Rear mount turbo

[SSE 4 2SS]

Originally Posted by LsxDoctor

I've done a couple... On an iron 6.0L used 2.25", spooled twin 57mm teriyaki tornados pretty quick and had good power up top! 2.5" on cold side.
I'm running a mix of 2" and 2.25" with a single 88mm in my car. Kit I made is similar to the turbonetics kit so there's a lot of exhaust pipe and it spools/works just fine.
I'm really considering going rear mount in a few weeks. One person on the internet cries lag and now everyone with no rear mount experience swears ALL rear mount setups have horrible lag lol

I don't see where everyone or anyone mentioning lag has no experience... I know for a fact Stevie is extremely well versed... Until you mention something other than (insert demeaning turbo name) and a diaghram pump for oil return, then I'll always side with his comments....

I'll agree that with a very specifically designed system, and small turbos, you can spool them pretty quickly.... but, the vast majority of evidence is that rear mounts lead to lag.

Building a system where you finally achieve commanded boost about the same time you run out of RPM's kind of defeats the purpose of having turbos in the first place.... The flip side is that if you use turbos small enough to spool in a reasonable time, then you run out of capacity before you run out of RPM's, spiking IAT's due to inefficiency.

Case in point.... We have a guy in Colorado that begged for a rear mount turbo kit for a C5 Corvette.... We built numerous iterations playing with pipe size, exhaust and boost piping, different size turbos, different size and shape of intercoolers, and the overwhelming result was a small pair of twin turbos that run out of boost on the big end as the IAT's climb into orbit, while providing the best power along the majority of the curve. We could run a slightly bigger turbo but it takes too long to spool them. The guy wanted a resale kit he could market, which is why we spent so much time with it...

We went so far as to measure exhaust temps at the inlet of the turbo. Smaller pipe provides higher flow rates and higher temps, but it also increases the flow resistance (backflow pressure) at the exhaust valves...

Yes, there are some moderately successful rear mount kits out there, but if the desire is to benefit from the weight transfer, there are better options.... Boost makes up for weight... I can add a lb of boost, or a degree of timing and easily make up for a hundred plus pounds of weight or more and never look back...

I also have to question the desire for air to water intercooling... That adds weight and complexity to both the front and rear of the car.... If you are talking about a ice/water box in the trunk and an air to water intercooler.... Hoses, pumps, water, ice etc...

Now OP, if you are looking to build a full on race car, that spends a majority of run time running at high RPM, and real weight transfer is a concern, then ok, but if this is a street car with a full interior, A/C etc, I see better options....

OP, As for the return pump... Turboworks EXA is the only way to go... Why risk expensive turbos on cheap or misused pumps.... I scattered a turbo at extremely high RPM and dumped bearings into the oil return pump... Pulled the pump, removed the turbine cover, dumped the two bearings out and it ran like a champ....

[stevieturbo]

Rear mounts only came about as cheap upgrades that could be installed after any emissions related equipment, so as to bypass some silly emissions rules.
And yes for that application, they had benefits.

But when a large amount of the work done by a turbo...relies on the heat energy as much as gas velocity ( and the two also go hand in hand ), putting the turbos way out back...are just counterproductive on both aspects.

Now of course they can make good power out there, but there will always be far bigger compromises with both spool and power by doing so, vs turbos mounted close to the exhaust valves.

[dreksnot]

Well, I guess rear mounts minimize your underhood temperatures greatly over top mounts or mid-mounts. Might even slightly help IATs due to the long cold side piping.

[stevieturbo]

Originally Posted by dreksnot

Well, I guess rear mounts minimize your underhood temperatures greatly over top mounts or mid-mounts. Might even slightly help IATs due to the long cold side piping.

Not even an issue, nor are charge temps with quality intercooling.

Those are fake arguments sellers of rear mounts try and use to persuade people to buy, but in reality have little substance

[Rem0v3r]

Twin rear mount ebay 61/61 (gt3582s) twin ebay 38mm wastegates. Ebay intercooler. Stock exhaust heat wrapped with cats removed. L99 stock cam stock converter.
1st gear in boost at 4.5k and stays in till i let off.
2nd at about 3.5k 3rd and up is pretty much instant boost when going wot

Iats sit about 10 above ambient and climb about 20 degrees f over a 10 second pull at 8psi.

Mines a street car on street tires. My previously mentioned oil pump pumps oil as its supposed to.. i can tell you feom experiance that the ebay pump works fine too.. its just fkn LOUD.

I totally understand that the performance snobs out there look down on cheaper parts and kits. Some stuff works, some doesnt. But hay, to each his own. My turbos cost 166 each lol.. if it dies, ill just spend another 166.. been alive for 3 years tho. As far as lag, my engine makes 400ft lbs n/a.. its not a big deal. And if i 2 step or foot brake then its really not a big deal.

Noone is saying rear mounts are better. But the fact is rear mounts DO work and work well.