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| Choosing the right Transmission (Page 1/3) |
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BruhMans06
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AUG 20, 01:02 PM
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I have an issue
So I just bought an 84 fiero, the engines totally crapped which is fine by me because I was planning on swapping the engine anyway.
The main issue is this, I have had the plan of buy an LS3 to swap out for the old iron duke, and to pair it up with an Audi 01e 6 speed trans. Which is all fine and dandy except that I might be a little over my head doing a longitudinal set up rather than the original FWD set up. I drew some stuff up and realized that I would need to push the rear axle back by around 5 inches if I wanted to do this. I would also have to extend the rear of the car by about 6 inches in order to keep the transmission from sticking out the back of the car. I was going to go with this set up because the trans is cheap and can handle my 800hp goal, it's also a set up not many have done before. I'm also a broke 16 yo who's never modded any drive train in any shape or form. Though this is not the first engine and trans build ive done, so don't worry about my skill set.
Long story short is this is going to end up being a very expensive set up. So im opting to switch for the LS4 FWD set up, but I can't find a maunal transmission that matches the LS4 bolt pattern, while also being able to handle 800hp. Most people say to go with the F40, which I would do but most people say they can only handle up to 300hp. Which is basically just the stock hp of any LS.
Are there any alternative transmission that can meet my goals? If not, would I be able to upgrade an F40 to handle the power I need?
Thanks much!
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James Bird[This message has been edited by BruhMans06 (edited 08-20-2023).]
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IMSA GT
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AUG 20, 04:30 PM
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BruhMans06
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AUG 20, 05:17 PM
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| quote | Originally posted by IMSA GT:
Most people who want to do a longitudinal setup use an automatic transmission from an older Toronado but that will never handle 800hp. Just for info, see this webpage.
http://www.nathanbittinger....fieroaddiction/sbc-l |
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Yeah I thought of this awhile ago until I realized it came out of a low hp Toronado from the 60s, this would be one of the easiest swap to do but I want something that would be able to hold up to the power of an LS
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BruhMans06
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AUG 20, 05:30 PM
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After a bit of thought I realized how stupid I sound trying to get 800hp with an LS on a weak 84 fiero. The car would probably fold itself under that so im wondering if I should mod the LS at all, or if I should just keep it stock as a stock lS4 already has 300 hp which would be pretty fantastic for a car of this weight and size. I'm kind of new to this so I don't know what the hell I'm doing.
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Spoon
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AUG 20, 06:06 PM
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Anything is possible. Not mine.
Spoon
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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut
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olejoedad
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AUG 21, 10:36 AM
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When choosing a transmission, the number you need to look at is torque.
Forget about horsepower ratings, torque is what gets the car moving.
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82-T/A [At Work]
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AUG 21, 11:15 AM
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| quote | Originally posted by BruhMans06:
After a bit of thought I realized how stupid I sound trying to get 800hp with an LS on a weak 84 fiero. The car would probably fold itself under that so im wondering if I should mod the LS at all, or if I should just keep it stock as a stock lS4 already has 300 hp which would be pretty fantastic for a car of this weight and size. I'm kind of new to this so I don't know what the hell I'm doing. |
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If we're talking about the same Toronado / Cadillac transmission... that's the Th-425... which is basically a Th-400 internals into a configuration where-as there is no driveshaft between the engine and transmission. It's still longitudinally mounted like Spoon posted... it looks cool, but my personal opinion is that it kind of defeats what the purpose of the Fiero is.
There are plenty of ways to swap in an LS motor though. I think you could easily do a 4T65E (4 for 4-speed, T for transverse, E for electronically controlled, 65 is the series and is the heavy-duty version). It can handle pretty much any LS engine you throw at it.
Also, I wouldn't worry about the Fiero chassis. So long as it's not rusted, and it's solid... the Fiero chassis can more than handle a V8 power-plant. The Fiero tied for first place with the Volvo 240 for best front and rear crash tested vehicle... it got 5-Stars. The chassis has what is called a "steel space frame," which is rock solid, and way more rigid than a mono-style chassis with a subframe connected to it. You literally don't have to do anything to the chassis to reinforce it... particularly because all the torsional effects are mostly on the subframe... which is solid. You can reinforce it if you want, but the biggest thing will be welding in some good motor mounts.
My biggest concern with having an engine that massive (my opinion)... is getting something this light to properly adhere to the ground, AND be able to stop as well. The Fiero is not very heavy... 2,500-2,700 pounds depending on options and engine. I don't know what the all aluminum LS motors weight, but an assembled duke is about 500 pounds. I think the LS motor will weigh a little bit less ...?
You'd really want to put on significantly stronger brakes.
The factory brakes for an 84-87 are barely adequate for the V6 that came stock in that car. As a teen, I used to thrash my Fiero and the disc brakes would be glowing red hot by the time I got home. So you really, really need better brakes. You'll also want much better tires, and probably want to do something about the suspension.
Basically, all of this is to say the chassis is not your problem... it'll be about making sure the car is safe after adding that much low-end power to it.[This message has been edited by 82-T/A [At Work] (edited 08-21-2023).]
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cvxjet
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AUG 21, 02:00 PM
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I personally would start out with a medium engine- say 200 hp, and then work my way up...Too much power in a mid-engine chassis can be a bit of a problem. Fieros (And all mid-engine cars) have a situation called Drop-Throttle-Oversteer (DTO)....You enter a turn and realize you are too fast, so you cut the throttle and the tail comes around on you...Killed a lot of people in early 911 Porsche's.
I did some mods to my stabilizer bars to improve BOTH the turn-in and the DTO- here is a thread explaining what I did; https://www.fiero.nl/forum/Forum2/HTML/140674.html
Also, when you are jacking the FIERO up and working underneath you need to be very careful- We lost a very nice guy who'd just started working on his Fiero- Wife came home and found him crushed under the car....Always check to make sure your jack-stands are solid and the car stable- always use blocks on both ground wheels Front & Back of tires- and re-check after car is ON the jack-stands. Here is a diagram of where to jack and where to support the car;
 [This message has been edited by cvxjet (edited 08-21-2023).]
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BruhMans06
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AUG 21, 03:41 PM
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| quote | Originally posted by cvxjet:
I personally would start out with a medium engine- say 200 hp, and then work my way up...Too much power in a mid-engine chassis can be a bit of a problem. Fieros (And all mid-engine cars) have a situation called Drop-Throttle-Oversteer (DTO)....You enter a turn and realize you are too fast, so you cut the throttle and the tail comes around on you...Killed a lot of people in early 911 Porsche's.
I did some mods to my stabilizer bars to improve BOTH the turn-in and the DTO- here is a thread explaining what I did; https://www.fiero.nl/forum/Forum2/HTML/140674.html
Also, when you are jacking the FIERO up and working underneath you need to be very careful- We lost a very nice guy who'd just started working on his Fiero- Wife came home and found him crushed under the car....Always check to make sure your jack-stands are solid and the car stable- always use blocks on both ground wheels Front & Back of tires- and re-check after car is ON the jack-stands. Here is a diagram of where to jack and where to support the car;
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That's valid, I didn't think about the snap oversteer issue. I'm gonna throw a stock iron duke back in the car until I can afford to buy a new engine. I also won't be driving it hard with the LS until I fully trust my ability to drive the car. I'll probably baby the car for about a year or until I've passed the break in period. I doubt ill get 800hp anyway. I'm also planning on adding some rear aero and I'll keep the rear suspension softer (obviously stiffer than stock). I didn't realize this was an issue until you mentioned it to me so I thank you very much for that and I'll definitely take it into account on how I should build this
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BruhMans06
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AUG 21, 03:54 PM
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| quote | Originally posted by 82-T/A [At Work]:
If we're talking about the same Toronado / Cadillac transmission... that's the Th-425... which is basically a Th-400 internals into a configuration where-as there is no driveshaft between the engine and transmission. It's still longitudinally mounted like Spoon posted... it looks cool, but my personal opinion is that it kind of defeats what the purpose of the Fiero is.
There are plenty of ways to swap in an LS motor though. I think you could easily do a 4T65E (4 for 4-speed, T for transverse, E for electronically controlled, 65 is the series and is the heavy-duty version). It can handle pretty much any LS engine you throw at it.
Also, I wouldn't worry about the Fiero chassis. So long as it's not rusted, and it's solid... the Fiero chassis can more than handle a V8 power-plant. The Fiero tied for first place with the Volvo 240 for best front and rear crash tested vehicle... it got 5-Stars. The chassis has what is called a "steel space frame," which is rock solid, and way more rigid than a mono-style chassis with a subframe connected to it. You literally don't have to do anything to the chassis to reinforce it... particularly because all the torsional effects are mostly on the subframe... which is solid. You can reinforce it if you want, but the biggest thing will be welding in some good motor mounts.
My biggest concern with having an engine that massive (my opinion)... is getting something this light to properly adhere to the ground, AND be able to stop as well. The Fiero is not very heavy... 2,500-2,700 pounds depending on options and engine. I don't know what the all aluminum LS motors weight, but an assembled duke is about 500 pounds. I think the LS motor will weigh a little bit less ...?
You'd really want to put on significantly stronger brakes.
The factory brakes for an 84-87 are barely adequate for the V6 that came stock in that car. As a teen, I used to thrash my Fiero and the disc brakes would be glowing red hot by the time I got home. So you really, really need better brakes. You'll also want much better tires, and probably want to do something about the suspension.
Basically, all of this is to say the chassis is not your problem... it'll be about making sure the car is safe after adding that much low-end power to it.
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I will be upgrading the suspention and brakes so it can handle the power, i already noticed how absurdly small the discs were stock anyway. I'll probably barely even scratch 600 hp and probably will only make 500 as I'm still debating whether or not I want to supercharge it. I'll probably just start with a stage 2 cam and a stiffer valve train. I just want the car and trans to be as prepared as possible for any power so I don't accidentally **** something up. It's just me being stingy and overprepared for what ever happens. Thanks much for the input.
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