turbo 350 vs turbo 400

[jakeshoe]

Comparison shot of 200-4R, Th350 and Th400.

 

[Scottie-GNZ]

A transmission with lots of big, heavy parts (technical terms here!) does not necessarily absorb lots of power when maintaining a constant rpm, but it will absorb lots of power to spool-up.

Excellent point but if you have enough power to warrant strength of a TH400, you are going to have a loose enough conveter that the spool-up becomes a moot point.

[dr_hunt]

A loose converter and a low rear gear always helps. My glide has a 1.89 first and with a 4.86 rear gear along with a 6100 rpm launch will get you 1.16 60ft. times.

 

Well, that and a light car.

 

6100 launch, damn, I'm about to shift right then, cause my cam peters out at 6500. Guess I need bigger cam and more rpm. Here you go, ruining my lunch, now I have to spend paypal money that was earning interest. See how you are!

[jakeshoe]

Excellent point but if you have enough power to warrant strength of a TH400, you are going to have a loose enough conveter that the spool-up becomes a moot point.

 

How is the converter going to effect spool up of the transmission parts?

 

If you have a 6100 converter, when it flashes, if the trans is still at 0 rpm, it would have to spool up quicker....costing more power.

The QUICKER you spin up the parts, the more power it consumes.

 

This is why I have mentioned, worrying about a few lbs of rotating weight in a car that isn't running 10.0's or faster is splitting hairs.

However the sub 10 second cars will see a difference because they accelerate fast enough that there may actually be a measurable loss, on a dyno or in ET.

Let's put it this way,

Grandma's 17 second boat on wheels isn't accelerating fast enough to matter.

My mid 12 second Chevelle isn't either.

A mid 9 second car would probably actually see a consistant ET loss with the added 5-6 lbs of rotating weight, 15 lbs of overall, and the .04 gear ratio differential, but it would probably be around a .1 in the 1/4 based on what I have observed.

So grandma's car might have lost a HP, the 12 second Chevelle might have lost 5, and the 9 sec ride might have lost 25 hp.

The power loss will increase exponentially, but doesn't have an effect until you get to a certain level.

[Scottie-GNZ]

How is the converter going to effect spool up of the transmission parts?

 

If you have a 6100 converter' date=' when it flashes, if the trans is still at 0 rpm, it would have to spool up quicker....costing more power.

The QUICKER you spin up the parts, the more power it consumes.

[/quote']

You might be a tranny expert but I think you are now splitting hairs. If someone comes off a t-brake at 6000, you are absolutely right that the trans has to spool up faster, so damn fast that the "HP loss" will not even be noticeable for the minute fraction of a second it will take to spool up the trans to the rev limiter. Now, if the car is launched at say 2200, it is going to take longer to get that tranny spun up to the rev limiter and I see that as having a bigger effect on HP loss. That's the point I was trying to make.

[jakeshoe]

Scottie,

I'm not trying to be argumentative here, I'm trying to explain a widely misunderstood auto trans power consumption myth.

let me know if I'm explaing this in an understandable fashion.

I'll use your quote:

If someone comes off a t-brake at 6000, you are absolutely right that the trans has to spool up faster, so damn fast that the "HP loss" will not even be noticeable for the minute fraction of a second it will take to spool up the trans to the rev limiter. Now, if the car is launched at say 2200, it is going to take longer to get that tranny spun up to the rev limiter and I see that as having a bigger effect on HP loss.

 

OK,

Me or you might not FEEL a HP loss in the 6000 rpm launch scenario you mentioned. However if we did back to back testing of either a TH350 and Th400 or a TH400 with lightweight parts vs. a stock TH400 especially if we did it on a dyno THIS is the scenario where we would actually be able to measure the difference.

The 2200 launch scenario is probably not going to spin the rotating parts up so fast because it doesn't have to go from a standstill to 6000 rpm like in the other scenario.

 

Even though the parts spin up much faster (in the 6000 rpm launch) and the DURATION of the HP loss is less, the actual amount consumed would be MUCH greater than the 2200 rpm launch because the HP consumed increases exponentially with the rate of acceleration.

The 2200 launch would spin the parts up slower (not as much instant rpm, and most likely also simply a slower car), the slower rate of acceleration uses much less HP although over a greater duration or length of time. The overall outcome would still be less power loss overall with the slower accelerating combo ( lower rpm launch).

[Scottie-GNZ]

Ok, peace. Let's not drag this out.

 

In normal street driving, when moving from rest with very light throttle, I can actually feel the difference. Under race conditions, the only thing I care about, not only do I not notice any difference, the car is faster/quicker with the numbers translating into more HP over the 1/4-mile. Maybe it has to do with the gearing and the turbo being under more ideal load conditions, but whatever it is, it negates any theoretical HP loss.

 

That is my experience and I only impart advice based on my own practical experience. Having said that, your experience and knowledge is valued here and having folks like you and discussions like this is what makes this the damn best forum on the Internet, PERIOD.

[A. G. Olphart]

Thanks Scottie!

 

 

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[JustinOlson]

So will a TH400 with a factory bell housing fit in the s30 trans tunnel?

[jakeshoe]

With some "clearancing". Not much difference in the TH400 and 350 bellhousings, but the TH350 will hit.