Turbo sizing?

[Fondle]

im gonna give the turbo another chance, i have been doing some more researching, and gonna take this build a little slower

but i need help on picking the right size turbo, i dont want something that will take years to spool, and i only want to run about 7psi, if i make 250 wheel n/a, what size turbo should i be looking for, my goal is to be 400+, after heads and cam +turbo

also, whats the pros/cons of doing a rear mount, obviously a little more turbo lag, but how much worse is it? what other things are affected

[Camaroman1221]

Re: Turbo sizing?

from what i have read a rear mount wont really have turbo lag if it is sized right, the pros are the turbo stays cooler, you don't have the heat in your engine bay and in most cases there is no need for a intercooler since the charge pipes have to run back to the front of the car, there cooled by the air flow under the car. CONS runing a lot of pipe to get the charge air up front were you need it, you gonna need a scavanger oil pump to get the oil from the turbo back to the oil pan, and rear mount systems don't provide as much proformance and front mounts

[Fondle]

Re: Turbo sizing?

well, i would only have to run one extra pipe wouldnt i? just the pipe from the turbo to the intake? i already have the hot side of the piping basically

another good thing is i can keep my headers, and wouldnt have a whole bunch of tight bends in the engine bay

would it be safer to run more boost with a rear mount?

can a nitrous line be used as a oil line?

[Camaroman1221]

Re: Turbo sizing?

Ya you would only have to run the pipe up to the intake, as far as i know you have to run more boost on a rear mount because of the extra piping, but i could be wrong i haven't looked into rear mounts tomuch, a good place to start would be with STStubro's they make a rear mount kit for the LT1 and LS1, i think i have seen on this forum somewhere about taking one of those kits and retro fitting it for the v6. As for the nitrous line i don't really know if you can or should use that for a oil line.

[Fondle]

Re: Turbo sizing?

ya probably not, i was just curious because i have a couple in the garage

i already have all the piping to do one, i just need the turbo and stuff, a buddy of mine works at lethal performance, so it wont be hard to fab one up

[El_Diablo]

Re: Turbo sizing?

lag will increase, think about this, you intake isnt 2 feet long, its now over 15 and it is still recomended you use an intercooler so you can be as much as 25-30 of plumbing

also, its recomended to keep a rather small exhaust to increase velocity to help spool the turbo, this will decrease performance yet again

on top of that, with turbochargers, heat on the turbo (the exhaust turbine atleast) is what you want, the more heat in the system the more energy being sent to the system so a lot of rear mount guys wrap the entire exhaust system with heat wrap and even then your not as hot as you could be so there will be increased lag even with a small turbo, as much as 300 to 1500rpm increase in boost lag, throttle lag will also increase in or out of boost

[Fondle]

Re: Turbo sizing?

its not 15 feet, maybe 10 feet at most, im thinking around a 60-62mm turbo, i can reduce turbo lag by using a smaller turbo, i dont need a big turbo,im only going to run 12pounds tops

[El_Diablo]

Re: Turbo sizing?

depends where you locate the turbo, most replace the muffler with the turbo which would mean the full length of the car plus the vertical sections (atleast 2 feet)

also, what will you be doing for an intake on that turbo? its not usually recomended to mount them that low, the turbos dont like water splash either as it will increase your spool times and could shock your turbo

have you thought about an oil pump? the good ones are over $200, add atleast another $100 to that for fittings and line, i would also recomend shielding the oil feed and return with heater hose or similar

oh, and as far as the 12lb's... boost is a measure of restriction, you need to know what your motor does N/A to calculate the correct V/E so you can size the turbo properly

[inheritthefire]

Re: Turbo sizing?

With the rear mounted turbos (I've been looking into doing this to my 2000 firebird, just don't have the cash) you don't need an intercooler because of the fact that the piping to move the pressurized air back upfront has a cooling effect.

If you go to www.ststurbo.com, they have an explanation of all the benefits... You don't need a turbo timer, you only have to run oil lines (if you tap your oil pan), you don't need a secondary pump as far as I know...

They put a similar set up on a corvette, and went from 350 whp to 550whp, running 8lbs of boost.

I think pound for pound a rear mount is more efficient in terms of hp gain per pound of boost, but I could be mistaken.

[ssms5411]

Re: Turbo sizing?

Their 8LBS of boost is probably 12LBS or more rather than if it was a FFH setup, so the turbo is working harder to flow more air to the front and keep it at a certain level of boost, because I wouldn't think they would take the PSI reading from the turbo in the rear , just off the TB where it is coming in. So LB per LB a FFH design would put out better HP levels than a rear mount. Also dyno #'s from a CO. I wouldn't trust only people who have done it. On our cars we have the space to put the turbo even if it is under the K or FFH's.

[inheritthefire]

Re: Turbo sizing?

I didn't actually think about that, but at the same time, (I know I'm quoting their sales crap, but it's the only "scientific" stuff I have at the moment) they say that the loss in pressure piping the air up to the front is only 1-2psi... but when you factor in the colder original air intake temperatures, plus the cooling that in inherent in the piping of the air, it makes more sense for the rear mount to be more efficient.

I don't know if anyone here has seen it, but there is a clip of HorsepowerTV installing this system on a Corvette, with amazing gains.
http://videos.streetfire.net/video/HPTVVette3_87092.htm

They actually do use an intercooler though, most likely for higher gains... but (again quoting sts...) you don't necessarily need it.

[ssms5411]

Re: Turbo sizing?

In high heat states you would burn the motor without a intercooler. You can dyno a car inside a 70 degree temp inclosed in a garage and get really amazing gains. In AZ I dyno mine under a covered out door carport where its still 105 degrees outside at 7 am in the morning. I don't believe ads I believe people who have actually ran their cars and have posted results.

[inheritthefire]

Re: Turbo sizing?

Fair enough!

[El_Diablo]

Re: Turbo sizing?

like i said, turbos NEED HEAT!!! your efficiency goes out the door when you take away 500+ degrees as your losing potential energy

also, the fact that they say the intercooler is not needed, bull****, a pipe is not going to be more effcient than a bar and plate intercooler, the intercooler is designed as a heat sink to draw heat out of the air, a round piece of exhaust tubing is not

let me ask you this.... have you ever done a rear mount? trust me... you'll want an intercooler even if you dont need one (nobody needs one but they help keep your motor and turbo alive, the drop of rate of lifespan is crazy without one)


also, why dont you need a turbo timer? have you ever owned a turbo car? even if its only seeing 800 degrees your oil temp could reach 270 which is not good for a bearings life....

as far as the oil pump, you'll want to evac the oil out of the turbo after shutting the car off or each time you start it up you'll have oil smoke and your seals will wear out much faster, as much as once a year needing a rebuild, and another little issue, how do you expect the oil to climb up hill? you have to have a pump no matter what on a rear mount, i guarantee you will, or again, your going to be blowing turbos


pound for pound, rear mounts are one of the least efficient turbo setups out there.....

http://www.airpowersystems.com/corvette/c5.htm
(to counter your vette example, note they dynoed it stock, not they started out with a lower stock power level)

[Fondle]

Re: Turbo sizing?

where did i ever say i wouldnt need a turbo timer? are you just pulling stuff out of the air or what? im aware i need an oil pump also