Bubbajones_ya

I have an RS 1991 TBI 305 camaro. I pretty much purchased it to take over my trucks duty of daily driving so I could get some better mileage, but still drive something I like. (Also I like having projects and this was a major one)


My goal is to have about 24-27 average mpg with about 75% highway driving, and around 250hp (or more! but mpg is my main concern)


I've done almost a full restoration (cosmetically) and some mechanical work to it where I'm getting pretty decent MPG numbers (19-20mpg mainly highway), but I know people get better.

[[Side note, the PO had the transmission changed (old V8 T5 must have died) and I found out it's now a T5 for a V6 (NWC), would this lower my MPG numbers compared to the V8 due to different gear ratios? I want to swap a T56 in eventually, but the complete package to swap is too hard to find around here currently.]]

The work I've done to it so far mechanically is:

- Open element air cleaner
- TBI spacer and TBI rebuild kit (cleaned it out and put new gaskets in)
- Hooker 2055 headers/y-pipe, 3" cat and exhaust
- new distributor, dist cap/rotor, wires/plugs, O2 sensor (original not heated)
- changed vacuum lines to get rid of any leaks


My questions are, what should I do next that will give my engine more efficiency? I would love to do stuff to get more power, but am aiming more towards a more efficient engine. I see that 24-27mpg should be attainable with mostly highway driving with my engine, so I want to get those numbers.

Is there a better camshaft choice than the stock for MPG (that may also give more power)?

Would changing stock rocker arms to something else help at all?

Should I get a different intake manifold (edelbrock or something especially now that I have better exhaust)?

Should I get different heads? (I've read the stock swirl ports are the way to go for MPG concerns, despite having pretty poor flow numbers.)

Would learning how to tune my car help with the current mods I have done (exhaust and air filter), or should I wait until more dramatic mods such as cylinder heads/camshaft? Or, is there an easy way out and a good not to expensive chip I should buy with my current setup?

Any other advice?




I know I'm asking a bunch of questions, it just seems as if these are the most relevant. I've searched but have not seemed to find out what may help when it comes to MPG. I know that the cost of some of the mods will take a long time to pay off (or maybe never in reality), but that's surprisingly okay with me. It's more about the convenience of not filling up as much at the station while getting more efficiency/power out of the engine. Plus, I have to spend my tax return money responsibly somehow so why not on my car!?


Thank you for your input and sorry about such a long post!

RS-Chevy-SS

Engine code L30 is the answer to your questions.

Bubbajones_ya

Thank you for the response!

I just did some quick searching about the L30. I was kinda hoping to prevent an engine swap for the time being because I don't have a hoist, nor have done an engine swap before (I know I'm capable though.)

I think finding the engine may be a little hard around here, and then I don't know what I would need to make it compatible with my current setup. It's definitely something I will keep in mind though. If it bolts directly up and I can use exhaust/wiring and everything else, then I may consider it very soon. Otherwise I may wait further down the road for an engine swap.

RS-Chevy-SS

Speaking from first hand experience, I think I documented everything required for the swap in my thread below. L30 is great

https://www.thirdgen.org/forums/tbi/...rtec-swap.html

Bubbajones_ya

You've done a whole bunch of excellent work in that thread. I didn't read through much, but I skimmed through a lot.

As of now, that seems like a much bigger undertaking than I am comfortable with doing. I use my car as a daily driver now, so I would like to be able to complete the work within a weekend for whatever I do to make it more efficient.

I may eventually go for an L30 because it seems like a great idea, just more work during the school semester than I would like to do.

I probably would rather save to get a T56 first, then an engine like yours, but I'll have to see.

Night rider327

iTrader: (13)

Open element air cleaner is not the best thing. Look into making a true sealed and ducted cold air intake system.

The open filter under hood is just pulling hot air into the engine.

I think a set of 305 HO heads would help you out.

Bubbajones_ya

Yeah I thought about the open element with hot air, but I think it's better than the stock. I may look into building something to have a cold air intake, but I am also pretty vain and want the engine bay to look nice too!

As for the heads, are 305 HO heads vortec heads? Would I be able to take some vortec heads (say from a 4th gen camaro) and bolt them up to my stock setup? Are there any aftermarket heads you would suggest that jegs or summit sells that I should be looking for? I wouldn't necessarily want to go with brand new heads as that could be easily around 1000, but if they will make a big difference in efficiency (and in turn mpg), I'm good to do that. (even know if will take a LONG time to pay back)

Fast355

iTrader: (2)

The stock swirl port heads are by far the best for MPG. Your best bet is getting a set of cleaned and flow matched injectors. I have seen as much as 10% variance reported in injectors. If you consider that ran as being +/- 5% from nominal that could be a substantial air/fuel ratio difference between cylinders. You only have one 02 sensor and the fueling for both banks and injectors is averaged by the 02 sensor. Flow matched injectors result in a smoother, more efficient running engine.

Bubbajones_ya

Okay I'll definitely look into the injectors. That seems like that should be a pretty simple and fairly inexpensive (compared to buying a camshaft or something.)

Are there any brands I should get for injectors or should I just search around? I suppose I'll do some researching about them too now that you informed me about them.

Another question, while I have the old injectors out, should I put injector pod spacers in place? I hear it is worthwhile, but I haven't really heard why or how. I suppose it is probably cheap enough to do though.

Boxxx

Since it hasn't been mentioned yet how you drive can have as big of an effect as anything else. Shift at 2,000-2,500 and go into 5th as soon as possible, cycle the A/C on and off as needed. Another thing is to make sure the car is in proper alignment and tires are properly inflated, brakes aren't dragging, etc... The TBI 305 5-speed was originally rated at 17 city and 26 highway, and has a revised rating of 15 city and 24 highway so anywhere in between would be considered good. Easy enough to check, but make sure someone hasn't put in a higher final ratio as that'd make a noticeable difference. Seems like you've pretty much covered most of it by doing a tune-up and making the exhaust more free flowing. Some legal eco tips you can do is to slightly increase the tire pressure as it reduces rolling resistance, try to use highways that are at 55 instead of interstates at 70, and restrain yourself from flooring it. Most places it's technically illegal to coast in neutral, but that helps as well. That and come to red lights slowly and most times you can catch the light. Lots of small things that add up, of course most would tell you to get something more fuel efficient but I understand wanting to drive something you enjoy. I wouldn't mind a 305 TBI 5-speed myself to use for a decently efficient daily.

Boxxx

Almost forgot, another thing is make sure the oil in the gearbox and differential is good. That and make sure the timing is right, etc... An intake should help a little and would compliment the exhaust work you've done. Some cams you can get are setup for economy, I'd give Comp and others a look.

Bubbajones_ya

Thanks for all the tips! Yeah I got pretty good at driving carefully since my other vehicle is a 96 bronco with a small lift an 33" tires. I manage to squeeze 14-16mpg out of it with the way I drive, which isn't too bad for the least aerodynamic vehicle out there (well close at least.)

I don't drive as carefully as I could, but I still drive pretty conservatively and am averaging around 20mpg (19.5mpg to 20.5mpg) now which is pretty nice. I do want to bump this up though to get closer to 25, which I have read a lot of people seem to obtain (with mainly highway driving which is about 75% of what I do.)

I will look into better intakes if that may help (plus my old one looks super dirty and run down and my engine could use a nicer shiny part in there.)

Would different type of rocker arms help any if I keep the same heads?

I will also give comp cams a call and see what they say. If I can install a new camshaft and it increase economy while boosting or keeping the same power, I'd be pretty happy.

I know that lots of performance mods have the potential to use more gas, therefore getting worse mileage, but also can also run more efficiently, therefore getting better mpg if driven correctly.

Boxxx

Based on the renewed rating 22 mpg would be about 75% highway and 24 mpg based on the original rating with 75% highway. Mainly the difference in renewed testing is the modern interstate speeds and A/C running time. The economy cams are generally very similar to stock, just fine-tuned for a mild increase in efficiency and torque. In addition to everything I posted it wouldn't hurt to do a compression check to make sure the valves and pistons rings are good as well. Also make sure you're running temperature is in the 190-200º range as running cold hurts economy among other things. You can figure out what final ratio you have by the rpm's in a given gear and speed, usually 55 or 70 in 5th is easiest way to get a more accurate read on rpm's. It's quite common for people to change out the rear gears in order to shift things more towards performance and away from economy. If you could end up in the 22-24 mpg ballpark I'd say you'd be doing well.

Bubbajones_ya

Alright, I believe my gearing is stock for the camaro (2.73 for 91rs 305?) but I will try and check what it may be. I'm around 2300rpm at 70mph, so I'll see if there is a website to calculate the gearing based on that. I know I have a V6 T5 which has a taller 5th gear (around .74 compared to .63ish for V8 T5. I just don't know which V6 T5 I have and the gearing is slightly different between years), so I think swapping in a V8 T5 may help with mileage on the highway if I can get the one I'm looking at.

I've been looking at a T56 swap too, but after doing more research, it may not be a good idea if I plan on keeping the 305 for a while (which I do because swapping in a different engine seems like it may take too much time.)

My A/C is not functional yet, but I plan on repairing it this weekend after I get my tax return money. Too bad it will lower the MPG, so I'm hoping I can get it above 20 with A/C.

A compression check would be a good idea too, so I'll try to get that done soon. My care runs around 200 degrees on the highway also so I should have the stock thermostat in there.

Thank again for all the info! I'll be excited to squeeze some more MPG and maybe HP out of my engine with my tax return money. Maybe I'll look into the flash EBL thing too. I just don't know much about tuning and don't have a whole bunch of time to learn during school.

Boxxx

Provided you have the original wheel diameter/tire size it sounds like you have a 3.23-3.42 in it now. From what it says here it'd originally have a 3.08 with the manual transmission, which if the speedo gear wasn't changed your speedometer will be off. Quick way to check that is with one of those free GPS speedometer apps for your phone. Though from the sounds of it the speedo gear was changed and you do have a 3.42-3.73, that's also provided the wheel diameter is correct mind you.

At 70 mph with a .76 trans ratio and 25.6" wheel diameter, 2,255 rpm with a 3.23 final ratio and 2,388 rpm with a 3.42 final ratio. 2,150 rpm with the stock 3.08 final ratio.

At 70 mph with a .62 trans ratio and 25.6" wheel diameter, 1,694 rpm with a 3.08 final ratio.

From what I found online the V6 has a .76 5th gear and the V8 a .62 5th gear.

Boxxx

More or less that'd account for the missing 1-2 mpg. The thing to take into consideration though is how long it'll take for what you spend to be returned to you via fuel savings. Also if I'm correct with your gearing situation, the acceleration will suffer some. So you have to decide if it's worth chasing the extra 1-2 mpg. Of course changing the rear gears and speedometer gear won't cost too much, but things like the cam and intake can get up there. The 5th gear shouldn't cost much to replace, it's just a matter of doing it and knowing how to do it. Manual transmissions are like clockwork, literally, so you have to know what you're doing in there. It'd be easier to find a V8 T5 and throw that in, but yet again is it really worth it? If you're needing a new clutch anyway, then from a labour standpoint yes. Financially though, ehhh maybe. Which if the clutch is slipping any that reduces efficiency too. Honestly I'd look out for a used intake on eBay to save money, no point in buying new on a non-wear item that may only need some cleaning at worse.

Another thing I found is the V6 T5 has a numerically higher 1-3, especially 1st(4.03 vs 2.95) and tapers until 4th which is even.

Bubbajones_ya

Thank alot for all the info! I just checked my tire size, its 225:55:16 in the rear so I think that's close to normal.

I installed a digital instrument cluster from intellitronix, calibrated it with pulses per mile, and verified it with a GPS from a CD player thing I put in (and my phone gps).

I tried finding some online gear ratio calculators but didn't come up with too much except one thing on these forums. It seems like I'm getting numbers close to what you were saying, so I think my rear end is about 3.42.

I recently had some work done to my transmission because the input shaft was damaged due to whoever installed before I purchased the car didn't bolt it up all the way. The flywheel needed to be resurfaced badly(and I didn't have money to at the time) and the clutch was okay. I'm not getting any slipping, but I'm getting pretty bad clutch chatter, so I want to get a new clutch set and resurface the flywheel soon.

I may decide to go with the 85 V8 T5 if I can get around 1-2mpg more with that highway. I won't like losing initial power, but I honestly can't effectively use first gear the way it is so I'll like something a little more usable.


I'll look into some used intake also. I plan on staying TBI and keeping EGR and stuff, but they probably make some good aftermarket ones with these options I would think.


Edit: Well it looks as if the T5 I was going to buy is actually a V6 one... I did find a V8 T5 but its an 84 so the 5th gear ratio is most likely .73 and not the .63 which I wanted. However, I think my current V6 trans has .78 now according to this website: http://www.f-body.org/gears/ . Either that or .76, so .73 overdrive is a LITTLE bit better but I don't know if it's worth it unless I change the overdrive gear.... I checked my gear ratio and it seems as if I have 3.23 rears. When I turned the tire twice around(one wheel off the ground, one on) it was a little under 3 1/4 turns of the driveshaft, so I think that's 3.23.

Boxxx

Stock tire diameter varied from 25.65" to 26.18" and yours is right in the middle. I would just hold out for the later V8 T5 as it'd better suit your car, naturally, along with the better overdrive. Being 3.23 I really wouldn't worry about changing it then. Newer cars don't have EGR anymore if that says anything, all it does is reduce NOx emissions and gunk up the intake. I know on OBDI cars it's just a matter of splicing the EGR temp sensor wiring to defeat the code, OBD0 I'd imagine the same would work.

Bubbajones_ya

I haven't been able to find a V8 T5 transmission and have decided to spend my money elsewhere for the meantime.

I purchased Bobr's EBL flash system instead. I've read so much about tuning being very important to these cars, so I figured this system will help me get better performance out of what I have now.

I don't know how big a difference a tune would do after an open air filter and 3" exhaust with a high flow cat, but I'm sure it can't hurt. I plan on doing more mods in the future so a tuning system that allows me to tune whenever with my laptop should be very helpful. Besides, I heard a tune on a stock setup still can make a decent impact on performance, so hopefully I can get something good out of this.

Apparently there is a lean cruise mode with the EBL system also that I believe should help highway mileage quite a bit (if tuned properly.)

I just have to learn how to tune now... I don't really know much about what the parameters mean and what to look for, so this will be a pretty big learning process. There are a whole bunch of threads on tuning, but lots of the information is not well organized and jumbled up in conversation making it too hard for a knewb like me to understand what they are talking about.

I'll learn eventually though. I just have to make sure it doesn't get in the way of my schooling!

seanof30306

iTrader: (4)

My L03 T5 came from the factory with a 3.08 gear. I'm pretty sure that was the standard gear ratio for T5s in these cars.

There's a very simple way to determine what gearing you have.

First, consider what that gear ratio means. My car had a gear ratio of 3.08:1. That means for every 3.08 rotations of the pinion gear, the ring gear will rotate once.

The pinion gear is attached directly to the driveshaft; it rotates right along with the pinion. The ring gear, the axles, and the rear wheels and tires are also directly attached to each other; they rotate in unison, too.

Put your car up on jackstands. Make a mark on one of the rear tires. Make a mark on the driveshaft. Put it in neutral, and have someone slowly rotate the wheel exactly 1 revolution while you lay under the car and count the turns of the driveshaft.

2.73 gears = right at 2 3/4 driveshaft revolutions.

3.08 gears = a nudge over 3 driveshaft revolutions

5.13 gears = between 5, and 5 1/4 revolutions, etc.

Works when the rear end is out of the car, too. Turn the axle one revolution, and count the number of revolutions of the yoke.

Also, when you're considering mods for gas mileage, consider the cost you have to recoup. Does it make sense to spend 500 bucks to pick up 3 mpg? That's for you to decide, but once you calculate how long it takes to recoup that 500 bucks in mpg savings, you might reconsider.

The average American drives 12,000 miles per year. Let's say that's what you drive, and your car averages 18 mpg. 12,000 /18 = means you use 667 gallons of gas per year. At 3.00 per gallon, your yearly fuel cost is 2,001.00.

So, you spend 500 bucks to get 3 more mpg; you go from 18 to 21mpg. 12,000 miles / 21 mpg = means you used 571 gallons of gas. That's 96 gallons less per year. At 3 bucks a gallon, you save 288 bucks per year, so it takes you nearly two years just to recoup that 500 bucks you spent.

Now, if you drive your car 20,000 miles a year, or gas goes back up to 4 bucks a gallon, that makes a difference, but for the average person, some caution and forethought on mods for mpg would be indicated.

Besides, the L03 is already designed for mileage. Before you start making mods, just make sure it's running properly, and focus on driving technique.

I'm probably gonna get flamed for this, but as much as I think open elements are bad for performance, yours might actually help with mpg. If you spend any time on mpg forums, you learn hypermilers look for warm air induction, not cold air. According to them, cold air makes power, warm air makes mpg.

The last time I drove my car from Atlanta to Tulsa, I got 26.4 mpg, and I ran between 70, and 80 mph all the way ... and that's with 3.42 gears!

My mileage in town actually went up when I went from 3.08s to 3.42s (when I could keep my foot out of it), and my highway mpg didn't go down at all. It's all about torque, and gearing the car to keep it in the most efficient part of the torque curve.

The L03 makes excellent low end torque. I always get a kick in parking garages by leaving the car in 1st gear, leaving my foot completely off the gas, and letting it climb the ramps.

When driving for mpg, you want to put that torque for work for you. In town, I drive with a very light foot. I'm out of first gear as soon as I get the car rolling. I'm in 2nd gear before I get through the intersection. I shift before 2,000 rpm, and I'm in 5th gear by the time I hit 40 mph.

I throw it in neutral and coast on downhills. I hold the throttle steady and let speed bleed off a bit on uphills. I focus my attention well ahead of me, and when I see a red light, or traffic, coming up, I throw it in neutral and coast well before I reach the obstacle.

This is energy management. You pay to get the car moving, and up to speed. Every time you brake, you're throwing away that momentum you paid to attain.

It actually makes mundane driving more fun. I'm much more engaged than I used to be; much more aware. I don't listen to the stereo anymore, I listen to the car.

I just put my car back on the road after it's having been sitting out in the driveway for 7 1/2 years. On my first tank of gas, I got 21.6 mpg, with about 60% of the driving in town, and 40% highway driving, and a number of full-throttle blasts along the way. Not having driven the car in so long, the speed always ends up at 75-80 on the highway. The mileage will come up considerably when I get used to the car again, and 60-65 comes natural.

There's more there. The tires are crap, and I'm pretty sure the right-rear brake is dragging. It was locked up, and took a couple of 'bumps" to break it loose. It doesn't roll as well as I remember when it's coasting in neutral.

I'd suggest working on your driving technique before you try any mods.

When it comes time for mods, I would go for EBL. There's lots there in the tune.

92GTA

iTrader: (11)

My 92 GTA when it still had the original 2.73 gears would get 28mpg all day long driving from Bakersfield to the bay area on I-5. I did it several times.

Unless TPI is just THAT more efficient than TBI, then it's all just your state of tune. My car was 100% bone stock back then.

Fast355

iTrader: (2)

I would say alot of the MPG difference is related to the shallower overdrive and lower overdrive gear ratio of his V6 trans and 3.08 gear rear-end.

Your final drive with 2.73s and a .7 od is 1.91:1. His final drive with a 3.08 and .74 od is 2.28:1.

Ghettobird52

Some how I found my mildly built EBL tuned 350 L05 did better than the L03 at 30mpg on highway cruising at 65 (stock rear 2.73gears and stock transmission) but worse in city at around 12-13mpg.

Might of just been because the 305 had 175K on it.

Mr.ChevyStroker

I read the first two posts. I have a factory 1997 vortec 350 with a factory fuel pump and a regulator, with a tune to run the engine and a tbi vortec manifold. Its factory 350 injectors.i have hooker headers, 3 inch exhaust, magnaflow. 3.73s and a 5 speed. Doing the speed limit of 65, i got 26. That's just cruising. I git 27 with the 305 and 3.08s before. Im going to go lt1 cam and performer rpm here in a couple minths even though i have now purchased ls stuff im staying sbc for a while. Im assuming around the same mpg.

Mr.ChevyStroker

Im also right around 250 at the whewls with the tune, exhaust and fuel pressure. Im going to get dyno tuned here after a while an know for sure.
I know that you said no engine swaps at the moment, if thats what it is for now, you'll have to just gain some patience. For now, haha. The l30 (305) and the l31 (305) are the same except the cubic inches. Be better off with 350 if you are going to do mods or builds unless you are set in building the 305.

83 Crossfire TA

iTrader: (2)

wow, this turned into a random brain dump:

An L03 should be knocking down significantly better MPG than an LB9, even with the worse gearing.

Add headers and a good exhaust, injector tower spacers and possibly a throttle body spacer (mostly increase airflow but will give you slightly better atomization steady state). Boost the fuel pressure to 12-13psi if you're running a stock tune (factory spec is 9-12, they tend to run best around 13), and higher than that if you can tune for it (more pressure = better atomization).

A good tuneup- make sure that _everything_ is right is manditory before throwing parts at it. You need a good baseline.

Try advancing _and_ retarding the timing some with the same gas in the tank. If it's detonation sensitive or you're getting junk gas less timing will probably work, if you're getting good gas (or tend to go premium) then more timing will work (I don't remember if the stock ecm in the LO3s used a knock sensor, if they do then _a little_ detonation will cost you a lot of MPG because the ECM reacts by a big timing cut. Without some form of knock retard most cars get best mpg with light knock).

Try running bigger plug gaps and consider side gapping the plugs. I've successfully gotten a big cap HEI to run .055 - .065" gaps, but it was at the ragged edged of what would work well. Hotter coils, hei modules and ignition amplifier boxes will help this, but make sure the coil is matched to the rest of the ignition (stock coils tend to work best with stock ignitions, "hot" aftermarket coils work best with ignition boxes, and there are coils that run the spectrum). On my LO5 (350TBI) truck I found it made best power with an accel coil and accel 300+ igintion, but best MPG with the same box and a stock coil (I had 2 stock coils, both ran fine but the original one that came with the truck got better MPG). Stock type plug wires will probably work better than "performance" or "low resistance" wires.

If you're going to do a lot of low rpm tooling around to try get MPG consider running plugs that are a heat range warmer, stock plugs will foul faster if you don't "blast" it every once in a while (used to be called an "Italian tuneup"). NO gimmick plugs either. I tried loads of plugs in my '83 Crossfire (305 with dual TBI's) and found that the factory AC delcos got the best MPG, were the least detonation sensitive and the best power. I kept carefully cleaning them off and filing the tips square on them after every time I tried a new plug and found that it didn't work as well). I later found that if I bought the same AC delco pn I got one of 2 different plugs in the box (they had different insulators), and one worked well the other didn't (if I was going to try some now my short list would be plain old AC delco plugs, probably r45ts, autolite 25 or 26, and the bosch super + (copper/yiitrium core, can be had at autozone for $1.89/each, don't know the pn off hand). NGK v-power would be a good choice if you have a _very_ clean tune but they have softer insulators that foul easier, autolites are the other end of the spectrum, very hard insulators that cause a lot of people to think they're junk, when really they cracked one of the insulators trying to install it, but if you get them in there without screwing them up they work well.

Try with and without the EGR connected. In theory EGR should help control detonation under light cruise so it will let you run more timing and + MPG. If your tune doesn't account for that then you may find that disconnecting the EGR helps.

Most intake manifolds that people try to run with TBI cars are too big, they will make more power, and more top end then a TPI on the same engine. Something with smaller cross section, smooth runners will work better for MPG (I swapped the factory crossfire intake with a custom top plate to fit the TBI from my LO5 TBI truck, with a spacer and swirl plates and gained almost 3 MPG, though the design was harder to tune for good driveablility).

Oh, lowering a car decreases cross sectional area, decreasing aerodynamic drag. In most cases _less_ body work means less drag (yes, most aero packages hurt mpg). 15" wheels are lighter than 17's, and tires (rubber and air) are lighter than wheels, so 15's with tall, relatively narrow rubber will get better MPG. Run as much air in the tires as you're comfortable with... harder tires = less rolling resistance. Alignment matters too... keep the camber reasonable (more camber decreases contact patch and should increase mpg, but it will also hurt braking and tire wear), just a little bit of toe in (1/16", so when the car is rolling forward and the suspension bushings compress you end up with 0).

A lot of what works WRT to these finer details is determined by how you tune for it. I really tinkered with this a lot in my '83 crossfire car, and at the time ECM tuning (at least mine) was pretty primitive, so making stuff work depended on compensating for it mechanically. Possibly as the result of this I found a lot of things that are "common sense" in what has become known as the hypermiler world didn't work in that car (I got best MPG with a 160* thermostat with bleed holes drilled, I couldn't get it to work great with the EGR connected...). FWIW, back then I was doing a lot of highway driving and I eventually got that car knocking down 36-37mpg on the highway between Maryland and RI, that was a 305 crossfire TA + 700r4 +3.23 gears, 235/60-15 F and 255/60-15 R (27" tall, effectively making the gearing lower), lowered almost 3"...

In contrast my current 3rd gen, an 87 LB9 (305 TPI) + 5 speed on 265/40-17 F and 305/30-18 R tires at stock ride height, with a very similar exhaust, and the rest nowhere near as optimized is averaging 22-24mpg in mixed driving (around the DC Metro area), but I've converted it to Megasquirt and can literally tune just about anything I do to it.

Both cars are good for low/mid 13's with stock long blocks.

Using less power (running just enough cooling fan to do the job, no more, small stereo, turning fog lamps off...) causes the alternator to draw less power keeping the battery charged. Any extra weight in the car hurts you (iron heads end up being an interesting trade off, they tend to be more efficient and get better mpg, but they weigh 50lbs more so that hurts MPG).

If you're going to get into internal engine mods... well then all bets are off. I made a lot of these changes to a friend's LO5 powered 2500 suburban + a bunch of internal changes, mostly to the cylinder heads and he claimed that he was getting up to 20mpg in it after I messed with it, high teens towing his race car...

You can keep going and going with this...

JohnOthniel

I put a cold air intake on my L03 when I first bought it as well as a true dual exhaust with high-flo cats and a magnaflow muffler. I also put in a lower temp t-stat and 200 degree fan switch. I installed a Hypertech chip that allows the computer to 'satisfy' at the lower temp setting. Car runs cooler - seems to be more efficient.

My 89 RS is my daily driver. I was getting 26 MPG on the freeway and 18 around town. However, since converting from 3.08 gears to 3.42 two months ago, my gas mileage has improved dramatically. Even with compensating for the speedometer/odometer discrepancy (because of higher gear), I am now getting 19.8 mpg around town (last 4 tanks) and my highway mileage hasn't diminished. I could not be more pleasantly surprised.

When I looked up my car's RPO codes, I found that the final gear on my T5 is 0.65. Very high gear. The combination of the 0.65 final out of the tranny and the 3.42 differential seems to be a pretty good combination all around with improved acceleration and better mileage.

Ron U.S.M.C.

If it has not been mentioned, setting the timing to stock and resetting the IACV, when setting the minimum idle speed can help.
I found that after doing the procedure my RPM's were set to high so the adjustment moved them to where they should be. It does make a difference.

Fast355

iTrader: (2)

My TBI 350 van got the best mileage on the stock chip with the timing 6-10° advanced and the fuel pressure at about 13-13.5 psi. With more torque you can stay off the throttle and out of PE.

Ron U.S.M.C.

I agree.
I like mine at 4* advanced but in order to set minimum idle speed I suggest the stock setting. Once the IACV has been reset and min. idle is set you can adjust the base timing to a higher setting.
Besides I'm sure some of the cars running around here missing the idle stop screw cover have been tampered with not realizing you don't just start turning it with out certain criteria being met.
There driving around wondering why there car will stall at idle.
Any way the correct procedure is one that is a "base" to work from. If its off the rest will also be off.

Bubbajones_ya

Well, I can say the V8 T5 has made a difference in MPG for me. Since this thread has been up, I figured out my rear gears are actually 3.23 so somebody swapped that in.

However I was recently getting around 16.5-18.5 MPG with my Camaro and the V6 transmission. After swapping in the V8 one, My mileage has been almost consistently 20. I was driving the car slightly "weird" too (shifting at sunusual RPMS and then getting frustrated it wasn't shifting well so I'd drive a little harder out of anger) because I thought the transmission was bad, but it ended up being my clutch wasn't disengaging. I ended up fixing that thankfully last weekend.

Last tank, I noticed a very strong fuel smell one trip. I had the car running for about 20 minutes with the smell before parking on campus. When I got out, I noticed a small puddle in front of my car when I backed up. I popped the hood and saw fuel pouring out of my return fuel rail.... I suppose I didn't tighten it well enough when I put my motor back in about 4 months ago!

Anyways, I tightened it back up and I drove my car a little harder the next day after that knowing my mileage wasn't going to be the best. When filling up, I still got 18MPG so I don't think that's too bad depending on how much fueling of the pavement I did. Now I have to install my 3 wire O2 sensor and try to tune my car a little better then see what my mileage is!