Is it just me Geoff or is Canada turning you into an out-and-out cynic? Has all that snow that's got to you?
Obviously the engine dyno posted above is a race version of our 4 litre with 320 degree cams and was designed to haul *** on track but is definitely civilised enough to run on the road. As I mentioned we have recently worked on the bottom end tuning and have managed to significantly improve the torque down there but there is more to come for sure.
It currently complies with UK non-cat emissions for pre 1993 cars, but (since you asked) we are working on a revised intake/cam/exhaust package that would make the engine compatable with post 93 MOT requirements and find the "missing" torque that you find essential below 3000rpm. As you know we are a small company who are independently investing heavily into products that we believe have a very real market, so its unfortunate that we cannot afford to test all possible variants at the same time and have to provide what the customers demand first. What you see is exactly that.

As for reliability, other tuners have used 104mm & 105mm cylinders in the past with a stock stroke and had reliability issues with the cylinder head sealing arrangements and cylinders going oval in use which is why (at a very early date) we adopted a 103mm cylinder. In 3 years of racing the 9m 103 cylinder has not suffered any signs of ovality or sealing issues; used in combination with the 80mm stroke crank, a longer rod than standard and a high pin piston we have also reduced rod thrust loads on the piston and reciprocating loads on the rod. Our rod also clears a stock oil pump (which is more than you can say for a Carillo with standard stroke!) so the engine can be assembled without requiring special knowledge. Reliability is only an issue if fundamentals of the design are wrong, although it does help when you have one of the leading F1 reliability/design engineers on the team.

 

Interestingly at the end of this season I experimented with a short ratio gearset in my 3.8RS CS, changing to a 4.0:1 R&P with a slightly lower 2nd gear with a view to improving my speed out of 40mph hairpins that seem common on UK hillclimb courses. In a straight line the car fealt noticeably quicker and on paper was much faster...

...however in practise I spent so much time changing gear in between bends that what I gained in acceleration I lost on the gearchange. For example at Harewood hillclimb I counted 8 extra up/down gearchanges which I know account for at least 0.3s per upchange, so overall should I be pleased that I got within 0.5s of my previous best time? Saying that it took me 4 runs to get all the gearchanges nearly right, so if you add in the possibility of a missed change there really is no question that the stock ratios are faster. What we really need to go faster everywhere are engines with wider torque curves, hence why 9m developed our 4 litre.

No prizes for guessing that I will be returning to my 3.44:1 R&P for next year for sure, whereupon the additional torque of the 4.0 litre will more than make up the lost time coming out of slow corners in a tall gear.

 

I don't but I can get them...maybe that is the reason he doesn't pull me as I thought he would. I'll e-mail them to you.

 

Time to get a sequential box there Colin....

 

Colin,
Snow ? Whats that ? We may not have snow for Christmas !

What I was gently leading towards was the need to have some kind of emmissions compliance for the USA . I am sure it will be an area that Geoffrey and yourself discuss !
I imagined that to get those results you were using a pretty big cam setup.
Be interesting to see how a milder version goes .No criticism implied or intended !!

Here , my "cat" is a growing furry creature that seems hell bent on eating anything that he can chew !

All the best

Geoff

 

No,No,that's not the point, we are talking about aircooled gearheads here!!!Love the aircool stuff!!!!

 

It's been pointed out numerous times here that just changing the final drive or ride height does nothing to help the gear spacing, particularly in the top 3 or 4.

I got a ride in Bill's blue car w/ the close ratio cup trans. That seems to be the way to go to me. At speed there is less than a 1000rpm drop, the motor is always boiling.

 

How does changing the final drive do "nothing" to help the gear spacing? It moves all the ratios closer together. Like changing all the ratios. It definitely DOES help the gear spacing, the drawback is that you lose a useful first and/or second.

As a matter of fact, a 4.000 final drive makes for an excellent 3rd-4th-5th using stock U.S. ratios.

 

You Sir, need to repeat Physics 101. Simple math tells you that the drops are the same no matter what the final drive or tire is.

using a short final drive preserves the rpm drops and lowers speed in gear, that is all it does.

The effect is that you will shift a lot but still be unhappy with the result. Drive a car with poper gearing someday. The difference is remarkable.

 

I learned arithmetic long before Physics. Simple math tells you that the final drive is an rpm multiplier, as is each gear, and the tire diameter. The drops are the same percentage wise, but smaller in rpms. So a lower final drive makes each gear closer.

Save the wiseass attitude, btw.

Here's a chart. Only thing changed is the final drive. Note the rpm drops (orange cells).

 

We are all learning a lot here, to borrow from Chris Walrod, "Is this a great place, or what?"

 

You may want to go back and check the math on your spreadsheet, something doesn't look correct. Here is an example gearbox, G64/21 (993C4) with the standard 3.44 R&P and with a 4.0 R&P. At the bottom, you can see the RPM drop between gears and it is the same with both R&Ps.

 

Talk about cross purposes?
Change diff ratio and the mph drops reduce unlike the rpm drops which remain the same.

In my case because I run very short circuits what I gained in acceleration I lost in the gearchange. With the torque of a 4.0 litre I would not have to be concerned about pulling 4000rpm out of a slow conrner in 2nd because I would have over 450Nm there to play with, whereas with this years 3.8 I had to wait for it to climb back on the cam and eventually start pulling with 400Nm at 4500rpm.

 

My point is that everything between the crankshaft (rpm) and the road speed (mph) has a linear relationship: each gear x final drive x tire. If you shorten any of those components, the rpms go up and/or the speed goes down. Shortening the final drive has exactly the same effect on a given single gear as installing a shorter single gear.

The valid drawback is that it doesn't make the best use of all the ratios. In my example, you end up with a ridiculously short 1st gear. Since the arithmetic is linear, you could lengthen first and second gear, and end up with the same effect as keeping the stock r & p and shortening the top few gears. Here's an example. In the first case, you use an 8:32 and lengthen 1 and 2. In the second case, you keep the stock final and shorten 2,3,4,5,6. In both cases you get a pretty neat close ratio 'box.

(this ignores practicalities like the mainshaft of course--just trying to show that the different approaches yield similar results)

 

Martin,
On west coast tracks like Willow Springs, Button Willow, Thunderhill & Laguna Seca the shorter gears will make a small difference but on temporary street courses that a lot of us raced in the Tecate Grand Prix series in the late 90's, the shorter gears make and made a huge difference for me.

As far as making a comparison with another 993 & driver that has shorter gears than you, it's more of an Apple to Oranges comparison due to the fact there are too many variables in play to say that's really an honest comparison.

I can assure you that there are other drivers that can beat your lap times in your own car very handily just because he or she is more skilled driver.
It can be embarrassing when it happens, but it goes to show that a huge part of racing 911's is really about experience & skill, not necessarily who has the best prepared car or the shortest gears, etc;

ZP44