Cons= more money & fab work.

 

from what i've looked at there is not much difference in fab work or the cost, except for oiling the turbo

 

is it a street car or race car? rearmounts are heavier due to all of the extra crap, although the weight is distributed more evenly front to rear. if you want fast boost response go front mount. all of the rear mounts i have been involved in are very "laggy" slow boost response. smaller hot side pipes and thermo wrap will help, but it is still slow to build boost.

rear mount 4th f body with a 6.2 swap ported heads and mild cam, m6, 3.50 gear (9"), 26" tire. took @ 3-3500 to make 10 psi.
front mount 67 stock 98 ls1/a4, 3.73 gear (9"), 26"tire. took 1000 rpm to make 9 psi.
both cars had the same spec precision turbo t76, tial bov, tial wg. both were tuned and results were verified on the same 224 dynojet.

 

Real fucking results first hand right there:smt035:smt035:smt035

 

very little street. mostly race. BBC 500+ c.i. - maybe 106 turbo

 

I'de front mount a 106.

 

Put 'em underneath!

 

Here's some interesting info about the pressure vs the heat that turn the turbine wheel,

This is from the book, "How to tune and modify engine management systems".

The system is going to be handicapped with any installation that reduces the heat to the turbine wheel.

 

Search Patrick Barnhill, he can tell ya all you want to know about rear mounted turbos.

 

X2

 

Josh,
I heavily researched this while building my hot side. Too many people making it work for some to make a blanket statement that it wont.
BTW shouldnt you be working on the ghost?

 

Josh,
I heavily researched this while building my hot side. Too many people making it work for some to make a blanket statement that it wont.
BTW shouldnt you be working on the ghost?

what's your definintion of work?When i see a rear mount that runs as fast as a frt mount with all the same components-i'll say it works-until then,it's not nearly as good.

 

The only benefit to them is packaging. If you can't fit you can probably fit them in the back.

 

paul major! outlaw drag radial...he has them

 

I have twin rear mounted 88's, they work great. It still new technoligy so give it time. There are some turbo options out there to help make it work also it has a lot to do with the converter.

 

There is some physics going on that developement will have a hard time overcoming. In a tire limited class it matter less that the rear mount loses some efficiency.

 

you need to talk to patrick barnhill of ptp racing he has rear twins on his nova . look him up on the bullet.

 

turbos in the back and procharger on the front

 

Made me laugh for a minute......then........
Front...

Rear.....

Only mods needed are a 3 in 1 out intercooler and engine capable of 120 psi........

Is there a class for illegal quad power adder Outlaws!!!!

 

I'm pretty sure Paul Major went into the 6s on radials with rear mounted turboes?

 

majors is the only one thats doing real good with the rear mounted turbo's as far as i know . he's gone in the sixes and his shit hauls ass .. i know murrillo had it but changed back to the front..

 

louie, i am working on the ghost. I got the engine back together with some minor changes, just waiting on the converter to set it back in.
The engine will be big enough and run plenty of rpms to spool the turbo. The main thing i'm concerned with is the weight in the rear of the car and having to add weight to the front. Plus the fact with it set up that way, can install a full size radiator, just if there is some fairly long distance street driving in the 100 % humidity we have the engine would stay cool.

 

Bumping an older thread as its on the right subject...

Has anyone measured EGT and backpressure at the turbine inlet on their rear mounts?

As turbos are spooled by flow, heat, and backpressure, and as flow should be the same, and heat should be less, backpressure should be more for the same amount of spool; but how much less and more? Ive never seen any real answers to this, especially on well designed setups.
Anyone tested this?
We know we can make it spool, but if backpressure is going to be a lot more I dont want to do it, but it would help with weight distribution and packaging on something we're working on now. Just dont want to go in to it blindly, were hoping people have been there before and are willing to disclose their findings...

 

Is that a no?

 

x2^

 

i just love when the naysayers are proved wrong ,,,lol

 

longer header plumbing & Longer intercooler plumbing = turbos working harder to produce hp. try blowing thru a garden hose
at 5 ft ,10 ft and at 20 ft. let me know how that works out.

 

This always makes me laugh esp when you see tons of front mounted cars with the intercooler in the back of the car and having twice the amount of pipe before connecting to the intake!

 

x100 bunch of monkey see monkey do clowns, sharing their knowledge of nuffin!!! i have been installing them and using them for at least 5 years, they work!!! and have great advantages!! as for the disadvantages?? i dont know.... had no problems yet!! and just luv to hear the arguements from people who have never tried em!!!:smt077

 

been involved with turbo technology my entire life. Jap cars,
buick v6's ,SBC AND BBC. I'm not saying rear mount wont work. I just dont believe its the most efficient way to plumb a tubo system.

 

I measure turbo back pressure at the turbo and have seen 51lbs with 37lbs of boost. As far as performance is considered the rear mount turbos work really well with the GT 4788's that I was using. I was able to run 4.80's 163 mph to the 1/8 mile at 3475 lbs with a set of Brodix BB2X heads. These heads only flow in the 370 range so we could have made more with a better set of heads. I only able to make a dozen runs on my car before I decided to change out to my new 12 degree Profiler heads. I am sure with the old setup I could have gone mid to low 4.70's on a 315 radial with the rear mount turbos at this weight.

Now lets talk about turbo selection for the rear mounts. I have tried several different turbos on my Nova on a chassis dyno and had mixed results. We need to consider that my cay may have 6-7 more feet of exhaust pipe than most cars due to the 110 inch wheelbase.

1) GT 4788's with a .96 A/R worked excellent on the track and the chassis dyno. We were able to spool them easily and make 12 lbs at 4600 RPM. These turbos work well in a rear mount application.

2) Pro Mod 88's with a 1.15 A/R. These turbos made great power on the chassis dyno but would not have raced very well on my car. I could get to the RPM that I wanted with the help of the VSC but could not get the turbos to make more than 4.5 lbs at 4600 rpm due to the larger exhaust housings.

3) I also did some testing on the dyno with Pro Mod 108's with a 1.15 A/R and actually saw the same results as the Pro Mod 88's. Because they share the same exhaust side as all of the other Pro Mod turbos the were very similar on the brake as the Pro Mod 88's only making 4.5 lbs at 4600 Rpm.

All of the turbos above pegged the dyno at 1500 hp so they all made great power but the graphs looked the best with the 4788's because the power came in much smoother. The Pro Mod turbos needed much more RPM to make boost that they would have not worked as well on the track with the 1.15 A/R housings. To make them work the 1.00 A/R housings would have been required. I never was able to test a 1.00 A/R but I feel they would have been awesome.

I can't say which one is better or worse because you have to treat them different. I think those that say that it isn't a good setup may have not used the right parts to have success. I know that I really like the rear mount setup but the only draw back is the additional weight from the exhaust. I am going to be running some Pro Mod 94's on my hot rod when it comes back out so I am thinking of moving them to the front only for the weight savings. I can drop almost 80 lbs by going to a front mount turbos system. The truth is that really do like the "junk in the trunk." LOL

 

I measure turbo back pressure at the turbo and have seen 51lbs with 37lbs of boost. As far as performance is considered the rear mount turbos work really well with the GT 4788's that I was using. I was able to run 4.80's 163 mph to the 1/8 mile at 3475 lbs with a set of Brodix BB2X heads. These heads only flow in the 370 range so we could have made more with a better set of heads. I only able to make a dozen runs on my car before I decided to change out to my new 12 degree Profiler heads. I am sure with the old setup I could have gone mid to low 4.70's on a 315 radial with the rear mount turbos at this weight.

Now lets talk about turbo selection for the rear mounts. I have tried several different turbos on my Nova on a chassis dyno and had mixed results. We need to consider that my cay may have 6-7 more feet of exhaust pipe than most cars due to the 110 inch wheelbase.

1) GT 4788's with a .96 A/R worked excellent on the track and the chassis dyno. We were able to spool them easily and make 12 lbs at 4600 RPM. These turbos work well in a rear mount application.

2) Pro Mod 88's with a 1.15 A/R. These turbos made great power on the chassis dyno but would not have raced very well on my car. I could get to the RPM that I wanted with the help of the VSC but could not get the turbos to make more than 4.5 lbs at 4600 rpm due to the larger exhaust housings.

3) I also did some testing on the dyno with Pro Mod 108's with a 1.15 A/R and actually saw the same results as the Pro Mod 88's. Because they share the same exhaust side as all of the other Pro Mod turbos the were very similar on the brake as the Pro Mod 88's only making 4.5 lbs at 4600 Rpm.

All of the turbos above pegged the dyno at 1500 hp so they all made great power but the graphs looked the best with the 4788's because the power came in much smoother. The Pro Mod turbos needed much more RPM to make boost that they would have not worked as well on the track with the 1.15 A/R housings. To make them work the 1.00 A/R housings would have been required. I never was able to test a 1.00 A/R but I feel they would have been awesome.

I can't say which one is better or worse because you have to treat them different. I think those that say that it isn't a good setup may have not used the right parts to have success. I know that I really like the rear mount setup but the only draw back is the additional weight from the exhaust. I am going to be running some Pro Mod 94's on my hot rod when it comes back out so I am thinking of moving them to the front only for the weight savings. I can drop almost 80 lbs by going to a front mount turbos system. The truth is that really do like the "junk in the trunk." LOL

Great post. Good seeing you at Bristol again last week.

 

Hey guy's,
just my 2 cents worth from across the pond...here in Oz we run a 69 camaro in a drag radial class, thats still what i would call a street car, it's a very basic 496 truck block deal with off the shelf edelbrock performer heads and a 650in comp roller, 2000cfm 4500 flange t/body with a morris hat...that's all fed by two plain bearing 4202 garret turbos mounted in the trunk which in turn feeds the engine through a 3" charge pipe that runs back through the car...the hot side consists of hooker 2 1/8 headers into twin 3" back to the turbos which have Tial v-band 1.00 a/r housings.
We run a powerglide with a Chance bolt together converter (i guess the most exotic part of the car), the rear end is just a leaf sprung 9" with 3.5 gears and caltracs, on 275 radials, it's all steel, all glass and weighs in about 3800lbs wet...it's efi thats been set up and tuned by myself with a little dyno time but most tuning being done at the track...i have been playing with the rearmount deal in various forms now for about 4 years and has evolved from a single 88 to the set up we have now...the best thing we have found from the data collected and laps made is that unless you have tried a certain combo and know what's happening in the pipes, the seat of your pants, the time slips and most importantly your data logger, don't waste your time listening to all the "specialist's" out there telling you how crap your combo is and how "that rearmount shit will never work!"
As we live about 100 miles from the track and I work in a family business, my time isn't as free as i would like, our race season has ended and we are left with some mid week off street racing where the track is less than perfect we have managed to make a few passes to test, with some ordinary 60' times in the 1.6's the car managed an 8.8 @ 163mph... our data tells us it was making 18lbs boost and had 18/19 lbs back presure at the housings, afr's of 11.1's and egt's in the headers of 1700 deg f, on pump gas with no intercooler...we have a water meth spray to still test but we've just run out of time.
My point is guy's, if front mounts work for you sweet but don't write off the dude that wants to try a different deal...our gear is nothing flash and i would think we're getting towards the end of our truck blocks reliability... so with some real good parts i think the rewards could be endless, Cheers and thank's for listening, George.

 

great post george, i have twin precision 88's with the t-4 flange .96a/r ex housing, these things spool great, make big power, and all are in the bed of my truck, no intercooler,blow thru carb setup, trouble free!! drive it everywhere!! its a 523cid stock block bbf right now, with low boost, and driving to the track and back!! i went 9.20@150 peddleing it twice!! 1.46 60ft... off from 1.35!!! and had to lift down track...so on a good pass she will go 8.90's no problem.. gonna turn up the boost and try and go 8.50's this year!!