Jump to content
SAU Community

Recommended Posts

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?

Link to comment
https://www.sau.com.au/forums/topic/51165-stresses-on-engines/
Share on other sites

ooh ooh a classmate :D

 

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 :D

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, :)

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 :D freakin computers...

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!!! :D

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.

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.

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.......

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

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.

:cheers:

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

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.

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Well, that's kinda the point. The calipers might interfere with the inside of the barrels 16" rims are only about 14" inside the barrels, which is ~350mm, and 334mm rotors only leave about 8mm outboard for the caliper before you get to 350, And.... that;s not gunna be enough. If the rims have a larger ID than that, you might sneak it in. I'd be putting a measuring stick inside the wheel and eyeballing the extra required for the caliper outboard of the rotor before committing to bolting it all on.
    • OK, so again it has been a bit of a break but it was around researching what had been done since I didn't have access to Neil's records and not everything is obvious without pulling stuff apart. Happily the guy who assembled the engine had kept reasonable records, so we now know the final spec is: Bottom end: Standard block and crank Ross 86.5mm forgies, 9:1 compression Spool forged rods Standard main bolts Oil pump Spool billet gears in standard housing Aeroflow extended and baffled sump Head Freshly rebuilt standard head with new 80lb valve springs Mild porting/port match Head oil feed restrictor VCT disabled Tighe 805C reground cams (255 duration, 8.93 lift)  Adjustable cam gears on inlet/exhaust Standard head bolts, gasket not confirmed but assumed MLS External 555cc Nismo injectors Z32 AFM Bosch 023 Intank fuel pump Garret 2871 (factory housings and manifold) Hypertune FFP plenum with standard throttle   Time to book in a trip to Unigroup
    • I forgot about my shiny new plates!
    • Well, apparently they do fit, however this wont be a problem if not because the car will be stationary while i do the suspension work. I was just going to use the 16's to roll the old girl around if I needed to. I just need to get the E90 back on the road first. Yes! I'm a believer! 🙌 So, I contacted them because the site kinda sucks and I was really confused about what I'd need. They put together a package for me and because I was spraying all the seat surfaces and not doing spot fixes I decided not to send them a headrest to colour match, I just used their colour on file (and it was spot on).  I got some heavy duty cleaner, 1L of colour, a small bottle of dye hardener and a small bottle of the dye top coat. I also got a spray gun as I needed a larger nozzle than the gun I had and it was only $40 extra. From memory the total was ~$450 ish. Its not cheap but the result is awesome. They did add repair bits and pieces to the quote originally and the cost came down significantly when I said I didn't need any repair products. I did it over a weekend. The only issues I had were my own; I forgot to mix the hardener into the dye two coats but I had enough dye for 2 more coats with the hardener. I also just used up all the dye because why not and i rushed the last coat which gave me some runs. Thankfully the runs are under the headrests. The gun pattern wasn't great, very round and would have been better if it was a line. It made it a little tricky to get consistent coverage and I think having done the extra coats probably helped conceal any coverage issues. I contacted them again a few months later so I could get our X5 done (who the f**k thought white leather was a good idea for a family car?!) and they said they had some training to do in Sydney and I could get a reduced rate on the leather fix in the X5 if I let them demo their product on our car. So I agreed. When I took Bec in the E39 to pick it up, I showed them the job I'd done in my car and they were all (students included) really impressed. Note that they said the runs I created could be fixed easily at the time with a brush or an air compressor gun. So, now with the two cars done I can absolutely recommend Colourlock.  I'll take pics of both interiors and create a new thread.
    • Power is fed to the ECU when the ignition switch is switched to IGN, at terminal 58. That same wire also connects to the ECCS relay to provide both the coil power and the contact side. When the ECU sees power at 58 it switches 16 to earth, which pulls the ECCS relay on, which feeds main power into the ECU and also to a bunch of other things. None of this is directly involved in the fuel pump - it just has to happen first. The ECU will pull terminal 18 to earth when it wants the fuel pump to run. This allows the fuel pump relay to pull in, which switches power on into the rest of the fuel pump control equipment. The fuel pump control regulator is controlled from terminal 104 on the ECU and is switched high or low depending on whether the ECU thinks the pump needs to run high or low. (I don't know which way around that is, and it really doesn't matter right now). The fuel pump control reg is really just a resistor that controls how the power through the pump goes to earth. Either straight to earth, or via the resistor. This part doesn't matter much to us today. The power to the fuel pump relay comes from one of the switched wires from the IGN switch and fusebox that is not shown off to the left of this page. That power runs the fuel pump relay coil and a number of other engine peripherals. Those peripherals don't really matter. All that matters is that there should be power available at the relay when the key is in the right position. At least - I think it's switched. If it's not switched, then power will be there all the time. Either way, if you don't have power there when you need it (ie, key on) then it won't work. The input-output switching side of the relay gains its power from a line similar (but not the same as) the one that feeds the ECU. SO I presume that is switched. Again, if there is not power there when you need it, then you have to look upstream. And... the upshot of all that? There is no "ground" at the fuel pump relay. Where you say: and say that pin 1 Black/Pink is ground, that is not true. The ECU trigger is AF73, is black/pink, and is the "ground". When the ECU says it is. The Blue/White wire is the "constant" 12V to power the relay's coil. And when I say "constant", I mean it may well only be on when the key is on. As I said above. So, when the ECU says not to be running the pump (which is any time after about 3s of switching on, with no crank signal or engine speed yet), then you should see 12V at both 1 and 2. Because the 12V will be all the way up to the ECU terminal 18, waiting to be switched to ground. When the ECU switches the fuel pump on, then AF73 should go to ~0V, having been switched to ground and the voltage drop now occurring over the relay coil. 3 & 5 are easy. 5 is the other "constant" 12V, that may or may not be constant but will very much want to be there when the key is on. Same as above. 3 goes to the pump. There should never be 12V visible at 3 unless the relay is pulled in. As to where the immobiliser might have been spliced into all this.... It will either have to be on wire AF70 or AF71, whichever is most accessible near the alarm. Given that all those wires run from the engine bay fusebox or the ECU, via the driver's area to the rear of the car, it could really be either. AF70 will be the same colour from the appropriate fuse all the way to the pump. If it has been cut and is dangling, you should be able to see that  in that area somewhere. Same with AF71.   You really should be able to force the pump to run. Just jump 12V onto AF72 and it should go. That will prove that the pump itself is willing to go along with you when you sort out the upstream. You really should be able to force the fuel pump relay on. Just short AF73 to earth when the key is on. If the pump runs, then the relay is fine, and all the power up to both inputs on the relay is fine. If it doesn't run (and given that you checked the relay itself actually works) then one or both of AF70 and AF71 are not bringing power to the game.
×
×
  • Create New...