Chev 327 with a 2.75 gear. Comments?

I run a '37 ford coupe with Chev's powerpack version but with 3 dueces. I currently have a 3.25 gear which is okay around town and for the 200-300mile trips two to three times a year. I plan to drive to Bowling Green for the Hot Rod Reunion-900 miles. With the 3.25 at 3000rpm is 70 MPH. Would like to get the rpm down , but would the 2.75 pull me off a piece of snot at a light? I know a overdrive would solve everything, but have driven this setup for 10years and it is so bullet proof. what do you think?

 

You will lose some power of the line.If you go with an overdrive you will have the best of both worlds.

 

Built a 40 coupe for a friend with a stout 327 (10.1 Sig split duration cam-good mid range), turbo 350 and 2.79 rear with 28" tires. Suspected it would be pretty "doggy" on the get go but am astonished at the way it runs. Will run away and hide from a similar 40 with 3.25 gears with a 350 290HP crate motor.

 

If all you want is lower RPMs for the trip just buy some rear tires a few inches taller, swap them out when you get home.

The best solution would be a set of 4.11 rear gears and a T56 trans with the .50:1 sixth gear, might cost about $3K.

 

If you are running 3,000 at 70, your rear tire must be right at 26". If you can go taller, say 28", you will drop to 2730. This would be more cost effective than a gear change, and easier to change back
The 2.75 will be a bit doggy in my opinion (I also have a 37 Coupe with a 327 and I run a 3.25 gear and I consider that weak off the line) and will drop the revs to just under 2500

Back in the day, as they like to say, cars were geared to run at that kind of RPM, that 327 will run at 3,000 all day long. We have just become accustomed to OD transmissions that drop down to as low as 1700 at 70 - but EFI is a great player in that, they run smoother with more cam at lower RPM than Carb motors do. if you are doing it for fuel mileage, I only think you are going to see about 3-4 MPG better at best, so if you figure $3.60 per gallon for your 900 mile trip, and you are currently getting say 17MPG, you will only save about $28.59, so think about how long it would take to pay for itself!

 

I'm running stock 327/300HP w/3.08 and a 29" tire, it is great on the freeway and I have no issues towing/launching my 1500lb boat.

 

You could get someone to push you for a mile I think that is what they do at B-Ville.

Just put taller tires on it.

 

I have the 2.75in my 36 its ok 2000 rpm at 55 and 2500 at 70 im putting over drive in car as i type this .

 

I found that a 2.70's gear far too long-winded. and I ran a 3.08 for years.
The way the GM cars get away with this, is by having a torque converter and various EFI tuning strategies. I'd add a few inches of rear tire diameter.

 

Your going to hate a overdrive with a 2.75 gear

 

I run 2.89 gear with 750-16 behind a T5 and i usually leave it in 4th on the highway, and i take off in 2nd gear from a light. I dont think the motor is much more then 200hp. Its great for when your late to work but you still want fuel mileage

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first of all, good choice on the hrr in bowling green. you'll love it i think. you didn't say is the rear a chunk type? or what kind? if all you have to do is swap out a chunk,id swap chunks. if its a gear change,thats a lot 'o work.overdrive is a thought, for one trip, i'd find the tallest tire i could fit under there and let it go. but just don't miss that show. jmo

 

If your gear ratio is the same as the tire height (i.e., 2.75 gear, 27.5 inch tall tire) you will need just about 2000 rpm to go 60 mph (3000 at 90). I ran this effective ratio in my roadster for a long time (3.00 gear, 30 inch tire), and it was a decent compromise.

I run the same combination in my '41 truck (3.00/30") as well, which is pretty similar to your coupe. The dig from a dead stop is a long way from thrilling, but it will certainly keep up with traffic.

 

I seldom tire at the sound of a sweet little small journal 327 at full song, but when I do, I usually just plug in some "Molly Hatchet"!!!

 

If my memory is right the theory we used when changing quick change gears in my late model you would drop about 500 rpm. I have a feeling that you might not see a lot of savings in gas mileage= I've always felt that every motor has a sweet spot that is when it's most efficient===you might just miss that spot!

 

X2 on trying taller tires, BUT:



2.47 Gears! 30" tall tires. Six cylinder. Runs 11s.
However, it has a 4000 stall speed converter.

If you plan to stay with the 2.75s I'd be tempted to up the stall speed to 2500 - 3000. Have fun, stay safe.

 

How about using the good old GM formula of the last few years. Most of their offerings have been equiped with 3.42 rear gear and a overdrive trans with a .7 overdrive. They adjust rear tire diameter to give approximately 70 mph at 2000rpm (or close) in high gear overdrive. They maximize cam profile/injection/timing to give optimum mileage in that range. So, adjust your combination with that model in mind and you've got about the best that current thinking on the subject relies on to sell thousands of cars every year.

Frank

 

What size engine? What fuel mileage are you getting now? How loose a stall converterare you running?

 

On the street loose converters are a compromise best left to the wild souls running a lot of cam and trying to get that misbehaving beast to idle in gear! On the track they are a tuning tool. Never the twain shall meet. Using a loose converter to make up for a tall gear is pretzel logic.

 

I just put 2:79's in a 62 Nova convertible with 305 TPI and 350th. I took 3:55's out. Test drive the other day had me still leaving traffic at the lights and I'm not a heavy footer. The charts will have me running about 2400 rpm at 70 with the tires I'm running. Works for me.
Here is a good calculator-
http://project33.com/tiresize.cfm

 

Some verry good comments above. peace

 

Good advice already given. I had 235/75-15s on my 40 with 3.08 rear and auto trans w/ stock converter. The 327 had a L79 cam, 9.8.1 CR and Rhoads lifters so I didn't have to drag the brakes in traffic. It would cruise at 60, but it loved 80++. I'd have traded for something in the 3.30 range in a heartbeat. I assume the 3-2s are progressive; make sure the end ones close completely and don't start bringing them in until the center is at least 40% open. I ran a good set of trips on a 327, and I found 1 4bbl ran better and got better mileage... not as cool.

 

I know the car,[it's my Dads,hi Dad!] runs a glide w/ford 9" if that helps on the replies. See ya in Bowling Green.
burnout,hows the leg?

 

Floater 03 don't go to Bolwing Green ,nobody will be there,,they are going to Bowling Green.LOL. Enjoy the trip!!!!

 

Sounds like you have an 8 or 9 inch Ford rear. If so, center sections are easy to swap in and out, so put in the 2.75 and see how it feels. If you are cranking 3000 at 70mph you must have some very short rear tires, because I am running 4.30 gears with a 29.5 inch rear tire and I crank 3500 at 70.

My Son is running 2.79 gears with a 29.5 rear tire and we thought that might be too high when we built the car, but it has actually turned out to be perfect. When he leaves a light and I am following him I have to push mine pretty hard to keep up, and he can cruise down the road just off of idle.

A looser convertor, as mentioned, will help too, something in the 3000 range.

Don

 

My fingers must be fast!!

 

the tranny is a powerglide annd the tires are 29 inches

 

How are you checking your speed?

With 29" tall tires and 3.25 gears in drive = 1:1 I am showing 80 MPH at 3000 RPM.

 

Bingo best advice

 

wow - you got a lot of opinions and ideas. I will add one. I also have a 37 Ford Coupe -engine is a base 350 although I actually started with a 307. My rear end is a 9" Ford with 3.00 gear and 28 inch tires. I would say it is a little weak off the line, but you have to consider what you want most. I have put 87,000 on mine including 2,200 going to Bonneville this year - running 80+ and it doesn't seem like I am winding it too hard. Actually it seems like from 60 up it just wants to suck up the road and go faster. Now if you are not going to be driving it a lot of highway miles - why get concerned with one 900 mile trip? Just drive a little slower or turn the engine enough rpms to go the speed you want. It's a SBC - you are not going to hurt it.