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Old 07-06-2015, 09:37 PM   #1
Wolfmazter
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Question Help with some basics.

Hey guys! Im new to the forum and have a question. First off let me say, I'm pretty mechanically inclined I've repaired rear axel seals, rear diffs, drivetrain, brakes, multiple engine components to 3 different engines. I've even custom built gaming PC's for people, so im pretty handy. However, I've never needed to fully rebuild a motor. Since I've never had the need to do that I've never had to pull a motor out of a vehicle. To cut to the chase I'm not entirely sure how power is transferred to the transmission. My question here is (this is a hypothetical situation) if my uncle gives me a 350 small block, how do I find a transmission that is suited well for that motor, what do I need to be looking for? I know 350 is a common motor and could probably find a trans easily, but what if it was a more uncommon motor, like a 455 for instance.

Thanks for the help guys!
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Old 07-06-2015, 10:07 PM   #2
Black Lotus
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Re: Help with some basics.

The very basics then--
Generally speaking, on a front engine rear drive American car---
Different engines have different bolt patterns on the large flange at the rear of the block.
The bellhousing of a manual transmission or the front housing of an automatic bolts to the flange on the rear of the engine.
Inside the bellhousing is the flywheel which bolts to the crank on both auto or manual transmissions.
On the manual, a clutch pressure plate bolts to the the back of the flywheel. The clutch disc is captured between the pressure plate and the flywheel, and is supported by and drives the transmission input shaft. The manual transmission is bolted to the back of the bellhousing.
On a automatic, the torque converter is bolted to a flywheel, and it drives the input shaft of the automatic transmission, which bolts directly to the rear flange of the engine block.
People generally pick an automatic if they are either lazy, or anticipate being stuck in traffic a lot. (which is a pretty good reason to me) Automatics usually are quite efficient in drag racing as the newer, or modified ones shift very fast .
A manual transmission is for somebody that wants to control all aspects of how the car drives. Sometimes they require a bit of talent when driven fast, and if you are a junior road racer, you have to figure out how to manipulate all three pedals with only two feet.
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Old 07-07-2015, 12:22 AM   #3
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Re: Help with some basics.

Quote:
Originally Posted by Black Lotus View Post
The very basics then--
Generally speaking, on a front engine rear drive American car---
Different engines have different bolt patterns on the large flange at the rear of the block.
The bellhousing of a manual transmission or the front housing of an automatic bolts to the flange on the rear of the engine.
Inside the bellhousing is the flywheel which bolts to the crank on both auto or manual transmissions.
On the manual, a clutch pressure plate bolts to the the back of the flywheel. The clutch disc is captured between the pressure plate and the flywheel, and is supported by and drives the transmission input shaft. The manual transmission is bolted to the back of the bellhousing.
Ok, all that makes sense to me (considering I know how [and prefer] to dive a manual.) I've replaced a few flywheels also so that helped a lot. I learned that clutch discs are held in place by trans input shafts. So im gonna reiterate my question and see if your answer fits. "How do I pick a transmission that will work with an Oldsmobile 455 motor?" Basically (if understood correctly) I can use any transmission I want as long as the bellhousing (I prefer manual) matches the bolt pattern on the back of the block. Is that correct?

-Wolfmazter
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Old 07-08-2015, 05:44 PM   #4
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Re: Help with some basics.

Theres a big difference between a flywheel for a manual trans and a flexplate for an automatic. These usually come with used engines from bone yards. But I do believe most of the better bone yards can answer your exact questions. They have this stuff cataloged and a lot of cross over info at their fingertips.
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Old 07-08-2015, 10:15 PM   #5
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Re: Help with some basics.

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Theres a big difference between a flywheel for a manual trans and a flexplate for an automatic. These usually come with used engines from bone yards. But I do believe most of the better bone yards can answer your exact questions. They have this stuff cataloged and a lot of cross over info at their fingertips.
I know there's a big difference between flywheel and flexplate (rather than knowing there's a difference, i actually know what the difference is). Im just trying to figure out how to pick a transmission for a motor that was given to me. Not the type of transmission (auto or manual) but the actual specific make and model of transmission.

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Old 07-09-2015, 08:00 PM   #6
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Re: Help with some basics.

Like I said...
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Old 07-09-2015, 09:48 PM   #7
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Re: Help with some basics.

Manual transmissions are more critical to select than autos. You need to know the general operating parameters of the engine.
Torque peak(and it would be nice to know the torque curve of the engine), power peak, redline, and a desired highway RPM of the engine which is mainly goverend by camshaft and cylinder head port sizing.
If the engine is stock, you can expect it to be pretty mild mannered, and it'll be happy at lower RPMs. And less critical of gearbox selection.
Also what you expect, road speed wise, from all the intermediate gears that are inside the gearbox.
The intermediate gears ratios in the transmission govern how much the rpms drop when you shift up to the next higher gear. And also, how much revs will raise in the next lower gear when you downshift.
Calculating the road speed also requires that you know the final drive (rear end) gear ratio and your tire diameter.
With a numerically high first gear, you can select a numerically lower final drive gear for the rear end.
Typically you will end up (SAME number of gears ratios with different gearboxes) with a tranmission with numerically WIDER ratio spacing between the gears, which makes your RPMs drop off more with each gear upshift than a CLOSE ratio gearbox where the revs won't drop off as much.
And sounds more like a race car
Unfortunately with a close ratio box and a low numeric ratio final drive (tall gears, )
the car may be difficult to drive away from a stoplight at the base of a hill, without slipping the clutch a lot.
Conversely, a wide ratio box might make the situation more pleasent, with minimal clutch slipping.
So, the selection of the lower gear ratios should match up with the final drive gear ratios.
and tire diameter.
Gearboxes-- try the Summit Racing or maybe Jegs website.
Try this gear ratio calculator--http://www.tremec.com/calculadora.php
Tremec is a transmission manufacturer, but not the only one.
Back in the bad old primitive days the GM cars came with Saginaw 4 speed transmission for the lower powered cars with non-tempermental engines. These were invariably wide ratio transmission.
The higher powered cars had Muncie 4 speeds. These were available with both wide and close ratio gearsets.
Just as an example-- the close ratio Muncie gear ratios were beautifully spaced at-- 2.20, 1.64, 1.28, 1.0.
Fourth gear was dirrect, so it was a 1 /1 input to output ratio.
The wide ratio Muncie used 2.52, 1.88, 1.46, 1.0.
See the BIG ratio drop between 3rd and 4th?
Nowadays, with more gears in the box, and overdrives in 5th and 6th, these numbers as a guideline are almost useless, so use an online calculator.
Or a pencil and paper and draw Speeds-in-Gears graphs.
Take a while, maybe a month+ (?) to browse the internet and accumulate info.
Hope this helps.
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Old 07-10-2015, 07:09 AM   #8
Wolfmazter
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Re: Help with some basics.

Quote:
Originally Posted by Black Lotus View Post
Manual transmissions are more critical to select than autos. You need to know the general operating parameters of the engine.
Torque peak(and it would be nice to know the torque curve of the engine), power peak, redline, and a desired highway RPM of the engine which is mainly goverend by camshaft and cylinder head port sizing.
If the engine is stock, you can expect it to be pretty mild mannered, and it'll be happy at lower RPMs. And less critical of gearbox selection.
Also what you expect, road speed wise, from all the intermediate gears that are inside the gearbox.
The intermediate gears ratios in the transmission govern how much the rpms drop when you shift up to the next higher gear. And also, how much revs will raise in the next lower gear when you downshift.
Calculating the road speed also requires that you know the final drive (rear end) gear ratio and your tire diameter.
With a numerically high first gear, you can select a numerically lower final drive gear for the rear end.
Typically you will end up (SAME number of gears ratios with different gearboxes) with a tranmission with numerically WIDER ratio spacing between the gears, which makes your RPMs drop off more with each gear upshift than a CLOSE ratio gearbox where the revs won't drop off as much.
And sounds more like a race car
Unfortunately with a close ratio box and a low numeric ratio final drive (tall gears, )
the car may be difficult to drive away from a stoplight at the base of a hill, without slipping the clutch a lot.
Conversely, a wide ratio box might make the situation more pleasent, with minimal clutch slipping.
So, the selection of the lower gear ratios should match up with the final drive gear ratios.
and tire diameter.
Gearboxes-- try the Summit Racing or maybe Jegs website.
Try this gear ratio calculator--http://www.tremec.com/calculadora.php
Tremec is a transmission manufacturer, but not the only one.
Back in the bad old primitive days the GM cars came with Saginaw 4 speed transmission for the lower powered cars with non-tempermental engines. These were invariably wide ratio transmission.
The higher powered cars had Muncie 4 speeds. These were available with both wide and close ratio gearsets.
Just as an example-- the close ratio Muncie gear ratios were beautifully spaced at-- 2.20, 1.64, 1.28, 1.0.
Fourth gear was dirrect, so it was a 1 /1 input to output ratio.
The wide ratio Muncie used 2.52, 1.88, 1.46, 1.0.
See the BIG ratio drop between 3rd and 4th?
Nowadays, with more gears in the box, and overdrives in 5th and 6th, these numbers as a guideline are almost useless, so use an online calculator.
Or a pencil and paper and draw Speeds-in-Gears graphs.
Take a while, maybe a month+ (?) to browse the internet and accumulate info.
Hope this helps.
This is more like what I was looking for! Time to start doing math! Thanks Black Lotus!

-Wolfmazter
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