M35 Bonnet Lift - Heat Extraction

[Equilibrise]

Hi all,

OK, you might think I am crazy for doing this. I've been looking for ways to reduce engine and intake temps and considering that our engine bays are pretty tightly packed options are limited. I thought of bonnet scoops ,etc but they are ugly and came up with the idea of lifting the rear of the bonnet. The idea is similar to the operation of a fireplace flew - hot air rises (actually cold air is more dense so it pushes the hot air upwards) and as it goes up through the confined space it creates a slight vacuum. With air passing over the outlet more of a vacuum is created and therefore more air circulation or heat extraction from the engine bay.

Results, as displayed by the informeter are intake 5-15deg lower temps (I figure its due to the sensor body or AFM not getting as hot) and water temps are much more stable ranging between 89-93 whereas before they were between 91 and 98degs.

My car is due for a tune and is running rather rich, so as soon as temps got high it would run like a pig. Now it runs more stable. The physical temperature of the plenum and associated piping is also much much more cool to touch after a drive.

All I did was install incremental spacers between the bonnet and bonnet brackets and remove part of the rubber seal. I also had to adjust the bonnet height spacers at the front, as the angle had changed.

It would probably be beneficial for those who do track-work as it could increase more down-force and possibly release any built up pressure in the engine bay, but that's just my imagination going mental again.

For those wondering about water getting in - it doesn't except if you hose it in while washing the car.

See the attached pics for what it looks like. You can see the intake piping in one of them.

[Brick]

Was talking to fishing freak about this the other day. Would be so good to be able to do this on an actuator system so when parked etc it could look really good and right

[scotty nm35]

I was always told it doesn't work well as that area is under pressure when driving, so the air would actually be forced into the engine bay from the top and less would flow through the radiator, but your results speak for themselves Adam. I might need to try this at the track sometime.

It would be interesting to place a few pieces of string under the lip to see which way the air is flowing... I suspect it's flowing out of the engine bay increasing airflow through the rad.

[Duncan]

Great if you are seeing results, but as Scotty suggested the base of the windscreen is a high pressure area, not low pressure, so air will be going in not out through this gap. The other part therefore is to look at the underfloor at the rear of the engine bay and make sure there is enough space for air to escape.

[iamhe77]

You may find these interesting Adam

http://www.autospeed.com/cms/article.html?&A=2159

http://www.autospeed.com/cms/article.html?&A=2160

http://www.autospeed.com/cms/article.html?&A=2162

[Equilibrise]

Thanks guys. All very interesting. Anyone got a magnehelic gauge I could borrow? I may just buy one as it would be interesting to know the exact pressure values in the engine bay with all the different configurations i.e. w and w/out bonnet lift, w and w/out under tray.

I will attach some string to the underside of the bonnet where I can view it now Scotty - if that is where you mean. That great test.

[Equilibrise]

rather: that's a great test

[Daleo]

Wow, Julian Edgar has come a long way from the days modifying ADM GTR g-sensors with washing machine parts, and subsequently smashing them backwards into Armco railings...

Not.

[Rudi_ARX-TURBO]

Or you can a Bonnet like mine, which was jet wrecks that has a vent nearly over the fan heat escapes big time?

[Dunc]

Didnt Craig try venting the engine by popping the back of the bonnet also? Could've sworn I'd seen this done before.

[Daleo]

Didnt Craig try venting the engine by popping the back of the bonnet also? Could've sworn I'd seen this done before.

He did indeed.

There are no new ideas, just new people to try them.

I'd much rather something like Theo's awesome vented bonnet; that thing is sex.

[Rudi_ARX-TURBO]

What abou my sex?

[Daleo]

What abou my sex?

Your sex is lovely, rude man.

[Equilibrise]

Sorry Dale. I didn't realise it had been done before and didn't realise that there is a better way.

I am just looking for ways to improve my M35. I experience a massive loss in performance when the temps get close to 100deg

Personally I don't like the hole in the bonnet idea. Its a bit harder to 'undo' if needed.

I am merely testing different ideas and posting the results and receiving feedback from more knowledgeable people, so thankyou to all the everyone giving positive feedback rather than just criticising.

So, the string test shows that as Scotty and dunc stated earlier that it is a high pressure area and the string gets sucked into the engine bay there, so probably not so good for the track.. I am guessing that it would be the same case with the hole in the bonnet like craigs...except would the plenum receive the same cooling with the hole, and would the heat generated from the exhaust manifolds and turbo be able to escape as easily?

[Daleo]

Sorry Dale. I didn't realise it had been done before and didn't realise that there is a better way.

I am just looking for ways to improve my M35. I experience a massive loss in performance when the temps get close to 100deg

Personally I don't like the hole in the bonnet idea. Its a bit harder to 'undo' if needed.

I am merely testing different ideas and posting the results and receiving feedback from more knowledgeable people, so thankyou to all the everyone giving positive feedback rather than just criticising.

So, the string test shows that as Scotty and dunc stated earlier that it is a high pressure area and the string gets sucked into the engine bay there, so probably not so good for the track.. I am guessing that it would be the same case with the hole in the bonnet like craigs...except would the plenum receive the same cooling with the hole, and would the heat generated from the exhaust manifolds and turbo be able to escape as easily?

Hey Adam, I didn't mean to come across like a smartarse; I was just being a bit facetious. The internet doesn't translate my sarcastic sense of humour very well at the best of times, so I'll back off.

I was butchering a Mark Twain quote to suit myself.

“There is no such thing as a new idea. It is impossible. We simply take a lot of old ideas and put them into a sort of mental kaleidoscope. We give them a turn and they make new and curious combinations. We keep on turning and making new combinations indefinitely; but they are the same old pieces of colored glass that have been in use through all the ages.”

It's a good idea to keep experimenting; and you sound like you're on to something, well done mate.

As a couple have said; the back edge of the bonnet/plenum area is traditionally a high pressure area, so it IS actually surprising to see an improvement in cooling, when the expected result is somewhat different.

To lower engine temps, I would recommend using a larger capacity radiator (2 or 3 core), and a Nismo low temp thermostat. These changes took my car from an average low temp of 92deg to an average in the low 80's.

Scotty's cooling mod also allows temperatures to normalise much faster after a temp spike due to high load.

Cooling these cars in hot weather is a tricky job, but all the little 2%ers do add up. Things like good ducting, and sealing gaps is incredibly effective if you're looking for cheap fixes too.

Cheers, Dale.

[Equilibrise]

Thanks Dale. That is a pretty good temp compared to mine. I don't have a nismo thermostat as yet. I have got a 53mm aluminium radiator, except when i installed it i didnt trim enough of the shroud off so when driving it for the first time after the install, when i came off boost the engine lurched forward and plowed the clutch fan into the shroud and thus destroyed both...so i installed twin thermos in a sealed shroud i made up. So until i can get my hands on a decently priced shroud and clutch fan i have to live with the davies craig setup.

On another note: i put the undertray back on today for the first time since i bought the car. Water temp is between 90-93, so 1 deg higher on the lower running temp;same on the higher end. Intake temps were lower!!! I think this is due to more air being channeled into the cold air intake (ducting next to the I/C).

[PN-Mad]

Electric thermo fans eat the dick on the DET motor.

I think a couple of people, Craig being one, and maybe Dale the other (?) have back to back tested and found a properly working viscous is far more efficient.

Contact a wrecker, and you should be able to get another cheap. And as Dale said, big rad, low temp thermo, and the cooling mod, and your cooling system is mint.

I did a 15 min track session, came in the pits as the tranny was starting to feel hot, and the thermo fans on mine didn't even kick in (<93 degrees).

[Daleo]

Electric thermo fans eat the dick on the DET motor.

I think a couple of people, Craig being one, and maybe Dale the other (?) have back to back tested and found a properly working viscous is far more efficient.

Contact a wrecker, and you should be able to get another cheap. And as Dale said, big rad, low temp thermo, and the cooling mod, and your cooling system is mint.

I did a 15 min track session, came in the pits as the tranny was starting to feel hot, and the thermo fans on mine didn't even kick in (<93 degrees).

Yeah, I hated the thermo's; aftermarket style ones just can't hack the pace.

I'm sure SPAL swept blade fans would do it; but they are much deeper than we can fit in our engine bay, due to the size of the motors.

Factory AU/BF falcon fan setups are supposed to go well (as do the V35/PNM35 Electric fans) but the blade design & motor size is the critical factor. HUGE current draw with Falcon fan too. The radiator I was using, would not allow the fitment of a modified BF fan setup; it was just too deep to fit.

The anectdotal evidence I've seen suggests that a clutch fan can flow around 3000-3200cfm of air @ 2000rpm (the locking of the viscous clutch breaks away above this point and even as revs rise; the fan spins no faster) whereas the BEST aftermarket thermo fans struggle to flow upwards of 900cfm (regardless of their claimed output).

So you are a long way shy of the necessary flow, even with 2 fans and a well designed shroud.

The OEM clutch fan & shroud is very effective (if a bit noisy) and very simple.

[Fishingfreak]

Yep got intake temps of 46deg today

Water temps 91-98

So I'm joining Rudi and cutting out the bonnet this weekend so fingers crossed

[Lakes101]

Keep us posted how you go with pics mate. Good luck?