bbong

That just doesn't make any sense, your hood vents will probably harm it more than help, unless you are PhD in Physics and have access to some gnarly tools to verify that your vented hood is actually helping. Just because you create another hole in the hood doesn't mean you will help it disperse more heat, while not hurting the dynamics and air-flow through high and low pressure areas. I'm not an expert in this, but have enough crazy Physics friends that would agree with me and why Toyota or a lot of other manufactures that build track ready cars never put holes in their hoods as it probably contradicts what you're saying.

This sort of takes me back to when I had the STI and removed the scoop as I went FMIC, changed it for just a hole with mesh, everytime when I took it to the track, I would cover the hole as I would notice temps to be more volatile than when I had it opened up. CCSR on the other hand has the vents, but I can bet you they actually tested, if their hood was functional, see how their pattern of vents is a lot different than what Seibon offers as it looks to vent along the pressure area.

JPxMODz

iTrader: (3)

That's awesome input! I can't prove that it does and you have no proof that it hurts cooling performance. Maybe someone with some actual knowledge on the subject can offer more useful input on the subject?

bbong

I've tracked my ISF in 105F weather, I'm mostly stock with some small mods and I'm by no means easy on the car, I did contemplate on getting the Seibon hood, but with my previous track experience and other cars I had, I would get non-vented hood just for weight saving if it had any significant over the OEM, and for the price I don't think the difference would be meaningful.

All those plastics that you see, veins, scoops are there mostly for a reason, so if you start modifying those, expect weird behaviors. I stopped removing plastics from underneath, cutting holes in the hoods and leave those things mostly untouched, because I'm not a Physicist nor do I have access to wind-tunnel, pressure sensors etc. to be screwing with design of much smarter people and company with deep pockets.

As for the OP, I'd like to see the weight of Seibon Hood vs. OEM, thanks for doing that!

JPxMODz

iTrader: (3)

Isn't the stock ISF hood made from aluminum? If so, I wouldn't imagine there's much of a weight savings?

JohnMorgan

iTrader: (6)

This is more relevant from a handling perspective than drag perspective, although with hardcore drag guys every lb. counts.

With all those turns you hit I'm sure you can feel the difference and notice the car not wanting to rock harder side to side.

Thanks for peeping the build thread!

These are more like the mods you would do after light wheels, exhaust etc. By no means should you get these before any of the other items if weight reduction is your goal if we're talking dollar per lb. saved

Same, although I was surprised that the OEM trunk only weight 21.5 lbs in the first place. I'm probably going to take a dremel and cut out some of the fiberglass inner skin on the trunk because you know, weight reduction

This. The engine cover keeps so much heat in there it's stupid.

If you look at the IS-F CCSR or even the CCS-P hood Lexus / TRD was adamant about cooling the engine bay via ventilation. Placement and size are another discussion entirely.

bbong

and that's exactly what I said. In respect to cars that have undergo proper testing, but cutting out holes just because it looks cool may not always have the same benefits. Once you start cutting out holes, you completely change the pressure zones. I would suggest this reading: http://www.autospeed.com/cms/article...art-1&A=113176 before jumping into buying vented anything.

Jwconeil

FFM

lobuxracer

iTrader: (2)

Sure the engine bay is hot after you stop. You're failing to consider what is happening while you are moving, and that's what bbong is talking about. No different than doing dyno testing without adequate airflow through the engine bay.

Your problem with drag racing is heat build up because the engine is running while the car is not moving. The assumption the engine makes too much heat and needs vents to remove it isn't based on anything other than supposition. Like bbong, I have tracked my car at 102F without mercy, and sure the engine gets hot because it's burning a gallon of fuel every two laps and two thirds of that heat isn't moving the car at all. A full third is being captured and shed by the cooling system, the other third escaping out the exhaust. The physics guys can tell us with pretty good accuracy just how much heat that is. The physics guys will also tell you the engine produces best power when it is fully heat soaked with a cooling system sized to remove only the excess. Every joule that goes into getting back to the fully saturated temperature does absolutely nothing to move the car. It's a tricky balancing act for sure.

At any rate, if you don't do an aero study on the car post install of any new holes, slots, slats, louvers, ducts, etc., you really can't be sure what happened. Many times the airflow is in exactly the opposite direction of what you hoped, especially with vents. I really doubt Seibon spent the time and effort to optimize the vent design. I also wonder exactly how much effort Lexus put into their CCS design. Not everything the manufacturers do has solid engineering behind it. They do plenty just for appearance's sake.

JPxMODz

iTrader: (3)

This was interesting. Hood vents starts at 4:12

Leander311

iTrader: (2)

Sub'd... Always been interested in a vented hood both for cooling and reduced under-hood pressures (increasing front downforce). As with home-fabbed plywood front splitters, hood venting seem to be common "best practice" in most racing circles for the above two benefits.

Agree w/Lance though on the heat-soak/physics points, though they typically impact heat soak of intake tract as well, and thus intake charge density... Definitely a fine line.

illwillem

Just to clear some of this up with empirical testing and data. Yes getting the vented hood from Seibon (what was tested) or novel WILL increase cooling ability on the ISF.

I have a bit of a background in this- while some of the above conversation has a healthy bit of skepticism i would offer that its generally always going to be beneficial venting heat. There are really two categories were talking about here- Heat loading and radiator efficiency.
The stock ISF had a decently efficient radiator for city/hwy use, but its blocked by a large AC condenser and trans cooler. Because of this, the OEM riffle design on the core has an angle and density that is optimized for these conditions. In laymans terms 'expects' to see a slower more turbulent volume of air cross its surface. I also noticed that the core is built with a narrowish water passage ( I also assume its a single pass design due to the narrowness of the water tubes) This reduction in volume restricts flow so that the water takes longer to pass though is inside the radiator, allowing the less efficient riffle design to sufficiently cool transfer the heat. Generally this type of car radiator cools well in most situations (what the OEM wants), but once over heated tends take a long time to bring temperatures back down from the brink.

Another thing about the OEM set up is that the exhausted air/heat that has passed through the element only exits the bay though some venting slits in the belly pan plastic just behind the core . The plus side to this, and why Lexus designed it this way, is by covering the engine bottom you decrease drag substantially and lower front end lift, both of these yield and increase MPG and top speed. The down side is that these slits are rather small and easily clogged with leave or other debris.

Now think about this- Since air is a fluid imagine standing your car up on its end and dumping a continuous volume of water into the bumper intake, with only the slits in the belly pan for it to exit you will soon have a back up of water. (Yes there is an aero effect of the low pressure air under the car helping draw the air out but this would increase though-put about 15-20% max). Now imagine that stacked up water is high pressure air, you cannot force anymore air into a volume, you've maxxed out the flow rate. The cooling air that you want though you radiator at speed is stagnating due to pressure... And this is assuming everything is in good working order! It should also be noted fans only work under 10-15mph and actually hinder cooling performance at freeway and track speeds.

Now lets introduce heat load, this is the temps coming from the engine itself off the block, waterlines and the 800* headers that are literally glowing red on both sides of you engine. This is effectively reducing the efficiency of cooling can be done by your radiator 'X' number under ambient temperature.

Now back to the same water pouring scenario as above but this time you have hood vents like the Seibon hood. You can now exhaust that much more water out from under the hood and keep the stream of fresh flowing air feeding though the heat exchanger.




So what are the small fixes?

1.Make sure your vents are free of debris, this is a big one.

2. Lowering your car increases the low pressure stream under the car and speeds up the air, thus increasing the vents efficiency, this is a small gain buy a gain none the less

4. Removing the bumper beam. It blocks about 1/3 of the flow to the radiator and trans cooler. Its obviously there for a reason but strictly speaking of cooling, its not doing you any favors.

5. Venting the hood. This wont necessarily increase efficiency of the radiator itself as the majority of that is built its its riffle and water-jacket design but will reduce the ambient temperature it has to operate in. This is why you will see the gains.




What are the big fixes for track driving (roadracing)

1. Change the radiator to a more performance designed unit, thicker core = more water and better heat capacity. Riffle design built for better efficiency at speed.

2. Remove radiator obstructions (beam, ac condenser)

3. Exhaust air through hood just behind radiator (similar to the novel hood)

3. Thermal coat or wrap headers to further reduce engine heat load and lower IAT's


I have tested bone stock set up with oem hood. 103 deg day at Chuckwalla raceway. 4 laps at race pace netted a spiked temp gauged and a 250* reading on the IR gauge shooting the water return hose. Swapping the hood and running 4 laps was a 235 reading still high but better.
Swapping to Koyo rad and vented hood I can run a full 20 min session at 219-220 water temps. OIl temps are more of the worry than water now.

parkison25

Sorry to revive an old thread, just wondering if you got the carbon fiber hood installed and were able to weigh the OEM aluminum hood you took off?
Also, seems to me pretty much that whole depressed center area of fiberglass on the underside of carbon fiber hood could be cut out neatly with a dremel for max weight savings? Maybe just leaving an “X” for structural bracing.

lexicon72

OEM hood is about 27 lbs. See my post #75 on my track build thread.
https://www.clublexus.com/forums/bui...ispreloading=1

I recently installed a custom vented hood from JMA racing (13 lbs) that has the side vents like Seibon and the center vent like Novel.
No empirical data yet as my next track day isn't until June 13.