Lots to respond to since I was last here, but I think I’ll just start rambling without specific quotes but starting with the subject of increased redline that I raised.
Why does the NSX get 90 HP/Liter? Obviously it has a reasonably high compression ratio (high by 1991 standards). VTEC allows it to use a relatively radical cam grind (by street car standards) without being lifeless at lower RPM. It also has exceptional head design including 4-valves per cylinder and huge unrestrictive ports. That’s definitely worth some ponies but only if you have something to pump through them. So in the case of the NSX a large part of the difference in output per liter is RPM. What kind of power per liter do you think it would make if redline were a more common 6200? Probably no more than the 1991 SHO Taurus 3.0 that put out 220hp @6200rpm. So what makes the NSX engine “more” special in terms of peak HP is almost purely based on higher RPM. (but don’t feel too bad, the SHO 3.0 isn’t really a Ford engine, it was built by Yamaha) Of course you need to build both the bottom and top end to handle and use that extra RPM efficiently, but the point is that the extra power would not exist without it.
Longer stroke & redline - One of the reasons that redline drops with increased stroke is the kind of stresses already noted. The longer the stroke, the higher the piston velocity, and the greater the stress when it needs to change direction. A longer stroke adds torque, but if the rest of the engine is properly designed and tuned (especially cams and intake) so it can breath, it does not necessarily lower the power band. The stock NSX engine has a stroke of 78mm (3.07”). That’s a pretty typical stroke for performance engines, although most admittedly don’t rev even to 8k. But they also don’t have a forged crank and titanium rods like the NSX. Now look at the S2000 mentioned above. Yes, they dropped the redline when they increased the stroke, but the original stroke rated at 9k was 84mm (over 3.3”), much longer than the NSX at 8k. If you use that old S2000 stroke value of 84mm and the 93mm bore of the standard 3.2 and you get a bit over 3.42L. The F-X 3.3 from stock stroke must use roughly 95mm, and if you combine that with our custom stroke you get 3.57L. And that still uses the same stroke as the original 9k redline S2000. Now I realize that you don’t simply change the rev limiter and start producing power to 8.5 or 9k. It requires different cams, springs, possibly valves, stronger pistons, etc. and other work to pull it all together.
Mind you I’m not really advocating a higher redline. The real point of my comment on this was to get Mr. satan to talk more about his plans. He keeps alluding to things like breaking new ground or being a pioneer in NA development of the NSX. Frankly, the number of things you can do are fairly limited and as well understood as the internal combustion engine itself. Look at the power curves of all the best high performance automotive engines that are somewhat civilized for the street and you can get a pretty good idea of what’s possible. Actually, look no further than the stock NSX and original S2000 because they already to a pretty good job. I could go on for pages about how you might drag more power out of them but the bottom line is that at a given displacement and RPM there are pretty clear limits to HP/Liter for a civilized NA engine. Try to exceed that and you are sacrificing something, generally either drivability or longevity/reliability. Of course a higher redline also involves sacrifices but it is a much more interesting challenge than just more displacement, which of course was one of the main appeals of our cars in the first place.
If you won’t increase redline then the radically stiff springs you talk about don’t seem to make sense. Some stiffer yes due to the increased lift you will probably design into the cams, but the primary reason to for super stiff springs is to avoid floating valves at high RPM. Since the stock one already handle 8k pretty well, I think you are asking to go through cams and valve train parts at an accelerated rate for nothing. Unless it were primarily a track car I would go with modestly stiffer springs which should alleviate some of the concern about the belt.
As far as frequency of rebuilds, there is a big difference between a street driven VTEC engine that spends relatively little time in the top 2k of the power band and a race engine that spends half it’s life there. Thanks to VTEC, those of use who roll up the vast majority of total miles on the street can have a car designed to do 9k but be totally drivable and docile at 2500. So I think that issue is not nearly as big as suggested.
Yikes, this turned out to be a long one so I’ll give it up for awhile.
I'm not doing anything magical...just applying what I know about other honda motors to one of the biggest baddest honda motors that has been underachieving for too long!
There is truth to your words, but they are more relevant in genuinely long-stroke engines and old-world engines. Clearly a 3.3" stroke can be managed very well at the 9k we're talking about.
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