I have a 72 Demon that was originally a 318 3 speed, the rearend is 8 3/4 with 3.23 gears in it, I am putting a mildly built 340 in it with a 4 gear based on expiences out there how does everyone feel about putting 3.55 gears in it?
Are 3.55 gears a good choice?
- Thread starter demon1972
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3.55's are a real neat street gear. But the nice thing about the 8 3/4 rear is, if you don't like them and have still have the 3.23's just change them out.
I ain't ever liked 3.55s. They get about as crappy mileage as a 3.91 and a 3.91 pulls a lot harder. I always either choose the 3.23 or the 3.91 and lower. I have a 3.55 right now in a 489 case I'll be tossing for a 4.30.
Depending on the tire size all cars react to gear sets differently. 355's are a prefered gear for many. But don't get rid of those 23's you may want them for a highway car show trip. MPG. I never cared for 355's in any small block I had. but I always ran at least 275 60's. My freind has a demon with factory 14 inch wheels and had 391's .He took them out and installed 323's. I myself would have left the 91's in and went to a taller tire.
terzmo
Well-Known Member
they are My preference with a short tire..26 inch but with a 28/29 I run 391's/410's even 430's..My 72 Demon has 355's with 26 inch tires and it's great for street and highway...not a track combo though
Salty Dog
Well-Known Member
Your not going to feel much of a gain and the ET clock will show it as well.
Exactly, if you have 3.23 now and you want that more seat of the pants feel then go 3.91 or numerically higher. I run 3.55, and I have another 489 case I'm going to set up with at least a 4.10 gear for some mild strip.
I have 3.55's in my 69 Dart with 235/60 14 tires and its great around town but not alot of fun on the highway due to hi rpms. I will eventually switch out 15" wheels which should help and for 323's for more versatility (so I can take an occ trip). Right now I would not consider driving more than a 1/2hr on a highway... just dont feel comfortable with engine screamin for that long.
I have 904 automatic, 3.55 Suregrip 489 - 8 ¾” rear end under my Dart with 205/70x 14 tires. 60 mph is a busy 3000 rpm out on the road. It drives me nuts after a while even with new quieter mufflers. Gas mileage is around 17.
The problem I have with this engine is the cam likes 3000 to 6000 rpm, and is a turd below 3000 rpm, she was a former drag queen. So driving around town, and on the open road is just under where the old slant likes to pull hard. Get the rpm up into 4000 range and this car comes alive, along with the secondary’s killing fuel mileage.
With 3.55 gears one needs a taller tire, and a low rpm torque cam to be a nice quiet street car. The other thing is, back forty years ago, no one gave 3000 rpm on the road a second thought, but today’s cars are geared to run at 60 mph just under 2000 rpm. We have grown accustom to our engines running just over a high idle for hours on end.
The problem I have with this engine is the cam likes 3000 to 6000 rpm, and is a turd below 3000 rpm, she was a former drag queen. So driving around town, and on the open road is just under where the old slant likes to pull hard. Get the rpm up into 4000 range and this car comes alive, along with the secondary’s killing fuel mileage.
With 3.55 gears one needs a taller tire, and a low rpm torque cam to be a nice quiet street car. The other thing is, back forty years ago, no one gave 3000 rpm on the road a second thought, but today’s cars are geared to run at 60 mph just under 2000 rpm. We have grown accustom to our engines running just over a high idle for hours on end.
I have 3:55 in 8 3/4 i am running in my rod with 400 poncho motor. The MT tires are about 26.5 " tall and it is a very happy medium compared with 3:73 I took out.
It turns about 2400rpm on highway at 55mph but stiil has great get up and go.If I was rattin light to light I would go with 3:91 or so but all around driveability is great with this combo.
Cheers and gears
Martin
It turns about 2400rpm on highway at 55mph but stiil has great get up and go.If I was rattin light to light I would go with 3:91 or so but all around driveability is great with this combo.
Cheers and gears
Martin
efriedrich
69 383S
They get about as crappy mileage as a 3.91 and a 3.91 pulls a lot harder. I always either choose the 3.23 or the 3.91.
X2, what stroker said.
X2, what stroker said.
412 Stroker
Well-Known Member
Yep I have 3:55's also, and mine runs @3500 rpm's at 70mph, so that means sucking alot of gas, IMO either keep the 3:23's or go 3:91 like others have said.
mopardude318
Well-Known Member
IMO, 3:55's are a good gear. I have them with a 24.5" tire out back. Kind of a short tire though.
lead69
hopeless car junkie
My advice is find a low 1rst gear four speed (3.09) if you can,they made some in the early 70s with std. output shafts (thats what I have-its a 1974) or you can covert an early trunion style over.When you look at the start ratio (1rst gear x rear ratio) my 3.23s are like 3.91s at take off but the freeway is smooth at 70+ since I have 275/60/15s (28in) tires.
I just picked up a 3.55 for my Dart. I have 3.91s in it now. I am running a T5 trans and plan on doing so road trips with it. With my 26" tires and the overdrive it should put my rpms around 2400 at 75mph. Randy's ring and pinion has a handy calculator that I used for my calculations.
http://www.ringpinion.com/Calculators/Calc_RPM.aspx
If I don't like it I will switch back.
http://www.ringpinion.com/Calculators/Calc_RPM.aspx
If I don't like it I will switch back.
abodyjoe
Well-Known Member
depends what you want from the car.
i have a 28" tire on my car.
i had 3:91 gear in my car for a long time. great around town but sucked on long road trips.
put a friends 3:55 in the car and it was quite a bit better but still sucked on long trips and the way i like to drive.
finally put a 2.94 in the car and i love them.. can cruise any where now. i still want a OD though. then i'll have the best of both worlds..
cudaspaz
Well-Known Member
A cheaper alternative may be to bolt on a set of taller tires for longer trips.
You would be surprised how much tire diameter affects rpm.
A 30" tire may actually make the 3.91's much more highway friendly but still have the punch you need off the line.
They work well for me with this combo but I can cruise fairly comfy at 65 mph just shy of 3000 rpm.
If I get tired of the rooms I just back it down to 60 mph.
The 3.23s were so nice on the highway and not bad off the line but not impressive nor good for burnouts like the 3.91.
You would be surprised how much tire diameter affects rpm.
A 30" tire may actually make the 3.91's much more highway friendly but still have the punch you need off the line.
They work well for me with this combo but I can cruise fairly comfy at 65 mph just shy of 3000 rpm.
If I get tired of the rooms I just back it down to 60 mph.
The 3.23s were so nice on the highway and not bad off the line but not impressive nor good for burnouts like the 3.91.
dodge freak
Well-Known Member
keep the 3.23 and put in a tight 10 inch converter and then see how it is.
I got 3.91's and love them, the prefect gear around town but yes, 3,500--4,000 on the freeway does waste gas--don't think it really hurts the engines-like a 340 which is made to rev but gas $$$ adds up and traffic goes 75-80 on the e ways
I got 3.91's and love them, the prefect gear around town but yes, 3,500--4,000 on the freeway does waste gas--don't think it really hurts the engines-like a 340 which is made to rev but gas $$$ adds up and traffic goes 75-80 on the e ways
HotLines
Realist - Free Thinker
In my 64 Signet, I run 3:55's with 245-60-14 rear tires and a push button 727. I've really got to run a higher ratio like 3:23 or 2:94's to satisfy my cruising speed when actually traveling. Around town they are awesome but puts a damper on visiting friends 2 and 300 miles from home. I guess I could do a trans swap with an OD but I love the overall presence of the buttons. Without an OD, it is what it is with little to no advantage as to gas mileage and cruising speeds at low RPM's. My truck has a T56 w/ 3:42 rear and cruises at 2000 rpm 90mph in sixth..
tekslk
Well-Known Member
Toss that thing my way I have 391 in a 489 case but im geared to low with them for street.
tekslk
Well-Known Member
Give me the 3.55 you wont be happy with them and I will put them to good use.
Blue Grey Duster
Well-Known Member
Since your asking, I'd say keep what you have until you get your car together and can drive it around. Wait until you really know for yourself.
If you drive that car a lot, forget that big gear unless you do what cudaspaz suggests, or swap out your pumpkin back and forth, when you need to.
With more gov. spending,the dollar will be worth even less, so gas ain't coming down, as long as the muslim is in charge.
Hey tekslk ! Give me your 3:91
If you drive that car a lot, forget that big gear unless you do what cudaspaz suggests, or swap out your pumpkin back and forth, when you need to.
With more gov. spending,the dollar will be worth even less, so gas ain't coming down, as long as the muslim is in charge.
Hey tekslk ! Give me your 3:91
X2! This is exactly what i'm doing now. I had to pay an extra 100 bucks for the early trunion style transmission, and am having the gear set swapped into a case with a slip yoke tail. Planning on running 3.23. Figured the bit larger jump gears was worth the trade off, and you're still under the rpm drop between gears than the overdrive 4 spd. Seems like a great happy medium to me.
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