Stresses on Engines?

[Roy]

Is my engine under more stress if i run the same boost (possibly less), the same rpm, the same approx A/F values but make more power. This also assumes that my radiator and oil cooler are suitably sized to remove any additional heat input.

Reason i ask is that i was told my engine may not handle the extra power that my turbo setup makes if i installed some cams. If im increasing the effeciency of a motor am i stressing it more?

[meggala]

depends o what motor turbo set up motors have certain power limits before the become weak. the cams will enable you to run less boost for the same power.

and tghe power deliver will be different if not better

cheers

[GTRgeoff]

You have to say yes.

More power at the same rpm means it has to be exposed to greater stresses due to the increased torque. Depends on how much more power though.

[Ustasa]

Come on Troy you slack prick

You whipped me in most subjects at the concrete cavern so that should be a easy question to answer

[GTRgeoff]

ooh ooh a classmate

Was Roy a real nerd then?

[Roy]

ooh ooh a classmate

 

Was Roy a real nerd then?

I was always too dumb to be a nerd And surprise, surprise too busy talking about the weekends pi55 up

I can do the mechanics of it all, but basically ; more air, more fuel more bang = more power.

The more bang is the concern. :Oops:

But if i keep revs sane, ie std at 7,200rpm, oil and water temps under control and only run 1.2bar, would having a set of cams that take power from 235-240 to 245-260rwkws really hurt a std RB20 that much more then running the extra 0.2bar of boost (i have my scramble set to 1.4bar...so when its pointed in the right direction i give it hits from 1.1 to 1.4 bar for the straights) :Bang:

Just added up what this whole RB26 cam farkup has cost me,

[predator]

There is probably an energy equation in there related to each cylinder i'm guessing.. and the amount of time that energy remains in the cylinder (which would be controlled by the duration of the cams amongst other things)

Unfortunately I forgot my maths nearly 10 years ago freakin computers...

[RBVS]

it would be easy to say there would be less stress on the engine when gaining power from cams then rasing boost as they both increase air flow but cams dont increase heat, like adding more boost.

I think that hold's true because what i have read of SK's posts being able to run reliable 250kw with cams and stock injectors but going about making 250kw with a fuel reg and boost the pistons burn and die. So 200kw becomes the reliable power limit.

SO GO THE CAMS!!!

[Warpspeed]

Thermal stress, or mechanical stress ? they are quite different.

You can quite easily blow up a stock engine by leaning it out, as we all know. Thermal stress is probably the most dangerous with a mildly modified engine, if it is badly tuned or not tuned at all. Detonation damage is another very quick killer of turbo engines. None of this has anything to do with the basic strength or integrity of the engine itself.

Mechanical stress is a completely different thing. Rpm and inertia forces are what most likely are going to break things and that has little to do with power output. If it is properly tuned and you stay within the factory redline it can make significantly more power without any additional MAXIMUM mechanical loading. The average loads will be up, and the torque be higher, but that will not break things, except maybe the clutch.

Bigger cams and valve springs might be dangerous if you then expect to wind it out to 10,000 Rpm all the time, or buzz the engine by dropping back to second gear at 160 Kmh. An extreme and silly example, but you get the idea.

[Roy]

LOL, its an internal combustion engine, and ppl never meantion cyclic loads:)

I may just wait 3 months and 10-15,000kms to see how the wrecker engine goes before i get the courage to lean on it a bit more with cams. Want to eliminate as many variables as possible so if the engine goes bang i at least have an idea of why.

[GTRgeoff]

But the power cannot go up at the same rpmif the torque doesn't, which means that there has to be more load on the piston, conrod and crank (as well as all the inbetweens) and so it goes. If it was RPM increase alone then sure, inertial forces increase, but more power at the same rpm means there is more air going in, therefore more fuel required for a stoich mixture, so a bigger bang must result.

I'd run a little extra power until you are able to get an oil change/oil analysis done, then plan the next power increase. Fuelling is not an issue for your setup though mate.

Your call.......

[DoughBoy]

Is it running yet?

[RBVS]

stress; (noun) strong physical forces applied to an object.

well cams arnt going to increase thermal stress and 250-260rwkw would be within factory spec rod's bearings etc so not too much mechanical stress, If you have time and money i wouldnt let stress stop me

my 2 cents.

[Duncan]

Is it running yet?

dont think so, he's spending too much time posting what if questions on here again

[R33vit]

I think you need to look at what cams are doing to increase your power. IE allowing more air flow. Isnt this what a turbo tries to do and increases stress.

[Chris32]

This is a interesting topic

Whats everyone's general opinion about the safe power level (assuming all the support systems are up to scratch) for each RB motor?

my understanding is -

RB20 - 240-250rwkw with around 7500 as a 'safe' RPM

RB25 - 290-300rwkw with around 7300 as a 'safe' RPM

RB26 - 300-320rwkw with around 7800 as a 'safe' RPM

I think revs and detonation are the real killer of RB's, keep both of them under control and I reckon there is no reason Roy your engine would be under any great deal of more stress

Chris

[Sydneykid]

This is a interesting topic

Whats everyone's general opinion about the safe power level (assuming all the support systems are up to scratch) for each RB motor?

my understanding is -

RB20 - 240-250rwkw with around 7500 as a 'safe' RPM

RB25 - 290-300rwkw with around 7300 as a 'safe' RPM

RB26 - 300-320rwkw with around 7800 as a 'safe' RPM

I think revs and detonation are the real killer of RB's, keep both of them under control and I reckon there is no reason Roy your engine would be under any great deal of more stress

Chris

Hi Chris, I would be inclined to believe that the RB20 safe rpm limit is more like 8,000 rpm. Ours has been at 225 rwkw for over 2 years and we run it to the rev limited 8,250 rpm all the time. I would add heat to your list of RB killers, especially oil temperature. But by far the worst thing for R's is poor tuning.

[Chris32]

Ok cool

mine currently has a rev limit of around 8200 with my re-programmed ECU

What would be a sensible every day rev limit for a RB20 running about 18 psi boost

Agree re oil cooler, I put one on early on, perhaps thats why mine has survived as long as it has

[Cubes]

Theoretically with a set of larger cams the dynamic compression ratio is lowered. Reducing the thermal stress and detonation issues.

The motor 'should' be a little more forgiving.

If a rod is going to let go it will let go. Not because of the cams making a little more power.

A good set of cams help the combustion process become more controlled and less likely to detonate.

It may explain why Steve's old R33 held 320rwkw without the usual issue of cracked ringlands.

Lowered comp 8.6:1 and a set of cams.

EDIT: Cam selection for NA is fairly straight forward being the larger the cam the higher the static comp needs to be in order for the DCR to be in a good range to suit the fuel. (otherwise it will make less power)

With Forced induction it throws another variable in to the equation.

[Warpspeed]

Joel is spot on. Have a look at the Mazda Miller engine, it will amaze you. Although supercharged not turbocharged, this engine has a static compression ratio of 10.2 :1 and runs 18 psi boost from the factory. And they don't detonate either.

The reason being the inlet valve closes 72 degrees after BDC. The piston is almost half way up the bore before the inlet valve closes, meaning only half the actual piston stroke compresses anything.

Think about it. If the theoretical compression ratio is 10:1 and if only HALF the stroke length is used it would only actually be 5:1. It is not quite that low, but you get the general idea. It is not that simple because of con rod angles and piston motion, but late inlet closing does reduce compression. The cranking pressure with a compression gauge will give a pretty good idea of this effect as well.

As Joel says, some of the normally aspirated racing engines run 16:1 compression ratio, but the cams are pretty extreme too.

With a turbo, what stuffs things up is exhaust back pressure, which is nearly always more than boost. On a stock factory engine it might be twice boost pressure. If you have turned up the boost yourself it might be closer to three times boost pressure.

A large overlap cam simply is not going to work with a small turbo. Small turbo, small cam. Big turbo big cam is the general trend.