I know you guys have turbocharged everything, so I came here to ask a question.
I have a customers race car(hillclimb and trackdays) here at the shop and he wants a new exhaust built. The car is powered by a 1JZ-GTE turbo making about 500hp on a very conservative tune. It will likely stay at this power output as it's more than adequate for the chassis set-up and driver. The current set-up has a 3" down pipe and then goes immediately to a 4" exiting straight out the back of the car. Due to clearance issues, he would like it remade 3" all the way and possibly exiting the body somewhere rather than going over the rear axle. Eventual exit location aside, what is the advantage or disadvantage of the current 3" to 4" design vs a complete 3" at these power levels?
Any insight is greatly appreciated.
Thanks
calteg
UltraDork
9/2/24 3:21 p.m.
Which 2JZ and what turbo?
My guess is that his current setup is probably ideal, he might spool a little later and lose some area under the curve going to a 3" system, but that's tough to say without knowing more
According to the owner, it's a stock long block with some head porting. No idea on cams, but the turbo is a 68/70.
**** edit to the original post, it's a 1JZ-GTE
I was recently researching similar stuff for a back burner project. I found this article comparing those sizes on a turbo LS, but, HP is air no matter the engine.
https://www.lsxmag.com/tech-stories/baby-got-back-turbo-exhaust-size-comparison-test/
Turbos do not like back pressure at all. I would expect that going from 4" to 3" on a 500 hp turbo motor is going to cost you both some power and some spool. Rule of thumb in the miataturbo.net world is that going from 2.5 to 3" is worth it around 250-300 at the wheels. If I was targeting 500 at the wheels, I wouldn't go less than 3.5, and I'd probably want that for the downpipe as well.
codrus (Forum Supporter) said:
Turbos do not like back pressure at all. I would expect that going from 4" to 3" on a 500 hp turbo motor is going to cost you both some power and some spool. Rule of thumb in the miataturbo.net world is that going from 2.5 to 3" is worth it around 250-300 at the wheels. If I was targeting 500 at the wheels, I wouldn't go less than 3.5, and I'd probably want that for the downpipe as well.
+1
Not sure of the benefit of 4" after being pinched at the 3" downpipe, so if packaging is the deal-breaker, staying 3" probably isn't going to hurt much, especially if you can shorten the overall run length. I suspect full 4" would give a bump in horsepower, but that is getting to be some pretty big pipe.
1988RedT2 said:
codrus (Forum Supporter) said:
Turbos do not like back pressure at all. I would expect that going from 4" to 3" on a 500 hp turbo motor is going to cost you both some power and some spool. Rule of thumb in the miataturbo.net world is that going from 2.5 to 3" is worth it around 250-300 at the wheels. If I was targeting 500 at the wheels, I wouldn't go less than 3.5, and I'd probably want that for the downpipe as well.
+1
Not sure of the benefit of 4" after being pinched at the 3" downpipe, so if packaging is the deal-breaker, staying 3" probably isn't going to hurt much, especially if you can shorten the overall run length. I suspect full 4" would give a bump in horsepower, but that is getting to be some pretty big pipe.
Plus it cools down as it travels away from the turbo so it's volume reduces so it might not hurt as much as you'd think
