What keeps a LB9, L98, LT1, LS1, etc. engine from achieving high RPM' iex. 6k, 7k, 8k. Whats needed to get a l98 above 6k? Why can imports and 4bangers run so high?

 

You need to have your entire rotating assemble balanced to the greatest degree and get the best valve springs you can to avoid valve float... you might also want to try praying.

It is easier to get shorter stroke assemblies to turn faster than it is for a larger one - just look at the exotic V12's... destroking will help you rev it. But in the end, why? The SBC makes it's power in the low and mid range, while the little 4 bangers don't make **** down low and to scrape the top of their RPM band to get their HP. Focus on torque, then you can get your horsepower.

 

my head/cam LS1 has no problem taking it close to 7,000 rpm.

 

LS1's are the wave of the future! Good ***...those motors are powerful enough. Headed and cammed, that thing must haul *****. By the way, I hit 6500 rpms in my 302 with stock bottom end and valvesprings only stiff enough to handle a .530-ish lift cam. Had no adverse effects, besides scaring the living crap out of me. But I was at the very end of the 1/4 mile..I couldnt very well slip it into Overdrive and sacrifice a mph or two. I just BARELY broke the 100 mph barrier on that run! 100.4.

 

lol, i just bought a set of shaft mounted full roller rockers so she should haul even more ***** when i put it all back together. As of now I am only shifting at around 6400 rpm, but she can easily go to 7000 with no problems. Man I just realized how badly i need some more gearing in the car. The stock 3.23 just aint cutting it.

 

the answer is mass and distance.


if a object weighs alot, the stresses on it moving are greater.

if a object has to move a longer distance in the same time, the stresses are greater.


a tiny motor can be wound out like crazy, and not have too much stress...
meanwhile a large motor would have ALOT more stress on it for the same speed.


this is why the stock bottom end cant goto 8k and stay together... it would fly apart.






so lets say you build and balance the bottom end to the point it will stay together. next prob is valve control



the problem is the same, mass and the distance... except now you have to close the valve quickly enough too...

if you can make the valvetrain move quickly enough, it will let the motor spin that fast..... hardest part is having the valve close quick enough. ducati solves this by mechanicly closing the valve instead of relying on a spring....... great idea in my opinon...

 

You would slow a stock l98 down if you revved it to 8000rpm. A stock l98 will run out of breath at 4500rpm. The stock TPI is just to restrictive. With some other type of port injection you may see hp gains higher up if the car was built to make power at 8000rpm and if it could supply the air/fuel.

I know a guy running a 347 (stroked 302) mustang drag car. He spins to 10,000rpm. I haven't talked to him in a few years...when he told me that I didn't know if that was good or bad...I knew nothing about cars...

Anyways that mustang ran 5.4s in the 1/8th with no power adder. He had nitrous to but Im not sure what it ran on the juice.

 

Man...and I thought my mustang buddy with a built, nitroused 306 that shifted at 8000 was crazy. He did 11.9 on the bottle and 13.2 on his OLD motor. He's got a cam meant for top end too though. I believe the cam lift is .598, and with his roller rockers, puts him somewhere over .600 lift...maybe .620 or so. I think he did staggered 1.6's and 1.7's since the cam is a single pattern. It's one wicked machine. Spins the slicks down the road til about 70 or 80 in 2nd gear. He'd walk my low 14/high 13 second car like it's standing still.

 

the single biggest pasrt of the high rpm equation is the ability of an engine to move air in and out as quickly and efficently as possible. second part would be the mass and distance parts had to move