what tranny with a SBC 350

[toddabrown]

I just got a nice 350 for my 66 c-10. I currently have a 3 speed Saginaw manual transmission hooked to my 6 cyl 250. I am wondering if i can stick with the Saginaw with the 350? i might have a chance to get a Borg Warner T-10. Is that a better choice. what type of fit issues are there with either? Any advice is greatly appreciated.

[Indian113]

Todd, both of the tranny's have a 1 to 1 drive in high gear. You won't gain much by using the T-10 except rowing the boat more. If it was me I would save my money up and get a 5 speed out of a Camaro or Firebird and have a overdrive to get better gas mileage. I jumped about 6 MPG's when I went from a 350 turbo to a 700r4.

[jocko]

to answer your question, yes, you can use the sag 3-spd. Indian makes a great point though, lots of bennies to swapping to an o/d config. Here's a thread on doing a T5 swap into a 66. Hope this helps. http://67-72chevytrucks.com/vboard/s...d.php?t=482069

[LVPhotos]

I used the stock bellhousing from my 283 / 3 on tree Saginaw hydraulic clutch. Firebird V8 and s10 tail shaft. Now running a 406 small block with 3.73 12 bolt with 28" tires. 20+ MPG with 400hp.
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[toddabrown]

Thank yall for the advice. i'll have to save up for the auto and o/d transmission and stay with the saginaw in the short run. will the bell housing on the saginaw match up with the 350 motor? someone told me i may need a new flywheel with the 350. any idea if that is true?

[jocko]

one more thought - I forgot to mention that a BW T10, although a great trans, will most likely result in a stick that comes up through the floor in a place that interferes with a bench seat. if you've installed buckets of some sort, then disregard. That's why you won't see very many Muncie 4-speeds or BW T10s in these trucks (although there are some) - folks like their bench seats in the 60-66s and want to retain them. Some have gone as far as the major job of removing a section of the bench to make room for a 4-speed, but it is major surgery to cut the seat frame, upholstery, make it look right, etc.

[toddabrown]

thanks for that tip jocko! looks like the saginaw 3 spd stays for now.

[toddabrown]

LV-20+mpg? that is very impressive!

[toddabrown]

how does the rear end set up factor in to the engine and transmission picture.

[jocko]

It doesn't figure into the "will the trans fit" question, but it needs to be considered in the overall plan for an engine/trans/rear end gear combo. Generally speaking, without an o/d trans, it's a tradeoff between the low end torque you can feel and higher speed low rpm cruising. A 3.08 (a higher gear/lower numerical ratio) equates to lower rpm for a given trans gear/speed. Whearas a 4.10 will eat your lunch money with very high rpm at highway speeds (with a 1:1 final drive trans, like sags, muncies, etc).

So, if you have a 4.10 or 3.73, they will give you the feeling of more acceleration off the line, but when you get to top gear your engine will be wound up to higher rpm for a given speed.

If you have a 3.08, it will feel like a bit more of a dog off the line, but you'll be cruising at a lower rpm at highway speeds. So, better mileage/cruising instead of off the line performance.

So, rearend ratio plays a big role in how the truck is driven. BUT, if you have an o/d, you have the best of both worlds. O/D transmissions (700R4/2004R/T5, etc) all tend ot have fairly deep gears 1st gears in the transmissions, giving you the same increased accel off the line like a 3.73 or 4.10, etc, while at the same time givng you low rpm at highway cruising speeds because of the .7-ish overdrive top gear.

Generally speaking, the most driveable overdrive setups utilize a rearend ratio of somewhere between 3.5-3.9-ish. 3.42, 3.55, 3.73 are very popular with an o/d trans, with 3.73 probably being the favorite. There's a good reason why GM used 3.73's in a lot of their early overdriven cars - like the Monte SS's etc.

If you have an o/d trans and run a 3.08 rear, you run the risk of being at too LOW of an prm at highway speeds, lugging the motor (or never using the o/d gear).

On the other hand, if you have an o/d trans and run a 4.10 or 4.57, etc - you somewhat negate the benefits of the o/d gear - but at least make it more highway friendly than it was. BUT, the big downside (remember that most o/d trans have a deep 1st gear) is that you will have so much torque multiplication in 1st gear, it becomes useless. In my 3.73 rear gear 66 with a T5 (1st gear was high 3's or low 4's in T5s) - I could only get about halfway thru an intersection before needing to shift into 2nd (because the rpm is so high quickly because of the deep 1st gear and deep rear gear combo). If i'd had a 4.10 or higher numerical gear, I would have been forced to starting off in 2nd gear and just utilizing 2nd thru 5th.

So, all I'm saying is that a balance is required. O/D transmissions are GREAT, but if you combo them with an extreme low or high rear end, you will likely screw the pooch.

So, that's my 2 cents. What rear end ratio does your truck have? It's a good exercise to sit down and plot out your drive ratio in each gear (i.e. trans gear ratio x rear ratio) and then compare those numebrs to any new trans combo you might be considering.

[jocko]

Here are some useful formulas. If you are Excel savvy, plugging in formulas will make it real simple to do comparisons.

mph = (rpm x tire dia") / gear ratio x 336)
rpm = mph x gear ratio x 336 / tire dia"
gear ratio = (rpm x tire dia") / (mph x 336)
tire dia" = mph x gear ratio x 336 / rpm


Here's a snapshot of how I compared things using a simple Excel spreadsheet. I used the first one to calculate the impact of a T5 swap into my 66 (1st pic). The 2nd one is the one I used to choose a trans for my 71 C20 - to calculate cruising rpm at various speeds, etc (2nd pic) (it currently has a 350/TH350/4.10 combo):

[toddabrown]

okay, Jocko, you have some great info. based on some quick research i think i have a 3.73 rear end. the truck seems to have a lot of low end power but does require a quick shift out of first. so what do you think about that combo with the sbc 350 and the 3 speed saginaw?

[jocko]

Here's a snapshot from the same file, but I sub'ed in your 66 3-speed ratios. The red rectangle shows what you'd have for gear multiplication in all gears and at the bottom, the rpm at 65 and 75 mph, respectively. The red circles show the comparisons between cruising rpm for the stock 3-speed as compared to a 700R4 and 2004R. A T5 would be roughly similar to the 700R4 rpms (depends on the T5 you choose as they have ratios from the .6-ish to .8-ish). But this should help you see what the combos give you - and note that this is specifically for a 235-75-15 tire size only. Your combo 350/3-speed will be geared just fine, but it will be a bit on the high rpm side above 65 mph or so. Not a big deal - that is how they drove when new, but gas wasn' $4/gal back then...

EDIT: Note, typo in then 66 3-spd 2nd gear ratio, it's 1.68 vice 1.60. It was corrected in the file and in the posts below.
Todd, please make sure the file I sent you has 1.68 vice 1.60 in the 66-3-speed 2nd gear green block. Pretty sure I had it corrected by the time I sent it to you.

[toddabrown]

Wow! Big difference it top speed rpms. Since I currently have that transmission and rear end combo with my 250 6 cyl, will i notice ant difference with the sbc 350 up front on that same tranny and rear end combo?

[jocko]

no, engine choice will not impact cruising rpm at all, strictly a matter of the gearing aft of the flywheel (i.e. trans + rear end ratio + tire dia). In other words, a 6 cyl with your 3-speed and 3.73 will be at the same rpm as the 350 with the same trans and rear end and tires (for a given mph). Now, whether or not a different motor is more "happy" at a given rpm is a different story..

[toddabrown]

Jocko, thanks for all the terrific information. I really appreciate it. I would love to have a copy of that spreadsheet if you are willing to share it. Maybe after the engine is in and we knock a few other items off the list we will start socking away some cash for an auto O/D transmission.

[jocko]

todd, I'll pm you. the only way for me to send the excel file is via email. i don't believe there is a way to post executable files on the threads (but not sure).

[Martin64]

With the 350 crate motor I just dropped in this summer and the stock 3 speed my truck is running 3K rpm at 60 mph. @ 55 mph it's turning 2500-2700 depending on the hill. My truck goes back and forth from El Cajon to El Centro every weekend so I'm looking for a gearing option. Gear Vendors has a divorced over drive unit for around $3000 that'll bring down rpms and bring up the cruise speed. I still don't know what I'm going to do yet.

[toddabrown]

martin- that fits with with the nice chart jocko posted. what is a divorced OD?

[jocko]

Martin/Todd - to compare, would need to know Martin's rear end ratio for Post #18.

GV o/u units are EXCELLENT, but also very expensive. For comparison, I got my T5 at the Pomona swap meet (or LA Roadster Show, I forget) for $450. Then after adding all the gadgets like new clutch, pressure plate, release bearing, shifter, boot, driveshaft shortening (which also had to be done with a GV unit), I had somewhere between $1000 and $1500 in the whole mess. (Gear Vendors over/under mounts behind a trans before the driveshaft and splits each gear. Think of it as an old quick-change rear end that is cab-selectable... splits each gear in two, so you can turn a 3-speed into a 6-speed, or, as most folks do - just split the high gear and use it as an o/d 4-speed).

Todd - thanks for the pm, I had to extract the pertinent stuff out of a bigger excel file and add some instructions. Just sent it to you, hope you find it helpful.

Here's a screenshot of it (sorry can't make it bigger or it won't upload, but it gives you an idear of what it will look like - instructions are also included with the file):

[Martin64]

This GV unit is electric and just splits 2nd and 3rd (according to the salesman). So you end up with a 2, 2.5, 3 and 3.5. So it'll give 5 forward gears. ALso with this unit, you have to build a crossmember to mount it to. If you don't have them mount it, you may get it cheaper. Gear Vendors is down the street from me so they quoted me the mounted price. I haven't persued it yet, just don't have the time right now.

I want to say my truck is running a 3:73 (and that just an assumption based on how it drives on the freeway compared to a couple other older Chevys I've had in the past).

I'll post my tire size tomorrow.

[Martin64]

Todd, a divorced unit is basically a stand alone unit meaning it's not part of the transmission. It mounts behind it. I'll see if I can find the email from Gear Vendors.

[theastronaut]

T-56 six speed from a 94-97 LT1 Camaro/Firebird will bolt straight up to a small block. Only need an adapter flywheel for two peice main seals, otherwise I think the LT1 flywheel will work on newer one peice seal engines (double check me on that). Much tougher than a S10 T5 (T-56 is rated to hold 450 tq stock) and there are kits to relocate the shifter farther forward to clear a bench seat. Use 4.56 gears and you'll be able to rip thru close ratio 1-4 gears, then 5th and 6th are both overdrive. Sixth is .60 if I remember correctly. Even with 4.56 gears, 75 mph is only 2000 rpm with 29" tall tires. Best combination of acceleration, strength, and mileage.
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[jocko]

HOW EMBARRASSSING! Caught a little error in the file above in post #20. Here's the corrected screen shot (mistake was that all final drive ratios were referencing the 4.10 rear end ratio... sorry about that - fixed them in this screen shot). By the way, if anyone wants this calculator, I'd be happy to email it to you. Just an excel file, you can use it, mod it, circular file it, but happy to provide. I've found it fairly useful on some project planning. I keep modifying it and trying to make it better, kinda like a truck.

[LostMy65]

If you zip a xls file, you can attach it to your post.
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