TH 400 vs 350 vs 200 metric

[Marvin Robinson]

Time to address my tranny -- heavy car (3750) with a big block engine combo. What kind of improvement will a TH350 w/low gearset have over the current TH400, and would a 200 metric (2.75 or 2.92) be an even better choice? If so, will the 200 metric stand up the the torque?

[gmonde]

i had a th400 in my stocker 3700 lbs,,went to a 904 (not an option for you but the 200 is close) shaved of a tenth so far and about 40 lbs ,but i dont know long the 200 would last against the big block,,,350 might be the better choice for reliabilty gmonde

[Alan Roehrich]

It depends on what is in the transmissions in question, what gear the car wants, and what RPM it turns.

Does your 400 have two aluminum drums and an aluminum reaction carrier? Does it have a straight cut gear set?

Are you talking about a 350 with two aluminum drums? Are you sure the car really wants a lower 1st gear?

Gains from the transmission are measured in hundredths, and the cost to change is often over $4K if you're looking for a killer light transmission. What else will $4K buy you that you need, and will it give you more than a few hundredths?

[Marvin Robinson]

Alan, I'm not sure what has been done with the TH400, but I suspect that it does not have any lightweight components in the build. I'm working on the 60' times. I updated the rear suspension and picked up .06 (but there is still some et left to gain with adjustments and the new Calverts going in the front). I've got a lot of weight that I will be moving around this winter that should help plant the tires better, so the trans is the next big thing I'm looking at to improve, and I'm trying to evaluate the options.

[Alan Roehrich]

There are plenty of options, including the Kilgore 400.

I just always suggest, even to potential customers, that they make sure they're not spending $4K or more on a transmission to get a tenth, and leaving a tenth and a half or more for the same price elsewhere.

A lot of torque in a heavy car, for example, a 455 Olds ( I used that because your avatar shows and Olds) may be too hard on a 200, they live in a lighter car with more HP, such as a 396/375 Camaro or Nova, but may be stressed in the heavier car.

Probably the most affordable option would be a 350 with aluminum forward and direct drums, and 250C sun gear shell and output shaft.

The next step would be either a Kilgore 400, or putting all three aluminum pieces plus a straight cut set in your 400. The all aluminum 400 is probably the ultimate in reliability, but may not be as quick as a Kilgore, but will possibly be within 1-3 hundredths of the 350, and last longer than just about anything.

[Kegracing]

While not perfectly back to back passes, I had almost identical weather and track prep, same track, and had a chance to test the 200 vs 350. Both were 2.75 low units, both pretty good trans and same converter. 350 had some light weight stuff and roller bearings, but was not a high dollar unit... This was a 87 Firebird, 305 stocker. Broke the 200 case. Put the 350 in it, and lost about .04 from best numbers I could measure, using incremental times, etc. The .04 was not worth the fear of breaking another 200, to me... MPH was about the same.

I stayed with the 350 in that car, and have a 350 in my current car. My opinion, we all have them, is spend the same (or less) money on a good 350 trans. vs the 200, and never have to worry about it. The 400 is stronger, but heavier and less efficient. A lot of the high dollar big block stockers, that could run anything (Fletcher for example) are using the 350.

I know there are some great builders out there, not trying to argue that, and all trans have their advantages... just my opinion.

Good luck.

Ken

[Alan Roehrich]

A low torque and HP car that turns a fair amount of RPM will see more gain from light weight transmission pieces than a high torque lower RPM car.

A car with less torque and HP that is turning a fair amount of RPM will often see fair amount of RPM drop.

The input drum spins at a percentage of the engine RPM, more specifically, the input drum is spinning at whatever the percentage of slip is in the converter at any given time.

On a normal 350 or 400, the 1-2 shift stops the direct drum, which has been spinning. Engine RPM drops, and so does the input drum RPM, so you accelerate the input drum again in 2nd gear, while holding the direct drum still. On the 2-3 shift, the direct drum instantly accelerates to the speed of the input drum as soon as the direct clutches engage fully. So 3rd gear shift you accelerate the direct and the input drum back up to whatever percentage of engine RPM the slip in the converter allows for.

Now, the further the RPM drop between gears, the more you have to accelerate those pieces. This soaks up some amount of torque, so, the less torque you have, the more there is to be gained with lightweight stuff.

Some of the higher HP cars have reported little or no gains from switching to a "trick" transmission such as a Pro Trans or a Kilgore, from a light 350, while others have reported 3-6 hundredths. The same applies to switching from a light 350 to a 200.

A fully lightened 400 can approach the same weight and efficiency as a 350, at a higher cost, with a greater margin of reliability, but at an increased cost, due to the cost of the gear set and the aluminum reaction carrier. The ET difference to a low RPM high torque car may not be enough to measure.

A car with a lot of torque may not even want or like a low gear lower than about 2.5:1, it may even slow it down, because of the extra time spent slipping the converter.

[Marvin Robinson]

Alan,

You are dead on, I'm running an F/SA 455 Olds .... it looks like the best bang for my buck would be either to "aluminize" my current TH400, or go with a properly built TH350. (I intend to run IHRA and some bracket events as well, so reliability is paramount - can't play the odds if the 200 metric is a weak link). The question of a lower 1st gear is still out there, the options are 2.48, 2.52, 2.75. I don't know whether the huge low end torque of the Olds needs a lower 1st gear or not when trying to harness it through a 9" tire. (I run Hoosier 30x9 radials). Right now, my power band does not go much beyond 5900, but a Bullet cam promises power up to 6400 or so. Don't wanna spin the heavy Olds stuff any higher with the components I'm forced to stick with in the rotating ***'y.

Hopefully I can gain enough enlightenment to get this combo right without burning thru cubic money I don't have....

[Alan Roehrich]

The 350 will cost less, and may be slightly faster. The low gear difference between the 350 (2.52) and the 400 (2.48) is negligible. I don't think I'd bother with a 2.75 low in your car. I'd be more inclined to buy the best converter possible. Of course, you'll be moving your crossmember and changing your driveshaft to accommodate a 350. The converter is the same, but your stall will go down when you put a converter that has been in front of a heavy 400 in front of a light 350. Maybe as much as 200-300 RPM.

I don't think you can make enough power or spin enough RPM to make reliability an issue with the bottom end of an Olds in Stock if it is well built. The stock F0 and F1 block is good to 600+ and 7000RPM (and that's 7000RPM while making good power, not 7000RPM going through the lights well after peak HP has come and gone). The stock cast crank will handle that as well, properly prepared.

[Marvin Robinson]

Alan, thanks so much for your expertise... it looks like I will be after a TH350, and have a converter done. I'll investigate the RPM potential next Spring after the Bullet cam goes in.