At what et do you need a 3.5 vs. a 3 inch downpipe???

[coach]

Hey guys,
Still laying the groundwork for my new engine. I currently have a 3 inch pipe with ex gate I believe 38mm or 46mm. Will this give me mid to low 10's or do I need a 3.5???

Thanks
Coach

 

[S2V6RACER]

You can run mid/low 9's with a 3" DP. I wouldn't consider it for your E.T. you have planned unless you plan on going much faster later on.

 

[bison]

Maybe a slight gain on a 3.5" if your car can trap over 140mph weighing over 3500lbs. Slower than that it does nothing but add weight

 

[GNBRETT]

Slower than that it does nothing but add weight

:biggrin:

 

[Chuck Leeper]

141+ @ 3710#, 3" pipe, thru the muffs.

 

[TurboV]

May have some clearance and heat issues with bigger than a 3" pipe which ive seen drive some guys a little crazy. (All cars are different) But mid to high 10s will be no problem with a your pipe and ext gate. Easy enough to upgrade later when 10s arent enough, but thats way out and why spend the extra cash now?

 

[ALVAROG1983]

I got a 3.5 dp and i hate it

 

[Limited87]

On a low 10 sec car and faster you will see a differance. The more horsepower the car makes the more it will help. Red A. has the exacts on this. They made back to back dyno pulls with 3 differant cars. The average he said was around 28 horsepower with a 9.50 car to a 10.0 car. He originally did not believe there would be any sig differance at all but he said the dyno results didnt lie and niether did the quicker time slips.

They tested and found the biggest hinderance is where the downpipe makes the first sharp bend out of the turbo. He said after that you could prob go back to 3 inch step down and not lose the power you gained but why choke it back down if you can fit it.

As alot of you know, he still runs ALOT of stock parts on his 9.3 car. You would not see a 3.5 downpipe on his cars if there was zero to gain from it I promise you.:wink:

 

[SS_Sean]

I got a 3.5 dp and i hate it

I got a 3.5" DP and love it! :biggrin:

 

[Super6]

low 10's

i have a 3.5" dp also. i figured it couldn't hurt me...it's tight but i like mine......Bob

 

[Limited87]

Same here.. You cant beat a quality American made piece. TH, TA, BW are excellant examples. The chinese knock offs alot of times fit like crap and you get what you pay for.

 

[S2V6RACER]

I think the mans question was does he need a 3.5" DP to run low 10's. He already has a 3" so if you are saying he needs a 3.5" to obtain this then it most certainly isn't possible to go faster than this without it. There is no doubt a 3.5" won't hurt him, but why spend the $$$ if you have the parts in hand to reach your goal then? He might as well throw a 4" DP on with a 88 turbo while he is at it.....

 

[steve hughes]

I swapped from a 3" to 3.5" down pipe at the race track. 3" pipe went 9.45 @ 143.00 2 passes back to back. with the 3.5" pipe it went 9.40 @ 143.5 mph 2 passes back to back. Save your money Coach.

 

[TurboV]

He Has the 3" already with an external gate. Thats more than enough for his goals and what hes putting together. he doesnt need the 3.5 and he can put that money to better use. They may have a slight advantage, but probably not necessary for him at this point. Just my $.02

 

[Turbo6Smackdown]

On a low 10 sec car and faster you will see a differance. The more horsepower the car makes the more it will help. Red A. has the exacts on this. They made back to back dyno pulls with 3 differant cars. The average he said was around 28 horsepower with a 9.50 car to a 10.0 car. He originally did not believe there would be any sig differance at all but he said the dyno results didnt lie and niether did the quicker time slips.

They tested and found the biggest hinderance is where the downpipe makes the first sharp bend out of the turbo. He said after that you could prob go back to 3 inch step down and not lose the power you gained but why choke it back down if you can fit it.

As alot of you know, he still runs ALOT of stock parts on his 9.3 car. You would not see a 3.5 downpipe on his cars if there was zero to gain from it I promise you.:wink:

Dyno's don't take into consideration some things. Monitoring what a car does, while strapped into a machine, is much different, than asking a car, to launch its full weight self on pavement, from a complete standstill.
You can make 500 hp on a dyno, and go nowhere on the street all day long.
Can you make a 9 second pass on a 3" dp? sure. But was that forced? And how much so?
I'm VERY confident, with most of these motors on this website, you could make a 10 second pass on a 2.5" dp as well. Well then does that mean 2.5 inchers are cool now? There's a BIG difference in what is 'sufficient' and what is just plain better.
What was capable by most members of this board, doesn't necessarily mean one certain part is sufficient. I'm not sure you could measure the total effectiveness of a downpipe on a dyno. With bigger turbos, I'm still thinking the extra .5 inches of flow will at least help with spool up, coupled with a good flowing exhaust...

 

[bison]

I'm still thinking the extra .5 inches of flow will at least help with spool up, coupled with a good flowing exhaust...

You should compare potential flow by providing the cross sectional area difference. Going from 2.5" to 3" is a lot different than going from 3" to 3.5".

 

[turboc87gn]

In other words if you already got a 3 in pipe cool but if you dont have one at all and are buying then buy a 3.5..On the other hand take all the "easy" hp you can get if you want you car to to run your goal without max effort and have a lil left on the table and you got the $$ layin around...

 

[KevinB]

I swapped from a 3" to 3.5" down pipe at the race track. 3" pipe went 9.45 @ 143.00 2 passes back to back. with the 3.5" pipe it went 9.40 @ 143.5 mph 2 passes back to back. Save your money Coach.

Coach, I'm with Steve. Save your money! Although I did see the 3.5" pipe the other day from DLS at the Extremeautomatics shop....it was a nice looking piece.....thought about replacing my 3" dp....but decided to save my cash.

 

[coach]

Thanks Guys. I do not need to spend the $$$ if I do not have to. I am happy with the set-up I have for this year, but if my job ever picks up, I will build my dream engine. Girdled 109, forged stroker, TA Aluminum heads, TA intake and doghouse,75mm TB,79# inj, Te45a w/ .85 ex, PTI stock location Cooler, Janis 200, and PTC 3200. I will keep my current DP and spend the $$$ on this stuff. I want a turnkey 11 flat/ 10.80 street car, capable of 10.50's or lower at the track. I hope this will do it.

Thanks to all,
Coach

 

[Limited87]

Dyno's don't take into consideration some things. Monitoring what a car does, while strapped into a machine, is much different, than asking a car, to launch its full weight self on pavement, from a complete standstill.
You can make 500 hp on a dyno, and go nowhere on the street all day long.
Can you make a 9 second pass on a 3" dp? sure. But was that forced? And how much so?
I'm VERY confident, with most of these motors on this website, you could make a 10 second pass on a 2.5" dp as well. Well then does that mean 2.5 inchers are cool now? There's a BIG difference in what is 'sufficient' and what is just plain better.
What was capable by most members of this board, doesn't necessarily mean one certain part is sufficient. I'm not sure you could measure the total effectiveness of a downpipe on a dyno. With bigger turbos, I'm still thinking the extra .5 inches of flow will at least help with spool up, coupled with a good flowing exhaust...

The cars also picked up on the track, not just the dyno. Its been several years ago now but if I rem it was a tenth an a half and a little over 1 mph average on the cars tested. Will this vary from car to car/set up to set up, absolutly. No question one is not needed to go 9s and certainly not to run llow/mid 10s and the money would be spent better in other places.

With that being said a guy with a car going 9s or capable and wanting EVERY possible horsepower his engine is capable of making would see gains with a 3.5 dp. It just boils down to how much is that extra tenth, mph or 20 horse worth to that individual. It could be the differance in a TSM or heads up style race when the cars alot of times are just that close and that little extra would get you the win.

Oh and not to mention they do look bad a$$ under the hood over the 3 inch.