Advanced Engineering Tech - Higher compression

Let's say we build an engine with 9 to 1 compression and increase the compression to 12 to 1 which results in a hp increase of "x"

Then we build the same engine with 9 to 1 comp and modify it with more aggressive cam timing until it produces the same same "x" hp increase as first engine.

My question is which engine will produce the most residual heat for the cooling system to handle or will it be the same? I know from personal experience that better exhaust help engines run cooler. If this needs to be somewhere else Mods please move it. Thanks.

Well, seeing as how increasing compression raises heat, but increasing cam duration doesn't...

I would have to say that increasing cam dur will increase heat some , but not as much as raising compression . inc cam dur will pack more fuel/air in which will cool related parts some , at the same time the added fuel/air will burn hotter . same amount of power using mostly added comp would add quite a bit more heat comparetively . having said that , if this theoretical engine had very much power the camshaft way , it would be impossible to match the output just by increasing comp ratio . Google "compression ratio calculator" , there are hundreds or thousands of sites that You can plug You're #'s into and find out some good stuff . In fact I am looking for a site that the link to is in this section somewhere that has evry engine spec calculator You can imagine . When I find it I'll send You the link or point You to it . Good luck:nod:

Hello again , Oops I was wrong , now I found the calc site . It's "Wallace Racing"

Also there is an article in "Hot Rod" magazine from about 12 years ago entitled "The 350 Chevy Should Have Made" . These 2 guys with mech engineering degrees ... build a 350 using a 400 block bored .030" over , a 307/327 crank(3.25" stroke) Ford 300-6cyl rods (6.209") , custom J-E pistons with wrist pins higher to accomidate rods .... Aluminum heads with 58cc chambers , stock dur and lift roller cam , 4bbl. carb , Hei , and on pump 87oct the engine dynoed at 435lb/ft and 412hp with 36deg total ign timing

I would have to say that increasing cam dur will increase heat some , but not as much as raising compression . inc cam dur will pack more fuel/air in which will cool related parts some , at the same time the added fuel/air will burn hotter .

If we really want to break it down...

We need to figure how much that 9 to 12 CR change matters. It will vary depending on the cam. Let's assume 10% power gain.

So, the jump from 9 to 12. 33% increase in compression heat.
Roughly 10% more fuel. 10% increase in combustion heat.

It's as simple as that, right? No.

Temperature =/=heat

High compression will give you air at a higher temperature.
More fuel will give you more air at a slightly higher temperature.

Heat transfer occurs through temperature differences.

That is what I thought from my everyday evidence. One of the reason some builds get into more cooling problems than others.

Without having a good amount of numbers, I would say that it would be too close to theorize. On one hand you have a mixture that will burn hotter b/c it has less fuel to cool the air, but on the other hand you have a mixture that has more fuel to cool the air, but burns internally longer...

The higher timing/lower comp engine will have a lower initial combusion temp, but will burn longer, whereas the higher comp/lower timing engine will have a higher initial combustion temp, but will burn shorter.

It seems like a wash to me in theory right now, but I may be off track and am not claiming to be correct here. Just trying to add another input while making myself think a little bit.

Correct me if I'm wrong cuz I'm trying to read this on my phone and I might have missed something but I thought that in the second scenario ChucksZ06 had asked about using more aggressive cam timing, not more aggressive cam duration, which would make a big difference. By increasing cam timing you raise the dynamic compression. I haven't played with cam timing enough to know for sure but going from 9:1 to 12:1 is a pretty big jump so I'm not even sure if you physically can advance the cam timing enough to make up the difference but even if you could make both engines have the same dynamic compression I still don't think that they would make the same amount of heat because when you advance the cam timing it makes the engine think it has a smaller cam so if you allow less air and fuel into the cylinder then there is less to burn so it makes less heat and it will also make less power. Power and heat are directly related, when you make more power you make more heat and vice-versa. That's my 2 cents, like I said i could be wrong.

Let's say we build an engine with 9 to 1 compression and increase the compression to 12 to 1 which results in a hp increase of "x"

Then we build the same engine with 9 to 1 comp and modify it with more aggressive cam timing until it produces the same same "x" hp increase as first engine.

My question is which engine will produce the most residual heat for the cooling system to handle or will it be the same? I know from personal experience that better exhaust help engines run cooler. If this needs to be somewhere else Mods please move it. Thanks.

Assuming that "more aggressive cam timing" means a longer duration camshaft, then given a similar tune, same AFR, and same RPM range, (all else being equal), the first example of increased dynamic compression will be more thermally efficient and therefore reject a smaller % of total heat to the cooling system. Given the same conditions, the higher compression engine would appear to run cooler.

In real life, where people that run much higher static compression ratios also run a much higher octane of fuel, then you often observe them having issues with excessive heat rejection, overheating in street conditions, and exhaust manifolds and pipes glowing orange.

This is because they have changed the tune as well as the compression.
Either reducing spark advance, or increasing the fuel octane, will increase heat rejection to the cooling system, especially during low-load conditions such as street driving. The same amount of fuel might be burning, but the timing of that burn has been changed, so that less heat energy is converted to torque, and more heat is rejected into the surrounding metal.

Being less thermally efficient, the engine with the larger cam has to move more air through the engine in order to match the same power output. The extra air will require extra fuel and therefore the total heat energy produced will be higher.