Boost on stock internals...

[encasemyheart]

This isn't the standard 'How much boost can be run on stock internals' question, but more of a theory question...so bear with me.

We all know that detonation kills a motor, detonation is caused by things which I will not go into here, but basically the better you tune the less chance of detonation. You can ward off detonation to higher and higher boost levels by tuning the motor very well, using race gas, water injection, alcohol injection, lowering compression, etc.

My question is this: Is it only detonation that kills a motor spontaneously? I know motors wear and that's not the question, is the only problem with running high boost levels the fact that there is an increasing chance of detonation, or does the actual pressure created by the turbo also responsible for motor failure? Meaning if it is only detonation that kills the motor and you tune well/use things previously mentioned to rid yourself of detonation, would it be possible to run 30+ psi on stock internals? Assuming no detonation of course. Or would the motor (without forged internals) fail due to the high stress caused by the massive boost levels on stock components?

[AceInhole]

the simple answer:at 30psi you're stressing the engine as a system far too much. I don't think the oil bearings could withstand that much stress without some treatment. I also think the pistons may not be able to withstand the pressure from combustion, but that is a fair amount of speculation.

I say the oil bearings can't handle, because I know of a car with forged internals that ran 30psi and developed a problem with the crank bearings due to what I think was oil starvation, which leads me to believe high stress on the stock bearings would lead to an eventual catastrophic failure.

I'll see if I can't dig up a bit more info though.

[encasemyheart]

I understand that, but imagine the stress put on the pistons N/A even, I assume controlled combustion is pretty harsh, I've heard that exhaust gasses travel at almost mach 1 out of the head, so I assume another 30psi isn't going to do much assuming it is controlled combustion and not detonation.

Could you run high boost levels (22 or so psi) on stock internals with 110 octane race gas and alcohol injection and a REALLY good intercooler sprayed with nitrous? (N-tercooler setup)

WD says you can do 15psi on stock internals with good tuning, so I assume with some of the above mentioned additions 22 is just a few steps away.

Wouldn't it be sweet to make 400+whp on stock internals...

[EZcheese15]

I understand that, but imagine the stress put on the pistons N/A even, I assume controlled combustion is pretty harsh, I've heard that exhaust gasses travel at almost mach 1 out of the head, so I assume another 30psi isn't going to do much assuming it is controlled combustion and not detonation.

Could you run high boost levels (22 or so psi) on stock internals with 110 octane race gas and alcohol injection and a REALLY good intercooler sprayed with nitrous? (N-tercooler setup)

WD says you can do 15psi on stock internals with good tuning, so I assume with some of the above mentioned additions 22 is just a few steps away.

Wouldn't it be sweet to make 400+whp on stock internals...

You are right to an extent, but running that much boost is impossible. Yes, the better you tune, the more boost you can run, but you get to a point that it is impossible to tune better.

Like Ace said, oil starvation would be one problem. Another problem is, if 30psi of air is coming in, that doesn't equate to 30psi extra exhaust gasses coming out.

For simplicity, lets say a NA car runs 0 psi (reality is it has vacuum, but that should prove my point I'm about to make even more so). With 0 lbs of air being pushed into the engine, the fuel mixture ignites, and causes X big of an explosion. Now you run 5psi. You now have 5 times the air coming in. 5 times the air means 5 times the size of explosion in the combustion chamber. Since gasses expand when they get hot, an explosion that started as 5 times the original, ends up as 5 times the original. So at 30psi, you are pushing exhaust out of the car 30 TIMES faster than at 0 psi. So if exhaust traveled out of the car at a theoretical mach 1 at 0 psi, then it would leave at mach 30 at 30psi. Ofcourse, this is all completely theoretical and approximate.

The other problems you run into, is that it gets exponentially harder to tune, not linear. If tuning a car to 14psi is twice as hard as tuning to 7psi, then tuning to 21 psi is 8x harder.

At those pressures, also, you are putting 30 times or more stress on all the parts. For instance, connecting rods. Lets say a piston normally puts 1000 lbs of force on the end of a connecting rod at TDC. Well, at 30psi, that is 30000 lbs of force.

So you should get the picture by now....lots of things come into play.

[cow]

AFAIK, and I'm no expert, you're basically right; detonation is the number one killer of motors. Making more power than stock only causes problems when you get into the BIG numbers (ie, more than 3x the stock output). You theoretically should be able to run a healthy amount of boost on stock internals, given a somewhat conservative tune and a very safe setup. Internals mainly help by lowering compression ratio and drawing heat away from the combustion chamber (one of the great properties of forged pistons). Of course, different engines vary; Supras can handle 600+ whp on stock bottom ends, while a Civic needs upgrading much sooner.

However.. the more power you make, the more likelihood things can go wrong. Not to mention that with a stock motor that's never been rebuilt you don't really know what you're getting. There are a lot of things that should go into a rebuild besides just new pistons and rods. Proper bearing clearances, a healthy coolant system, aftermarket head studs and a full inspection of all moving parts can go a long way toward helping a high HP motor last a long time.

[AceInhole]

I THINK this is mostly correct.... at least logically it seems to be (I'm studying for a thermo exam actually.... so my fried brain has probably already gone whack).

Well, at 0 Vac (ideal WOT) in the plenum, you're getting about 1atm of pressure, which is 14.7psi. Running 30lbs of boost is effectively running 44.7psi of air, roughly 3 times the amount of air. On a KA engine with 9.5:1 compression, where normally you'd suck in 14.7psi of air... you're getting 44.7psi, which is then compressed in that 9.5:1 ratio. Where P1*V1 / T1 = P2*V2 / T2, assuming T1 = T2:44.7 * 9.5 = P2 * 1P2 = 424.65psi in the combustion chamber, before combustion even takes place. The effective volume ratio to atmospheric pressure would be:14.7 * V1 = 424.65 * P2So... V1 would be about 28.89, giving a ratio of 28.89:1. Now... how well can you expect stock components to survive with a compression ratio like that?? (Assuming my calculations make sense).

[cow]

For simplicity, lets say a NA car runs 0 psi (reality is it has vacuum, but that should prove my point I'm about to make even more so). With 0 lbs of air being pushed into the engine, the fuel mixture ignites, and causes X big of an explosion. Now you run 5psi. You now have 5 times the air coming in. 5 times the air means 5 times the size of explosion in the combustion chamber. Since gasses expand when they get hot, an explosion that started as 5 times the original, ends up as 5 times the original. So at 30psi, you are pushing exhaust out of the car 30 TIMES faster than at 0 psi. So if exhaust traveled out of the car at a theoretical mach 1 at 0 psi, then it would leave at mach 30 at 30psi. Ofcourse, this is all completely theoretical and approximate.

This is not accurate at all. To determine the amount of air entering the engine relative to atmospheric, you have to find the pressure ratio in relation to atmospheric pressure (~14.7 psi). So, at 5 psi you are putting in about 34% more air (14.7+5/14.7 = 1.340). Furthermore, a higher pressure air actually moves SLOWER. If you have a closed system with a gradually decreasing diameter the velocity will increase but the pressure will decrease. Either way, however, velocity of air is not really relevant in determining the lifespan of engine components.

And I mean, come on.. Mach 30? :|

Quote »The other problems you run into, is that it gets exponentially harder to tune, not linear. If tuning a car to 14psi is twice as hard as tuning to 7psi, then tuning to 21 psi is 8x harder.[/quote]

I think this is a fair statement, although you cannot really quantify how many "times harder" it is to tune one situation from another, but I would tend to believe that it is not a linear situation.

Quote »At those pressures, also, you are putting 30 times or more stress on all the parts. For instance, connecting rods. Lets say a piston normally puts 1000 lbs of force on the end of a connecting rod at TDC. Well, at 30psi, that is 30000 lbs of force.[/quote]

This is also not true. A double increase of mixture (which would be 1 bar, theoretically) will only increase the average pressure by about 20%. So a 1000 lb force will become.. 1200 lbs. No biggie.

[cow]

I THINK this is mostly correct.... at least logically it seems to be (I'm studying for a thermo exam actually.... so my fried brain has probably already gone whack).

Well, at 0 Vac (ideal WOT) in the plenum, you're getting about 1atm of pressure, which is 14.7psi. Running 30lbs of boost is effectively running 44.7psi of air, roughly 3 times the amount of air. On a KA engine with 9.5:1 compression, where normally you'd suck in 14.7psi of air... you're getting 44.7psi, which is then compressed in that 9.5:1 ratio. Where P1*V1 / T1 = P2*V2 / T2, assuming T1 = T2:44.7 * 9.5 = P2 * 1P2 = 424.65psi in the combustion chamber, before combustion even takes place. The effective volume ratio to atmospheric pressure would be:14.7 * V1 = 424.65 * P2So... V1 would be about 28.89, giving a ratio of 28.89:1. Now... how well can you expect stock components to survive with a compression ratio like that?? (Assuming my calculations make sense).

I believe those calculations are correct; I remember reading something about turbo pressure in relation to engine compression ratios but I can't seem to recall it.

But I digress.. like I said before, the pressure will not really increase THAT much over the entire power stroke. The peak pressure may increase greatly, but this pressure only occurs during a small portion of the crankshaft's rotation. This would be a hell of a lot easier to illustrate graphically because I can't really explain it that well in words..

Although I do think 30 psi is pretty hopeless on stock internals, I don't think 16-18 is out of the question.

[EZcheese15]

Ok, so you got me. So I'm tired. I admit I didn't think it through very thorougly

[C-Kwik]

Heat, heat, heat. This is the root of the problems of just about any turbo problems. More boost, you get more heat. The cooling system may be overworked with too much boost for too much time. This only makes the situation of more boost even more of a problem. Heat also takes it's toll on the oil as well. You'll need a more vigorous maintenance schedule.

As far as Supras vs Civics, Most Honda motors are quite strong. With the exception that th open deck design makes it prone to having the cylinders shift under high pressures. The bottom ends are pretty strong. Supras are a wonderment to turbocharging. They are way overbuilt. But detonation can still do damage just as easily. A buddy of mine and I had to rebuild his Supra motor years ago when he overboosted it and the #6 cylinder overheated causing detonation.

[WDRacing]

Lets look at it from my perspective, I'm a boost addict, I've blown up motors for the last 4 years by turning up the wick till they pop. I've used knock sensors, A/F gauges, and enough alcohol to make Torry hungover for a month.

If I built a fuel system for a stcok block to run as much boost as possible, I'd say I could probably run 20psi. In short bursts I could probably hit 25 psi or so. But the motor will unass itself if you do it very often. The ringlands and rods are just simply not strong enough to keep the force in check.

For 20 psi your going to need alot of tuning, alternative fueling, copius amounts of thermotech wrap and huge FMIC.

I'll probably build a KADET with a stock block when I get home just to find out how much and what it takes to get there. I definitly wouldn't recommend going over 12-15 psi unless you don't mind swappin out engines.

WD

[encasemyheart]

So final answer is: it is more than detonation that kills a motor...thanks.

I couldn't understand why forged internals were even used (aside from lowered compression) because people just said they handled detonation better, well I plan on not getting detonation even WITH forged internals, so I didn't see how thye helped so much.

Another question: the actual compression ratio of a car seems to only affect off-boost driving, so would an extremely lowered compression engine be ideal for racing only where you don't plan to be off boost at all? Do race cars lower their compression to insanely low levels? If not, why?

[AceInhole]

Another question: the actual compression ratio of a car seems to only affect off-boost driving, so would an extremely lowered compression engine be ideal for racing only where you don't plan to be off boost at all? Do race cars lower their compression to insanely low levels? If not, why?

The compression ratio affects a bit more than off boost driving. For one, you'll spool quicker with a higher compression ratio with more exhaust flow (as in a sense the exhaust gas is being compressed "more"), and for another, you wouldn't really have to run as much boost to get to a certain power level.

For a race car, you run race gas, and can run quite a bit higher compression with quite a bit of boost. It will differ per application though, whether an engine will need lower compression. A higher compression engine (like a stock KA) will have a quicker response and faster spool up, which is something you may want on a track. If you want to dump tons of boost into an engine, 8:1 or 7:1 compression wouldn't be out of the question, but you're making all your power with boost by then.

I definitely think there's a point where you can go too low for compression... so no, I don't think race cars ever go with insanely low compression ratios.

[encasemyheart]

So the race car driver would decide what power level he wanted to achieve and by that number decide the best compromise between compression ratio and boost.

In N/A applications, adding more compression to anything above 9:1+ hardly increases power, and the higher you go the less it increases. So in turbo applications, would the power gained by each compression point raised be magnified by the fact that you are pumping boost through it?

[cow]

In N/A applications, adding more compression to anything above 9:1+ hardly increases power, and the higher you go the less it increases. So in turbo applications, would the power gained by each compression point raised be magnified by the fact that you are pumping boost through it?

This is not entirely accurate; with all things remaining equal, yes, changing a compression ratio yields less power the higher you go. However, 9:1 is pretty low, IMO. My car runs 10:1 stock, and some cars (S2000, Celica GT-S) run 11:1 or higher.

But more importantly, static compression must be raised in order to compensate for a drop in dynamic compression caused by a big cam with lots of overlap. This is where you can see nice power gains from a big bump in compression.

[cow]

If I built a fuel system for a stcok block to run as much boost as possible, I'd say I could probably run 20psi. In short bursts I could probably hit 25 psi or so. But the motor will unass itself if you do it very often. The ringlands and rods are just simply not strong enough to keep the force in check.

I think there actually was a guy who ran 20 psi on a stock block for a little while. I read about it on here somewhere. I'll see if I can find it later. IIRC it didn't live very long.

Quote » For 20 psi your going to need alot of tuning, alternative fueling, copius amounts of thermotech wrap and huge FMIC.[/quote]

This is true.. tons of preperation is needed for something like that. I believe a full blueprinting is also in order if you hope it to last any decent amount of time.

Quote » I'll probably build a KADET with a stock block when I get home just to find out how much and what it takes to get there. I definitly wouldn't recommend going over 12-15 psi unless you don't mind swappin out engines.

WD [/quote]

This sounds like a pretty reasonable estimate.. maybe slightly higher or lower depending on your octane of gas available.

[EZcheese15]

Another thing to add as far as increasing the compression...

The higher compression you run, the better volumetric efficiency you have. The more VE you have, the more power you can make per cc of fuel, because less power is being lost through heat.

So theoretically, higher compression is better for performance on any car, even boosted applications. The only reason people lower compression with boost, is because it's easier to lower compression and add boost, then to tune high boost *and* high compression. But if you can do the latter, it's even better....if you can keep it from detonating.

[keepingthe240]

The topic of low comp/high boost vs. high comp/low boost was covered in sport compact car with in the last 2 yrs. The lower compression will allow you a higher rpm since clearance between the valves and the piston is greater. Since hp. is all about torque @ 5252/rpm, low comp/hi boost is more impressive in the hp. department.

[Mikel]

If proper knock resistance was providied (read - octane), you could run over 20psi on stock internals.

[C-Kwik]

The topic of low comp/high boost vs. high comp/low boost was covered in sport compact car with in the last 2 yrs. The lower compression will allow you a higher rpm since clearance between the valves and the piston is greater. Since hp. is all about torque @ 5252/rpm, low comp/hi boost is more impressive in the hp. department.

If you have issues with valve clearance, problems at higher RPM's then you likely have valve float problems. The valve events should be the same in relation to the crank at any RPM if it is a fixed cam system(non-variable). I've seen some literature on very minor issues where there is a bit more flex at higher RPM's but nothing to the extent valve to piston clearance is compromised. It had more to do with bore wear.

As far as the HP equation, it has nothing to do with this topic. Increase torque at any given RPM, and HP will increase at that RPM.

Using lower compression is really a compromise to the crappy fuel we have here. With lower compression you can run higher amounts of boost before you start getting detonation(provided proper fuel requirements), and ultimately make more power than running a lower boost with a higher CR.