Like the title says, I'm plannying on putting a 4sp. in my si to help boost the fuel economy and I dont think 5+mpg is out of the question by doing so. I've done a million d series swaps but all have had 5sp and I was wondering if I use the 4sp. if the linkages from my 5sp. are all compatible and will work normal with the 4sp. trans. or if they will be any issue using it in my si...Leland

 

Strictly speaking from a mechanical sense the only problem you would have would depend on what year the two transmission are coming from.

1988 - 20 Spline, 180mm flywheel (from memory don't completely quote me on sizes)
1989 - 21 Spline, 190mm flywheel
1990-2000 - 21 spline, 210mm flywheel

Something like that, anyways so if you have matching year transmissions if not you might have to change up you're clutch and flywheel combination.

 

Yea im not worried about the clutch or flywheel issue in the 88, i'm hoping the trans isn't an 88 tho.lol, if it is I have a clutch and **** lined up already. So you think it'll drive like a normal 4sp. would in my 5sp. car? I thought so but wanted to make sure b4 I bout it.lol

 

Here's a chart, depending on how you drive you can figure out whats best for you.

 

so what do you think if i'm driving it like a normal person. I have a 500hp del sol and i'm not interested in racing my dd ef,lol. So i'm thinking it should get close to 50mpg. I know my buddy had an ef hatch w a 4sp. and it got 50mpg all day long.lol

 

i got about 35mpg in my bone stock STD with 4spd and 70hp d15b1. i think with mods i could have gotten a lot better. also i went with a dx 5spd eventually and it was a lot better for highway driving.

 

well my car has the si motor so its like 92hp I believe so I figured w that and the standard bolt on's it'll do pretty good. I guess we'll see.lol. Its gonna be weird driving a 4sp tho.lol

 

My opinion, either swap the final drive from the 4 speed into the si transmission or get a DX trans.

 

Get a HF tranny.

 

Very time consuming and not worth it, plus harder than just swapping the FD

Makes %100 more sense.

 

yeah i say get the hf!!!

five speed and looooooong gearsss

^_^

 

Seems like a waste of potentially fun si. Why not trade it for an HF? I am sure there is a bunch of people who would have wanted a trade like that.

 

for real..

just trade for a real HF

super light

weak *** engine

5spd

thats what you need


IMO

 

I dont "need" anything. This is a thread about a 4sp into a 5sp. car and not what you think I should do otherwise. I already have the 4sp and its not hard swapping it in there and wtf would I wanna tear anything apart like that? I know I could do it but it totally un-necessary. So if your not commenting on the 4sp swap then just move to another thread. Thank you.

 

u'd have to change ur knuckles cuz 4 speed axles are skinnier....it does work..my friend did the same thing u are

 

no you wouldn't, the inner hub on the axle is all the same, just the outter ends are different. OP, it would be like any other trans, although you'd be ending up with a really sucky, no acceleration 4spd tranny. if that's what you want then go for it. i personally don't like it, because it makes pulling out in traffic a bitch cuz the car doesn't take off like it would with a five speed (i have a std civic) but again it's up to you. pull out the si tranny, if you get a 4spd from an 89-91 you can just re use your clutch fly wheel etc. if its from an 88 you have to use the 21 spline stuff.

 

cool its a 90 and i'll see what hpns with it. I'm not worried bout the lack of power bc its going into a motor with 20+ more hp so we'll see w hpns. I'll do a write up on it for future reference.