Car got slower with an ATR 3" DP

[DougsfastZ]

Installed an ATR 3" DP (stock style wastegate) last week and took the car to the track on Sat. I was consistantly running 103 traps @ 17 psi with the timing set at 19/21 on the stock DP. Mods are in my sig. I ran it with the cutout open and the boost fluctuated between 16 and 19 with the traps going down to 101. I was told stock turbo's don't like the lack of backpressure of a cutout so I capped it and ran 101 all night. Knock was minimal at 1 degrees, 02's around 750 and the boost stabilized with the cutout closed at 17 psi. I played with fuel pressure a bit and the car seemed to like 44 psi static.

I'm wondering where my MPH went. I'm at a bit of a loss on how to tune the car. Should I invest in an EGT guage and/or a wideband in order to tune the car better?

Doug D

 

[Blazer406]

IMHO Air temp and quality can make a huge difference on turbo motors. This alone could be where the difference lies. The only real accurate test would be to run it with the stock DP, unbolt it, install ATR DP and re-run. IMHO turbo motors don't need any backpressure.....the less the better IMHO. It is a fan curve..... and if there is pressure on the backside of the fan..... it changes the fan curve... negatively.

 

[DougsfastZ]

IMHO Air temp and quality can make a huge difference on turbo motors. This alone could be where the difference lies. The only real accurate test would be to run it with the stock DP, unbolt it, install ATR DP and re-run. IMHO turbo motors don't need any backpressure.....the less the better IMHO. It is a fan curve..... and if there is pressure on the backside of the fan..... it changes the fan curve... negatively.

That's what I figured. But a guy at the track said that stock turbo's needs some back pressure in order for the wastegate to hold boost properly. I figured that is why my boost was all over the place with the cutout open.

Doug D

 

[DCVING 6]

I'm wondering where my MPH went. I'm at a bit of a loss on how to tune the car. Should I invest in an EGT guage and/or a wideband in order to tune the car better?

Doug D

I would say definatly YES on a wide band. The stock narrow band setup really leaves too much room for error. I'm sure many will say you can get by without one, or I ran 11's without one, but I can guarantee no one with a wideband will tell you it was a waste of money.

How were your 60' times this time out? Seems pretty strange because the 3" downpipe was the piece that woke my stock turbo car up more than anything.

 

[Grumpy]

stock turbo's love open exhaust ...ahhh the good old day's :biggrin:

 

[murphster]

I doubt you'd notice much difference until you started getting into the lower 12's. Last year I switched from a 3" downpipe with stock elbow and Flowmasters to a THDP and ATR 3" exhaust. Car ran around the same times (mid 12's). There are too many variables to guess why you slowed down. I doubt you picked up or lost much.

One thing to look at would be your 1/8 mphs if you think there is a possibility you lost something. Probably a better indicator if you think it has to do with spool, etc. And then look at your 1/8 to 1/4 mph gain on similar runs (ie no spinning, etc) to see if you gained or lost on the top end. For example, when I changed converters, my overall mph went up 2-3 mph and I gained 23mph from the 1/8 to the 1/4. However, my 1/8 mph was quite a bit slower and my overall 1/4 times were a little bit slower. The new converter killed the low end enough that the better top end couldn't make it up.

A good investment may be Directscan, if you don't have it. EGT is good too, and not too expensive. These things will help you come up with a good baseline so that when you go faster or slower, you can see what changed and why you are going faster or slower. I also have a knock gauge mounted high up so I can see it. Easier to tell if its false knock and easier to see if the knock is coming from leaning out or not enough octane (when I don't have Directscan hooked up). The knock will come up sooner if I need more octane (because I'm running too much boost or timing) rather than coming up at the end of 3rd gear because I'm leaning out and need more fuel. This is very easy to see on Directscan. Of course, an adjustable chip like the newer Turbotweak chips will help you maximize the tune.

 

[DougsfastZ]

I do have directscan but didn't use it, I just watch the scanmaster during the runs. I did work out all the knock like I did when I had the car running 103, so I know that wasn't killing MPH. I also have a translator plus to tune fuel (and thats how I have timing set to 19/21).

My shorts were awesome, with the best of a 1.71. For example my best run on a stock DP was 13.19@103 with a 1.80, but with the 3" DP I ran a 13.02@101 with a 1.71. I know the car would of had 12's in it if I had my mph. Boost with both sets of runs was set at 17.

So I'm still confused as to where my MPH went, I was hoping for 104 ish with the cutout open and at least match my 103 with the 3". I'll have to go back and check my 1/8 mile ET and MPH.

I can't recall what the weather was when the car was going 103.

Doug D

 

[murphster]

Sounds like the car was running very similar. When you run better 60' times, sometimes the overall mph goes down a little. Without knowing the weather, seems like it could definitely be running the same within the margin of error for weather conditions. Definitely check the 1/8 mphs to see where you lost the mph. If you ran the same 1/8 mph, then maybe you were too rich or lean on the top end. Thats where the EGT would come in handy. Now, if you ran a slower 1/8 mph and picked up the same mph from the 1/8 to the 1/4, chances are that the car bogged down a little from the better launch. Leaning out the first gear fuel, or something else similar to help you get out of the hole faster may be the only way to get the mph back with the better 60' times. In the end your overall ETs will be better though. With a 1.6 60' launch, your 1/4 mph might be even slower, but the ETs will improve.

 

[DCVING 6]

Looking at your setup again, I would say throw some better gas in and crank it up. 17-19psi and 19/21 timing you probably won't do much better than low 13's/high 12's.

 

[Blazer406]

My shorts were awesome, with the best of a 1.71. For example my best run on a stock DP was 13.19@103 with a 1.80, but with the 3" DP I ran a 13.02@101 with a 1.71. I know the car would of had 12's in it if I had my mph. Boost with both sets of runs was set at 17.
Doug D

This seems odd to me. Usually (if something else isn't going on here) if you drop 60' times.... you will drop more ET..... you dropped ET.... but 60' times stayed about the same...... but you lost 2 mph.....? Where you going into a headwind on the 101 mph or a tailwind on the 103.... or some combination of both? Is it possible you lifted just a hair early (i.e 1310 ft?) You can really scrub off mph fast when you lift..... and if that occured right at the lights..... it could have made the difference.

It is kinda wierd to gain almost 2 tenths.... but loose 2 mph.... and the 60's stay the same.

I agree with the post above.... there is really too many variables to pinpoint what caused this.

 

[DougsfastZ]

Guys I found the issue.

The converter wasn't locked up, what a moron, I never thought about it. I must of disconnected the battery before I left for the track and there fore lost my settings in the Extender chip. When I was running 103, I had the converter locked up at 77mph (right as it shifts into 3rd), and I just checked it and the converter lock up wasn't set.

I still want to get at least an EGT gauge for tuning purposes. What is a good number to shoot for?

Doug D

 

[murphster]

That car seems pretty fast for running only 17lbs boost. Lets say you pick up 2/10ths with the converter locked. You'd be at 12.8. With a 1.6 60' you'd be at 12.6-12.7. That would be awesome for that timing and only 17lbs boost. You sure you don't have any other mods? :biggrin:

As far as the EGT, each car is a little different and you'll have to find the sweet spot. For rough approximations, low 1700s and higher usually means you're probably on the edge of lean while mid 1500's and lower typically means you're rich, but there are exceptions. If you are running real rich, EGT's can run high though, but you'll probably be able to correlate the O2 readings with that. You'll only use the EGT for the end of 3rd gear though, as most EGT gauges will hold the max reading (EGT rises throughout the run). A wideband O2 would help for finer adjustments throughout the run. The EGT helps when you make changes to the car and want to see where everything is. Will really help dial the car back in.

 

[DougsfastZ]

It honestly only has a stock turbo and intercooler. I didn't realize it was a fast car for the mods. I figured if I had the converter locked it would help MPH much more then ET.

Any recommendations for and EGT gauge and a Wide band?

Any ideas as too why boost would be flutcuating with the cutout open, but steady when closed?

Thanks,

Doug D

 

[John Wilde]

Add a lbs or two of fuel pressure.
The car could be a little lean.
I head to do this when I put headers and dp on my stock GN 8 years ago.