicker. Likely a fluke, clouds came over or something, but none the less:

My question was, will a good aftermarket exhaust flow as well as a cutout. It seems the answer is yes.
Click to expand...

You bet.
 
INTMD8,
What day were you at the track and what track did you go to? I was at US41 on Sunday and saw two other GNs running was one of them you? As for the cutout question, I always gain when I open the dump pipe. 3mph and a way better 60ft from the faster spool up. Boost stays at 17psi and creeps up to 19psi in 3rd if the dump is open or closed. Never goes past 19psi with the stock style adjustable wastegate.
 
Hey, death4, i had heard us41 may be in insurace trouble and might be closing. this may be just a rumor but i heard it from a friend that works at 66. I hope not
 
Originally posted by DEATH4
INTMD8,
What day were you at the track and what track did you go to? I was at US41 on Sunday and saw two other GNs running was one of them you? As for the cutout question, I always gain when I open the dump pipe. 3mph and a way better 60ft from the faster spool up. Boost stays at 17psi and creeps up to 19psi in 3rd if the dump is open or closed. Never goes past 19psi with the stock style adjustable wastegate.
Click to expand...

Yeah, I was at US41 on sunday. I only saw one other GN, but I didn't get to see it run. Mine was the 'not so nice' GN. Other than the cutout, what kind of exhaust do you have?
 
jetmech,
I think the people at 66 are just pissed because they have a very nice strip but nobody wants to pay $30, or whatever it is now, and only get three runs in at a crowded track. Plus the NHRA tech is to strict for most of the "street" racers in the area. US41 and IHRA rules are a little more forgiving as roll cages go. This could lead to insurance problems too. I hope US41 stays around.

INTMD8,
One of the GNs had stock rims and came with a red Mustang and an LS1 Trans Am. The other GN I think had "Pro Stars" on. If you came with the Mustang I was pitted between you and the track with the "Draglites" next to my buddies black Talon.As for exhaust I run the stainless 2.5inch ATR with Pitbulls.
 
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