Best transmission and internals to use for a budget 350 sbc swap? (Page 2/3)
fieroguru MAY 16, 07:04 PM

quote
Originally posted by 88FGT:

Also, between the F23 and F40, which transmission do y'all think is better? In my opinion, I favor the F40 due to its 6 speeds and the fact that it offers more room for a larger power band, but I have heard that 1st gear isn't really that useful, as it is very short, and its obviously a bit pricier that the F23 to put in. Is there a way to get around this problem by changing the ratio on 1st gear, or would you have to change ratios on all six? I am not all that keen on how transmission gear ratios work or which ones are better, so any information that would be helpful as well.



Better? There is no answer to that question, it is all about intended use and personal preferences.

Cheaper? - F23 hands down.

Smoother shifting - F23 hands down

Useful 1st gear? - neither is great. 1st gear is 3.77 in the F40 and 3.58 with the F23. The F40 has a 3.55 final drive (13.38 overall launch ratio) vs. the F23's 3.94 (14.1). So stock for stock w/o any gear swapping, the F23 has an overall shorter 1st gear. There are no numerically lower first gears for either transmission... so you are stuck with those. Both the F40 and F23 have a numerically lower final drive that can be swapped. The 3.63 is available for the F23. This lowers the launch ratio to 13.0. The F40 has 3.35 (12.63) as well as 3.091 (11.65) final drives available - but neither are available in the US and will have to be imported from the UK.

I spent a month swapping between my LS4/F40 and Trinten's SBC/F23 on a daily basis. I would drive my car to work, then when I got home would jump in his car for tuning, shakedown runs, and just reliability verification. Both cars were over 400 fwhp, both had similar cam specs, I found myself always looking for another gear or two with the F23. WHen I would normally be in 3rd with the F40, I was in 4th with the F23, which wasn't necessary bad, but when the F40 was in 4th, the F23 would be in 5th and the F40 still had 2 more gears. So for me and my driving style, the F40 gearing was better, while still being less than ideal.

After I did the 3.091 final drive swap, it really changed the feel of the car. 1st gear is good to 44 mph, 2nd takes it to 81 mph, and 3rd is 126 mph, I can run 80 mph on the interstate at less than 2100 rpm, and it can pull down 28-29 mpg with 382 rwhp @ 6800 rpm.

Between my SBC/Getrag and LS4/F40, I have logged close to 100K miles with V8 FIeros, driven them daily 3 seasons each year, used them for 200+ mile daily commutes, and completed many 3000 mile 7 day road trips. So my priorities/expectations from the swap and transmission are a different than most.

Would I have a F23 in one of my personal fieros? Not a chance.
Are they a perfectly fine transmission for other people? Absolutely.

[This message has been edited by fieroguru (edited 05-16-2021).]

88FGT MAY 27, 12:34 AM

quote
Originally posted by Trinten:

In addition to the other thread, I can tell you my F23 swap was very inexpensive. Most of the cost was in labor!

This is from memory, though there is a thread documenting when it was put into my car - however a lot of the pictures are gone. Still good info.:
Transmission: $400 (low mileage, and it was one of those yards that pulls the parts for you, so you might find it cheaper)
Flywheel: $300-ish?
New HTOB: $50
Original Spacer: $25-ish
FieroGuru later upgraded the spacer setup... not sure what he would charge to make another one.
Cables: California Push-n-Pull has the right cables for this swap 'on the shelf' now, one cable is a standard Getrag cable, the other is from Push-n-Pull, and was about $125
Slave cylinder adapter: ~$125 bucks?
Optional - there is a Quaife ATB Helical LSD (gear driven, no clutches or springs!), but that adds about 1000 bucks for the LSD, and around 100 for the Kent tools to put it in.

The transmission takes a beating. And in my 350 on the highway, I was getting around 21mpg. I don't recall my final drive. I think at 70mph I was turning 2800 RPM?

One issue I did have was with axles. Apparently the after-market axles for the Fiero are about 0.25" shorter than OEM (so they can work on more than one application). My F23/350 swap didn't quite leave room for that tolerance. When I broke a tripod at the track, the aftermarket axle kept popping out when driving. FieroGuru kindly supplied me with a factory original.

It sounds like the 350 isn't in the Fiero yet, so other stuff you'll need, in general, to put the 350 into the Fiero. (Again, from memory, not exhaustive, please check out some build threads!)
1" adapter plate from Archie to bolt the engine and transmission together (and create provision for starter), or make your own if you have the machining equipment/skills.
Oil filter relocation setup, with the return tube going to one of the other ports on the block (cradle makes it nigh-impossible to use as intended)
Electric water pump (optional, but could make your lift with belts much easier)
Appropriate fittings to hook up remote electric water pump.
Block hugger headers
Low rise air filter for the carb (Holley makes a triangle shaped one that works well, though the foam filter in it is prone to melting/damage, especially from any backfires from timing being off or carb not having the right jet sizes... I know from experience!)





Say, if I were to put a Quaife LSD in, which model of theirs would be best suited? It seems they made a lot of OEM diffs, but I’m not sure which one would be best for a Fiero axle.
Trinten MAY 27, 08:55 AM
They only make one that works with the F23 (also called the Getrag 287 - probably for use in foreign calls like Vauxhall). The part number is QDF17B.

To my knowledge they do not currently make any others for transmissions going into Fieros. They used to make a few others, but those are discontinued.

My personal opinion is that helical style LSDs are best. Unless they physically break, you never need to maintain them.

There are other companies out there that make the other styles of LSDs (I think you want to avoid Phantom Grip and a few other names they are sold under). Engineered Performance makes some for the Fiero that I've heard good things about, and another company called "Gr8Grip", but I do not have any second-hand knowledge on them, so please do some searches and see if anyone has had issues before buying.

Depending on your power goals, intended use of the car, and driving style, you might not see a benefit. That is a topic that others have debated about. In my opinion, if you want it and can afford it, who cares if you need it. Get it because it will make you happy!!

As Cowspatoot has said to me "No one needs a V8 swapped Fiero!" Though he always does it with a grin, because no one needs a lot of the stuff we do to our cars... him included!
2.5 MAY 27, 11:41 AM
How much tougher than the Factory Getrag are the F40 and F23? How is it measured, torque rating? Does clutch matter to life of the trans, and how?
Trinten MAY 27, 11:56 AM

quote
Originally posted by 2.5:

How much tougher than the Factory Getrag are the F40 and F23? How is it measured, torque rating? Does clutch matter to life of the trans, and how?



There is a fundamental problem with the newton rating on transmissions (at least from GM). That is GM does not "test until failure". They design them with what they expect to be the highest output they'll put through them, then the take the alpha and beta and some production units, put them on automated test setups, and run them through cycles (sometimes 24 hours a day, if they are in an area they can get away with the noise pollution). It's not only to make sure they survive the power, but to emulate how much abuse they'll see during the warranty period. The costs that the dealership/manufacturer has to eat for Warranty is calculated and baked into the price.

If the transmissions survive, it get stamped with that number. This is from someone who was an engineer with GM.

So when you see the max torque/newton rating for a transmission, keep in mind that was not a "99% of them survived up to this, 10 more ft/lbs and they blow up!". Which is why people are putting double, triple, or more power through some of these transmissions.

There is one person (JNCOMUTT) who had a twin turbo charged 3800 buckled up to the F23, and was doing clutch dumps and laying out 60' burn outs... and the transmission was fine.

I beat on my F23 as well, transmission lived (CV Joint... not so much).

So if anyone says "It can only handle this much power!" what they mean to say (or should say) is "It was only tested for this much power!"
2.5 MAY 27, 12:34 PM

quote
Originally posted by Trinten:
There is a fundamental problem with the newton rating on transmissions (at least from GM). That is GM does not "test until failure". They design them with what they expect to be the highest output they'll put through them, then the take the alpha and beta and some production units, put them on automated test setups, and run them through cycles (sometimes 24 hours a day, if they are in an area they can get away with the noise pollution). It's not only to make sure they survive the power, but to emulate how much abuse they'll see during the warranty period. The costs that the dealership/manufacturer has to eat for Warranty is calculated and baked into the price.

If the transmissions survive, it get stamped with that number. This is from someone who was an engineer with GM.

So when you see the max torque/newton rating for a transmission, keep in mind that was not a "99% of them survived up to this, 10 more ft/lbs and they blow up!". Which is why people are putting double, triple, or more power through some of these transmissions.

There is one person (JNCOMUTT) who had a twin turbo charged 3800 buckled up to the F23, and was doing clutch dumps and laying out 60' burn outs... and the transmission was fine.

I beat on my F23 as well, transmission lived (CV Joint... not so much).

So if anyone says "It can only handle this much power!" what they mean to say (or should say) is "It was only tested for this much power!"



I see, in this case, were the F23 and F40 tested to more power than the Getrag? On paper?
Trinten MAY 27, 01:10 PM
Per wikipedia:
F23 can handle torque inputs of over 230 newton metres (170 lb⋅ft).

Per wikipedia and another source (including one I think from our very own members!!)
F40 is rated at 400 Newton metres (or 295 lb-ft)

Anecdotally - The GM transmissions are usually numerically designated in newton metres that means F35 is rated at 350 Nm, the F25 at 250 Nm, F40 at 400 Nm, M32 at 320 Nm, and so on.
Raydar MAY 27, 06:29 PM

quote
Originally posted by Trinten:
...
Anecdotally - The GM transmissions are usually numerically designated in newton metres that means F35 is rated at 350 Nm, the F25 at 250 Nm, F40 at 400 Nm, M32 at 320 Nm, and so on.



It's kind of interesting that the Cobalt guys break F35s with stunning regularity, with some of the stuff that they're doing. I very seldom (well... never?) hear about a broken F23.
Not based on anything scientific. Just what I've gathered from reading forum comments, elsewhere.
I personally don't know anyone who has broken an F23. And they seem to get "beat on" a great deal.
88FGT MAY 28, 10:41 AM
Say, I did some looking around, and managed to find another Quaife diff that could potentially work for the f40. The par number is QDF21B. The only thing I’m worried about is if this one is only designed for Euro-style f40 transmissions like the ones Saab or Opel uses. Is this true, or would this diff work across all platforms?
Trinten MAY 28, 03:28 PM

quote
Originally posted by 88FGT:

Say, I did some looking around, and managed to find another Quaife diff that could potentially work for the f40. The par number is QDF21B. The only thing I’m worried about is if this one is only designed for Euro-style f40 transmissions like the ones Saab or Opel uses. Is this true, or would this diff work across all platforms?



I would shoot Quaife an email. Their pre-sales support is great (or was when I was investigating this not only for my F23, but other transmissions). I would say just that "I have an MR6/F40 transmission made for a car in the US. Will your part QDF21B work?" They will tell you right away.

My guess is that it will work, as just the bell housings change (to my knowledge!!), but I'm too close to 50/50 to put any money on it.