Marc’s 500 HP BaschBoost Extreme NSX

[NetViper]

I was reading this article located:
http://www.nsxhelp.com/amnsxlit/Marcs_files/Index.htm

I thought it was good, but one thing I did not get was this.

"The short gear set is a direct replacement for the North-American spec mainshaft, 2nd, 3rd, and 4th gears. Switching to the shorter Japan spec ratios keeps the car in full VTEC range through each gear, taking nearly one full second off of the car’s 0-to-60 time. "

According to the prime FAQ, the difference is maybe 0.3 seconds.

Why does he claim to get nearly a full second? Is that with all the extra power that it becomes more time off 0-60?

Does the short gears and R&P make a bigger difference with the BBSC? or any FI?

If you have a comptech SC, and you are getting boost lower in the RPM range, do you really need to short gears?

Also, would it be easier to lower the VTEC engagement point instead of changing out the gears? Would that create the same effect?

 

[Brian2by2]

I have no clue, but a FULL second on TOP of the BBSC...GOOD LORD that must be quick!!! 5.5 seconds- say .5 seconds for the BBSC=5.00...then one second for R&P= 4 seconds!!

 

[sjs]

Keeping it brief for now...

Firstly I’ll repeat something you can find discussed here at length, which is to dispel the notion that the reason “short” gears improve acceleration 0-60 is staying “in VTEC range”. The vast majority of the difference is simple the lower gearing of the replacement 2’nd gear, giving you greater torque to the wheels. As you can interpret from the NSX torque curve, or read directly from an actual acceleration chart previously published by me, acceleration (measured in G’s) is not significantly less during the few hundred RPM before VTEC than it is after. Furthermore, if you just think about how long it takes with stock gears to pass through that first few hundred RPM till VTEC switches (a fraction of a second) it clearly isn’t possible to shave off even that amount of time no matter what the power differential. Follow me? There have been numerous good explanations about the real vs. perceived benefits of different gearing options, but the bottom line with the short/close set is that what it gives through one MPH range it must give back at another because it still ends with the same fifth gear.

Secondly I too question 1 full second, but I also question 500hp even at the crank.

Thirdly, I noticed a good observation when you asked whether greater torque made gears less or more advantageous. Logically, I would expect if your mods increase low-end torque and/or extend it lower in the power band then there is less benefit from the optional gears. However, I think that applies more to turbos than to SCs. Even the CTSC is no torque monster at the bottom end. As for lowering the VTEC cut-over, yes that can help if you have the mods to support it by delivering the correct fuel and air, but it will likely be minimal on a stock engine. The Dali chip may drop it slightly?

Lastly, I’m amused that he quotes 0-60 at all which is surely the least impressive performance measurement for the BBSC given the typical power curve, but perhaps he has the small pulley working better than we’ve heard thus far.

 

[sjs]

Hmmm… and excerpt from the article “The peak horsepower numbers do not tell the whole story though, it’s the torque, and more importantly, where the torque comes in that really makes the seat-of-the-pants effect that the driver feels. To manipulate the torque curve, all we need to do is download a different fuel map, depending on what kind of driving we plan to do that day. Although I must admit that most of the time, I just happy to keep everything at the basic street/track 12 PSI setting…that does just fine” says Marc. “

I’m not clear how messing with the fuel maps would significantly manipulate the torque curve. The fuel maps should be set for correct mixture at all points in the RPM/load matrix and left alone. You could dink around with ignition timing (not mentioned) but even that is pretty much optimal or not. The only real ways to move the power curve around are cam timing and where boost comes on. They certainly are not changing the cam timing (unless there is also a VTEC controller, also not mentioned) and I gather that the onset of boost is always as early as they can get it with the pulley used. So I really don’t see how they can do much in the way of tailoring the torque curve to the driving style of the day.

One more detail. In the pictures I see a block with fresh pistons and maybe sleeves, but no deck plate as described.

I enjoy this type of article, but I’d like them to be a bit more precise for those of us interested in the details.

 

[nsxtasy]

According to the prime FAQ, the difference is maybe 0.3 seconds.

On a stock '91, the difference in 0-60 time is 0.22 second, lowering it from 5.31 seconds to 5.09 second. The short gears generally hurt acceleration above 70 mph, which is one reason why the 1/4 mile time is only affected by 0.10 second.

Why does he claim to get nearly a full second? Is that with all the extra power that it becomes more time off 0-60?

Does the short gears and R&P make a bigger difference with the BBSC?

It is possible that the short gears (but not the R&P) would make a bigger difference with the BBSC. Unlike most mods and unlike the stock engine, the engine with the BBSC does not have a flat torque curve. So it is possible that the short gears can have a bigger impact with the BBSC than with other engines.

Think of it this way. The short gears remove the first gear acceleration in the 4400-5000 RPM range, and replace it with third gear and fourth gear acceleration in the 5900-6300 RPM range. (Granted, this "replacement" occurs above 60 mph, but this is how the short gears affect overall acceleration, not just 0-60.) With the stock 3.0-liter engine, that means you are removing acceleration where torque is around 205 ft-lbs and replacing it with acceleration where torque is around 205 ft-lbs, measured at the crank. Even with the Comptech supercharger, the torque figures are very close; you are removing acceleration where torque is around 268 ft-lbs and replacing it with acceleration where torque is around 271 ft-lbs. As often stated before, you don't achieve much in the way of acceleration gain from an increase in torque; you only achieve gains due to gearing, and the closeness in the ratios. And the gains at lower speeds are negated by losses at higher speeds.

The BBSC is different. With the BBSC, you are removing acceleration where torque is around 220 ft-lbs and replacing it with acceleration is around 255 ft-lbs (measured this time at the wheels). So you are getting an acceleration gain from an increase in torque, in addition to the gains due to gearing.

Whether those gains actually add up to a full second 0-60, I doubt it. But it might represent a bigger gain than you would get from the stock setup. OTOH, you are already starting with a quicker 0-60 time even before you change the gears, so it would be tougher just to get the same quantitative difference as you would from a stock engine. I doubt that the short gears make as much as half a second difference on a BBSC car, but the numbers could be run through a model adjusted for the torque curve on the BBSC car to calculate the actual difference.

If you have a comptech SC, and you are getting boost lower in the RPM range, do you really need to short gears?

As noted above, the difference in the RPM range doesn't create a whole lot more torque with the CTSC, just like with the stock engine; the gains come from shorter gearing, not from added torque.