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Which is worse for reliability, high revs or high boost

I hate taking my friends for a ride in my 930 because I inevitably do stupid things I know I shouldn't, like push the car hard when it is not properly warm or other things. But, I've noticed that if I'm at mid rpm range in a higher gear and punch the gas, the turbo boost builds up to the max before the revs max out, but if I rev it up higher in lower gear the revs max out and the boost is lower. Which one is better (or less worse on the engine)?

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Old 02-13-2017, 11:15 AM
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Depends on many factors, which I am sure will be explained by others below, but high revs means great speed of the reciprocating parts. Energy in relation to speed is V-squared. Thus a high revving engine is typically more expensive to build than the same boosted power, since the load on the parts increases exponentially.
Roads take a tremendous tensile (I believe is the word) when the piston is pulled back Dow. By the rod.
- V-squared is what cost money and power.
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Old 02-13-2017, 11:58 AM
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My opinion is that rpm up to redline is safe, and boost up to a certain amount is safe, but going over on either one is bad news. So I don't think high revs or full boost (up to the theoretical safe values of each - say redline and 0.9-1.0 bar boost) have any real effect on long term engine health.

Redlines are not just some arbitrary number and neither are the boost limits. The engineers have built the engines to operate normally within those tolerances and unless you are running full boost at redline all day long, I cant see why it would be a concern.
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Old 02-13-2017, 12:47 PM
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I think what you are talking about is really about the nature of a turbocharged engine.

A turbocharger is a load based devise. Load as in trying to start off on a bicycle in 5th gear vs 1st gear. More load the faster boost builds. If I'm cruising at 70mph in 4th in my 930 I'm running around 2500rpm with 0 boost and if I floor the throttle within 500rpms I have full boost because I've created a lot of load by leaving it in 4th. However, if I start off my car in first and floor it it will not have any boost till maybe 5000rpm unless I'm going up a decent hill(load), because you have very little load on the turbo in first gear. Does that make sense?

So basically you're asking if the amount of load you put on the motor affects the amount of wear.
That is a good question
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Last edited by matsuzaka; 02-13-2017 at 02:07 PM..
Old 02-13-2017, 02:01 PM
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if I'm at mid rpm range in a higher gear and punch the gas, the turbo boost builds up to the max before the revs max out, but if I rev it up higher in lower gear the revs max out and the boost is lower


I would be concerned about this.
I have my boost set for .9abr, it hits that no matter what gear I am in. I can turn it up, even at 1bar it still hits it.

what turbo is he running?
I would look for air leaks on the pressure side.
is the blow off valve vented to atmosphere. I would check to see if it is popping open under boost, my synapse was doing that, got rid of it.

BTW, hi boost is worse for it. anything above .9 I would make sure the fuel system is set up for it.
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Old 02-14-2017, 04:36 AM
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Too much boost puts a hole in a piston and breaks the rings, too many RPMs throws a rod out the side of your case. Which is worse?
I always run less timing and higher octane than is needed for the hottest day of the year while stuck in a traffic jam. When rebuilding an engine we always use ARP head studs, rod bolts and heavy duty valve springs. Leave the over-rev and over-boost protection intact. Do these things and you'll never have to worry. I hit 7000rpm in the red rocket every time the tires broke loose, hit 1.2bar once when the waste gate malfunctioned. Rev limiter cut out and overboost switch put my teeth in the dash. Not even a hiccup from the engine.
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Old 02-14-2017, 04:52 AM
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Old 02-14-2017, 05:17 AM
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Quote:
Originally Posted by matsuzaka View Post
I think what you are talking about is really about the nature of a turbocharged engine.

A turbocharger is a load based devise. Load as in trying to start off on a bicycle in 5th gear vs 1st gear. More load the faster boost builds. If I'm cruising at 70mph in 4th in my 930 I'm running around 2500rpm with 0 boost and if I floor the throttle within 500rpms I have full boost because I've created a lot of load by leaving it in 4th. However, if I start off my car in first and floor it it will not have any boost till maybe 5000rpm unless I'm going up a decent hill(load), because you have very little load on the turbo in first gear. Does that make sense?

So basically you're asking if the amount of load you put on the motor affects the amount of wear.
That is a good question
That's about what I see... in 1st gear, might hit full boost by redline... in 4th, east to hit full boost...

A year ago I was getting misfire/farting/knocking at full acceleration in 1st gear at 3000-5000 rpm... Long story. Retarding the timing fixed it.

But now that you mention it, I never had that issue in any other gear. Yet, the car was at full boost just the same from much lower RPM's...

Suggest to me, that a motor accelerating quickly (1st gear), building boost, is where the highest risk is.

My issue, best I can figure, had something to do with the car running too rich under boost in 1st gear...
Old 02-14-2017, 05:28 AM
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"Which is worse for reliability, high revs or high boost"

yes

8-)

I never redline my motor, upshift soon as the power to noise ratio goes inverse - which, for my turbo and setup is currently ~ 6,100 (3LDZ was 5,400!)

beyond that you're unnecessarily stressing the valvetrain, rod bolts, etc

keep your boost @ 1bar or below (with a good I/C and w/o dual plug) and you're good to go

What did make me cringe however is your mention of boosting / rev'ing before up to temp - NO NO NO NO NO NO NO... (I'm e-smacking you over the nose w/ a rolled up newspaper). BAD 930owner!!! 8-)

no, really - that's pretty dumb (aka: bad). Don't.

HTH
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Old 02-14-2017, 08:14 AM
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Quote:
Originally Posted by jwakil View Post
I hate taking my friends for a ride in my 930 because I inevitably do stupid things I know I shouldn't, like push the car hard when it is not properly warm or other things. But, I've noticed that if I'm at mid rpm range in a higher gear and punch the gas, the turbo boost builds up to the max before the revs max out, but if I rev it up higher in lower gear the revs max out and the boost is lower. Which one is better (or less worse on the engine)?
Its a sports car, and its turbo'd, which means it revs quicker, parts are lighter, and the whole drive train is connected to it will take the "beatings" a owner will dish out. So it will wear out more rapidly than a pick up truck, a family sedan, and any other ride you can think of. Reliable sports car? No such animal, reliable hot rod? No such animal.

You should always possess a healthy credit card when owning a super car. Fast Freddy!
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Old 02-14-2017, 08:26 AM
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i have my rev limiter set to 6500.

forgot to ask, how much boost are you trying to hit?

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Old 02-15-2017, 04:25 AM
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