Downpipe Size

[scpls19398]

Good afternoon all,
Question as to what size downpipe to use 3" or 3.5"??? I am unsure if there is any advantage in a 3.5" downpipe. I am interested in a downpipe upgrade but with a turbo with a 3" inlet and 2" outlet is there any advantage in the larger downpipe.

 

[vader87]

Depends on your goals. People are running into the 9s with a 3 inch downpipe.

 

[RUQWKNF]

You won't see a real gain with a 3.5" downpipe until you are in the 650 or more flywheel hp range. Anything slower than 10.50s really does not need a 3.5", but most people go with the bigger is better thought when it comes to exhaust. However, there is nothing wrong with running a 3.5" downpipe on a car with less horsepower, or that is slower.
I personally went 10.ohs with a regular 3" downpipe with external Tial wastegate.

Just my O2's worth.

Patrick

 

[scpls19398]

Thanks, Alot of good parts going into motor, I sure don't need to run that fast, mid 11's is where I am shooting for in an 1971 Camaro. I have a balanced and forged rotating assembly, mild port on heads, bigger valves, sodium filled exhaust valves, copper o ringed, ARP studs (rod,main,head), high volumn oil pump, 70mm throttle body and a bunch of stuff that cost 5-10 dollars that adds up really quick. I have not decided on the turbo yet but am looking at the precission dbl BB with a downpipe with an internal wastegate. I just ordered Hooker super comp headers from Jetcoat with their extreme coating on them and am trying to find out whose downpipe to use. also have a Razor Alky kit. Any suggestions on the downpipe would be appreciated. please explain the pros-cons of an external wastegate such as the downpipe that cottons sell.

 

[mikestertwo]

I just ordered Hooker super comp headers from Jetcoat with their extreme coating on them and am trying to find out whose downpipe to use. .

You may not like those headers

 

[scpls19398]

Why would I not like the best headers available for the TR.

 

[87turbot-type]

Pretty sure those aren't the best headers for a TR.

I've seen some prototype ones that make the TA's or the ATR's look like junk. And there probably the best ones for a good solid street car.

 

[Underboost]

Why would I not like the best headers available for the TR.

The spool is slow with the Hooker Headers my Dad had them on his. TA is the best IMO.

 

[vader87]

I agree about the headers. Stay away from the hooker headers! Do a search on here and you will see what we are talking about!

 

[boostingbuick]

I had Hooker headers once. Spool up time was horrible. I felt like I lost 100 hp till the top of first gear. But they make good power after it spooled. Just too much piping from the heads to the turbo. Not my first choice, but better than the china knock offs!

 

[scpls19398]

OUCH!!!!!! If it spools slow, I'll just spray it.

 

[scpls19398]

Any comments on internal vs. external wastegates? Pro's - Con's.

 

[JZ 97 SS 1500]

Rule of thumb we use for proper downpipe size. Turbine exducer X 1.25. That will give you typically what the turbine wheel needs for proper flow. That is based on a full catback.

For wastegates....typically external has better flow, control and allows you the use of better flowing housings.

Con is added price and space need for the gate and dump area or pipe routing back into the exhaust system.

 

[cool 84]

Why would I not like the best headers available for the TR.

You would be so, so much happier and faster reinstalling the stock headers. Mark my words, you will end up taking them off. Total crap.

 

[bison]

Why would I not like the best headers available for the TR.

Their the best if you want want your turbo to spool like a turd. Stockers are much better. TA and TH are the other 2 that work well with little fitment issues.

 

[t-typex1]

Stock headers have went much faster than your goal. It wont slow you down in the least bit. Save yourself the headache now, you can clean up the stock headers, check for cracks, and get them jet-coated (optional) and be better off. Just some helpful advise

 

[scpls19398]

Thanks, I still make mistakes, gotta hate a 900 dollar one thou, I will call about TA in the morning. Stanless or Mild Steel??? Is the only upside to the stainless its longevity?

 

[bison]

Thanks, I still make mistakes, gotta hate a 900 dollar one thou, I will call about TA in the morning. Stanless or Mild Steel??? Is the only upside to the stainless its longevity?

stainless retains heat which is what you want pre turbo.

 

[scpls19398]

Thanks, I called today and cancelled my order, cost me a 15% restocking fee, lesson learned. Help me with recomendations, I have the factory headers but the drivers side looks like a huge chunk of slag along the bend. I believe there is some issues on the passenger header also. This is going to be a show/track car with limited street play time. As mentioned above a 1971 Z28 is the vehicle. Are the stainless TA headers worth the aditional cost?

 

[ChavoLC2]

Worth the 15%

You did the right thing even if it cost you a little!