At what displacement are external coolers needed?, Building an alternative engine for my six Options

[Speedo]

I have read that the general consensus is above 180 hp an external cooler is needed.
I am at a crossroads with the 2.2 T I am building. I have 2.2 S pistons and cylinders and and cams. If I stroke it I get a higher cr 2.4 S. If I don't stroke it I get a decent 2.2 S which would still be a nice choice. I have everything I need for the 2.2, but if I stroke it I will need to source a 70.4 crank. Curious what the board thinks about the "red line in the sand" for needing cooling. It goes without saying that I am not interested in cutting on the six for a cooler up front.
Having said that...I spoke with a friend over the weekend with a 76 911 with a 3.2 transplant that doesn't run a cooler. He says his temps never go over 210...which I question as I have a stock 74 2.7 with a modified pulley setup that runs 200 but will show 230 when pushed. I think I need to measure his temps with a pyrometer to double check his temp gauge. (IMG:style_emoticons/default/bs.gif)
Tell me what you guys think! (IMG:style_emoticons/default/idea.gif)

[767driver]

From personal experience I can tell you there is no clear line in the sand. My 2.3 (approx 9.5 cr, solex cams, 40mm Webers, 165rwhp) needed more cooling. I ended up with a rear under-trunk cooler with fan.

[horizontally-opposed]

Running a 2.2 "S" that put 169hp to the rear wheels, so 190-200hp maybe?

Highest seen indicated so far is 215 F during a freeway trip on a hot day, which doesn't have me all that worried—but I have been thinking about a small cooler in the back of the car to keep things at 190-210 F. (IMG:style_emoticons/default/idea.gif)

[ClayPerrine]

From experience...

I have a 2.4 ST motor (S cams, S pistons and cylinders, T heads) that I took out of my six conversion for the 4.0. With an HB fifth gear, I could not run at 60mph. The fan was too slow to keep it cool in fifth, and it would overheat spinning it in 4th. I switched fifth for a ZD, and was able to keep it close to cool. I put a 911 Carrera cooler in the left rear corner next to the muffler and sway bar, and it dropped the temps by about 80 degrees. You may not experience that in Boulder, but it was definitely needed in Texas.

If you make that engine a 2.4, you will have to run premium gas, and you will need to look at a twin plug setup. The compression using 2.2S pistons and a 70.4mm stroke comes out to about 10 to 1. Great performer, but not a great street car. And you will definitely need some sort of external oil cooler on it. If you can afford it, Elephant racing sells a set of front oil cooler lines, and the coolers to go with them.

Clay

[mb911]

I would suggest a front cooler.. I am going to run a front cooler with no engine cooler.. Should be perfect for my 2.4 s built engine.

[SirAndy]

I know of several 3.2L 914s that don't run any external coolers and seem to do just fine.

Those are strictly street driven cars though ...
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[gereed75]

I do not dispute any personal experiences or recommendations on this subject and they seem to be all over the map. I can only relay my personal experience

I run a 2.4 with 9.5 CE pistons ( actually measured static), ported T heads, mod Solex cams, single plug, 40 Weber’s and I also run conservative ignition advance 26-28 BTDC.

Nothing but stock cooler, temps never above 210. I do not normally do a lot of extended highway cruising which seems to be the worst condition for cooling. Stock four cylinder side shift trans.

I did run an under trunk floor cooler for awhile. My thread is on here somewhere. It effectively dropped temps about 15 -20 degrees and I ran 20 minute track sessions with it no problem.

My opinnion based on this experience and a lot of experience running aircooled flat four Lycoming in aircraft applications - every engine is different, mixture, compression and ignition timing have a huge influence.

Bottom line - I think you can run a 2.4 S without extra cooling if everything else is good. By the way, this is a great street motor, good clean torque and VERY entertaining from 4500 - 7000 rpm!

[Ferg]

Lars, here at 5500 feet elevation and all roads going up with sustained grade, they all need coolers.

Given your house location, on a 90 degree day, I"m certain you would see 240 from your work to home. I don't believe your friends reading.

[mepstein]

Every engine is different but most modified engines need coolers. More power = more heat.

[horizontally-opposed]

These do seem to be all over the place, which is par for the course on this subject. I too have heard of multiple street cars with 3.2s that run just fine without a front cooler.

Should've mentioned my car is running factory tank and cooler, piston squirters added, Solex cams, Weber 40s, and headers. E pistons with a bump in compression, but nothing wild. Have never heard it ping on CA 91 gas. I'm running a stock 914-4 gearbox for now, and have no interest in lowering fifth—but I wouldn't mind lowering 1-4 or 2-4.

[Speedo]

Well I guess I got what I asked for. Quite the consensus...not really.
For starts I will shim using base gaskets to bring the cr down under 10:1
Next, as nice as the kits are for running front coolers...that is not going to happen on this six. I spent too long welding steel back in, to consider intentionally making holes in the chassis. I'm not going to race it...but I do live at altitude and there is less air up here.
I realize the more hutspa you ask of an engine, the hotter it deserves to get. So should I leave well enough alone with the 2.2 S and not run the risk of stroking it to 2.4 S specs?
Whats the difference at the crank...15-20 hp maybe? Would that be worth an additional 15-20 degrees?

[gereed75]

I have no direct personal experience, but the bigger difference in a 2.4 will be more torque. That will make the 2.2 no less fun, and the rev characteristics of the short stroke are sublime.

Take a look at my thread on the under trunk oil cooler. http://www.914world.com/bbs2/index.php?sho...=314444&hl= My objective also was no cutting on my six. I made a bracket that mounts the whole cooler and fan off of the trans mount plus one additional bolt off of the sway bar mount. That part all worked great.

It is all Still mounted under the car, minus the plumbing. All back to stock due to an oil cooler leak because I did not include a bypass for low temps/high oil pressures. Got it 95% right! Running now with more conservative timing and no more track days (BTDT) and all temps seem well.

I think it I felt compelled to do it again, with the same objective of not cutting the six, I would use the ever contentious under the engine lid idea, or re- plumb mine with a bypass.

If interested, drop me a line, all hardware could be yours for a very reasonable number. I’ll throw in the 100’s of engineering and fabrication hours for free.

[thelogo]

Just seems like common sense to me if you have
A higher performance air or oil cooled car .then you need a oil cooler unless you live in alaska .

Stock coolers do and can work well but front cooler are great insurance in case your caught in traffic

I could see not using one on a stock 1.7
But when your engine starts costing more then 5k
Budget for a remote oil cooler /heat exchanger

[Larmo63]

My 2.4S motor has a full on front oil cooler along with the engine cooler.

I hardly see the needle move much, happy engine.

[Steve]

Prior to my 3.2, I had a 2.7. The 2.7 ran hotter than the 3.2. Over stressed magnesium case versus under stressed aluminum case. My 3.2 front cooler thermostat only comes on when I’m stuck in traffic in the middle of summer in so cal.