Only a slightly theoretical question at this point – is there anything inherently different, or different in practice, between the oil cooling set up needed to keep a 2.7 L flat six cool versus the same displacement 2.7 L big Type 4?

It would seem like the flat six would have smaller displacement per cylinder and that might have less heat and more cooling fin surface area?

Kind of an interesting topic I think / hope.

Happy Friday.

is the 4cylinder going to be a dry sump motor?
and stock -4 cylinder type cooling fan?


a lot different
my years of experience with both motors tells me the 4 is going to run hotter...
the design, bearings, and complete "system" was for a lower output motor

where as the -6 was designed for that displacement and was factory engineered to handle that heat better

Dry sump oil system, more outer cylinder surface area.
Especially once they went from 5 blade to 11 blade fan.

The 2.7L Type 4 is a wet sump but had a 914/6 style Front oil cooler set up .

I didn’t run Type 4 2.7L in anger a whole lot but with that set up it never really got hot, it had an oil pressure problem, but it wasn’t due to the oil getting overly warm.

Sounds like the answer is “at least as much if not significantly more” cooling is required for a big Type 4.

I’ve seen that some flat 6 2.7’s run trunk mounted cooler successfully, but let me be pushing it for the i’ve seen that some flat 62.7‘s run trunk mounted cooler successfully, but let me be pushing it for the Type 4.

This is kind of neat (World member's car I believe).

Click to view attachment

That's the first time I have seen a set-up like that. Looks like it should work well. I hope they screened the fronts of the coolers to protect them.

Where is the muffler going to go?
Bob B

Yup. Area of a cylinder cooling fin varies as a function of radius squared. Just like two smaller valves can have more flow area than one large valve - so it is that more small cylinders will offer more cooling area than larger cylinders.

911 cylinder heads have significantly more cooling fin area than a T4 head + additional thermal mass of the cam towers to absorb transient thermal spikes.

But, don't forget about the influence of oil cooling. 911 2.7L has piston squirters and much larger oil cooler both on the engine and the 2.7L OEM trombone cooler had lots of oil line to/from the cooler that alllowed for additional oil cooling.

Right through the coolers!

Assuming he had straight pipes.

While not exactly "squirter's" you can mod the /4 rods to sling/shoot oil to the bottom of the pistons. Oil coolers have been covered to death.

Neat, thanks Rich.

So is cooling the cylinders the bigger issue here than keeping oil cool?

It's really not an either or thing. Cooling an engine is a sytems engineering problem.

The best example I can give is back in my college days participating in Formula SAE (look up details if interested) it was common to yank an engine from a Honda CBR600. Water cooled.

The engine was usually shoe horned in right behind the driver seat and had zero airflow.

Even with zero engine modifications and more radiator area than stock, the engines had a tendency to overheat, especially under load. Why?

Turns out that although the engines are water cooled, when they are used in a motorcycle (even with a fairing), they still get alot of air cooling of the aluminum block, head, and transmission housings. Sticking it behind the seat with zero airflow had unforseen implications becuase we didn't look at it as a system.

@superhawk996 - very helpful, thanks.

I suppose at some point you just have to try it but wondering if even with keeping the oil cool via one of the cooler set ups if more cooling for fins is still required. As I bought it there as no rain tray and it had a larger grill area.

If I recall your big bore engine already had aluminum cylinders. The aluminum cylinder will have far better heat transfer than cast iron.

Since for all practical purposes you can't add more cylinder cooling fins, that leaves the following options:

1) More and/or cooler air for cooling which has a bounded limit.

2) More oil cooling. But given that oil has a better heat transfer coefficient than air, it will be the bigger knob. It too will be bounded at some point too.

The upper bound to both #1 and #2 is what eventually forced Porche to water cooling.

@superhawk996 - Great discussion, thank you.

I know the answer is it depends, but staying in the realm of theory can you cool the oil enough to offset the heat from the less than optimal cooling that goes along with the bigger cylinders?

In other words if the oil cooling set up was highly efficient/capable and you kept temps in the 180-190 range does can that offset the heat soak from the larger piston combustion area.

I do have aluminum fins on the iron bores - good memory!

@Tdskip

I know lots will disagree but I fundamentally disagree that oil temp in the 180-190 range is desirable. That is too cool. Oil itself has no issue with being 240F-250F especially on an air cooled/oil cooled engine. Just look at how the gauges are calibrated. Red Zone doesn't even begin unitl 300F using the 200C taco plate and 250/260 using the 120C or 150C tempsensor.

The iron bore is a bigger limitation on heat rejection. This is where Nickies have a big advantage. Very thin wear surface and the rest is aluminum for greater heat rejection.

The bottom line is the six is going to run cooler cylinder (and oil temps) and have better durability since you're getting more relative cooling from the H6 aluminum cylinders. As previously stated. Same for the H6 heads.

However, with a larger volume oil pump and enough oil cooler upfront and getting cool airflow, a 2.7L T4 would survive for a while. The bottom line is that a T4 that big (2.7L!!!) is going to be challenged for longevity. That is a 35% displacment bump.

If your shooting for a 180F oil target, my gut says you can't get there but I haven't done the modeling or math to prove that.

If you allow for an oil temp target of 240F and just plan on chaging the oil every 3-4K miles, my gut suspects you could get there with enough oil cooler and this monster T4.

I think if you look at Jakes 2316 engine as a baseline, he even states that engine wasn't intended to have as good of a lifespan as his 2270. You are way beyond either of those known data points that have some dyno durability behind them.

As I think about how to do the math or modelling, it would 1st need to start with a baseline known oil flow rate, oil temp in and out of a baseline cooler, known cooler area, and known airflow temp and airflow rate. That's quite a bit of data acquistion. Not impossible but it would become a project on it's own. From that known data, you could do the math to see what needs to be changed to hit a oil temperature target on the outlet of the cooler.

To get back to your OP question. I think you're going to need more oil cooling on a T4 2.7L engine than you would need on the H6 2.7L engine. You could determine the baseline oil cooling area (inclusive of case area) of the H6 2.7L and then upsize T4 by some % as a start point. Purely a speculative guestimate.

If you're dry sump . cant you just increase
Oil pressure , campasity, cooler size, fans, until
Its happy ? Brad pen


And i haven't seen these until a car show today

But where does the accusump fit it .

Do any /6 s run these . do 911s have em ?


And dumb but

Could you use a innercooler or water meth chargecooler to lower the temp that way .
Even know it isnt a turbo . it would still lower head temps?

https://www.elephantracing.com/tech-topics/...nd-engine-life/

Thanks for all of the responses.

Changing the oil every couple thousand miles isn’t a big deal, longevity is probably fine if I can get 40-50K out of it. Going to take me a long while to get that sort of distance in.

Let me just state that I know this is all bit daft, I kind of just really want to do I and I know I’ve got non-trivial trade offs.

The 2.7L Type 4 will boot right in since the front cooler is already set up for it and it would go right back in to the car it came out of.

Uhh, who made that chart?

I have never seen one like it. I’ve never looked for an oil temp one, but there are statistics drive water temp vs life which are not like that at all. Cooler is not always better...

See my thread on trunk mounted oil cooler install. I had a conversation with Jake years and years ago. At that time, his suggestions for oil temp/pressure were 180-225 to be a good goal for warmed up operating temps. 225-245 change often. 250+ shut it down and figure out whats going on. And change the oil. For pressures 45-50 @3k rpm at 200 temp.

These values are not carved in stone, as every engine is different, and oil has probably improved in the last 15-20 yrs since we had this conversation. My system on the iron cyl 2056 runs right around 200 fully warmed up, with oil pressures using valvoline ZR1 high zinc 20w50 right in line with expectations.

And I'm good with that. IF (when) I were to build a bigger 4, I'd use nickies, the tangerine racing flat fan conversion, and shoot for the same oil temp figures, 200-220. If $$$ allowed, I'd dry sump it.

Thanks @ottox914