Regearing my Honda (1994 Del Sol VTEC)

[evolutionmovement]

I have an Excel sheet that calculates acceleration in g's and time and engine rpm that you can use to play with tire sizes and gearing. It could help give you an idea of what you'd be looking at with various ratios or a tire change and I can post it for you later on if you want. I have a whole list of project car ideas and a couple actual cars already plugged in, so it's a little cluttered, but should be pretty easy to make sense of. Checking it against real cars shows it to be fairly accurate, but for best results I also have a table that can generate acceleration numbers by calculating off power production every 500 rpm, but it requires a dyno chart.

[brucepick]

My '97 Civic HX does about 2300-2400 rpm at 60 mph. I wouldn't be surprised if one of those trannies would work out nicely in your Del Sol. If I seriously need more power I downshift. Duh.

I'm only a semi-mechanic at best, but from where I sit I recommend a tranny swap over a gear swap. You may be willing to spend the time but my guess is, when you get the tranny opened up and see what you need to do inside - and when you start learning about special purpose tools you may need to get the gears off their shafts and back on, and how to set up all kinds of adjustable tolerances - you'll wish you were swapping the whole tranny instead.

Definitely take care of the O2 sensor and any other needs first. In performance modding circles they call it "Stage 0". All the improvements come after you get the basics straightened out. I sure hope you've aired up your tires by now.

[Shortie771]

Yes i plan on taking care of the o2 sensor before i mess with anything that will actually cost me any money, as soon as i get my check im buying a new o2 sensor. Ok you guys have changed my mind about being difficult, i see now that a full transmition swap would be my best bet and would be a lot easier and probably better for my wallet. I think im gonna do the Integra LS swap... Of coarse that will be after i fix my o2 sensor and any other problems. So what do you think that will do to my FE?

[theunchosen]

Its a little hard to say. With mpg in the mid twenties I suspect there might be something else at play. The combined for the car is like 28? O2 sensor might be the only problem. . .but there is a big difference between 24 and 30(what I got before actually trying to drive conservatively at all).

If I were able to do the LS swap, I'm pretty sure that puts it at 2.5-2.6krpm at 60-61(my cruising speed) and I'm pretty sure I could squeeze at least up to 36 with an otherwise stock Del Sol(what size tires do you have?) and probably 38 on mine(up from 35).

[LeanBurninating]

is there some way to trouble shoot the MAP sensor.. assuming that the 02 sensor does not get his MPGs outta the hole?

[theunchosen]

Not really. . .the only way to do it is to plug in an advanced diagnostic unit that reads what the ECU is saying. So I don't know much about your scanguage or mpguino, but auto mechanics have them and they should be able to tell the throttle position(or what the map/maf thinks the throttle position is) and compare that to what it should be at idle.

Other than that. . . The only thing I know would be to watch how fast the cat gets hot. If its dumping fuel the cat will get hotter faster(as its burning alot more fuel).

The only other option is get access to the wires and connect a DMM to it and check the output voltage on the wires to see what it thinks it is and compare that to a chart for what the voltage ought to be at idle. . .

[Shortie771]

Originally Posted by theunchosen

Its a little hard to say. With mpg in the mid twenties I suspect there might be something else at play. The combined for the car is like 28? O2 sensor might be the only problem. . .but there is a big difference between 24 and 30(what I got before actually trying to drive conservatively at all).

If I were able to do the LS swap, I'm pretty sure that puts it at 2.5-2.6krpm at 60-61(my cruising speed) and I'm pretty sure I could squeeze at least up to 36 with an otherwise stock Del Sol(what size tires do you have?) and probably 38 on mine(up from 35).

I dont drive much at all so ive only logged one trip. I went 71 miles, mostly highway around 70mph with the bad o2 sensor, low psi, there was a headwind, and not many other cars on the road to block the wind. All bad factors and to make things worse i hadnt learned about any fuel efficient driving techniques yet (like P&G or even using cruise control) so needless to say i wasnt driving very conservativly. Replacing my o2 sensor is my top priority right now and ill have that done as soon as i get my check, which should be sometime this week i hope. BTW to answer your question is kind of complicated lol i bought this car used and have only replaced the front 2 tires, i just realized the rear tires are slightly smaller with a max psi of 40 instead of the front 2 which the max psi is 44... dont worry i plan to get new tires later on. Well since its a front wheel drive car ill tell you what my front tire size is. The sidewall says0 185/65R14 86H

[brucepick]

Aha.
Go to tirerack.com and look up the stock tire size for your '94 Del Sol VTEC.
Turns out it's 195/60-14.
You've got 185/65-14.

As it turns out, the 185/65/14's are nearly identical in circumference to the stock size, just a hair larger. And skinnier is good for mpg due to less squirming as it rolls. 185/65-14 is the standard size for most Civics so it's understandable that's the size you have.

Now go to my favorite tire size calculator, at
Tire Size Calculator
where you can compare the two sizes.

According to the calculator, when your speedometer says you're going 65, you're actually going 65.73 mph. That's because your slightly narrower (185) and slightly taller profile (65) net out to be just slightly larger in diameter and in circumference than the stock size. They don't put the overall diameter or circumference in the tire size. Dang.

So when you calculate mpg you can add the 1.011 percent increase. Give yourself credit where it's due. Not a big difference but if your mpg is 30 that would be corrected to about 30.337 mpg. And do remember that the cop's radar sees the real mph which will be nearly 1 more than what you read on your speedometer.

[theunchosen]

Yeah those are the exact same tire size that I have. And I think Tire rack is incorrect on the stock tire size. I've got a set of rims that came from the dealer with tires and they are 13s. Oops no my mistake. The vtec had slightly larger wheel tire combination.

I'm guessing its the O2 sensor tripping and the MAP being slightly off on its own. AFAIK the Del Sol ECU reads the two and if they are within tolerances it averages the readout for fuel consumption. So if your O2 is just reading lean and your map is reading normal it will dump slightly more than normal fuel.

Replacing the tires for different size is not too huge of a deal as long as you don't load the car down heavily(passenger and fill the trunk) as there is not alot of load on the rear tires anyway.

One thing you also want to watch the front left tire will deflate substantially quicker than any of the others which will cause it to wear much faster than the others. The weight bias on the front of the car leans to the driver side(driver and engine are focused on the left of the car). It's just something thats caught me on both of the Sols I maintenance.

I, at a safe and legal distance, trailer surf and it makes a big difference because the car is relatively small to start with. Slowing down to follow an acceptable. . .wave. . . is enormously beneficial, but becareful because on rainy days(especially with different size tires) it can push you around very easily.

[MadisonMPG]

Originally Posted by Shortie771

15-20mpg from swapping my trans? i dont think it will help that much, i was thinking it would give me about 3 more mpg maybe... lol but idk. BTW my friend who is the machanic doesnt think that swapping the 5th gear or even swapping the transmition is a good idea. He says it isnt worth it but since he himself has never done that for one of his cars he is unsure of the advantages/disadvantages it would have and is willing to help me when i figure out what im going to do.

24 plus said O2 malfunction= 38+5ish for trans = 43
19mpg improvement.