Why not NOS?

[Kirk]

I'm re-reading the book "Forced Induction Performance Tuning". There's a chart on page 77 that's helpful. It shows what boost level is recommended for a modern stock engine (most of the book is focused on race engines) at different compression ratios. With a 10.2:1 CR and a nicely 80% efficient intercooler you're looking at maybe 5 psi as being safe. I think that helps to illustrate why our 11:1 engines with no intercooler would be pushing it with any kind of boost - whether from a turbo or nitrous.

An interesting website I found today is this one:

http://www.flat6innovations.com/performance.htm

It will be interesting to see what these guys can develop. It looks like some lower compression pistons and stronger connecting rods for the 3.2L may be on the horizon. It sure would be fun to build one of these engines for boost, but their prices make it a pretty costly proposition.

To really push it though you need an intercooler and they point out that there is a real packaging issue with fitting an intercooler on the Boxster. But with a good front trunk I would definitely be willing to sacrifice my rear trunk, it's close to the engine, and you could fit a very big intercooler back there. You'd have to modify the trunk to bring air in - maybe a scoop facing forward on the trunk. Then you'd have to vent air out the bottom of the trunk, but that's all do-able.

Seems like with a rebuilt bottom end for strength and low CR, plus an intercooler, twin turbos, and some exhaust work you could push 400 HP pretty reliably. Fun stuff to dream about! Throw in a wide body kit and wider rear wheels and you'll help that wheel spin problem.

Kirk

[insite]

the problem with going strong on forced induction with these cars has always been cost. it's much cheaper to drop in a 3.4 or 3.6L motor and go from there. hell, you can even add a set of schrick cams, sick exhaust & intake, etc for MUCH lest than the cost of cracking open the motor to lower the CR & upgrade the rods & go turbo.

BTW, one of the nice things about nitrous is that the gas cools the charge by nature, so detonation won't occur until cylinder pressures are quite high. obviously no need to intercool a nitrous charge.

kirk - i have seen a turbo app on a boxster where they put a large intercooler in the trunk. i will see if i can find pictures.

[Kirk]

I agree insite. It's not just cheaper to drop in a 3.4 or 3.6, but you also get OEM reliability. Still there's more power potential by going to forced induction.

I said it was fun stuff to dream about because it's really a dream for someone like me. See I live in the communist state of California. Here you could do an engine swap (and then get it approved), but a custom turbo setup would be completely illegal.

Right, I understand the cooling effect of nitrous, which is why some folks use it to cool their intercoolers... The point is that A. Graham Bell claims a stock 10.2:1 CR engine can maybe do 5 psi boost with a very efficient intercooler. The original question here was what can a Boxster do on nitrous. Based on Bell's chart I'd estimate that our 11:1 CR engine could probably handle 3 psi with a cool charge. What would be the HP shot equivalent in nitrous of a 3 psi boost from a turbo? Hmmm... maybe around 40 HP or so is what I'd guess.

Pics of that intercooler install would be "cool".

Kirk

[dmcutter]

Turbowerx includes an intercooler with the 3.2 turbo kit. Marc says he feels like he has a good factor of safety with 5 lb of boost with stock internals. Of course I don't know what sort of longevity testing their mule went through and I don't know how many of their kits have been installed.

The orginal question about NOS was driven by a curiosity about cheap horsepower. Obviously a system that is properly engineered for our engines would not be cheap relative to an off the shelf kit for a big block V8, but may still be "cheap" relative to a turbo or engine swap. I like the idea of a turbo better though because as Randall said it's always right there at your right foot. And since our cars are not about straight line power and I think a hefty shot of NOS would be tough to modulate in a curve, the turbo is more real world usable.

I was discussing this with Jay this am and I said one of the appealing things about the 3.2 is that it makes about 80% of peak torque at such a low rpm. If you went with a low compression piston to boost boost, I think you would give away low end. With a turbo, you still have stock low end with the extra forced induction power being icing on the cake.

NOS is an interesting academic exercise, but I don't think a practical app for the Box. I do still plan on going the turbo route this fall or winter, though, as finances allow.