THoughts on running 3.31 gear with a 200r4 tranny???

I have a 290-08h TA cam motor that is 520hp 560Tq and 26 inch tires. I know you dont want to get to low on the RPMs while driving down the road. I currently have 3.73 gears and a 400 switch pitch with 27 inch tires.

The car is basicly a show/street car. I know just keep the 3.73 but I would like to use them in my street strip car that has 3.90s in it now.

 

Put the 3.90 rear in the car that's getting the 200-4R and put the 3.73's in the street/strip car. With that engine I think the 3.31 is too high a gear for a 200-4R unless you plan on leaving it in 3rd gear which defeats the purpose of an OD. I have a 3.73/200-4R combo with 26" tires and I don't hit 2000 rpm's until 70 mph when in OD.

 

I had 3.31 gears in mine, but switched to 3.73. With that cam the engine won't like to be below 2100 to 2200 rpm with the lock up conv. on. You will feel the engine surging. I am running 275/60/15's which are about 26.5 tall, I think. This combination works well for me. Hope this helps.

 

They're advertised as 28" but mine are 26.5" also if measured from the ground to the center of the wheel with full weight on the car.

 

Yep 28" tall and when the car is rolling at 50 the tire will be at its more true diameter. tire will buldge outward...AND ALL this does not matter if the combo works for you and your car...EXCELLENT.

I personally have 3.31 and 295 50 15 (26.5) and will be moving up to 3.55 JUST alittle to much freeway 80mph is the sweet spot for driving

I have a 272 crane HMV cam 212 duration STILL runs 13.40 at the track as is.

GOOD enough for me as I have a drag race car so I do not want another one.

The 1973 camaro steering box (CAR PARTS WAREHOUSE REBUILD) was a GREAT upgrade and recommend it to ALL
NO alignment or anything needed extra BOLT IN AND GO! very nice...NO MORE BUS TURNING

Jim

 

Larry, With a Drag Radial BFG 275/60/15 28 in tall and 355 gear would give you what effective gear? :TU:

 

Thanks Larry.:TU: Love your new motor.:3gears: Does your new engine have the new water pump from TA Perfomance?

 

I ran years and years with an odd-fire 231 V6, 3.23 gears, 26" tall tire and a TH2004r trans. If any combination is going to have a problem pulling 4th gear, it's that one, but it didn't. It would down shift out of 4th on 4+ % grades, which isn't too unreasonable. Your RPM's will be a tad higher plus a ton more torque, you'd have no issues.

I currently am running 3.08's with an even deeper overdrive (.64 vs .67) and the 26" tall tire behind a 455 with no issue.

 

What's the goal for Overdrive? (Re: 3.31 gear with a 200r4 tranny???)

Dear Topless64-455,

Sorry to intrude in my ignorance, but I'm trying to make a similar decision, but I find myself looking at the problem very differently. So hopefully I'll learn something out of this discussion.

When I tried to figure this out I crunched some numbers and tried to figure out what my cruising RPM would be at 70 mph. Here is what I did:

My car is still "imprisoned" at the body shop, so I needed to compute the radius of the wheel from tire parameters. I found this formula on the Internet:

T*A/1270+W (in inches) which for a 205/70R14 tire becomes: 205*(70/1270)+14 = 25.3". The parameter is 2*PI*R or 79.5"

To compute number of revolutions in required to travel at 70 mph I first needed the distance traveled in one minute at 70 mph. Microsoft Excel did this for me: 73920 inches.

Divide the perimeter of the tire by distance in inches traveled at 70 mph in a minute to compute wheel RPM at 70 mph. In my case 930 RPM.

So now to get the propeller shaft RPM, multiply by the rear-end ratio. that turns out for me to be about 3100 RPM with your choice of 3.31 rear-end ratio.

Your engine cruising RPM in overdrive would be 0.67 times that or about 2050 RPM.

All this said - what's the goal here? When I do this calculation I come up with a radically different conclusion. I'm trying to get a super fuel-efficient car. On my configuration (if I've done these calculations correctly) I can bring the cruising RPM down to about 1900 RPM with a 3.08 rear-end ratio. That's 5% fewer turns per mile, that should be 5% better highway fuel economy. As far as I can tell, the engine will have all the power it needs with the 200-4R spread of gears. So for me, I want to use the smallest rear-end ratio that will still meet my performance objectives (in my case, move a heavy trailer.)

Could somebody first check to see that I haven't made any mistake in calculations (always useful! :grin and second could someone explain to me why folks are using such "short" rear end ratios? Is this purely to get quick acceleration at the start of a race? As other folks have pointed out, "short" rear-ends will limit your top speed, so there is a trade-off here that I know nothing about.

Still, if you want your car to have a life outside the race-track, you might want to ponder how to balance the economy advantages of an overdrive transmission. Does the 200-4R have benefits beyond the overdrive? Does it have advantages for racing that I'm not aware of?

I'm all ears to learn more about rear-end ratio selection! :Smarty:

Thanks for any and all wisdom!:TU:

Cheers, Edouard :beer

 

Larry,
I didn't check the tire height before I posted, probably should have. Thanks for the correction.:beers2:

 

Ed im going to be running the same cam later this year, and am trying to figure out what gear to run.

Can you describe the driving behaviour of the car? Maybe shed some light on the rest of the combo (intake? headers?).

Curious to know where that sweet spot is right after its done surging, and also where does it surge and lugg?

 

I have 275/60-15 rear tires with 3.73 gears and a turbo 200-4R and a 2200 stall lockup converter. Your torque converter will also come into play. If you have a loose converter that stalls over 2200, you will never get over that and produce more heat when not in OD.

For my setup, even with my milder Comp Cams 268H, I turn, confirmed with GPS, 2,100 RPM at 70MPH when locked up. Knock it out of lockup and it shoots to 2,600 with a slight hill at 70MPH. That is exactly 1,000 RPM less than with turbo 400 with 3.73 gears. It will lug around at 1,500 at 45 but it sure doesn't like it with my mild cam.

If you want an ideal gear/tire/economy setup, what you need to do is find your engine's sweet spot, where it smooths out and pulls the most vacuum. Get an upper and lower range where the vacuum first reaches peak and the highest RPM it will maintain that peak. That should be your sweet spot for normal steady state cruise RPM. Then, work backwards from that.

For example: If the minimum is 2000 and the max is 3300, you have your range to work with. Pick your lowest OD/lockup cruise speed and try to set it to the theoretical 2000. Lets assume it is 60 and you have two pieces of the puzzle. All you have left is the gears and tires. Get the gears as close as you can and fine tune with the tires.

To continue this example, assume an average 27 diameter tire. To find the proper gear, fill in the three pieces we already have and you get this formula:

TireDiam(27)*RPM(2000)
---------------------------------- = RearGear(4.0)
336*MPH(60)*FinalDrive(.67)

I have a spreadsheet with this stuff on it that lets you find any piece you don't have. So, if you have a rear gear already and need to tune with the tires, it becomes this:

RearGear(3.31)*MPH(60)*FinalDrive(.67)*336
---------------------------------------------------- = TireDiam(22.35)
RPM(2000)

So, you see where it all has to come into balance.

 

Just for the sake of comparison, I have 275/60-15 tires, 200-4R trans and 4.10 gears and it runs 2,400rpm@70mph.

 

I'm running 255/60/15 tires that are 27 inches tall with 3.23 gears and a 700R4..at 2100 RPM's and the lockup engaged my speed is about 72 MPH. I've got the the Poston 116 cam that is 214/228 @ .050. A lot smaller than the 238/248 @ .050 290-08H cam.