gears and rears

[Anthony]

Originally Posted by jwd

A vacuum advance unit (connected to a CONSTANT vacuum supply) is mandatory for optimum street performance. It will not only cause your engine to run cooler, you'll get better throttle response and MPG. There are plenty of articles written on the subject. Those that disagree, don't understand basic engine tuning and vacuum advance operation.

Jim

I kind of agree with Jim. Unless you are running a vacuum advance on your distributor, no matter your mechaniucal advance setting, you are not optimal for cruising. The engine can tolerate, and benefit from more advance at low speed, low throttle cruising that can be obtained with a vacuum advance, and still preserve optimal (lower) mechanical advance settings for full throttle performance.

[diegokid]

Why don;t you call SA and ask him your gear question. I would think he knows his engine, and what would be the best gear set-up.

I did, he said the 3.31 would be good and pull real well but the 3.42 would be better.

[Excaliber]

Steve, thats not a bad example of a good low rpm torque motor. Looks like max torque is around 4000 rpm, the lowest rpm noted on the chart. Max horse power is under 6000 rpm. I built my motor for a lower rpm and better torque but have never dynoed it. It too pulls nicely from about 2000 rpm, but it likes 2500 better. My max rpm is now around 6200, down from 7000 +! I also run a vacuum advance now, by the way. I get 10 mpg or better when I cruise it at about 65 mph and 2800 rpm, thats UP from the 6 mpg I got with the old 'monster' motor. I suspect cruising at 2000 rpm with a .6 OD would not result in better mpg or a happy motor in my case, but I could be wrong.

The hyd roller is a great setup for a lower rpm engine, I'm running a solid flat tappet myself.

Top loader, 3:31 rear gear, dual fours.

[xracerbob]

You can always go with a G-Force t-5 and the .75 OD.

[xlr8or]

Sorry I forgot you were the all knowing authority.

[Cobrabill]

Originally Posted by xlr8or

Sorry I forgot you were the all knowing authority.

All knowing?Nahhh,but this timing issue is so basic that ANYONE who owns a Cobra should know it.

[Excaliber]

I believe there is indeed such a thing as 'light cruise' vs 'heavy cruise'. Example that comes to mind is Interstate Highway 3 (H3) here in Hawaii. And don't get me started on the "Interstate" thing on an 'Island'.

Anyway, it's a modest grade and one of our local guys (Hi Cobra, Flip) has noted his 351 with T5 in OD 'struggles' up the grade at cruise speed. This is what I would call 'heavy cruise' load vs light cruise load. SO, he adds a little aviation fuel (readily available to him) to his premium fuel and is able to cruise comfortably with the higher octane rather than downshift. The higher octane is not required on the more flat H1 and H2 highways under 'light cruise' conditions.

[iwantacobra427]

Do you guys think I made a mistake with this setup: TKO 600, 0.64 OD, 3.77 rear end, 331 stroke with Comp Cam 280 HR10 cam (HYDRAULIC ROLLER: Street machine and limited high performance street use. Best with 5 speed, 3.40 to 4.10 , aftermarket intake and headers.). This setup should produce 2500 rpm at 78 mph. I'm in West Texas with little traffic and 70 + mph speed limits on the highways so I'll be going 70 - 75 mph most of the time. It was this setup or the 0.82 with 3.54 which would produce 2500 rpm at 62 mph.

[427sharpe]

[quote=iwantacobra427;828729]Do you guys think I made a mistake with this setup: TKO 600, 0.64 OD, 3.77 rear end QUOTE]

I think you'll love this set up. 2.41 final drive is pretty good for cruising. it's the guys that go nuts that get into hot water, with a final drive around 2.0! All a gear that tall will do is bog the engine unless you're running at Daytona. I always like my final drive to be in the 2.50-2.70 range and you're RPM will hover close to the beginning of the power ramp of the cam at cruising speed most of the time. That is the ticket....probably more than one, too....
Just monkey with the REAR gears until they suit your trans. A lot easier to find differential gears than get Tremec to make a trans for you!

[Excaliber]

It's possible that cam will work quite nicely at 2500 rpm. ANOTHER big problem I have with a typical T5 is the ultra low first gear, when you combine that with a 3.5 or especially a 3.7 it becomes all but useless. You could use 2nd gear to start out and very likely get BETTER 1/4 mile ET times using 2nd to launch! 1st becomes a 'stump puller' tractor ratio, a real tire smoker of a ratio (might be fun ).

WATCH out when you grab 2nd gear in a corner even with LIGHT throttle, it will break the tires loose and swap ends on you in a heart beat. I know, I used to run a 3.5 rear with a T5 and Goodrich TA tires, whew, what a lousy combination for traction that setup was. I 'spun out' THAT car with it's measly STOCK 302 more often than I've ever spun my ERA with twice the horse power. The ERA has some fat tires, great traction and a MUCH higher 1st gear ratio. That all adds up to 'control'.

Myself, I'd shoot for gear ratios eqivulant to a wide ratio or close ratio top loader with a 3.5 rear gear and a .8 OD AND some 'sticky tires' (for safety). I think that would be the perfect all around gearing setup.

[WarrenG]

I have 3.54 rear gears and the TKO600 0.64. 65 mph is about 1900 rpm, mileage between 20 and 21mpg. The engine cruises fine at that level and accelerates without loading up unless the pedal is suddenly floored. For "instant" (rarely needed) acceleration I downshift.

If I was to do it over again I would probably use 3.77's with the 0.64 or go with the 3.31's and the 0.82 OD for better response.

[iwantacobra427]

I bought the TKO 600 over a year ago before Richmond came out with their 0.75 OD. I think a 3.54 with the Richmond would be nearly perfect for all around driving. I'll just have to get a pair of 295 Avons out back and shift into 2nd at around 30 mph (~4250 rpm)!

[767Jockey]

Remember back in the day when guys would talk about their engines coming up "on cam"? It seems with all the really good tech info on this thread about cam profile and ignition advance, without knowing it that's what we were talking about back then.

When it all comes together and the engine hits it's "sweet spot", you want that to happen by the time you hit your normal cruising speed. I have a fairly hot solid roller going in, and a 3:31 rear. I chose the .82 TKO trying to keep the engine in it's slightly higher than normal RPM "sweet spot" during cruise.

I know, it's not a highly technical term, but sometimes easier is better. Sort of the KISS principle.

By the way, just FYI, I got my .82 TKO 600 in two days from Mike Forte. He's got a bunch he keeps in stock, great guy to deal with as well. I was very pleased to work with him.