"Parmas" Motor

[Blown_xa]

Originally Posted by Tamago

positives for top mount
1. less than half the piping
2. cleaner engine bay by simplifying piping and routing
3. puts that gnarly scooped hood to actual use
4. does not block radiator (engine runs cooler)
5. can be thicker than front mount because of Euro NCAP (more room under hood)
6. because of the shorter piping, you see less pressure drop and quicker throttle response
7. because it sits horizontally in the engine bay, it can be sprayed with water easily for quick cooling
8. not damaged by road debris

negatives for top mount
1. if improperly set up, will be less efficient at cooling than a front mount
2. it's not "cool" looking. many ricers equate turbos with front mounts, and if you don't have a front mount, you obviously aren't making any power (this really should be a POSITIVE THING not a negative thing lol)


Positives for front mount:
1. looks cool
2. can be generally longer than a top mount (however, short fat intercoolers are more efficient [less pressure drop] than long thin coolers

Negatives for front mount:

1. silly piping running all over the place (in the case of rear mounted turbos, which is what this is about.. in a longitudinal engine, i.e. supra, front mount is perfect because the exhaust is on the passsenger side and intake is on the driver.. obvious routing is obvious)
2. less efficient because of all the extra bends and charge piping bends. every time you go WOT the turbo has to fill the entire length of charge piping AND intercooler before you actually see boost. this can exascerbate turbo lag
3. attracts unwanted attention (law inforcement comes to mind)
4. susceptible to road debris
5. blocks radiator and AC condenser
6. safety may or may not be compromised (bumper beam hacked) to make the IC/piping fit


that's all i have folks.

good points. A top mount will never provide the efficiency of a front mount though. The main reason WRC Subarus use a top mount is so the intercooler doesnt get ripped off landing crazy jumps. And WRC cars im pretty certain don't run on pump gas, so they don't need the cooling efficiency to supress detonation.

There is a forumula to calculate temperature drop vs. pressure drop. The benefits of temperature drop far outweigh pressure drop. And also the general formula to see the benifits of temperature drop in the charge stream. For every 10 degree drop is a 1% gain in hp. That may not sound like much, but a good example is my car... I ran no intercooler but with WMI. My MAF sensor temp probe was reading up to 280 degrees @17psi (Blow through set-up, before meth).

I just dropped in a Evo intercooler, The charge temps are now the same as ambient, in fact on a few dyno pulls during my last tune the temperature DROPPED a few degrees when boost hit. That's over a 200 degree drop...
At the same boost with the same timing I gained 25whp and 32ft.lbs. of torque. Also my spool up is within 200rpm as before, that isnt even noticable.

I have installed many front mount kits on STI's and Mazda speed 6/3's. Tuning past 250whp (with top mount) on our dyno is like pulling teeth for gains because of the heatsoak. To prevent risk of detonation more timing needs to be pulled. Any good tuner would agree to that. Even the Cobb base maps for the MS3 are specified for either a top or front mount(more conservative timing for top mount).

One thing I constuctively dissagree with is that the engine bay is cleaner with a top mount... I don't think so. Especially with the yaris and Ms3. Just about the only place for the top mount would be on top of the engine cover. I always found it to be a pain to have to remove pipes to service the car. They are routed to where you have to remove them to check spark plugs( which is something to be checked often on a aftermarket boosted car). And on the Subie you have to remove the intercooler to service the transmission /turbo/downpipe. The newer Subies have a smaller sized top mount with composite casing which makes life easier for working on the car, composite casing is for less heatsoak.

I say front mount.

good build, and whp numbers yet?