Just installed a 3inch test pipe on my 86' 951 and also did the rear with 3inch and a straight thru borla xr-1 muffler. when back to the dyno and got 210hp and 234tq at the wheels. before the exhaust I had 215hp and 234tq. basically i lost 5hp. This car has stage 2 chips and except for the new exhaust, everything else engine wise is stock with 120k miles. Something is obviously wrong with this car because i see similar setups making 250-260hp at the wheels. I talked with Tim at SFR today and he gave me a few things to check, I also wanted to run this by you folks just so I have a bunch of ideas. The car does run rich on the dyno, before and after the exhaust. like between 10:1 and 11:1 air/fuel. I'm going to try to adjust the AFM and lean it out some but I figure if i actually lost hp by installing the exhaust that something is screwy. The car drives nice and smooth and runs real good, just the power isn't there. The fuel regulators are stock, I installed some new stock fuel injectors and that didnt seem to change anything. Just looking for ideas so i can go attack the car

Thanks in advance.

 

Did you dyno the car just before you put the exhaust mods on, or were the higher HP numbers from awhile back? If the high HP numbers are not from the same day you did the mods, then you can not confirm the exhaust caused you to lose HP. There may be other issues which resulted in the loss.

I've got the SFR 3" cat back waiting to go on my car as well. I did not expect to gain anything as the stock muffler doesn't have much restriction anyway - I'm more after a deeper sound. But I'd hate to be losing HP.

 

Have you checked to see if your cold-start fuel enrichment sensor is bad?

If it is it will cause the car to run rich(it thinks it is always cold).

To test it, let the car warm up to operating temperature and unplug it. This should cause the car to shut off. If it doesn't shut off - the sensor is bad.

The sensor is on the head towards the front on the manifold side.

 

FWIW, I had a similar situation (installed 3 inch test pipe from SFR) and I found out that the exhaust was flowing out the wastegate due to a weak spring (Autometer boost guage was showing 12 lbs.) Replaced the stock wastegate with a Tial and Presto, problem solved.

87 951, HR stage III MAF, HR stage II turbo, ARC2, ARM1, Authority stage II chips, MBC, SFR fuel lines, stock BOV, HR hard pipes, SFR test pipe, Tial 35mm wastegate.

 

In addition to replacing or shimming the stock waste gate, I would check headers for leaks, especially 2-3, and check the welds on crossover pipe fittings. I had a leak in both places... had the crossover pipe fitting welded up and replaced the 2-3 header with used part. It's like having a new car.

Good Luck!

 

What kind of power increase is the pipe supposed to give you?

 

[quote]Originally posted by icat:
<strong>Did you dyno the car just before you put the exhaust mods on, or were the higher HP numbers from awhile back? If the high HP numbers are not from the same day you did the mods, then you can not confirm the exhaust caused you to lose HP. There may be other issues which resulted in the loss.

I've got the SFR 3" cat bak waiting to go on my car as well. I did not expect to gain anything as the stock muffler doesn't have much restriction anyway - I'm more after a deeper sound. But I'd hate to be losing HP.</strong><hr></blockquote>

I doubt you would lose any horsepower, my issue is something wrong with my car, I just need to track it down and fix it. My horsepower numbers are way low for the mods I have done.

 

[quote]Originally posted by Peckster:
<strong>What kind of power increase is the pipe supposed to give you?</strong><hr></blockquote>

The 3inch test pipe is supposed to by about 25hp on a stock vehicle.

 

[quote]Originally posted by TKT2RDE:
<strong>In addition to replacing or shimming the stock waste gate, I would check headers for leaks, especially 2-3, and check the welds on crossover pipe fittings. I had a leak in both places... had the crossover pipe fitting welded up and replaced the 2-3 header with used part. It's like having a new car.

Good Luck!</strong><hr></blockquote>

Whats a good way to check for leaks in the crossover pipes? I dont hear anything unusual near the exhaust looking in the hood area? The stock wastegate is shimmed already, they came with the chip upgrade.

What kind of boost are you guys seeing at say 5000 rpms? 6000rpms? It sounds like I need to get a real boost gauge.

I'm also gonna check that enrichment sensor. that sounds like something to check too.

 

I just had a custom s/s 3" exhaust built for my car (everything but the turbo downpipe). Today was the first day I've driven it since the new exhaust was fitted, as I just got it back last night. I had the car out at a DE track day today, so I really got to feel the difference. My seat of the pants dyno tells me I'm definitely making more power than before, and the boost hits sooner and builds faster. Before this new exhaust, I was running a stock system with a gutted cat and a straight-through Sebring muffler. I think the bigger exhaust makes a more noticeable difference with a modded car like mine though (big Garrett, 52# injectors, MAF, etc)

Funnily enough though...I am experiencing boost creep now. My deltagate always worked fine before, had it set at 15psi, and it would sit there nice and steady. Now it creeps up to 17psi at high rpm, even if I turn the boost **** down. Does this have something to do with having less backpressure in the system???

 

Ian, I had a similar experience to yours. Originally I was debating the cat-bypass vs. cat-back only upgrade. So I drove around for a while without the cat-back section installed and didn't notice any improvements except for the noise and exhaust-fumes whafting into the cabin at stoplights.

So I figured I needed a cat-bypass at the minimum, so I built a 3" one-piece exhaust from the down-pipe back:



I didn't have time to shop around or mail-order so the only place that had 3" pipe was a truck/RV shop and only in super heavy-duty 12-gauge. So the exhaust weighs about 15lbs more than it could (about the same as stock). The muffler is a quick-release design so I can swap it out for a straight pipe at the track in under 2-minutes:



Anyway, I noticed an immediate improvement in power (with either muffler or straight-pipe) and got 1.5psi more boost. So I turned the controller back down to 15psi and the gains were still there, I guess 20-25hp. The wastegate held OK though. I think in your case, perhaps the Deltagate's not flowing enough exhaust out to slow down the turbo in the upper RPMs?

 

[quote]Originally posted by 951carter:
<strong>Have you checked to see if your cold-start fuel enrichment sensor is bad?

If it is it will cause the car to run rich(it thinks it is always cold).

To test it, let the car warm up to operating temperature and unplug it. This should cause the car to shut off. If it doesn't shut off - the sensor is bad.

The sensor is on the head towards the front on the manifold side.</strong><hr></blockquote>

I dont see this sensor? What does it look like, what type of electrical connection does it have?

 

Phil,


The temp sensor has a fuel injector type connector on it.

 

[quote]Originally posted by TurboTim:
<strong>Phil,


The temp sensor has a fuel injector type connector on it.</strong><hr></blockquote>

ok, I found 2 things that have injector connectors in that area. one right behind the airbox and connects to a square outcropping on the very top front of the head. the second is near the center off the top of the head and is connected to a round cylinder that is strapped in under the intake manifold.

As a side note, I tested the blow off valve and the diaphram was ruptured, i replaced it with the unit from my neon that is only about a year old and that didnt seem to change the performance any, also the boost seems to be about the same looking at the gauge. I was sure that the blow off valve was it when I found it, but the performance still stinks.

I also noticed that the DME fuel quality switch was set to position 3 and according to

<a href="http://members.rennlist.com/951_racerx/FQS-adjust.html" target="_blank">DME FQS Adjustment</a>

its set 6.3% rich, I set it back to position zero and still performance stinks.

But at least I feel like i'm fixing things in the progress. boy was that blow off valve toast.

 

The item under your manifold(strapped down) is the idle air stabilizer valve. Your temp items, the one with the fuel injector type plug is the one for your DME sensor(cold start richness). The temp sendor, for your gauge cluster, is the one with two wire connectors, both male, one larger than the other. HTH.