For years I was under the impression that, if you had a Ford engine, you had to use a Ford transmission. After watching numerous car customizing shows, I realize this isn’t necessarily the case.
How would you determine if a certain transmission could be used with a certain engine?
Obviously, you wouldn’t want to mate a 4-speed VW Beetle tranny with a 502 Cadillac engine.
There are a many barriers to hooking up dissimilar engines and transmissions. One of the most important ones is the power and torque handling capability of the transmission itself. Running a 350 Chevy through a Toyota 5-speed from an MR2 isn’t going to work very well in most any application you can think up.
A critical factor is making sure that the input shaft and clutch system/torque converter line up properly, and can fit with the flywheel/flexplate of the engine. This often is very difficult.
Another factor is the physical connection of the bellhousing to the engine. Fabricating adapters and custom bellhousings is sometimes needed, and not normally easy to do.
Then, if you get all that done, often the driveshafts will not line up or will be the wrong length, the shift linkage is all wrong, plumbing for the hydraulic clutch or cabling for the manual clutch doesn’t work, etc.
In theory you can fit any engine and any transmission together, if you have the skills and money to fabricate or have fabricated parts. But it’s usually best to do as little of this as possible.
In my time, I have seen:
Shudder
From my motorhead days of the 70s, adaptor kits were available to mate most of the more popular blocks with equally popular trannies. The one that many of us worked around was the A727 Torqueflite MoPar transmission-a true workhorse automatic. I’d imagine speed shops would be a good source of kits for this purpose. Now I’m thinking of some stuff I’d seen: Corvair engines in Beetles, a 327 in a Vega, a 392 Chrysler hemi in a 55 GMC flare side pickup truck.
Sunoco 260 gasoline for .399 per gallon. Memories
Back in the old days (1960’s) you could buy a commercially manufactured adapter for almost any engine/transmission combination. (Anyone else grow up on Honest Charley catalogs?) This was because there were only a few transmission and engine designs and they were quite similar. Once you had a bell housing manufactured with the correct bolt pattern it was easy.
Today, the higher tech manufacturing and, in some cases, reduced margin in design makes it more desirable to keep the original engine and transmission combination.
My only experience is with chevy engines older than about 1985 or so. Note that chevy, olds, buick, etc. are all the same thing with a different label. Most of the chevy engines use the exact same bolt pattern on the flywheel, so you can hook just about any engine to just about any transmission very easily.
If you want to put a 502 in a VW, you probably wouldn’t want to keep the original VW transmission (or the back seat, for that matter). It’s much easier to fabricate a custom piece to join the differing drive shafts together, and use a transmission built for the 502. You’d probably have to do some welding to beef up the frame in the back as well.
I know someone who put a chevy motor in a ford. I don’t remember what transmission he used, but I do know he fabricated custom engine mounts for the thing. If you’ve got the ability to weld and have access to a machine shop, the sky’s the limit.
As for how you can match up parts, in the top gear most transmissions use a 1:1 ratio (one revolution of the engine equals one revolution of the drive shaft), unless it has an overdrive gear. As long as you match the engine and transmission together, you’ll get a nice range of gears for that engine. If you use significantly bigger wheels than what the engine/transmission were originally designed for, the car is going to be a bit more sluggish off the line but will have a higher top end speed. Conversely, tiny wheels will give you greater starting torque but a reduced top speed. You’d have to get things really far out of whack before you ended up with a car that was difficult to drive, so it’s pretty hard to customize a car that isn’t drivable even if you aren’t fairly intelligent about how you match up parts.
Hello guys! This is my first post in the SD forum!
Well, one of the purposes the gearbox accomplishes, is to keep the engine running at optimum RPM, ie at the RPM range where maximum torque is generated(power band). That said, different engines have different gearbox requirements.
For example, a diesel truck has a very powerful engine, but a very narrow power band (between 1000-2000 RPM). A typical petrol sedan has small power but much wider power band (2000-6000). Some racing cars have both narrow power bands and also the power is delivered at very high RPM (for example 9000-12000 RPM).
When increasing the hp of a car, what usually happens is the power band getting narrower and going at higher RPM. That’s basically why the gearbox has to be changed.
From my experience I’d say that gearboxes are a prety tough piece of equipment. In most cases a stock gearbox can accomodate increases in hp up to 75-100% with no major problems
OMG, KenGr! Honest Charley catalogs were the motorhead equivalent of a Penthouse mag. Now you’ve got me thinking of Moon Footie pedals, Hurst Line-Lock kits, flywheel blankets, and six packs. And also how much time I’d spend setting up six packs before I bought one of those throat manometers to measure flow. 
Is/was Honest Charley like JC Whitney?
I think your answer might have to be tempered in terms of automatic versus manual transmissions, would you agree?
My experience has been that manuals can be a little forgiving in terms of power increases (I mean, so long as the torque is under control at the power level, then it becomes more a cooling issue than anything else, right?), but I don’t know if they are so forgiving about peak torque increases. I’ve seen more than a few broken manual transmissions as a result of being overtorqued. I used to have an almost perfect half 1st-gear from an Opel GT that had a 50% or more torque increase to it. The owner popped the clutch to race a Triumph, and then there was this horrible sound…blech. I also saw a few MGB transmissions with broken gears from racers who overtorqued them, but those damn transmissions were poorly designed anyhow.
Maybe the difference is my experience is with vehicles primarily under 2000cc.
And there is also the clutch to worry about too - even if you can keep the gearbox, you may need a much beefier pressure plate and friction disc. And a beefier spring might require a switch from a cable linkage to a hydraulic linkage.
Well, a little like that. Honest Charley was based out of Chattanooga while JCW was based in Chicago (known as Warshawsky and Co. locally where ethnicity was not a marketing negative.) But the big difference was that Charley dealt mainly in serious performance equipment and quality dress up stuff while you had to spend a lot of time sorting through a JCW catalog to get past the junk.
Honest Charley still exists. It was sold a few years ago and now concentrates on truck and van accessories. Here is a history link:
Una Persson, what I had in mind was manual transmission. And my experience is basicaly with small engined cars, eg Peugeot 106, Citroen Saxo VTS, Fiat Punto and the like. Apparently, increasing the hp from 120 to 200 which is typical for these cars, is not the same as for example a Ferrari pumped up to 700 from 400hp. So the 75-100% increase I posted earlier might not hold in every case.
What they sometimes do to strengthen the gearbox is dismantle it, and heat the parts using an acetylene blow-torch untill red-hot and then cool it rapidly by immersing in water or oil. Its the cheapie way, I don’t know if this actually helps or how many gearboxes die during this hardening process!
I see what you are saying, but I was differentiating between a peak power increase and a peak torque increase. The two are somewhat related, but not directly. I mean, since power is a function of the torque and the rpm (over a constant for conversion), a higher power at the same rpm means a higher torque at that same rpm. But if the rpm is higher too, the actual torque may not be higher.
That is, a FIAT X1/9 originally at 70hp and 70 ft-lbf of torque might have no problem with going to 120hp peak and a peak torque of 70 ft-lbf (barring cooling issues), since that peak power is most likely at a much higher rpm. But if the peak torque is increased to 120 ft-lbf but peak power remains at 70hp, that’s a whole different animal.
I would expect a lot of gearboxes die that way. The gears are often already hardened. I almost wonder in subcooling them in liquid nitrogen might do better for changing the crystal structure and increasing toughness. My understanding is lateral thrust becomes a serious problem, as well as axial thrust on the shafts too. And there’s not much you can do for that except stronger bearings and a stronger casing.
Going back to the old hot rod days, a lot of large modern V-8 engines were mated to Ford 3 speed transmissions originally built for 60 HP flathead V-8’s. A surprising number survived. One theory was that in the old, relatively lightweight cars with street tires, you couldn’t put too much torque through the transmission because the wheels would just spin. As a counterpoint, I’ve seen relatively stock (high performance) cars, when fitted with racing slicks, shell out transmissions, break driveshafts, etc. It’s all a matter of balancing the components.