bheinen74

Okay, lengthy thread and tell me if there is another thread to research.
I have had over 5 1991 Si Hondas, 2 91 CRX Si, and 3 91 Si hatch, and a 91 SiR RHD.
I know I get in stock form , 38.5-39mpg avg per tank on the stock everything.
I had a 1991 CRX Si stock, drove it from 99k in 1993 til 226k in 2002, it got 39mpg per tank. I then sold it due to rust, and bought a 91 Si hatch, with 65k on it, and only stored it, but did drive it about 3k miles and it got 39mpg. I also got another 91 Si hatch and it had 100k on it and burned oil and it got about 35mpg so I sold it. I had a 91 EF9 Sir RHD hatch b16A1 with Y1 lsd, it got about 40 mpg on US pump gas.
I have a 1991 CRX Si with 39k on it, geting 40mpg. and have a 91 Si hatch with 90 k getting 38 mpg.

Now to the question. Who has swapped to a HF trans for real, and report the mpg benefit. What mpg ddi it go to after HF trans swap.

PS> I also tried a 2011 CR-Z Hybrid, and only got about 42mpg liftetime. Not much better than a CRX Si.

Again all my current Honda's are stock and less than 90k Original miles. Can i expect any better with the HF trans? All stock down to the tire size......which most don't even run now, i am old school.....

JMZ400

I have been driving a CRX Si since 1991 and have never gotten the mpg's you are. I just finished swapping in the D15z1 (civic vx) engine and tranny and have gotten 37.3 onfirst two tanks with o2 sensor disconnected (bad one).

The VX tranny is close to the HF and what I can tell you is it's great to be at 2500rpm at 75mph... very quiet compared to 3900-4000 rpm with Si tranny.

JMZ400

Oh I am running 195/50/15 on a 15x7 wheel. I wouldn't go HF unless you just need the MPG's you're doing great as it is. Plus you still have get up and go. Nice to meet you fellow old school'er:-)

bheinen74

forgot to add, i had a 94VX and that stupid pos with 90k on it only got 41mpg IF lucky and was a dog, and no AC no Sunroof, rolled like heck in the corners....no huggin seats, no power, no sunroof, it really sucked to a Si 91 etc.. the VX avg less than my Si's all around and it was in tip top shape. I went back to the EF and Si after the VX try.

also tried a 91 Si prelude once, but it burned oil too lol......and only about 31mpg highway which was less than my 96 Tl 2.5 I had.......


the 91si hatch, now am running 96 HX 14" wheels lightest they made on 185.60R14
I want a little better in the 91 Si's, than stock, maybe a vX trans or HF so let me know what you guys do....no motor swaps needed in a less than 300k car....once the 300k mark is met, then yeah swap possible, only B16A1

also still on stock exhaust for the look and quiet....i am 38 now and dont' want attention.

bheinen74

gotta bump my own thread.
my DD for summer is a 91 CRX Si, and I just picked up a 89 CRX Hf at the beginning of the week for the TRANS (parting out the HF in another thread)
So, my 89 HF has the correct splines on the output shaft, so I should be able to drop out my original Si trans and put in the HF trans soon. Going for MPG. If I don't like the other gears, then I will have to do the hybrid 5th gear for overdrive speeds only.

Keep ya posted.
my daily drive in about 34 miles roundtrip for work, mostly flat and mostly at speeds of 60mph….i have been logging the MPG with the stock Si trans for several years. Wonder what I can expect with the HF trans….will be finding out soon. Oh, and I am not 38 anymore lol.

doner car is 89 HF with 152k
car going into 91 Si with 155k

Riceburner247

iTrader: (1)

I have an 89 si all stock, been wondering about this exact situation. At 3000rpm I'm barely doing 60mph. I feel bad revving the engine any more than that for long periods of time, haha. I'd be more interested in swapping an HF 5th gear into my stock si trans if possible. Close ratio 1-4, then tall 5th for highway cruising.

bheinen74

I just hate the thought of "ruining" (hybrid) 2 perfect transmissions to get the 5th gear I am looking for. I guess I Will see how the HF trans does in a higher revving higher hp SI strictly for the best MPS.

Aquafina

iTrader: (3)

Unless you have the HF engine and ECU, your fuel economy will drop going from x trans to an HF. Lower RPM does not equal better fuel economy.

bheinen74

I don't see how that is possible, I drive 99.9% open highway at 55-60mph
in driving of 17.6 miles to work, I am shifting 1st-3rd 4 total times to drive that 17 miles, once out my drive, once to get on the road, and once at a stop sign. I am in 5th gear for 19 of the 20 minutes.
this is why i am not splitting cases yet, going to giver her a go leaving trans intact/

i can guess the performance sluggisheness change will be similar to just starting movement in 2nd, then shifting to 4th skipping 1sty and 3rd in a normal Si geared car… The Si starts out fine in 2nd for most spots
maybe the HF 5th is more for speeds higher than i travel….But I just can't see why dropping the 60mph RPMS down 1,000 RPM won't benefit my overall mileage, - unless it really just is too low of RPMS for the best torque spot in the motor.

baller status

I also dispute your numbers. I have had two stock 1992 Civic VX's and the highest I ever achieved was 41 IIRC. The average was 38, and that was at high elevation on a work route with few stops and little traffic (no freeway). I have a 1988 CRX Si. I don't drive it very consistently but it gets around 33. One tank might be 35 but then the next will be 28. You have to take a long average to get real numbers. I've had a lot of Civics and Acuras and they all landed right around the 33mpg mark which is good. I think you aren't calculating your mpg correctly. You also need to double check your numbers by keeping track of how much gas you buy and how often.

There are two HF trannies: a CA and a federal. The federal version's final gear may be too long for anything other than long flat road trips. Short gearing is better for city driving with lots of hills, traffic, and stops. Long gearing is good for freeway cruising.

Aquafina

iTrader: (3)

Higher RPM = less throttle needed to maintain speed. I have a DX 4.058 FD and MFactory 1.000 5th gear, 80mph = 4,850 RPM and I get 47mpg. In an ITR switching from the stock 4.4 FD to a 4.928 with no other changes causes the car to consume 14% less fuel at 75mph.

I've run nearly every D series gearing combo possible on multiple engines. Unless you have an ECU and engine designed around long gearing, you will get worse fuel economy by using longer gearing.

bheinen74

so thinking about this swap to HF trans again maybe this spring when i pull the car from winter storage.
Is my 89 HF trans going to accept the stock 91 CRX Si axles? Will the seals on the trans be the right one for Si axles if they accept them?
Anything about the speedo that will not be right with this?
On my clutch, I would probably only think about a new clutch disc. What clutch disc do I need to buy, assume just the one for the 91 Si flywheel and pressure plate….

Again, I think I will go this swap soon, the 91 CRX Si is probably due for T-belt change too (don't have records of the car, and it now has about 158k on it), so will do the T-belt, valve adjust, plugs, and mate the HF trans with a new clutch disc all in one weekend, goignt to ask for a day or 2 vacation at work to get this done.

already have a gates t-belt sitting in my parts bin for the last 2 years so it isn't getting any fresher sitting there, also have the mizumoto valve cover gasket and grommtis sitting there too

would like to get my parts needed on order. Not going to do the water pump, as I assume it was done probably at the 70k mark but will inspect it all. Heck maybe I pull the cover and will see a newer belt and scrap that idea of new t belt, just I ahve t and its cake to put on

Tyson

Tranny seals are the same. That's not the side that is different.

One could simply just swap out the 5th gear if you want lower rpm at highway speeds only.

But I'm inclined to believe that lower rpm does not always mean lower MPG. Seems too simple of a relationship for something more complex than simply rpm.

24TEN

iTrader: (2)

You're forgetting about how much power you're making at a given RPM. Think about a power/torque curve, and look what happens when you compare say 4000rpms to 2200rpms. Your car needs "X" amount of power to maintain a constant speed and if at that RPM it isn't generating it, what do you do? You push the gas pedal a little harder.

Just to make it it clear I've done it. I've converted my 94CX to 16 valve, different reasons but same end result. Original engine was an 8valve just like an HF and the transmission is pretty close to the same thing. After the conversion I dropped by nearly 5mpg. What it felt like was the gearing was dropping out of the powerband with every shift and with the lower cruising RPM I was completely out of the powerband.

bheinen74

kinda figure on the roads of 55mph speed limit, stay in 4th gear, but on the interstate at 70mph go to 5th then….
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