PaulC

Have there been any back to back dyno runs using these setups and seen gains or losses between the two? Both have their advantages and disadvantages but does one have a efficiency advantage to make more power?

enginjoe

iTrader: (11)

No one that I know has done back to back dynos of a rear mount versus front mount, but the subject has been beat to death here as far as what the differences are. You can get all the power you want out of either type of system. It just depends on what you want.

engineermike

Forcedinductions.com did a back-to-back dyno test as you described. The results were as expected.

geeteego

iTrader: (1)

link?

Sideways240sx

iTrader: (22)

If you use the same turbo on the same motor, everything else is the same, the front mount will make more power, and be more efficenent every time. If you dont have the space to put the turbo up front/ or turbo's cause they are massive, stick them in the rear. People with turbo's in the rear generally run smaller ar hosuing to help it spool up quicker but then they usually run out of steam quicker.


Chris

detroit_903

iTrader: (8)

Well I did remember reading a article in hot rod magazine I beleive about the differences between a front mount vs rear mount turbo set-up. They did a dyno test with the same turbo and everything - The front mount spooled up
1k rpm quicker then the rearmount - that was it. They said you could wrap the exhuast and play with the a/f to make up the difference thow. But the front mount spooled up alittle quicker.

smoke20

iTrader: (2)

now you went and did it, the the front mount guys will be pissed that they are only 1k more efficient

stevegrizzle

1000 rpm of spool up is a TON quicker, not a TAD.

smoke20

iTrader: (2)

not really it goes pretty quick between 2500-3500, watch your tach and see if you can measure the difference between the two it happens very quickly. it does provide a little edge to the front mount guy if you both took off from an idle , but with 2-steps and trans brakes you can be in boost off the line and that does not become such a factor, just as Major Spray !!!

stevegrizzle

It seems everyone is biased towards their own setup.....

Yes, of course there are way to improve spool up.....but I'm pretty sure he was asking for a comparison with ceteras para bus. The big advantage I see is in cooling Rear mount = lower under hood temps.

RooRnZ28

iTrader: (14)

the main difference is spooling... otherwise, 10psi is 10psi regardless if it gets blown from the front or rear, ceterus parabus.



edit: ceterus parabus: all other things equal

engineermike

That's not entirely true. Actually, it is true only in the case where the exhaust gas does not lose any heat during the long trip to the rear of the car. However, this is never the case.

Mike

Schantin

iTrader: (6)

Your point is true if the assumption is made that there isn't excess exhaust energy to spool the turbine....which in most cases there is excess...way excess.

I support that a pound of boost is a pound of boost....no matter where it comes from. A car doesn't care what the brand name associated with that pound of boost is....only people do. The real difference per application is how HOT that pound of intake air is (how dense). I fully support that the front mount will more efficiently spool (ie spool faster) than a rearmount for a given turbo of a given size. I can state this cause a rearmount will always make 10-20HP more on the 2nd dyno-pull if doing "back to back" runs. Seems the 1st run heats things up, and the 2nd run shows the real power. So, a front-mount might thus make more power under the curve, but not more peak power for a given boost level all else equal.

Just my $0.02

candlelit

iTrader: (21)

you rear mount guys suck. you're making my decision harder on whether I should do the front mount or rear mount setup.

enginjoe

iTrader: (11)

I have a rear mount now, but I didn't have the choices you have available to you. I would buy an APS twin kit since I need the A/C. If I didn't want to keep the A/C then I would buy a TTI kit.

gametech

iTrader: (1)

The rear mount setups have some small advantages. Plug changes are easy, weight distribution is better, and underhood temps are lower. Front mount setups have huge advantages in efficiency and power, as well as less total weight due to less charge piping. On my rear turbo GTO, if I had the experience I do now, or if a front mount kit had been available at the time, it would have a front mount. As it stands, the difference is not enough for me to redo my entire setup.

stevegrizzle

Try typing latin into a spell checker.....And that wasn't my point, if ten psi comes on at 3000 instead of 4000 whos going to make more power under the curve avg. from 3000-7000 rpms?

/hijack

On a street car the only reason I wouldn't do a rear setup is if I was worried about it getting stolen...

candlelit

iTrader: (21)

that's one thing I've cautiously thought about too. not even just your car stolen, but someone could get under there and torch off your turbo.

engineermike

Ok, so you admit that a rear-mount makes more power on the 2nd pull because the exhaust is hotter. That's a start. Now, apply that same logic to a front-mount. A rear-mount will never get the exhaust as hot as a front-mount. A front-mount has hotter exhaust all the time and, therefore, will make more power all the time.

If you like, I will explain the thermodynamics behind all this. Basically, cooler exhaust requires higher dP to spin the turbine, resulting in higher exhaust pressure and less power.

Guys, a pound of boost IS NOT JUST a pound of boost! I thought everyone knew this by now.

Mike

smoke20

iTrader: (2)

1 pound of boost measured at the manifold is the same for everyone, how you get there may be slightly different but 8 psi on a front mount is the same pressure as 8 psi on a rear mount, i will agree with you that the front mount will get there slightly faster and will make more power under the curve. i think the biggest difference is not in the charge side as much as the back pressure in the exhaust side for the rear mount. you have some great info and i have read several of your posts.