GrannySShifting

iTrader: (10)

Wheres the bottleneck happen? I cant see being able to make more than 700 flywheel hp or so with a 3" downpipe. The small motors seem to wheeze out around there with the 2-3 L stuff

XtremeDime

iTrader: (16)

Depends on the turbo, if you have a 3" outlet then running a 4" is overkill. Pretty much just stick with outlet size of the turbo.

black98ws6ta

iTrader: (77)

I have seen over 800 rwhp on a 3'' downpipe. It really depends on how long the downpipe is, bends, mufflers, ect.

GrannySShifting

iTrader: (10)

Of course, not talking about a straight dump, but something your taking behind a motor then running to the rear of the car

Josh@KY-Turbo

iTrader: (120)

Been over 750rwhp with a TC76. 3" DP 3" in/out Dynomax bullet. Dumped 12" Off the muffer. Never had an issue with Back Pressure or chocking. Done it several times on customers cars.

GrannySShifting

iTrader: (10)

750 rwhp, so 155-160 mph cars depending on weight?

Josh@KY-Turbo

iTrader: (120)

If it was only that easy. I have several customers with 4 digit numbers that dont run those speeds in the 1/4. Just because you make a given HP number on a dyno doesnt mean Jack. Suspension, Weight, Traction, Tune Up, among other things play thier roles.

GrannySShifting

iTrader: (10)

I hear ya there, just trying to draw a comparison to number that Im used to seeing on my dyno. You cant say a 3" downpipe is good to 800 hp on dyno A that might be a "happy dyno" and expect it to be ok on dyno B necessarily.

Josh@KY-Turbo

iTrader: (120)

I look at it like this. Turbos are made to flow a specific amount of Air ( lbs/min ) at a given Discharge outlet be it 3", 3.5", 4", or 5". A TC76 is rated for given HP potential with a 3" Discharge. The way I see it is that if you are chocking the turbo with the 3" DP then you are out of that turbo's effective efficiency range. A bigger DP is a band aid at that point.

If a car is happy with a 3" DP and 800rwhp on dyno A then whats the diffrenence in Dyno B? If it works it works. The only way to really tell if the DP is effiecient is to measure the Back Pressure. Dyno numbers are not gonna give you the info you need for that.

skinnies

iTrader: (33)

I'm pretty sure one of Jose's customers car made 900+ and went 150+ in an lt1 car with a 3" downpipe, been a few years ago though, but if I remember correctly that car only had a 3" downpipe.

Fireball

iTrader: (21)

We choked with a 4" downpipe at ~1700 hp...motor would not boost any higher than 32psi due to backpressure....still had plenty of compressor left.

GrannySShifting

iTrader: (10)

Brian, was that basically a dump or 4" back behind at least the seat area?

Fireball

iTrader: (21)

went 1 to 1.5ft behind the back of the motor

HydroStream6

iTrader: (16)

Different car, but my buddy's Evo with a 3" downpipe all the to the back of the car with a 44mm wastegate dump out the front has gone 157mph in the 1/4. Raceweight is about 2800 I believe.

98Z28CobraKiller

iTrader: (17)

Weight of the vehicle plays a huge factor in how much power it takes to run XXX mph in the quarter mile. For instance, most HP calculators will put me right at about 750rwhp running 142 MPH at 3800 lb race weight.

Very true. This is why I'd rather use a calculator off my ET/MPH to calculate HP rather than to actually get on the rollers.

What size was the discharge on the exhaust housing?

Fireball

iTrader: (21)

4" turbine...5" discharge

GrannySShifting

iTrader: (10)

It definitely does but as speed increases the effect starts diminishing as well. You throw 100 lbs on a 8.30 car its not going to slow it down like a 13.30 car would. The power/weight difference isnt nearly as drastic.

The ATI calculator seems to hold fairly well to flywheel numbers (and the comparison to the rearwheel number on our dyno parrallel well also), but the rearwheel calculators are f'ing worthless everyone Ive seen, they are all over the place.

@750 hp at 3600+ lbs on my dyno goes has been well over 150mph thats what dyno numbers are hard to talk about unless you know the correlation from that particular one

GrannySShifting

iTrader: (10)

A turbo may be "rated" to some xxx HP but that is often never going to be seen form most of the stuff we do where the compressors are undersized and your not running them at pressure ratios where they are most efficient. I never trust what a manufacturer says is right myself, Id always like to see real results, the guy making castings might determing another reason for putting a certain size flange on something other than max potential on a certain application. 72mm S400 stuff has a 5" vband, but Im pretty sure you dont need a 5" pipe on a compressor moving 88 lb/min or so (Unless maybe its got a 400 shot on top of it )

qqwqeqwrqwqtq

We've made around 920rwhp with a PT76 GTS and a 3in downpipe in a 6 speed car.