adam c

iTrader: (2)

This is not for a track car Fritz. It's a "weekend fun car". For his use, the vented hood will be the best choice.

jmadams74

This is not particularly responsive to your question. . .BUT, I am the original owner of my '93 RX7 and have gone the stock mount IC, heavy duty radiator, etc. Nothing every took care of the cooling issue until I installed a v-mount setup. Cool as a cucumber ever since (PFC set to turn fans on at 88C and it rarely gets there. Of course A/C turns fans on sooner in the summer). I also have the BNR Stage 3 setup and v-mount works great. Mine is the Rotary Extreme setup, but many others are available. Save yourself a lot of money and headaches (not to mention water seals and engines) and just do it right up front. . .Just my $.02 on the cooling topic. PS, I did also covert touring model to dual R1 oil cooler setup.

Fritz Flynn

iTrader: (263)

I disagree. No better test environment than the track. On a DD type car go 99 front bumper VS vented hood and the 99 bumper will absolutely run cooler than the one with a vented hood. Sure it may be a little cooler when Idling in traffic but if your idea of driving your FD is idling in traffic then you have the wrong car.

YEP

Sgtblue

iTrader: (16)

I disagree. Apples and oranges. What may work on the track with constant airflow at the front of the car may not necessarily apply to the street. And my idea of owning my car is to enjoy the car on the street...where you have to deal with traffic lights, stop signs and the occasional train crossing. A bigger nose opening won't help. But I think a vented hood would. For reasons others have mentioned, but also because the fans are responsible for moving much of the air through the radiator on a streeted car. The fans are already positioned to pull upward. That and physics of hot air rising and aiding low pressure behind the radiator makes me believe a vented hood would be more effective. But then I have no more data to support that than you have for a bigger nose.
That is NOT to say I would have either. I personally have no cooling issues. Car runs consistently cool relative to how I drive it and ambient. And all the aftermarket noses and hoods I've seen are expensive and with fitment issues to one extent or the other. And some are just plain ugly IMO. The OP seems to have settled on one or the other. I think there are other things he might consider first.

Fritz Flynn

iTrader: (263)

Jim,
Been there done that. It's not about what may work it's about what does work

As I said I own a car with a shark tooth mod and it runs cooler than my cars with a stock front bumper. I put a vented hood on the car with the shark tooth mod and saw no benefits from the vented hood on the street. I'm sure there would be a small benefit to rolling around in stop and go traffic with the vented hood on but increased flow through the nose would be a greater benefit for keeping a car cool even if you lived in a busy suburban area where you may be stopped in traffic for 2 mins every 5 mins. Not too mention I've tracked this car for 14 years and improving air flow through the radiator and oil coolers is SUPER IMPORTANT to keeping temps in check AND a vented hood doesn't help noticeably in this regard.

Absolutely when at a stand still with fans on a bigger front bumper won't help much but believe it or not it's still going to help in this situation however once you start moving even at 20 mph you have tons more airflow with a large ducted opening versus a small semi ducted opening.

The best thing anyone could do (besides serious measure like VMIC) to improve water, smic/air intake cooling is simply removing the front bumper taking out the air guide adding aluminum side ducting to the existing under tray and employing the shark tooth mod. A 99 lip may help here as well. https://www.rx7club.com/3rd-generati...th-mod-859281/

If getting hot air out of the engine bay worked better than air flowing through the radiator your fans would be somewhere else.

Riccardo

iTrader: (1)

My car acts very differently than most. I heat soak when stopped, then when the car moves (with all the ducting and remedy pump) my cars temps actually go down the harder and faster I push the car. (I have a stock hood).


I have the exact same problem - HEAT SOAK IN TRAFFIC
Car gets hot, A/C turns off...unbearable situation

PS I do not have the remedy pump or done any ducting....

What can be done ?

nycgps

iTrader: (4)

seriously, if you worry so much , why not both ?

rxtuner79

iTrader: (1)

Fritz, if you're feeding more air through a larger front bumper doesn't it need an easy place to escape? Where does it go if not through the hood? It seems like that would be the least resistant path. I'm not challenging you, just curious and trying to tap into your knowledge of the subject.

jmadams74

I'm not sure you can ELIMINATE heat soak in these cars in hot weather, stop & go traffic. . .But, with the v-mount setup, you do eliminate water temperatures getting over about 90-95C, and while air temps will rise (on my car) to 50-60C, they do recover quite quickly once you get moving. I find this quite acceptable with stock hood and nose. PS: A/C does not make it any worse with this setup. Actually, since the A/C kicks in one of the fan speed relays, it actually runs cooler most of the time!

Fritz Flynn

iTrader: (263)

The same place it goes when you are going 150 mph at the track or 80 mph down the high way. OR it goes out the back side of the engine and under the car. I think air actually flows in through the back of the hood high pressure area forcing more air out of the low pressure bottom back side engine area. I don't know much about aero though so I may have this completely wrong LOL. HOwever it goes somewhere in a hurry. Bottomline the engine bay is designed to flow air in through the nose and back out and it is well known that the factory bumper wasn't very efficient but looks great The 99 bumper was a big improvement but still not really track worthy without lots of modification and duct work.


The VMIC is so awesome because it forces lots of air through the radiator or does the same thing a well ducted large opening front bumper would do.

Nope the rotary runs hot as hell so no way to prevent heat soak other than getting the intercooler out of the engine bay FMIC wrapping pipes etc.... but VMIC is an improvement over smic. I'm not saying a vented hood won't help but it's not going to make enough of difference to really mess with for a street car IMO. Much better plan is shark tooth, 99 or if extreme cooling is needed something like a GTC.

Enthu

iTrader: (1)

Okay, So. I can change this up a bit after all the reading. I do drive the car and take it on high speed cruises with the local evo guys on the southern MN roads. When I drive on weekends with the wife, there are quite a few stops in minneapolis. So, what if I did this: A V-Mount setup with a new front bumper. I do intend to continue building the car up and it will get water injection and everything else eventually. I do like the stock look on the car too, so this may be my best option as it will lower my intake temps too.

TomU

iTrader: (11)

Engines transfer most of their heat through the radiator, not raidiantly. You want to focus your effort on making the radiator as effecient as possible and airflow is key. A vented hood provides negligsble benefit to radiator effeciency (blocked airflow exit is flawed thinking becacause there's large airflow exit area under the car. Radiant cooling (vented hood) may help whe there is low flow over the rafdiator (stopped with no fans running).

lOOkatme

iTrader: (19)

my temps go up till the fans kick on (the higher speed ones) if I am idling forever. Not much you can do.

I typically cruise for a while after bad traffic to get my air temp sensor reading th actual air temp going into the engine and cool everything down before getting into it.

lOOkatme

iTrader: (19)

I think using a little logic can get you the results you want.

V-mount is the superior set up. It has fresh air going through your intercooler and radiator.

a bigger front bumper has more mass air flow. This is what cools your radiator/intercooler/oil coolers. You need to upgrade to (2) oil coolers IMO.

What goes through the engine to cool it?

you have air going into the intake, water cooling around the chambers, and oil going through the engine inside of it. All three of these allow the engine to run cooler. a front bumper brings more mass air flow to the exchangers of all three of these variables. a vented hood does what for these?

ducting is probably more important than even the front bumper, air likes the path of least resistance. you must force the air to go through the heat exchangers. If you have a ton of mass flow coming at a heat exchangers and you froce it all through through it....guess the outcome?

Here are some graphs with a 1.8 FT^2 front dam area and showing the effect of altitude and ram air flow. Also the heat removal of this front dam area related to HP. I share this because we have the short end of the stick here in colorado. We run our turbo's harder to run the same PSI (higher pressure ratio) creating more heat or higher air temps, and then have 25-40% less air density to cool with. damn right we run dual oil coolers, large radiators, remedy water pumps, and duct it to hell with large front bumpers. We also all run single turbo's up here because the stockers struggle like all get out. just a bunch of hot air blowers.

ohnono

iTrader: (1)

On my car, I have v-mount set up, intake, mini battery, abs-delete, air-pump-delete, dp, ducting for intercooler and radiator, 99-spec bumper, r1 dual oil cooler, ceramic coated uim, midpipe...... and so on, oh and not to mention vented hood and water injection. I live in so-cal so my air temp reaches 60C if im stuck in traffic for so long in summer. My water temp ranges 84-88C but never exceeds 90C (only on street). You can see from my mod lists that my modifications are all for cooling. But, i feel that no matter what I do at this stage, the heat soak just wont go away. I did the heat dispersant ceramic coating on UIM because people told me it would help with lowering intake temp. After month of driving the car, i feel that the ceramic coating only works for minimal effects (maybe i should coat the LIM as well). I dont know what else I can do to improve the cooling further. Hopefully when i go single turbo in the future, by ditching the oem exhaust manifold, i would get a lower temp in my engine bay

Riccardo

iTrader: (1)

Based on the above then it seems that the most efficient way to combat heat soak is to install a V-Mount and then possibly a hood will help when the car is not moving

I must also note that the way the hot air escapes the engine bay is probably counter intuitive as said before, it often escapes from the bottom (vs. hot air rises) and this is due to the low pressure areas below the hood....which also brings me to the next question / remark - due to the various vented hood designs, not all will act in the same manner....any views on this ?

lOOkatme

iTrader: (19)

That is about all you can do. I have a single turbo and when I idle and am stuck in traffic, my air temps hit the 50's C. I have a FMIC biased upwards and duct air under the fmic to the radiator. I have the stock hood and my temps are exactly the same as yours in all scenario's.

Tem120

iTrader: (5)

Bumper , as longas you get it to mate with teh oem UNDERTRAY , or some custom ducting .

I had a Mazda speed GTC replica , and my temps were always good .

I went to a smaller more OEM looking bumper , and my temps suddenly went much higher , at the time I was running a front mount intercooler, so temps were always exaggerated .


But the mazda speed GTC definitely ran colder .

I also have a Vented hood , and the vented hood helped alot with heat soaking .

BUT the bumper made the much bigger difference when driving .

ohnono

iTrader: (1)

I guess going single turbo does make a difference in temperatures (60C vs 50C). Sorry I forgot to mention, im not running the oem undertray as my radiator fan expels air towards the bottom of the car. Maybe i should duct my vmount intercooler to the opening of the vented hood?

ohnono

iTrader: (1)

The GTC bumper has huge openings which i think help feeding a lot more fresh air than 93 and 99 spec bumpers. The biggest drawback to me is that the GTC bumper looks way too aggressive on the street...

Enthu

iTrader: (1)

I've decided to start by adding the v-mount setup. Any recommendation on the better setup available for the money? A bumper will come immediately after I install the v-mount. I would like one that works with my existing Koyo N-Flow radiator.

lOOkatme

iTrader: (19)

I am helping a guy set up his car right now. He isn't on this website but we run a smaller intercooler (just large enough for 400WHP or so) and we shifted it to the drivers side. We re-welded his radiator to a V-mount configuration. Added a second oil cooler and made the brackets ourselves. we used Seatrab 19 row oil coolers.

We are custom making an intake to stick the filter in the area where the intercooler and radiator come together and are making a box around the filter to suck the cool air coming in the front.

He spent like 120 shipped on the intercooler, piping is probably another 60-100 with couplers and clamps. He spent $200 on welding I think, brackets were all done by hand and a vice, maybe $30 in material. Another 40-50 for sheet metal ducting for everything. Intake was 100, filter another $30, oil cooler lines were $100 used off a friend, new oil coolers were about $380 or so.

We built a V-mount, dual oil coolers, intake and re-done his radiator for about $1,110 and probably another 100-200 in unexpected stuff, so maybe $1,200-1,300 in total. We aren't done yet, should be today, but here is a quick picture of the unfinished product. He will get the intercooler piping welded later on (over winter). Notice that nice pocket he left for a nice large intake filter. he is going to make a box around it.