ptuomov

Greetings. I've got this "roll your own" aftermarket turbo 928. The kit is made by John Kuhn and the car is trouble free. Although the engine coolant temepratures stay nicely within the range of the stock thermostat, I am thinking about doing something about the underhood temperatures. I already have thermal barrier coating on the exhaust manifolds, but want to do more.

One idea that I have been toying with is adding NACA hood vents to the 928 hood, similar to those on 968 Turbo RS and S. I have some questions to you guys, since you're the experts on how those work.

(1) How do you deal with rain with those NACA scoops? Is there some trick used to prevent rain water from making it to the engine compartment or is it just one more coolant that's coming thru the hole? ;-)

(2) What kind of benefits are you getting, in terms of underhood temperatures, from the passenger side NACA scoop? With or without a heat-shield shroud that guides the air flow to the exhaust manifold?

Thanks and best.

Here's the car:



Here's why it's hot down there:

odurandina

it's just horny.

MM951

Wow, can't help you with your question... but that sure is a strong 928. 665 rwhp!!! Just about double what I put down !

Vids?

FRporscheman

I don't have first hand experience with NACA ducts, but I believe the only way to mitigate rain entering the ducts is to not drive in the rain.

From what I remember was discussed on this forum before, the passenger side duct is mainly for aesthetics, as it aims air right at the distributor on the 968.

Nice build!

Damian in NJ

I'd suggest a call to Carl Fausett at 928 Engineering, he's a Rennlist sponsor and recently developed a supercharging system for 968's, so we've gotten to know him here. He races a high hp 928 and may have an on the shelf solution for you.

odurandina

Tuomo,


was going to ask you the other day if you wouldn't mind if i posted your exhaust photos on the 944 turbo forum.....



guys seem a bit confused on how to design a good exhaust for the LS1 swaps they're running.



Allan

ptuomov

Knock yourself out! The exhaust was built by John Kuhn, it wasn't me. For a normally aspirated car, I'd add a cross-over pretty far upstream.

ptuomov

I thought some of the RS's had a duct/heatshield that directed the air flow to cool the components near the exhaust manifolds. Is this true? That would be for more than just aesthetics. Maybe Turbo S has it for looks but the RS race car probably had nothing drag-inducing just to make it prettier.

I don't want to cool the exhaust manifolds (and it wouldn't be possible anyway, considering that I am running ignition advance in the low teens), but I do want to cool the components right above them manifolds next to the valve covers.

Lemming

You may want to check the 951 forum, there have been quite a few treads on underhood heat dissipation and I've been reading them (along with other sources) since I'm installing an SC in my 968. From my reading, I think a better solution is to let heat out the top of the engine by adding hood vents. Hood vents should also allow more air to flow through the radiator and intercooler by decreasing the engine bay pressure.

I'm starting my project with a large hood vent similar to what is seen on Subaru's. It will be place directly behind SC but still towards the front of the hood where there is good negative air pressure to "suck" air from the engine bay. Below is an image of the vent that I have, should be installed on my car soon.

ptuomov

The hood vent indeed increases the air flow thru the radiator. That would therefore be an excellent solution if my car's coolant would run hot. However, it's not. In 80-100F weather with A/C fully on, I drove about 920 miles in very varying traffic conditions and the coolant temperature remained nicely within the thermostat regulated range.

What I am concerned about is not so much the coolant temperature but the underhood temperature and in particular the temperature of the components next to and right above the exhaust manifolds. If I add a hood vent such as that in your photo, this will reduce the air flow near the exhaust manifolds and may add to the cooling problems?

Lemming

That's possible, but adding the naca duct could decrease airflow through the radiator by adding engine bay pressure. Might be worth thinking about running both, like the Turbo RS. NACA duct to cool a specific area/part and the hood vent to allow increase flow to the radiator.

Thom

The passenger side naca ducts on the 968 turbos cool down nothing at all bar the top of the power steering bottle.

odurandina

i am running almost the same exact exhaust as you, cept for only 4 cylinders...

https://rennlist.com/forums/924-931-...to-heaven.html


got a similar design resonator.... and muffler is basically the same as your Borlas... your buddy Carl in Needham drove my car and wrote a nice review about how it sounds on page three of my exhaust thread.... he drove it hard hrough the twisties (after midnight) behind High Rock and going back into Dover, and loved the sounds....



i posted your photos....


https://rennlist.com/forums/924-931-...-thread-2.html

ptuomov

Spy video by a coworker of me just cracking open the throttle leaving the parking carage:
http://picasaweb.google.com/lh/photo...eat=directlink

Maybe on Turbo S, but what about Turbo RS?

Thom

Ask Jason Burkett at Paragon Products, he's got one.