6 speed transmission swap

[nutritious]

Alright, I live in cali, and I'm not sure if everyone else in the country is effected by the rising gas costs, but its killing me. I commute long distances for work in my daily driven 5 speed SR swapped 89 240 and I can just see my fuel gauge draining when I hit 3500-4000 rpms while just cruising on the freeway.

So, I've been thinking about switching to a 6 speed with a crazy 6th gear that'll hopefully put me below 2k rpms at around 65 or so, anyone know of any suggestions? I doubt I'll be able to get away with this without some custom work done on the tranny, but there's always hoping for a cheaper alternative. =)

I'd really appreciate hearing back from anyone who has done this kind of mod to their car already.

[mr_240sx]

well if you plan on driving in 6th below 2 grand....... id hate to ruin it for you but youd be wasting more gas below too grand then at 3500-4000 because your motor would be lugging sooo bad and it would be boosting to try and get it to gain speed...

the 6 speed tranny would help if you kept the ratios the same and it might bring your rpms to about 2800 which then would help gas mileage a bit more..... but once again, if your worried about gas mileage, get rid of your sr/240 and get a jetta tdi.

[S14DB]

The VSS is the rub in that swap.

[jmauld]

You can also look into switching to a different final drive.

Also, changing your driving habits (I know it sucks) would be the cheapest way to save money on gas.

[Zemus]

Instead of a whole new trans, look into getting a diffrent final drive ratio. I know you can get brand new ones a Courtesy Nissan, or find another shortnose R200 R&P that works. Try like 3.4 or like a 3.7, Your acceleration will slightly suffer, but your revs will be lower at 65

[nutritious]

Obviously I don't want to pick out an rpm that makes the car lug, so lets take the next step, how about in the low 2k's? Could you elaborate on why I would want to keep the same ratio? Basically, I want to bring the car up to speed using the 5 gears, then when I hit the speed I want to cruise at, switch it over to 6th. I don't care about acceleration at this point, just want to keep a constant slight pressure on the gas so the car remains at whatever speed I have it at. If I need to accelerate, I know how to downshift =)

Ultimately, what I'd like to have is a 5 speed close ratio tranny with a 6th over drive gear. Has anyone tried switching out the final drive? Any numbers on what rpm you're at with respect to speed?

Heh, get a Jetta? I love my 240, bro... I have a little 100 hp civic hatch sitting around collecting dust because I love driving my 240 too much to use the civic as a commutor... is it so wrong to want to try and make my car more efficient? My friend has a corvette and tells me he gets around 30 mpg on the freeway, I didn't believe him until he showed me how low his rpms were in his 6th 'overdrive' gear, so now I want to do the same, if I can.

[RightWheelDrive]

The corvette has double overdrive which accounts for its gas mileage. You already have a overdrive gear, its called 5th gear. If you want better gas mileage, you should start driving at 65mph instead of at 3.5k-4k. There would be an increase in mpg right there and you wouldn't need to swap any parts. There wouldn't really be a practical solution to your problem except driving slower. If you have a civic commuter, just drive that. If you like driving the 240 more than having $3.50 for every gallon you use in your pocket, then drive away.

[nutritious]

At 65, I think I'm at 3.3k. The change from 4th to 5th gear in my car is a difference of around 400, not much of an overdrive. The other two mentioned swapping out the final drive gear, why don't you think that is practical? Is there any 6 speed trannies that mount up to an sr20det that does cruise at low rpms?

Gas is one thing, I would love getting more mpg from my car. But also, since its a DD, with all the miles I put on it, I'd like to keep the rpms lower when I'm on the freeway, save some wear and tear on the engine?

If there isn't a tranny out there for me, then its no big deal, so you guys don't have to give me additional tips on how to save gas or drive slower or drive a mpg friendly commuter. I was just coming on here to see if anyone else thought up what I am trying to do and did it or knows what to do if it is even possible to begin with.

[Pank]

My friend has a corvette and tells me he gets around 30 mpg on the freeway, I didn't believe him until he showed me how low his rpms were in his 6th 'overdrive' gear, so now I want to do the same, if I can.

The reason he can do that is because he has a huge displacement v8, that makes torque way lower than an SR. He's probably making at least 200lb/ft at 2k, which allows him to pull a car along. Your car is probably making 50lb/ft at 2k, and lugging an engine is the worst way to save gas. Also, i'm sure my numbers are off, but you get the point. Drive that Civic around, man!

[fliprayzin240sx]

Umm sorry to burst your bubble but the SR 6 speed and the 5 speed has the same final drive ratio so either way...you will use up the same amount of gas. Like stated before, your best bet is changing the ration in your diff.

[jmauld]

My friend has a corvette and tells me he gets around 30 mpg on the freeway, I didn't believe him until he showed me how low his rpms were in his 6th 'overdrive' gear, so now I want to do the same, if I can.


Yes, you can do the same!
http://www.hinsonsupercars.com/partsMainS14.htm :D

Seriously, your best bet, if you must change something will be your final drive ratio. Even then, there's no guarantee that just because you lower your cruise RPM that you'll use less gas.

[nutritious]

Damn, forgot about torque. So I guess realistically, to move the car at 65, you need to have your rpms closer to 3k than 2k. Alright, thanks for the input =)

[NemeGuero]

As AJ said... VSS is on Diff on S15...
Search.. 'cuz this has been covered before.

[TheTimanator]

seriously though....how bad is your gas mileage? I got 25 mpg (before I switched to an atmospheric bov, which I'm gonna fix soon) I bet I could have gotten better mileage if I had it tuned cuz I was still running rich. I mean, if your really that concerned about gas mileage you'd drive your civic. Plus your just putting more wear and tear on your 240...

[S14DB]

As AJ said... VSS is on Diff on S15...
Search.. 'cuz this has been covered before.
actually there is no VSS. The ABS computer has a speed output to the ECU.

[NemeGuero]

All the more reason he should search.. HAHA 'cuz I mis-inform!! w000t

You were the one who said something about the VSS... so I went off that.. and I remember something about the diff sensor...

but the memory is shady..

So... SEARCH.

[Siberian Husky]

driving habit changes and tune ups would better benefit you than an extra gear...i agree on ridding of your sr if gas effects you so much..
i have an RB and gas is somewhat inconvenient seeing as how its my daily and i drive a good 60 miles a day everyday if not more..but i feel i dont have room to complain because it was my decision to go 6cly boost

[fliprayzin240sx]

You think ur gas mileage suck...im lucky to see over 200 miles on a full tank of gas city driving. That narrows it to roughly 16 mpg.

[NemeGuero]

750cc injectors will do that to you, Ray.

[EchoOfSilence]

jeez that's almost a whole liter a minute @ full duty

[NemeGuero]

And he's still slow.. ;)

[fliprayzin240sx]

750cc injectors will do that to you, Ray.\

740 fooker...740...get your numbers right!!! i shouldnt have pointed out that boost leak and help you out....would have been funny watching you figure out why your cars running like poop. :fart:

Yah cars so slow evan...thats why i had to wait for you catch up and lower my boost to 7 psi.:smash:

[NemeGuero]

You had to wait 'cuz of the guy in front of me!! HAHA
I was riding your bootay after that. ;) 740.. I apologize.
<3

[PoorMans180SX]

Spend the big bucks on an S15 6-speed swap? seems like an even split between gas costs/6-speed. I would change my diff first. Seems the most cost effective.

[mrmephistopheles]

you'd be better off getting a lower-geared final drive.

[HKsilvia]

theres no way for 65 below 2k, the actual rpm is 2.5k 65 mph for S15 6 speed transmittion

[cookie]

thats about correct for the s15 6 speed (i know i have one)

Also the 5speed and 6speed have no gear ratios the same.

So whats your fuel price like per litre, here is $1.88 per litre , i spend about $120 per week on fuel (normal commute , 450 miles per week)

[eds13]

is the final gear ratio on the HKS 6-speed any different?

[jetblackskye]

http://www.raceonusa.com/index.asp?PageAction=VIEWPROD&ProdID=1939

lol, I dunno but that doesnt look too cost effective, for $12000 I think they would let you choose the gear ratios.

How easy is it to bolt a S15 tranny onto a S13 redtop?
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[jdmbrian]

if you got a walbro fuel pump... believe me its that. i have a stock sr20 fuel pump on a stock blacktop. and my friend has a walbro fuel pump on stock bacltop and he wastes much more gas then i do. bigger fuel pump = to increased fuel delivery = to increased fuel pressure.

thats the only reasonable explanation i could come up with for the amount of fuel being wasted my friends walbro equipped car vs. my stock fuel pump car.

[S14DB]

http://www.raceonusa.com/index.asp?PageAction=VIEWPROD&ProdID=1939

lol, I dunno but that doesnt look too cost effective, for $12000 I think they would let you choose the gear ratios.

How easy is it to bolt a S15 tranny onto a S13 redtop?
HKS is not a good solution for the US. Especially at that rip off price. HKS started making tranys cause it was so ridiculous to import Hollinger trannys from Australia. It came out to about 2x the price. You should be able to get a full custom tranny from Hollinger for less than $5k.

S15/14/13 all have the same bellhousing.
if you got a walbro fuel pump... believe me its that. i have a stock sr20 fuel pump on a stock blacktop. and my friend has a walbro fuel pump on stock bacltop and he wastes much more gas then i do. bigger fuel pump = to increased fuel delivery = to increased fuel pressure.

thats the only reasonable explanation i could come up with for the amount of fuel being wasted my friends walbro equipped car vs. my stock fuel pump car.
Upgrade the FPR.

[cookie]

s15 box will bolt to any RWD sr20de*.

You will need the flywheel(dual mass),gearbox and starter bolts and propshaft.
Also a custom speedo sender from the diff.

And sounds like a knacked FPR to the walbro question

[bmwjdmking]

what is the advantage of a 6 speed?

[S14DB]

what is the advantage of a 6 speed?
Keeps you in the powerband of the motor.

[HKsilvia]

and it does save some gas, imagine u are going 65 on 2.5k and 80 on 3k rpm, then hitting speed cut at 4.5k 6th gear (dammit...)
But think about it, if u want to save some money on gas y wasting big bucks on swapping 6 speed tranny? the money u waste will take 4ever for u to fill up with the gas u saved.

[S14DB]

and it does save some gas, imagine u are going 65 on 2.5k and 80 on 3k rpm, then hitting speed cut at 4.5k 6th gear (dammit...)
But think about it, if u want to save some money on gas y wasting big bucks on swapping 6 speed tranny? the money u waste will take 4ever for u to fill up with the gas u saved.
Wait, What's the 5th gear ratio in the 5 speed and the 6th gear ratio in the 6 speed?
5 speed
Gear Ratios - Manual Transmission
1st 3.321
2nd 1.902
3rd 1.308
4th 1.000
5th 0.759
Reverse 3.382
Final 4.083


6 speed
Gear Ratios
Manual Transmission
1st 3.626
2nd 2.200
3rd 1.541
4th 1.213
5th 1.000
6th 0.767
Reverse 3.437
Final 3.692

[HKsilvia]

i dunno really know about the ration stuff, but judging on the way the car behave, i feel like the 4-5 gear of 5-speed turns into the 4-5-6 gear of 6-speed. and it runs really smooth. :)

[kenversusryu]

I experimented a while back.. cuz i thought i was running lean past 3k.

I shifted at 2.8 rpm at first gear and every gear after that i shifted at 2.5. Basically i kept it between 2.0 and 2.5 through the last four gears. no rabbit starts. In the highway I went a painstakingly slow 65.. which was around 3k. (couldn't really go faster than 65 anyway cuz my steering wheel would start to shake due to wheel imbalance). I never opened my windows in the freeway, no a/c and kept the vent temperature at medium to keep the engine somewhat cooler (probably didn't help anyway but didn't hurt to experiment)

Point was i got 30 miles to the gallon. About 1/4 city 3/4 freeway. Usually i get about 23 miles to the gallon driving moderately with the same amount of city/freeway driving. no joke... try it for a gas tank. Way cheaper than getting another gear.

[4thHorse]

Well for the price of the 6 speed you could get yourself a beater honda or toyota.

[surge s14]

there are vg30 trannys hub convertions to bolt on the sr but expensive