dial8

iTrader: (4)

That I already knew.

That I had an idea about, and I know that the ITS guys van still go about 140-145 so thats no a problem.

This is the part that needs explanation. I thought higher rev matched with closer ratio would give massive accel without messing with the lower top speed. Faster and quicker.

dial8

iTrader: (4)

Well said.

dial8

iTrader: (4)

O-chido!

classicauto

iTrader: (3)

Well, take a stock setup for example.

Raising the redline and keeping the same trans and rear end will only do two - technically three - things. Change the rev's you shift at, and the revs you start the next gear in (presuming you shifted at your now higher redline) and also raise your top speed.

Having a closer ratio and a higher redline may be a good thing, may be a bad thing it would depend on powerband and the gears. The idea with a close ratio box is to match the powerband and keep the engine in it. If you build a high revving engine, the power band gets narrower so according to math, its would seem better - but math doesn't always add up in the real world....you'd have to build the engine and match the gear set to its power for the optimum results. And even then you still deal with the problems of close ratio where there's also more shifts and more gears to pick from when decelerating into a corner etc which = more room for error from a driveability standpoint. As well as the massive cost.

If you want huge acceleration, a broad torque curve is the main concern and thats not something a peaky little high revver will give you.

Roen

iTrader: (2)

It also depends on the shape of the power curve. In our case, we trade off low end torque for higher rpms matched with a close ratio gear. If we wanted to gain the same amount of torque as piston engine, we'd probably have to use a F.D. gear that's 1.5x what we have now (so a 6.5 gear for those with 4.33 and a 6.15 for those with a 4.10)

You can also apply that conversely for an engine of a lower redline. Resize their top gear to match their top speed with an F.D. that's 2/3rd's what they currently have, and then resize the rest of the gears optimally. They'll exhibit lack of low end, but be able to hold gears just as well as we can.

As long as power is the same between the two engines, you can change their characteristics with gearing.

dial8

iTrader: (4)

But I thought a higher peak HP number no matter where the torque left would be a faster car. And driveablity gets negated after you "get to know you car" and learn how it feels, responds, reacts. Basically after you've been with it for a while.

dial8

iTrader: (4)

As a track dog, whats better? Power or gearing? Compromise between the two? Idealy I'd like to find some 4.77s, but those are uber expensive and even more rare for the FC.


But I have to go back to work. More from me later, thanks for chiming in...

Roen

iTrader: (2)

the fastest car is determined by the average power that you stay at, not necessarily the peak power. Normally, cars with higher peak power do make more power over time, but there are exceptions to that.

classicauto

iTrader: (3)

Not necessairily.

Example:

Two cars race, one makes 300hp from idle to its 8K redline. The other makes 600hp, but only for the last 1000rpm of its rev range, which is 9K.

Which do you think will win in a straight 1/4 mile race with the same gears and final drive?

Yes, the example is entirely extreme, but the point is as you narrow the power band (even though you're increasing your peak #) if you can't keep the engine at that peak by way of gearing you are actually slower. And the thing with these engines is the powerband is already fairly narrow - making it even narrower might necessitate super close ratio's to keep it at its peak power.

Whereas if you have an engine making acceptable power throughout a large portion of its revs, you can keep accelerating with a wider (ie. stock) gear set because it has power all the way through each gear.

GTRay

If you really want a great example of this... take a look at the outright winners at LeMans recently. Turbo Deisels!

Comparatively low revving, comparatively high TQ, and moderate power.

The ballpark specs are as follows:
~800+ lb/ft TQ
~650+ HP
useable power band: 3000-5000rpm!!!!

if this doesn't demonstrate to everyone that TQ and gearing win races than almost nothing will...

The goal for your "Time Attack" motor should be to create as broad of a power band as possible. Don't get caught up in revving to the moon. If you can establish a relatively flat TQ curve that starts around 3000 rpm and can take you to 8000RPM and gear it appropriately you will outpace your competition.

Try not to reinvent the wheel on this build. A 6port high compression motor has pleanty of potential to make power in the 350 HP range. For Time Attack you will want to keep your motor AND turbo in their sweet spots. Generally a smaller turbo will perform better at this than the big honkers that i've dubbed as "sig ****."

Keep it simple and remember to have fun with it.

Ray

dial8

iTrader: (4)

^^Thanks Ray. Again I'll cliff what I've learned so far to see if I got it right.

1. Larger than Street Port port work req.
2. S5 N/A rotors will work
3. Tunining is the deciding factor for success and reliablity with this application
4. Don't build for specific goals in the engine, build around the application
5. Turbo, torque curve, and gearing have to match to make it really meet its potential

Thanks guys, I consider this a successful thread.

dial8

Black91n/a

Well tuning can kill a motor with one good ping, but if it's not built properly to withstand constant high rpm running and you're doing it anyway then that'll kill the motor pretty quickly too.

It'd be a good idea to do race rotor bearings, 100+ psi of oil pressure, oil loop line, ported oil pump inlet/outlet, multi-window main bearings and all that jazz anyway to keep it as reliable as possible.

diabolical1

iTrader: (3)

number 4 is pretty much the jewel you should take away from this thread.

dial8

iTrader: (4)

+1. I was thinking along those lines, but hearing here just solidifies it.

dial8

iTrader: (4)

I guess, I'm not really disagreeing with you, I just thought that was the creative part of the engine building. Of course, that may have been why I blew two Honda motors in three months earlier this year...