Vented hood anyone?

[5t341tH]

Hey guys. I have completed my SR20 swap into my datsun and now I'm looking to cool it down a bit. Underhood temperatures after driving is insane. I'd like to see if anyone has done vents in their hood  before. I saw a picture of some 620 guys in Thailand that had carbon fiber hoods and I wanted one so badly! If not, I would buy a hood and try to fabricate some vents for my own

[G-Duax]

About given up on finding a pre-made drop vent hood, so I am going to pick this fiberglass drop vent:

 

Universal drop vent

 

[Crashtd420]

5 hours ago, 5t341tH said:

Hey guys. I have completed my SR20 swap into my datsun and now I'm looking to cool it down a bit. Underhood temperatures after driving is insane. I'd like to see if anyone has done vents in their hood  before. I saw a picture of some 620 guys in Thailand that had carbon fiber hoods and I wanted one so badly! If not, I would buy a hood and try to fabricate some vents for my own

 

So is it only an issue once you stop driving and park or is it an issue If you come to a stop light also?

Are you using electic fans?

I have mine wired to constant 12v and a temp switch so they stay on for a minute or so after the engine is off....

 

Or do you really want the hood vents....

 

[datzenmike]

4 minutes ago, Crashtd420 said:

Or do you really want the hood vents....

 

 

This is often the case. I prefer the looks of a stock uncut and messed with body and repelled by cars with add on pretentious hood scoops and spoilers for example. L28s had a small electric fan with ducts to blow cooling air from under the car onto the injectors. Far better than a vent at low speeds that requires forward motion or convection when stopped.

 

[Crashtd420]

3 minutes ago, datzenmike said:

 

This is often the case. I prefer the looks of a stock uncut and messed with body and repelled by cars with add on pretentious hood scoops and spoilers for example. L28s had a small electric fan with ducts to blow cooling air from under the car onto the injectors. Far better than a vent at low speeds that requires forward motion or convection when stopped.

 

The Suzuki katana motorcycles did that too.... it would blow cool are on the bottom of the carb....

[datzenmike]

It's just me. I don't like body piercings either. Cutting a stock body just seems like mutilation. Breast implants are ok though.

[5t341tH]

It's a need. I'm not trying to do something that's distasteful to the truck. I will make it classy as possible of course.

oh I forgot to include a picture

Edited July 19, 2019 by 5t341tH

[datzenmike]

Can you raise the rear of the hood just enough to vent hot air? Maybe the slots like the 1980 Nissan 720. Least noticeable 

 

[5t341tH]

4 minutes ago, datzenmike said:

Can you raise the rear of the hood just enough to vent hot air? Maybe the slots like the 1980 Nissan 720. Least noticeable 

 

I was thinking of that. Raising the rear end a bit to allow ventilation. Or cutting louvers into it

[5t341tH]

this is what I really want to accomplish

 

[G-Duax]

Mike, openings at the back of the hood don't work.

Why ?

Because that is a high pressure area at speed, and is why rear facing scoops are used to boost power, and cabin air intakes are located at the rear, before the big air damn, the windshield.

Any air is going downward, into the engine bay, and adding lift to the vehicle.

Not to mention that openings over the engine let water in, directly on the engine.

 

A drop vent (at the front of the hood) is at a low pressure area, allowing air coming from the radiator to exit the bay, and reduce lift at the same time.

The opening is at the front of the engine, so rain won't come down directly on the engine.

 

[G-Duax]

11 hours ago, datzenmike said:

 

L28s had a small electric fan with ducts to blow cooling air from under the car onto the injectors.

 

 

 

They had that fan & ducting because early fuel injection system design sucked...

[wayno]

I have a 1980 Datsun 720, when it had the L20b in it I noticed that the rain ended up on the air filter housing top and engine, if it sat a long time water could sneak thru the bolt hole holding the air filter housing top on and go right down the carb into the manifold and right into the engine if a valve was open.

This very thing happened when a truck I got sat a long time outside without a hood under a wood shed roof, sideways rain got into #3 cylinder and sat there so long that the piston could not get by the rust when he tried starting it and then it sat some more till I got the truck.

Here is the manifold below where the carb was.

 

 

And here is the #4 cylinder that had a valve open.

 

 

 

And here is when I finally got the piston to move away from the rust.

 

 

Holes in the hood are not good if in the wrong spot, you definitely do not want a hole over an air filter housing.

 

Edited July 20, 2019 by wayno

[datzenmike]

18 hours ago, 5t341tH said:

Hey guys. I have completed my SR20 swap into my datsun and now I'm looking to cool it down a bit. Underhood temperatures after driving is insane.

 

34 minutes ago, G-Duax said:

Mike, openings at the back of the hood don't work.

Why ?

Because that is a high pressure area at speed, and is why rear facing scoops are used to boost power, and cabin air intakes are located at the rear, before the big air damn, the windshield.

Any air is going downward, into the engine bay, and adding lift to the vehicle.

Not to mention that openings over the engine let water in, directly on the engine.

 

A drop vent (at the front of the hood) is at a low pressure area, allowing air coming from the radiator to exit the bay, and reduce lift at the same time.

The opening is at the front of the engine, so rain won't come down directly on the engine.

 

 

 

I was thinking at lower speeds and heat soaking while sitting.

 

 

27 minutes ago, G-Duax said:

 

 

They had that fan & ducting because early fuel injection system design sucked...

 

The point was a fan can ventilate cooler air into the engine bay. Hell if you have electric rad fans have a timer that runs them for 2-3 min after shut down.

[distributorguy]

I really like the wind tunnel effects shown above, but keep in mind they are likely taken above 100 mph.  Below 45 mph, rear venting works exceptionally well, as there's plenty of turbulence that actually helps low speed airflow out of the engine bay.  Yes, we've done extensive testing with the race truck, which has very different airflow characteristics than a Mustang.  

 

I'd hunt for a shop that could add a few louvers to your hood.  Around here, punching louvers are $1 each at the bigger car shows.  The real solution however is to find out how and why your engine bay is getting heat soaked and fix the CAUSE of the problem.  Lean fuel mixture at cruise, maybe an electric fan that runs after the ignition is shut off, a more efficient radiator, ceramic coated exhaust, ???  Ask where is the heat coming from and how can you reduce it instead of trying to put a band-aid on the symptom.  You don't treat a fever with a fan.  😉

[bigboy620]

I’m looking into venting the hood as well but like Mike said I don’t want to add an ugly scoop or vent. I like the idea of an air duck with a fan. What would be better? To push air into the engine or to pull air out?

[datzenmike]

Depends where the inlet outlet is. If the carburetor is getting too much heat soak then blowing outside air on it would help. If sucking air near the carburetor you will pull air towards the carb. 

 

You have a '78 so there should be a hose from the air filter housing snorkel to the rad support to draw in outside air and not heated air from the rad. Make sure this is there or make one.  Outside ambient air is preferable to hot under hood air. Same with the Roadster. 

[Eric]

On 7/19/2019 at 3:33 PM, 5t341tH said:

It's a need. 

 

How come it's a need? you swapped the engine but didn't swap the matching cooling parts? Every SR20 has a fan and radiator and shroud that keeps it at the right temperature even when you are in a traffic jam. So something must have gone wrong.

Edited July 24, 2019 by Eric

[banzai510(hainz)]

4 minutes ago, Eric said:

How come it's a need? you swapped the engine but didn't swap the matching cooling parts? Every SR20 has a fan and radiator and shroud that keeps it at the right temperature even when you are in a traffic jam. So something must have gone wrong.

EXACTLY!!!!!!!!!!!

[Duncan]

I would add a cowl induction hood, then add a scoop on top of that just to be sure.  

 

 

 

 

[5t341tH]

Ok ok. It’s a need as well as a want. I have aftermarket manifold on it so it exposes the BMC to pretty direct heat. I will have to fabricate a heat shield to help with that. My swap does have aluminum rad and electric fans. I removed the driver side high beam to let in some cool air into the filter 

[datzenmike]

Ah SR swap.

 

First  IS there a problem??? Or is it just warmer than a stock L20B???? Does it quit on you? Is it hard to restart? Does it idle poorly? There has to be a problem in order for a cure to be used.

 

 

Run a sealed pipe from intake to in front of the rad for cool air to run on. You have to make air go where you want it.  Brake masters are used to 200F heat but radiated heat is different. Make an aluminum shroud or use header wrap on the hot pipes.

 

The absolute LAST resort is cutting up the hood.

[banzai510(hainz)]

stock Nissan Sylvias did Ok with out them from the factory

[FrankRizzo]

NACA duct from a 280ZX turbo!

 

.

[Ozz]

I have a cowl induction hood on my 1973 620 that I bought almost 25 years ago. It is a 'glas lift-off with pins...keeps the temps pretty cool. They are still available.