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Rear mounted radiators


ROGUE TROOPER
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As the temperature difference between air and rad is a big factor in cooling rate I'd guess cooling in parallel is more efficient than in series.

Agreed - also there will already be extra restriction on the water flow due to the long pipes to the back - putting two in series would then restrict flow even more - two in parallel would (of course) ease the flow.

TwoSheds

* My bit of the above is 'in theory' I have no experience of rear mounted rads...

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I racer that I look after has two radiators in series in the front. Only the front rad has an electric fan (driver/co-driver controlled) the rear of the two rads is cooled by the engine driven viscos (sp?) fan.

I personally don't find that in this senario that the pair of radiator does anything other than add capacity to the coolant system which is probably what keeps the engine cool.

Not sure if this really adds to the discussion but it is what I have observed with twin radiators in plumbed in series.

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if you are going to rear mount a rad wouldn't you be better off getting an huge ali rad from the likes of summit racing (for not much money) and just using one rad?

you can get ras from them for as little as £100 which will happily cool a big block chevy.

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if you are going to rear mount a rad wouldn't you be better off getting an huge ali rad from the likes of summit racing (for not much money) and just using one rad?

you can get ras from them for as little as £100 which will happily cool a big block chevy.

Yes maybe thats the way to go............

Its will be running Twin Turbos as well as electric water pumps (im doing away with the mechanical thing...........BTW anyone got a knacked 3.9 water pump they dont want?)

I have heard about the "swirl" effect behind truck cabs is a pain as the hot air does not escape.

Ta

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A friend of mine ran a rear rad in a hardtop, taking air from the floor and exiting through the rear door using fans. He found at low speed the fans were running all the time, so went for a roof scoop and exiting through the rear floor ahead of the crossmember. In both cases the biggest benefit he saw was no mud clogging the rad all the time.

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Petal's rad works really well and it's only a small TD one. Miketomcat has a similar setup and he also seems very happy with it. In both cases though they have good roof mounted scoops to get airflow in there. Neither seem to have any troubles with stock water pumps and long pipe runs.

With the lack of mud blockage in the cooling equation you could probably do as MogLite's done and put a fine-finned ali one in from a modern car or van, b*ll*cks to paying £100's for a "racing" ali one when there are loads of shapes and sizes of ali rads sat in the scrappy with decent fans attached too. Cooling is more a function of BHP than engine size so aim for something with a few horses and you're laughing.

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Cooling is more a function of BHP than engine size so aim for something with a few horses and you're laughing.

that's useful to know- in the absence of any proper knowledge i had theorised that required cooliing is related to engine efficiency- ie a very efficient forced induction 2.0 engine making 350 bhp is going to need to less cooling than a very inefficient Rover 4.6 making 250bhp- on the grounds that in a low CR RV8 alot of the fuel burn just exists as wasted heat, in a high specific output engine alot of energy is going towards movement of the engines parts.

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I'm sure an adult (Bull Bar Cowboy) will be along in a minute to splain it but that isn't quite how I understand it. There is the BSFC number of your engine but, unless you have a turbo this is reasonably similar across the board. Since all engines are about the same at converting fuel into motion, the cooling is a % of the BHP produced. Turbos give >100% VE numbers but that's a bit of a smoke screen, it doesn't mean they're more efficient at making power, it just means a smaller engine can fit a bigger bang in in the first place.

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that's useful to know- in the absence of any proper knowledge i had theorised that required cooliing is related to engine efficiency- ie a very efficient forced induction 2.0 engine making 350 bhp is going to need to less cooling than a very inefficient Rover 4.6 making 250bhp- on the grounds that in a low CR RV8 alot of the fuel burn just exists as wasted heat, in a high specific output engine alot of energy is going towards movement of the engines parts.

As a generalization ……….. the more power any given engine makes, then the hotter it runs and cooling becomes more critical………………..

But the forced induction engine would probably have a lower CR then the RV8 ………. Otherwise detonation would occur ……..the biggest engine killer of all time……..

I guess another argument to that would be that the very large capacity low efficiently engine has a greater mass in which to dissipate the heat …………. But also if its inefficient its workload will not be great……..

BTW: Turboed RV8’s are not pleasant engines …………… everything has to be perfect to get them to run right ……….. Ideally it would be the 8.3CR and fitted with composite head gaskets to bring it down to 7.7ish so that a decent amount of boost can be used…………. Also it would need to have forged pistons like KB, Omega or Badger as the standard items wont withstand that sort of punishment for long………………I only know of one that has run anything like correctly and that is in an SD1 in the Netherlands………… you can make more power by a little careful tuning and a shot of two of NOS. ……………….. however, put a blower on it and that’s a different story………….RV8’s go well with the right blower

:)

Ian

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Rule of thumb from my IC engines lecturer - a third of the fuel's energy is coolant heat, a third of the energy is exhaust heat, a third of the energy appears at the flywheel (and in the manufacturer's propaganda). So yes, that's >100hp of heat dissipated by the radiator in a Tdi.

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