Factory Five Racing Forum banner
1 - 6 of 6 Posts

·
North Florida
Joined
·
682 Posts
Discussion Starter · #1 · (Edited)
So im thinking the GTM being rear engine and all has enough problems that its not being constantly washed with air like a normal front engine car ... that why on earth would you put the pipes through the engine area ?

I would think it would help substantially with sound since the pipes arent rattling the quite literally undampened tin can as much if ran from underneath the back area instead of right through the middle of it ... comming out through the hatch doesnt look all that great to me ... so what the heck ?
Has anyone tried running them underneath the car ? Got pictures ?
 

·
Registered
Joined
·
94 Posts
Without knowing the specifics and relative geometry of frame components, suspension points, etc., I'll just throw this out there. Is there room to dump the exhaust out in front of the rear wheel ala SLC or Porsche 918? I always thought the side exit exhaust was cool. :confused1:
 

·
Junior Charter Member
Joined
·
1,146 Posts
It's not really much different than a front engine car. The only difference is that the radiator on a front engine car dumps it's heat on the engine.

Airflow under the car entering the rear engine bay will wash over it; it's a big open area that allows expansion. It gets so much air that it actually travels forward up the tunnel, which causes a lot of cockpit overheating issues.

Having the exhaust on top and dumping into the rear of the airflow behind the car can work quite efficiently. It's been done for over 50 years, the science of how to do it isn't something they teach in high school mechanics, tho. It's advanced design considerations, a 300 level course, so to speak. Lots of builders don't get it right when the engine is up front, either. Radiators must have a shroud, the fan has to be enclosed by the shroud by at least 1/2 inch past the blade tips, and the fan has to be able to move at least 2500CFM to cool the car adequately when hot and operating over 95 degrees ambient. Violate those rules, and you gets posts on "Why is my car overheating?" Toss in an underdrive pulley system and it's gets funnier -

GT40s, Mk 4's, Panteras, Mangustas, Lamborghinis, Ferraris, Maseratis, Porsches, Lotus - lots of exotics designed by former front engine makers who transistioned to mid and rear engine designs with no problem. Yeah, Porsche still ranks - they made front engine cars in the 80's, toyed with the reverse.

It's about knowing your engineering. Rear engine is no different, you just have to pay attention to major laws of physics, then apply them. Heat travels toward cold, make it go the way you want it to, and prevent it going ways you don't.

There's more to making a design than resolving triangulation issues in a tube frame chassis, or having adequate panel depth in a monocoque. The mundane issues of sealing the passenger compartment from external temperatures, noxious fumes, or the vagaries of weather, for instance. Most of us actually drive coupes and sedans with roofs and windows. It's the preferred method world wide.

Chassis or unibody, take a long look at a gutted car in the salvage yard next time you're there and start seeing the other side of the automotive coin - the boring stuff that makes your daily driver comfortable and practically unmemorable. No noisy metal interior, loud exhaust, or convoluted entry, no vibration or harsh ride. It's what previous generations worked their collective butt off to be able to afford, because their forefathers didn't have it. The Model T's major improvement was not having the exhaust of a horse's digestive system in direct view.

It's a matter of perspective.
 

·
Registered
Joined
·
16,319 Posts
Wow Tirod.

To the OP, I don't think it advisable since the gas tanks are right there. Even if you could find the space.

As I posted previously, the new exhaust system we will be trying shortly on the Mendeola Transaxles Baja Designs FFR PDG GTM will be an "up over the top" design, as opposed to the "go down low" design that is "normal" for this car.

My theory is that there is no reason to put the heat source down low in the engine compartment, especially on this particular car, where the air flow comes up from under the car and exits out the rear. To me it makes no sense to have the first thing that cool air encounters be the hottest thing under the hood. It just heats all the air in the engine compartment instead of just the air at the top and headed out the rear.

We shall see shortly.

The proof will be in the pudding.
 

·
North Florida
Joined
·
682 Posts
Discussion Starter · #5 · (Edited)
Im gonna be the first to come out and say it ... when I had a turbo under my hatch and exhaust all around the top of the tranmission area in the stock location... even with a cooler... my transmission was so hot from just normal cruising ... that you couldnt even touch it !!! So if you are rompin on it, dont expect your transmission to last, not from torque, but from HEAT !.. Im simply not convinced this car is seeing air flow like a front engine car, not at all really. I can feel the heat comming through my seat, and it aint from recirculation through the tunnel. Alot of it is that the stock thermostat is 220, but with the pipes right through the middle of the car and the way the car is intended to be driven, its just plain dumb to have them through there. You really have to think, on the stock setup, the crossover tube is less than 3 inches from the intake hole on the manifold... isnt that kinda like $#[email protected]& where you eat ??

And dont say wraping the pipes makes it cooler.. because it just makes everything hotter in the long run.
 

·
Premium Member
Joined
·
13,237 Posts
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top