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We made a 3`Stainless straight ultra quiet exhaust and WOW, what a difference...

TwinV6GTP

TwinV6GTP

New member
I just bought a pretty clean 97 GTP with a low miles engine and trans last sunday about 4 days ago. Me and the crew made our typical stainless straight through exhaust with our drone eliminating technology (Turbo Dynamics Canada)
The exhaust starts at the bottom of the down pipe, goes to 3" (catless) 2 resonators style muffler 2 bigger mufflers on each side near the bumper (divides 3 to 2.5 inch).
exhaust sounds beautiful and is extremely quiet, no drone at all even with no rear interior.
We also took out a lot of weight out of the car around 300lbs. The front of the car is still all there including the leather seats.
I installed a very large AEM air filter picking up where the old airbox used to be. I'm still running the stock 3.8 pulley...
I have a small race tank running a Walbro 255 HP external pump through the stock fuel lines.
Everything else is all stock. The tires are actually still 18" winter tires, far from ideal for performance.

I Plan to do a twin engine GTP with it, but first, I have to make it run pretty fast FWD. Then we will add the engine in the back.

I installed HP tuners downloaded the stock 97 tune from the ECU, didn`t touch it then datalogged our run.

1st of all the car's performance increases are massive compared to when it was 100% stock. I was shocked.
I expected around 10-15HP max from the exhaust and large air filter but it is easily double that if not more. My guess is that, the exhaust gave more 40-50HP is that even possible for a GTP ?
My ass dyno is usually pretty close as I do a lot of tuning.

The car is a monster now for how little mods are in it. Before it would spin a little and hook and go. Felt like a 14.7 car @ 94 mph or so my guess.
Now it spins all through 1st gear until the shift to 2nd... way quicker than before. Yes the weight reduction made a big difference equivalent to 27HP but the difference is way more than this.

I then started playing with the transmission tune and raised the rev limits and shift limits looked.
Wow pulls even better by staying in the powerband. Now with the exhaust the car feels like it wants to shift past 6K unlike when it was stock.

Now my HP tuners datalog on my stock MAF says I'm running a peak of 31 lbs/min at the 6000rpm. I'm touching 8 psi at Redline on the stock 3.8 pulley.
The car feels amazing, now I'm starting to understand why many don't recommend smaller pulleys.

This is on 91 octane btw and I was also shocked to see I had massive knock. Before the rev limit increase knock wasn't bad but I would get 3-4 deg often.
With the rev increase knock up to 9 deg , yikes... I then added Torco octane booster to my small race tank. And that helped a little but didn't get rid of the knock.

Then I put 50/50 C16 and 91 and BAM, the knock is GONE. Not once did I see even 1 deg. So it is Real knock at only 6-8 psi with the stock pulley with a very high flow exhaust.
Those steel heads are in large part responsible for this in my opinion. This is why intercooler helps so much, it keeps everything around the core cool, With an iron head the heat from the combustion stays trapped.

Anyhow I logged a 4.9 0-60mph by modulating throttle and 100mph in 12 seconds. Not bad for a start and on winter tires.
E.T. street 18 inch radials should be in next week, and that will drop the time by a long shot.

Tomorrow, methanol injection, 2.8 pulley from ZZperformance...

btw this isn't an ad. We have no plans to make exhaust for GTPs.
 




TheNoob23 said:
Vids or it didn't happen
Click to expand...
Maybe I have a factory freak I don't know. It didn't feel that crazy stock. That stock exhaust really is a cork it seems.
Huge increase in power. I don't think it`s the cone as it had a smaller cone placed closer to the manifold now it's closer to fender.
I can show you my logs if you want. We test the car on our straight road close to the shop

Keep in mind it is about 60F here, so It's nice and cool and we are at 500feet altitude only
 
Fivefingerdeathpunch said:
So you plan to run a full inch smaller pulley with meth injection while still running the factory exhaust manifolds?
I don't see this ending good.
Click to expand...
I think there is a lot of awesome information in these forums. Lots of very knowledgable folks here.
However, it is my opinion that there is a whole lot of misconception due to information being taken out of context.
For example, yes headers will help a typical street GTP survive because it reduces back pressure and transfers less heat and retains less heat which in turns reduces knock.
Which then in turns keep your pistons and block happy.
But I will always monitor knock and will not let any KR happen at all. If the block breaks, it is because of excess power, not because of my manifold choice.

That said, if I keep the front engine Supercharged, I will definately get a set of headers (too cheap to purchase to make them ourselves)
 


The only thing that's a cork on the exhaust is the u-bend. Minus that, the stock exhaust is actually good for quite a bit of mods/hp. The only reason to change the rest of the exhaust to a bigger diameter, or better flowing mufflers is for sound. At this stage in your mods, it makes virtually no different in power to do anything else to the exhaust aside from getting rid of the u-bend.

How the car "feels" to you is not scientific data. What you should have done was gotten actual dyno numbers before and after the change to show just how little difference it made.
 
Because there is no gas tank we could go straight on the exhaust...
Of course once the engine is in the back it will have to be re routed completely.



 
I just see an issue with the amount of air that you are going to be bringing in, I just can't see how the car could even get it out with the stock manifolds.

Like you said, scanning is key. But I doubt adding race gas will fix that issue with airflow.
 
RareGMFan said:
The only thing that's a cork on the exhaust is the u-bend. Minus that, the stock exhaust is actually good for quite a bit of mods/hp. The only reason to change the rest of the exhaust to a bigger diameter, or better flowing mufflers is for sound. At this stage in your mods, it makes virtually no different in power to do anything else to the exhaust aside from getting rid of the u-bend.

How the car "feels" to you is not scientific data. What you should have done was gotten actual dyno numbers before and after the change to show just how little difference it made.
Click to expand...
Yes I agree, not too scientific. But there are many other signs when driving the car, it just is a totally different animal.
Yes that U-bends really does look like the main problem. I did read that the stock exhaust flowed pretty good.
How many HP is the U-bend good for ?

Btw the car runs 12.2 on my AEM wideband and the stock O2 reading from HP tuners agree at .87V
 


It seems like you maybe over think things sometimes? Thousands of people have already been down the path your starting down, myself included which is why the same answers come up over and over. It is simply that the people that have been there and done it, seen it drove it and blew it up twice dont need to examine the theories behind it they just know what works and what doesnt. Also it has been proven time and time again that the factory catback has very little restriction and on a stock setup you would be lucky to gain anything from changing it.
 
Fivefingerdeathpunch said:
I just see an issue with the amount of air that you are going to be bringing in, I just can't see how the car could even get it out with the stock manifolds.

Like you said, scanning is key. But I doubt adding race gas will fix that issue with airflow.
Click to expand...

It is on my to do list that`s only if I keep the S/C in front. The engine in the back will definately be Turbo 500-600whp or so, with built tranny. Any suggestion on where to get it built would be appreciated.
We don't build auto transmissions here. Front engine will be around 400HP since the traction is limited, not much use of going to crazy. I want this car streetable.
 
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