apsolus

iTrader: (2)

i have an 89 vert na and boy do i love this car, other than the gear box, seems they are just to far apart. every upshift drops around 1 to 2k rpms and if i wanna stay in the power band that means i gotta up shift at over 5k rpms. getting old having to ring the thing out all the time. so i plan to do the miata gear swap into another na trans, 5th gear and all. i belive that with the shorter gears ill make even better fuel economy too.

so to go with the new gears i was thinking of when the motor is gonna need a rebuild ill do a large street port taking better advantage of the new gear ratios, what yall think?

and do you think the full racing beat exhaust is worth installing? i already have there cat delete pipe and presilencer. so any tips for improving this set up?

SDrotary-FC

Headers on a n/a should be your next mod and slap some 4.88 in the rear end that will wake it up

Dak

You could get a header to replace your cat delete pipe and exhaust manifold. Then the catback of your choice and come out cheaper than their full exhaust. Though their road race exhaust may make alittle more power I'm not sure how much.

I like the 4.3 rear in mine. Not sure how it would pair with the Miata ratios.

apsolus

iTrader: (2)

666 posts dak!!

apsolus

iTrader: (2)

dak, is your car even streetable? 0_o wired open vdi, no 6 ports and street port and full intake and exhaust? DAM

Dak

Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666. Revelation 13:18

"6 6 6 the number of the beast. Hell and fire was born to be released" Iron Maiden


To me it is. I don't have 500mi. on the motor yet so I haven't gotten above 4500rpm. Diveability is fine. Just don't let the revs fall below 3k and power is fine in 3rd. 2.5k in 2nd. I had them wired open before the rebuild so I completely removed them and the rods in the manifold when I put it back together. Never missed them really. Everybody always talks about it sucknig without them. I am begining to wonder if the 4.3 rear end is what has let me get away with it without the percieved ill effects. On my last motor(stock port ) I just shifted around 4 to 4.5k and power seemed fine.

As to intake and exhaust. Intake is the Bonez cone filter from Rotary Performance. Exhaust is a R.B. header/presilencer to the old HKS 50mm catback places used to sell in the 90's it was discontinued in the early 2000's I think. It's about done for so will eventually have to get another catback. Probably buy or make something using Racing Beat cans.

Dak

This Miata swap sounds interesting and I had heard of it before. I wonder if I wanted to do it if I could keep my .756 ratio 5th gear to keep the revs down on the highway? My 3rd gear syncros are about shot so transmission time is inevitable.

Tui

iTrader: (2)

A lot of threads on this subject. Cliffs notes I found:

If you have the downpipe and presilencer and running stock under the hood, performance wise you're there. Headers are noisy and don't contribute much more and the cat back is bling with a better exhaust note.

Put in a lighter flywheel when you pull the tranny.

Maybe try and find a LSD diff out of an S4 GXL. GTUs would be better, but much harder to find.

And if you're staying stock, finishing touch would be a SAFC.

jjwalker

This is the advice I always got. Funneling money toward an SAFC and Dyno time is way more productive than slapping headers on. Do that before you just try to bolt headers on.

apsolus

iTrader: (2)

thanks for the advice.
i do belive i have posi but only because when i spin the drive shaft by hand both tires move and in the same direction. i might be wrong but when i saw that i assumed it was posi, am i wrong?

another one of the main reasons i want to do the transmission mods so much, as opposed to the rear end swaps is for a few reasons, first of all my new short shifter is very loose and im sure its because the 300k transmission is just flat wore out. i know shifters can sometimes make noise but this one is also loose so im assuming the place the shifter rides has been worn out of round. also i have either a inputshaft bearing or throw out bearing going out, when the clutch is engaged i can hear a loud humming noise, might just be the thouw out but im not sure. and lastly i really feel this car needs the shorter gears, on the highway im heavy in the throttle trying to maintain 80 up hills if i was pulling closer to 4k at those speeds i doubt the engine would have trouble. so there you go, critic if you like. why the light flywheel? isnt that more off the bottom end? ive heard it helps your top end but does 5 pounds really make a diff?

i do plan to do a large street port in the future as well. another reason i feel the gear swap would be beneficial, keep it in the powerband. why would mazda put such spread out gears with such a low torque engine?? anyway, so would you recommend i do the full exhaust knowing im gonna street port? i do love the way the car sounds now its very low tone and deep, beautiful i love getting on it almost sounds like i got a turbo when im decellerating ! and 350z exhaust tips welded to the stock muffs so it looks nice out the back too, horrible under thou :p

apsolus

iTrader: (2)

and that fc tuner sounds like the way to go, im def gonna get one when i start trying to add power.

Evil Aviator

Iron what?

Dak

Maiden. You know 80's metal band who's mascot is in your Avatar. Probably too old for alot of these youngsters in here to have heard.

Dak

I didn't think the verts had LSD from the factory but that is one of the ways they say to check.

You could wait and do the exhaust when you street port if you like. I will say I had the stock muffs for awhile with the header and it didn't sound too good above 4k. Kinda like a kx85 or something. So get the catback with the header if you can. As others have mentioned on a stock port car you may not get much more from a header than with your current set up. Probably won't see the full benefit from exhaust until the street port and tuning fuel( which is my next goal. A way to tune fuel).

Supposedly the weight being close to the center of the the lightened flywheel vs. out toward the edge helps as well. So it is the combination of the 5lbs and being closer to center that helps. It does rev up faster( at least to 4.5k) than I remember it doing before.

apsolus

iTrader: (2)

ive got both the fc and miata trans in my possesion. does anyone know of what gaskets ill need? where is the easiers place to get them? i know ill need input and output seals but what else?

apsolus

iTrader: (2)

today i was able to get the miata trans apart and it all looks great in there! perfect gears everythings good. i just got the rebuild kit with new bearings blocking rings and seals off ebay and ill be installing the gears in my transmission soon! im going to use the miata fifth gear. anyone think i shouldnt? imho i belive if the motor is spinning more rpm it will have to work less at speed, thus actually improving fuel economy. im always going up and down hills so i think it would work for me. thoughts?

Dak

I think you would want to use the Miata 5th gear. I think 5th for all but the GTUs model was .697 so your revs would drop the same as they do now when you went to 5th. If you don't like how the revs drop from 4th to 5th or how it pulls in 5th usethe Miata one. Don't know how it will effect mileage but my 4.3 rear and .756 5th didn't get any worse mileage than others before my street port. I averaged about 20mpg but could get 23mpg highway only. Haven't checked since the rebuild.

apsolus

iTrader: (2)

cool, see thats exactly why i want to use miata fifth. cool, and wow 23 mpg thats insane! i havent done a mpg test sence before i found out i had no 6 port sleeves and it was only 15 combined. as far as ive read i have a 4.3 gear so i already got a great set of gears in the back. so my thinking is that if you keep the revs up on the highway it will increase mpg especially in hilly terrain because your not lugging the high rpm low torque wankel

Dak

Did the previous owner swap it in? It has always been my understanding that the 89 and 90 GTUs models were the only ones with the 4.3 rear end( other than the Infini model in Japan). All others had the 4.1 except the automatic which had a 3.9.

apsolus

iTrader: (2)

its 4.1 my bad. least thats what i remember reading

Tui

iTrader: (2)

all S4 Verts were also 3.9 stock