Trying to make a decision here of what to go with. I'm ready to drop in my 6.0L LQ9, and I'm trying to figure out if I should bolt my TH350 back up to it, or get the 2004r I've been eyeballing. My pockets do not run deep. Keeping the Th350 and getting a proper TC for the LS1 saves me the chunk of change of a new tranny. Though overdrive would be nice, the price really shys me away from a new one.
So if I keep the TH350, with the rear gearing I have - 2.73, what would be a decent TC for this drive train? What RPMs am I looking at on the highway? The car will be a cruiser/highway flyer. I don't know what TC it's got in it now. The only thing I've had done to the engine is had the heads cleaned up, and installed a cam with the following specs.

Cam motion Stage 3 cam, Part # 03-01-0006
Intake duration @ 0.50" Lift: 220
Exhaust duration @ 0.50" Lift: 230
Intake/Exhaust valve lift: .553"
Lobe separation: 117 deg

Cheers

 

More of a transmission sub- forum question than external engine question may get more info there. Also more info on your car would help. What weight? Tire size?

FWIW with with the TH350's 1st gear being a 2.52 ratio and your rear rear being a 2.73 for about 6.89 over all in first the car will likely be a real dog off of the line. I would consider a rear gear change to 3.23's or 3.42's if keeping the TH350.

However, I'd really look at a 700R4 or better yet 4L60e. It will cost more but your car will likely perform better off the line and on the highway. With the 3.06 1st gear and 2.73's that gives 8.35 overall plus an over drive. Putting a set of 3.73 gears in the rear end will likely be near ideal. Good highway with the over drive and good out of the hole too.

My 72 vette has a TH400, 3200 stall & 3.08 rear gears and weighs 3180 with a full tank of gas. This works OK due to the lower weight. However, the car would be far better with 3.73 gears and a 4L60e transmission instead of that TH400 as a fun driver and highway car. Car drives near stock with the tight Yank 3200 stall converter. I've dome many 1,300 mile road trips in the vette as described. Don't be afraid of stall with a quality converter and properly matched set up.

BTW Later TH350's are designed for lock up converters so you might wire up an electrical switch to manually lock the converter if you have one of those TH350's.

As for stall probably something in the 2,400 to 3,600 range depending on the other details of your car, weight etc and which transmission is used.

 

No where near enough information to say anything about gearing. What vehicle are you working on? Tire height? Weight?

Keep in mind pretty much any ls with a cam is going to want to be turned to 7k rpm or you may be better off with the stock cam. So really long gearing is not gonna work well.

 

Sorry, car is a 4 door '69 Chevelle, weighs about ~3300 - ~3400 lbs I believe.
rear tires: 275/40/18

 

Moving this over to the Auto Trans section where it belongs.

 

IMO getting rid of the 2.73:1 gear set would be the priority.

Both the THM350 and THM200-4R transmissions can be great and even be built-up towards 1,000 HP.
The THM350 will be a more affordable build; especially if building for higher HP.

Do you plan on keeping the engine as is?
You seem to have a nice mild cruising type of engine build.

FTI Performance torque converters are active and supportive on our message board.
If they do not jump-in and say hello, give them a try.

FTI Performance: 866-726-8358 or FTIPERFORMANCE.com

 

If it were me giving the info that you have i would go atleast 3.42 for the th350 or 3.73 for a od transmission. Those would be easily highway cruisable.

you could go more aggressive but anything over 3.73 will probably limit your comfortable cruise speed on the highway for the th350. Then 3.90s for the od transmission.

http://www.pszweb.com/car/gears.htm

There's a nice gear calc for you to play with.

 

How do you plan to use the car? race only, daily, weekend cruiser,street strip? This will help to decide which route would be best keeping budget in mind at the same time.

 

Yeah, the engine will be kept pretty much as stated. It will be a cruise only car. No strip/racing, .Eventually I'll probably get around to replacing the rear end to something like 3.55 or 3.73. But for now it'll be driven with the 2.73, the decision on Trans/TC is the current project at hand. I'll check out FTI for TCs.

 

So it sounds like budget is a concern, therefore I'd rather have a really nice converter with a TH350 vs. having to possibly spend less on a converter to afford the swap to a 200-4R. The OD is nice and the 200-series trans has a little more aggressive internal 1st gear ratio, but if this means having to cheapen out on the converter then it wouldn't be worth it to me unless it was a simple daily driver where economy and frequent expressway use was the primary goal.

That said, I have to agree with the guys above that a TH350 (2.52:1 1st gear) plus a 2.73 rear isn't going to be a great combo for an LQ9 with those cam specs @3400lbs and a 26.7" tire. As mentioned above, the 2.73 wouldn't be so bad if you had a trans with a much more aggressive 1st gear, like a 700-R4/4L60E, but with the weight, tire height and a TH350, the combo is not well matched for a fun street cruiser. A top shelf custom built converter would certainly be a big improvement in this department, but the combo still needs a better final drive ratio IMO. There are several options in the 3.08-3.55 range (depending on if you have an 8.2" or 8.5" rear - assuming it's one of those two) that would all be a great upgrade and good compromise for a street cruiser that's never going to see the track.

 

Great info! Thanks. So I guess if I'm looking at keeping the TH350 - A good TC and changing to rear end to 3.55 would be a good compromise with no OD transmission. Anything specific for stall range I should be looking at?
If I jumped to a 200 trans, a TC & rear 3.55 would be ideal? Is that safe to say?

 

For the stall RPM on the converter we can help with that. If you stick with the TH350 and go to 3.55 gears I would do something around 32-3600 to keep drive-ability nice since its a street cruiser that doesn't get raced.

 

In the meantime until the rear end is switched out, with a TH350 & 2.73 rear would you recommend the same range TC? How do you think it would act just cruising around?

 

I would knowing you plan to switch to 3.55 gears in the future. As a few of the members mentioned above, gearing and converter work together as a system so they need to be matched up correctly. You can run the same 3200-3600 stall converter mentioned with the numerically lower gear but it the best setup.

 

All I can think right now is "God I hated my 2.73s" lol. Made a jump to 3.73s. I think 3.42s would be the happy medium for an auto. Don't like the 3.73 at 70mph turning 2600rpm or higher but damn do they get fun up around 90. Depends on driving style. But 2.73s just seemed dead behind a 4l60e.

I'd say 3.42 with a 3600 to 4000 stall would be perfect for a street car...with 4l60e of course.

3.55 would be a good option!

 

2.73 with a 4L60E isn't really so bad, at least from a performance perspective, as long as you have an optimized stall speed in place. With the 3.06 1st gear of a 4L60E, having a 2.73 is comparable to having a 3.31 with a TH350 at launch (which is where gear ratio will have the biggest impact on measurable acceleration rate). On the other hand, there is the matter of "looseness" at part throttle, which is mostly a matter of perception and won't strike every driver to the same degree. Of course, looseness becomes more noticeable as stall speed increases (all else being equal, including quality of the converter), but the actual WOT acceleration improvement of a gear swap, even up to 3.73, is pretty small once stall speed is optimized on a 4L60E/2.73 combo. With a stock converter though, a 2.73 to 3.73 swap can provide some noticeable gains.

If you like the launch and 1st gear of a 3.42 with a 4L60E, you'd have to move to a 4.10/4.11 to get something similar with a TH350 (due to the 2.52 1st gear) - which isn't really an ideal/balanced ratio for a street-only application without OD or a TCC (unless tire height is huge), especially if highway/distance cruising is on the agenda.

3.55 is a nice overall balance, but not an available ratio for some GM rears (such as the 8.5" 10-bolt). The OP's car should have come with an 8.2", but that could have been changed over the decades.

 

Do not forget about Tire Diameter...

For example; when our differential gear sets were originally being designated by ratio (example 2.73:1 or 3.73:1), it was based the use of a 28" tall tire (diameter).

So... being that many of you guys drive low to the ground low side-wall tire vehicles...
Most of you guys will have tires with a smaller diameter than 28".
This essentially has the effect of having a slightly higher ratio gear set.

For example... My third gen camaro has 315/30/18 rear tires for street driving. That is a tire diameter of 25.5".
These tires essentially make the 3.73:1 gear set in the car act as if they are aprox. a 4.27:1 gear set.

 

I went ahead and ordered a TC from FTI thru Summit Racing, https://www.summitracing.com/parts/fti-esr6082. This will work with my TH350 and current 2.73 gearing until I upgrade the gearing to 3.55 or something.