Oh lord, my brain hurts from reading this thread.

On the original subject: asking this question is entirely pointless. Be a little more specific please. There's no such thing as "which one is better" without talking about a specific qualification such as which one will make more power, or which one will take longer to bow up, or which one will be cooler to brag about to my friends who don't understand the technical details of my choice anyway.

About cams, you will not get reversion from excessive overlap. If you have a long duration on the exhaust cam then it's possible for reversion to happen but it would take a lot of backpressure. Generally any set of "turbo" cams will have high lift on both intake and exhaust, longer-than-stock but not excessive duration on the intake and relatively short (i.e. shorter than the intake) duration on the exhaust. That lets the motor take nice big gulps of pressurized air and at the same time provides short powerful pulses of exhaust gas to help spool the turbo.

 

So, uh... what seems to be the hypothetical problem people?

The rules of making power change with boost, and they also change with your method of boost. SC? Nitrous? Fine, stay with low overlap, high lift and high duration. Turbo? Overlap in the low mid-range is your friend, it helps get that turbo spooling several hundred RPM faster, especially given the fact that a turbo will flow enough air to maintain a given PSI in the intake manifold, what happens if some skips the cylinder while both valves are open? It hits the turbine and keeps it spooled, so it will still maintain the PSI, and wow, you don't drop out of boost... What's the downside again?

As far as the CR issue: cylinder pressures and the right amount of fuel is what makes power, get cylinder pressures too high for the amount of usuable fuel and things burn and melt. The thing to keep in mind, however, is that the gains of higher PSI usually outweigh the benefits of having a high static CR, but you can make just about anything work.

 

I'm looking for the most power I can get.... and what is OVERLAP?

 

Overlap is the time when both the intake and exhaust cam are open.

 

I'm not trying to sound harsh here, but you're going to have to be more detailed than "I want the most power I can get." That's not a sort of a logical question which we might answer. More power can always be made somehow. Think about how much power you want your car to make, or how fast you would like it to do particular benchmark tests (i.e. 1/4 mile) and then pose the question of what you will need to accomplish this goal. Some examples:

"I have a GSR and want to make about 250-260 whp with a turbo. What kind of setup should I look at?"

"I have an LS and want it to run 13's with a VTEC motor and a turbo. Any suggestions?"

I think you get the idea.

 

Do you know what mostly spools the turbo? HEAT! THere are 3 things that show energy in a gas: heat, pressure, and volume.

The turbo's exhaust wheel is specially designed. I will first explain that at the end of the combustion stroke, combustion is still going on which raises pressure as the piston pushes it out. And I would think an exploding gas would have more pressure than say 10psi of boost. Now does exploding/exploded gas have a higher temperature than say compressed ambient air? Now would 0.45L (1 cylinder's displacement) have more energy then a small leaked amount of boost?

With that said, you saying that the comrpessed air will spool the turbo is like saying You can spool a t88 on your teg like it was a t3. That leaked boost will almost do nothing to spool the turbo :fawk:

 

Ah, that's what I was looking for. So the LS engine is better for boost than a GS-R or Type R engine because it has a lower CR and therefore can boost more on stock internals without doing damage. I've heard this a hundred times but didn't have any info to support it. Thanks.

 

Yes BUT GSRs have the advantage of VTEC and the cams that come with it. I've got my money on the GSR engine making more power stock + turbo vs. stock + turbo.

Of course, with equally built bottom ends the GSR will walk all over the LS...

 

Properly done, overlap will be such that the exhaust valve still closes before the intake valve fully opens. Your concern over losing power from a drop in boost in the cylinder is moot. As long as your maintaining a good pressurization of the manifold, that's how much boost the cylinder will see.

You made a comment about heat carrying energy in a gas, how observant, so let's see... overlap after burning a pressurized mixture, and being helped forced out by a bit of incoming boost, what happens? You evacuate all [or close to all] of the spent exhaust from the cylinder [since scavenging can't really take effect in a turbo design like it would in a header], and replace it with a strong, fresh intake charge, that little bit of boost helps make sure the gas maintains all of it's heat, guarantees that it's velocity stays high, and... yep... keeps the pressure just that little bit higher along with the greater volume caused by heating the mixture during combustion. Sounds like it would spool faster than a zero overlap setup to me. :fawk:

It's all physics and tinkering people, I have both.

 

True, but to keep the manifold pressure the same, the turbo will have to spin faster. And when the turbo reaches its limits, then you will start losing power because the turbo cant make up for the lack of boost. And aince you are leaking boost, you are slowing down the turbo's cycle, causing boost lag. That air/fuel that got lost would have spooled the turbo alot better if it had combusted releasing its energy.

I know you are not so naive, that you think that the intake charge will push out 100% of the exhaust gases. They will intermingle, causing a vortex due to the extreme pressure differences. Which will amke it virtually impossilble not to leak boost and retain some exhaust gas in the chamber.