I've installed one of Summit's 350/290 hp engines in my 84. I have the 350 trans, with the lock up converter. However, since I removed all the smog equip, the lock up converter no longer works.

I also have the 2.41 rear gear in it. I know, that isn't anything in the way of performance, but, first things first. At 55 mph I'm turning 1950 rpm's. What I'm curious about is, if I install an overdrive transmission, just how much is the rps's going to drop, if I stay with the 2.41 for now?

Is it going to be worth the cost to do it, utilizing the 2.41 or should I just wait till I can change to a 8.5 and some 3.23 or 3.42 gears? Will the economy increase with the overdrive?

Thank you in advance for any help/suggestions/thoughts.

Don

I changed my transmission to a 2004-R this spring. I had the same stock 2.41 rear end. I can tell you that with stock wheels and 225 60 14s you will be at 2,000 RPM at 70 when the transmission is in lockup. I got 22 MPG on a 200 mile trip with that setup. Lots of people on this site warned it would never work, but it does, it is not ideal.

I changed the rear end to a 3.08 and I am real happy with that setup. I have a throttle body injection setup on my stock 305. The computer controls the speed that the transmission goes into lockup. I had that re-mapped to 55 MPH. It drops out of lockup at 50. Now at 55 MPH I am at 2,000 RPM in lockup. Around town with a fairly heavy foot I get 18 to 19 MPG. I don't give a hoot about stop light racing in my Elky. I can merge onto the highway with ease. It is no tire burner, but it is not a slug.

I've installed one of Summit's 350/290 hp engines in my 84. I have the 350 trans, with the lock up converter. However, since I removed all the smog equip, the lock up converter no longer works.

I also have the 2.41 rear gear in it. I know, that isn't anything in the way of performance, but, first things first. At 55 mph I'm turning 1950 rpm's. What I'm curious about is, if I install an overdrive transmission, just how much is the rps's going to drop, if I stay with the 2.41 for now?

Is it going to be worth the cost to do it, utilizing the 2.41 or should I just wait till I can change to a 8.5 and some 3.23 or 3.42 gears? Will the economy increase with the overdrive?

Thank you in advance for any help/suggestions/thoughts.
Don

Check with an expert, but I think your TH350C non-lockup problem is most likely that you lost the "lockup signal" when you eliminated the smog stuff. Hook a fused 12V source back up to it (perferrably via your brake pedal switch) and it'll operate as before.

I wouldn't run an O/D tranny with the 2.41 gears. The O/D will drop your high gear RPMs by 30% (almost 1/3). That's very likely much lower than your engine should run under those load requirements. Swapping to a [numerically] higher rear end adds to the total conversion cost.

Since you already have a decent mileage gear with your current setup, the ONLY advantage I can think of for you going to an O/D tranny and changing rear ends is to gain 1st gear take-off torque. I'd think long and hard before spending $2K or more on the O/D conversion.

However, if this is your goal I think it would be just as effective, cheaper and easier to install a higher stall torque converter that'll give you more "launch" yet still allow your 350C tranny to lockup on the highway.

Glen & Mike;

Thank you both for your input. No, I'm not trying to build a tire scorcher with the Elky. Just a nice pleasant comfortable cruiser. I don't use it for everday travel, maily on the weekends, an an occasional trip for "the grocery getting duties".

I do want it to run nicely, but am just more concerned with being able to merge onto the Interstate, and pass the occasional car when needed. I'm real happy with the performance the way it is - I would just like it to get a little better mileage when on a small trip.

This past Saturday we took a small trip up to Concord, NC to visit the Cannon Mills factory store, and stayed in the 65/70 MPH range. The best mileage I could get was 16.7. That is why I was thinking of going with the overdrive, just for a little better economy. However, if I can manage to get the lock up working on what I have - I'll be content with that. I'm sure that will give me an additional 1/2 mpg, and if I can get it in the 18/20 range, I'll be REAL happy.

I did fail to mention it does have true duals - ceramic coated headers - no cats - Edelbrock Performer Intake - and a 600 CFM Holly.

Gentlemen, I do thank you for your input - it is greatly appreciated. :cool:

Don

Mike

I've been meaning to thank you for some time now. Everytime I log on, or sometimes just read the threads, I forget until I have logged off. . .

At any rate, your suggestion worked great. I now have my "lock up" back, and it has greatly increased my mileage. Prior to getting it fixed, I was running 1950rps at 55mph. Now, I'm running 60mph at 2050rpm. So, I gained 5 mph for only 100rpm.

Haven't taken a long trip yet (going to Tennessee this weekend) but I expect my mileage will increase 2/3 mpg.

Thanks again, for the info. . .

dcar-please explain exactly how you made this hook-up. Which wire on trans. connector, which terminal on the brake switch-does it lock only in third gear etc? I to am looking for any fractional increase in mpg these days. Thanks in advance.

Yes, I would also like to know how to hook up the lock up torque converter switch. I have an '85 and my trans 4 terminal plug has 3 wires a green w/ white stripe, a brown w/ black stripe and a solid purple, I think one is a ground, but which one.

Maybe this well help

Lockup (http://www.chevyhiperformance.com/howto/53562/)

Storm, that article in the link is for overdrive transmisions. I think the question being asked is how to make it work with the 350C. At least I'd like to know how.
Thanks,
Gerry

I made a 200 mile trip last weekend. After an additional 153 miles of in town commuting I had driven 353 miles total on one tank of gas. I got 21.8 MPG. My overall average in the last two years of mostly driving to and from work I get 17.6 MPG. I never have a problem merging when I get on the interstate. With 258,000 miles on the original 305 engine I can't complain.

I bought my Elky 17 years ago. Back then I made the same trip when the Elky was 100% stock and had just 42,000 miles. I was lucky to get 12.5 MPG and the original 17 gallon tank was near empty after 200 miles.

The TBI injection, 2004R, a 23 gallon tank and a 3:08 posi rear end was all worth the investment. Now with gas over $3.10 per gallon the difference in drivability and economy made it all worth while. The increase in gas mileage paid back the cost of the improvements. I drive 12,000 miles a year on average. That equates to over 900 bucks a year in savings on gas alone. If I did more highway driving it would be even more.