View Full Version : Slow to boost

U S Marine
10-30-2002, 05:03 PM
First off, I commited a cardinal sin. I changed a lot of parts at one time. I know better than that, but I really wanted to have some stuff done for the SVO show, which I missed! Ok, the car builds boost very slowly. It gets up to 10 PSI in first, then hesitates when shifted to second, then goes immediately to 10 PSI and starts to climb to about 14-15 PSI right at red line. Same thing in third, and so on. When it was stock the turbo reacted MUCH faster. I put on a 3" ATR downpipe, race tube (no cat,) 2.5 Pit Bull (ATR) stainless cat back, adjustable fuel pressure regulator and guage, adjustable boost controller, compressor by-pass valve, cold air intake, 255 LPH fuel pump and a plethora of water/vac hoses. I replaced the TPS and set it to .95v. I tuned it up about a week before I did the mods and it ran great. I figured the car would pull much harder than it did before. I did these same mods to an RX-7 turbo and that car hauled A$$. (13.1xx) on street tires! Any Advice will be GREATLY appreciated.

10-30-2002, 06:12 PM
just curious Tony...cause I don't remember seeing it off when I was there, but did you remove the timing belt? Does it have an adjustable cam sprocket on it? Sounds like it's timing related. If the motor isn't pushing much out...it can't spin the turbo hard/fast enough. Having the cam retarded too much would act something like you're describing.

and....did you redo how the adjustable boost controller was hooked up?

U S Marine
10-30-2002, 06:50 PM
Bud, yes I did re-do the boost controller. I have the arrow on the bottom pointing to the wastegate. So, in from the turbo housing and out to the wastegate. The timing belt was redone right before I bought the car. As I had stated, the car ran superb before I did the mods. Boost levels were fantastic and very rapid in increase. I went over everything 3 or 4 times. I've built NUMEROUS cars and troubleshot many hard to find problems, but this one has me scratching my head! Just so you know, I set my fuel pressure at 41 PSI without vacuum, and it's at 38 with vacuum. If I rev the engine the fuel pressure rises no problem. My A/F mixture gauge reads right at the far scale of stoich and rich at idle, then rich upon acceleration. Driving vacuum is about 15+ inches. I'm stumped. I would think that I should be around the 250-260HP range with this set-up, but it's slower than it was before.

10-31-2002, 09:40 AM

Based on the info you posted, make sure the by-pass valve is fully closed under boost. Easiest way to test is to remove it and cap the tubes. Just a thought?

U S Marine
11-02-2002, 01:34 PM
I don't know what happened, but I drove the car today and in first gear the PSI went to 12, then it shot up QUICKLY and pegged the boost guage at 30 PSI! I got out of it quickly. Did no damage. I slowly pushed the accelerator in third gear, and by 1/2 throttle the boost RAPIDLY went just over 20 PSI. I backed out once again at that point. I read the "too much boost" post in this forum. I'll check the wastegate. I attempted to turn the BC down about 2 turns...nothing. It still wanted to over boost. Anything else I should check? If the wastegate is bad, who should I get one from, and what brand would be the best? I can tell you this.....WOW! If you could run 30+ PSI all the time, what a rocket these would be! The turbo really sounds unbelievable at that boost level. It was sorta cool to hear the turbo, then the tires struggling for traction. If I had a pocket full of cash, I would have let it go for a while! Well, any suggestions will be greatly appreciated.


11-03-2002, 04:10 AM
hey there boost bud. 2 questions.... One, what kind of boost controller are you running? And Second, do you still have the boost controll silonoid pluged in?

It all sounds like it's related to the selinoid. If it's still connected, check the vacume hoses that connect to the turbo...they get old, frayed and then rip...leaking out all pressure to the wastegate, hense overboost

turbo starts to sound great after 18 doesn't it? Loud whine, car is like a F'n rocket.....can't wait to finish my build-up

11-04-2002, 08:30 PM
I agree with everyone above, make sure you check all of your hoses and clamps. Also check to see if your turbo to exhaust manfold bolts are tightened.

Semper Fi

11-06-2002, 03:02 PM
At next year's reunion, we ought to rig up a Chevy like Tony's boost-mobile. Then start it off wide-open down the drag strip, and offer a prize to whoever can find the farthest-away engine part from where it blew!:cheers: