Street and strip 6 speeds, UPDATE

I haven't look into any of the current manual tranny with over drives for a street and strip car, are the six speeds the way to go or are there any 5 speeds that are as good or better
I like stick shifts and have several NP833 standard 23 splines as well as several NP O.D. but they(the NP833 O.D.) scare me due to the size of the gears inside
I'm going to build one more street and strip car that will have a Dana 60 with 3.73 gears in it so having a O.D in high gear or even two O.D. gears may be nice for longer trips, what say you guys using them
I've always ben a drag race guy so hard street driving in a manual tranny street car is some thing I need all the help I can get on buying the best parts I can get on this build
Thanks in advance,Cab
EDITED: I should have mention this tranny only needs to hold up to around 700 to 750 HP at 6500+ RPM with half way sticky street tires.
I ended up using a NP833 in my current street car build, I'm going to sell this one as a street car and distant driver, not for strip use.
Thanks for all the help and info sharing

I think that with the classic engines, the only advantage a 6th speed gear can do is to allow a greater top speed. Cruising at 70 in 6th, an rpm of 1400 with a lumpy cam??? Soggy throttle response, fouled plugs, worse mileage...
I'm going with a 5 speed setup. The gear ratios for the overdrives are often 5th: .75 and 6th: .50

Depends on the 6spd of choice. I have the close ratio T56 magnum that runs a 0.63 6th gear, I run about 70mph at 2,000rpm with 3.73s. High enough to not lug it constantly but low enough to run down the Texas highways at 80-85 while under 2,500rpm.

Here's my trans vs the old 1:1 904

I don't think 3.73 gears are deep enough to run with a 6 speed. You might need something in the 4.50 range. If it was me I'd shoot for an overall final gear ratio of 3.55 in 5th and then something around 3.0 in 6th. This all depends on tire size and the torque curve of the engine of course. The second OD in 6th gear is so high that it kills most performance engines. You end up lugging the engine down the freeway with a performance cam. The OE's get away with it since they have variable cam timing. We don't have that cool stuff so we have to compromise.

3.73 is no problem with the close ratio Magnum gear set. Basic non-VVT 425hp Hemi.

True, but that isn't what Cab is building. Cab is old school so his 700 hp engine is going to have a big cam and he'll probably have a Holley carb on there. That engine will be lugging going down the freeway if he tries to gear it like a 2019 Challenger.

The Crower cam is only 262 @.050 ground on a 105 LSA is what I remember Rear tires are going to be a set of 275x60x15 probably so maybe the standard 5 speed with .64% O.D. will be a better choice, especially here in Oregon where most of speed limits are 55 MPH or slower
My last pump gas street car rumped quite a bit at 1700 RPM in high gear
Thanks to every one on this

Yeah....What the heck is with the stupid 55 mph limits ???

The T56 Magnum is amazing, being totally honest with you, its the best choice overall, though you are getting close to the 700 lb-ft rating. None of the 5-speeds are going to shift that nice. Even the tremec guys admitted it.

I have the 2.97:1/ 0.63 6th version with a 3.23 gear and 275-35-18 which is a 25.6" tall tire. 1900 rpm at 70 mph in 6th. With a stock stroke 340 and MPFI (with a 227/231 duration at 0.050" lift hydraulic roller) it will pull a hill at 1300 rpm. Fuel control is really important for being able to pull low RPMs.

I can assure you it shifts amazing at 6500 rpm. There is no comparison between its performance and an A833.

My personal experience with 5-speed TKO is with a Modular Mustang Racing beefed up TKO-500. The engine I have that it behind is a 408". MMR chryo treated the gears and did some shifter work and made it good to 700 lb/ft / 700hp. In the TKO you have 1,2 on a separate shaft than 3,4,5. This causes a major bummer in speed shifting. The tranny is great to shift through except for 2-3. You have to shift 2nd - 3rd gear like a dump truck. Fingers crossed but I have heard of quite a few TKO failures from a combination of grip, RPM, and the 2-3 shift (even in light cars with street tires). Spirited driving is fine but, just remember, the TKO is NOT a trans for drag racing an you'll probably never have a problem. I can't say for sure what RPM I'm running at 65 mph in 5th but I have 3.55's with a 228 @ .50 cam on a 114 LSA and she's in her sweet spot.

Have you looked at the Passon overdrive gear set. May be a good option if you have a 4 speed already and no cutting of floor.

G Force GFR5 is the only way to go for a true multi purpouse high hp car that is over 3k lbs.

Something like this:

G Force on Ebay

That looks like the old Doug Nash, that Richmond bought out?

It is similar looking externally yet much stronger.

I have a Richmond 6-spd, 3.01 first, 1:1 fifth, .84 sixth.
Have not driven it yet.
Gears / input shafts are available after a long dry spell.
The Richmond is the only trans that has a 3.50" shaft C-to-C separation besides the A833, that I know of.

As its is destined for the strip, perhaps you should look at the start line ratio over the final drive?
Depending on your stroke and weight, your looking at a low number for SLR with what you have listed, you may have to do a 2nd gear take off (3rd?) depending on the box...

https://www.5speedtransmissions.com/calculators

the richmond will get to where you need to be, but tis only rated at 600 lb/ft, the gf5r has many options too and is listed at 1300 hp... gosh...

I ended up using a NP833 O.D. in the current car I'm building, I am thinking of buying a used later model SRT 8 Hemi motor and 6 speed manual trans for the next stick shift street and strip car I build, if I live long enough
Thanks for all the help on this

I agree with you on the gearing. I have a 6 speed with a .63 6th gear. with 3.91’s and a 26” tire, the happy spot in my car was ~90mph in 6th. Cool and fun, but not conducive to keeping my drivers license. Driving from San Jose to willow springs was mostly a 5th gear deal. Especially over tehachapi going into Mojave. I’m thinking of going to a 4.10 or 4.30. Tremec has a good calculator that has gear ratios for the popular transmissions built in which helped me out a lot.

Do not make the choice on the option of 5 or 6 gears. Look into the ratios you need.

With that said there are many ratio choices for the T56. I have a close ratio and find 5th to be pretty much useless. I love the close ratio 1 to 4 and would not be dissappointed if 5 was super tall for cruising and there was no 5th but it's there and it's okay.

Like Goldduster said, nothing shifts like it. If that is important to you, T56 Magnum is your only option.

Fyi there is a new set of t56 guts that will hold 1000 ft lbs tq. Doesnt fix the shifter issue but surely somebody has it figured out by now?