Thread: any insite on the 700R4??

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Originally posted by TRUCKGUY
never heard of it but if it was designed for trucks it probly would be geared low and not be good for racing would it???

i have a 4 speed truck tranny

They were the optional 4wd tranny and the standard towing tranny If I remember right, with fairly high diff ratio ( say a 3.00 maby( might be too drasticly high but, you get the point ) you would deffinetly be a contender for drag racing, a little diffrent approach than most because most put the low gears in the diff and have a high geared tranny. You could actully, in theory have a better chance than most because the low gears are in the transmission and go away when you shift up a gear, when there less and less needed but, with a car/truck with the low gearing all in the diff, there always there. Mind you, this is all based on theory and logic and I have yet to see a truck granny tranny be used for drag racing.

I have been busy working on a sun room for my wife and bogged down with finding someone to do a double-flare on my stainless brake lines but this topic is right on my thinking for my roadster. I purchased a rebuilt street version of a 700R4 from the MegaMonster (Eat my shift) folks in Florida but it will be at least a year until I can test it while I finish the roadster. Here's the question as related to this thread. The recommended converter that came with the 700R4 is a 1600 rpm stall speed and now with the four speed and the OD I can have mileage and acceleration, BUT (!) with my existing 2.79 8 inch rear the 0.7 OD is way too high and now I can and must change the rear gear to a lower value. Note for this discussion that the MegaMonster 700 R4 has a hydraulic lockup for the OD and NO WIRES! Using the site given below and with my 735/75/15 tall rear tires I find that a 3.55 ratio will just reach 1600 rpm at about 56 mph where I suppose lockup will be complete. Although the shift points are determined by the trans settings, the converter will still slip if the rpm dips below 1600 rpm?? I know Streets says we ought to research the old threads and I have looked at quite a few threads discussing rear gear ratios. So far it looks like a 3.55 rear gear is a safe bet over 55-57 mph but what happens if I am doing 45 mph on a black top two lane road, will I be in third gear or worse a slipping OD? From this point of view maybe a 3.70 rear gear would be better so that I could stay in OD at lower speed without converter slip? So, the question is which is better keeping in mind my desire to get over 20 mpg AND a quick car. By the way isn't the low gear of a 700 R4 3.06?

3.55 rear, 2.485 OD above 55 mph

3.70 rear, 2.59 OD above about 50?

Thus won't I actually get better mpg with the 3.70 rear by going into OD at a lower mph? Then again in one of the old threads Streets recommends a 3.70 rear gear so that you don't have a NASCAR restrictor plate situation on the street. Again trying to remember performance of early Ford 3.78 rears with less than 100 H.P. it would be neat to keep the 3.70 gear now with a 270 H.P. SBC! So the question is can I run in the OD gear at lower speeds with the 3.70 gear and still get over 20 mpg? Maybe Henry Rifle can answer the mpg question since he has quoted a 3.55 gear 700 R4 in a Vette and a 3.70 rear in a Model A/B? Part of my motivation is caused by finding a nearby Kit car builder of Cobras (York Sport Cars, John York, Ashland VA) who will be able to do the double flares on my brake lines (3/16" stainless) and he casually mentioned that he uses 3.70 rear gears in the 9 inch rears he builds along with a five speed manual trans having a top gear of 0.68. He only uses 351 Windsors but rated at 350 H.P. so I guess he can lug the OD better with the 3.70 rear. SO which is better for performance AND mileage, 3.55 or 3.70?

http://home.tampabay.rr.com/1bking/c...calculator.htm

Don Shillady
Retired Scientist/teen rodder

700R4 is O.K. but if ya want the strongest try a 4L80E

http://truckmoxie.tenmagazines.com/i...e_transmission

Don
I may be wrong here but it seems that you have the misconception that the OD lock is going to stay locked in once it reaches the speed required to reach 4th gear. It doesn't, it will shift down when your speed drops below your cable controlled settings, just like a 3 speed turbo 350, or your rpms drop accordingly.
I'm running 3;08's in my pick-up (full size) and will haul up to 1500 lbs. most of the time to the tune of 15 mpg. and I go over the mtn. passes all the time- never overheats, pulls strong, and thats a 5800 lb. truck.

Hambiskit, Thanks for your continuing advice. I guess what I am asking is whether a 3.70 rear will allow a shift into OD at lower mph than if I use a 3.55 rear gear? I hope Henry Rifle can answer since he has both setups and knows the comparison. It seems to me that shifting into OD at 50 mph rather than staying in third gear of 1.0 will increase mileage while at the same time a 3.70 gear will give tremendous response in low gear. Is the originator of this thread aware that MegaMonster can convert the electrical OD lockup to a hydraulic lockup without wires? Also for the answer to this web question I learned that of the three 700 R4 rebuilding companies I studied, all three would not rate a rebuilt stock 700 R4 as handling over 250 H.P. Maybe this is their way of generating sales for their beefed-up versions, but maybe it is also true that 250 H.P. is a pracitcal limit for a stock 700 R4? I am trying to understand the four speed auto trans. On my Pontiac Sunfire ('98) once it shifts into 4th at about 50 mph you can decelerate and stay in 4th down to about 30 mph before it down shifts, but I do not know the stall speed of the converter in the Sunfire.

Don Shillady
Retired Scientist/teen rodder

Don,

You can expect average mileage to vary pretty much according to the ratio of rear axle gears. When I changed my '93 Vette from 2.90 to 3.55, my mileage dropped from 25 to 20 - about 20% - about the same ratio as the gears. Going from 3.55 to 3.73 would drop you about 5% - from 20 to 19, for example.

They may say that a 700-R4 is only good for 250 HP, but the one in my 93 Vette has lasted 110,000 miles.

I'm not sure how the hydraulic lock-up works. The Bowtie Overdrives electrical system always locks the converter when in OD (4th), and has a disengage switch in the brake line in case you lock up the tires in OD.

OD is the most important gear to lock the converter because of the torque needed to overcome the reduced mechanical advantage. BTOD also supplies a manual switch so that you can lock up in 2nd or 3rd gears if driving for extended periods in lower gears.

Henry Rifle,

Thanks a bunch, I value your experience and maybe if I get my roadster running within the next year I can visit you on the way to the beach! I wonder why the 3.27:1 ring and pinion for the 8" rear is so rare and expensive, except that maybe that is what everyone wants and they are out of stock? I only found one site that has 3.27 gears for the 8" Ford rear at a price of $750! Anyway, you offer real data so maybe I need to look at 3.00 instead of 3.55 since the low gear of the 700 R4 is, I believe, 3.06 which is quite a bit lower than low gear in either the TH350 or TH400. Anyway I am trying to learn about the auto trans 4 speed operation. "Experiments" with my '98 Pontiac Sunfire show that there is probably only one setting for shift points at about 3500-4200 rpm, but once in 4th gear you can coast down to about 20 mph and stay in 4th with the tach showing about 1900 rpm. Then you can goose the engine up intermittently with an increase in the tach reading and only a small change in speed, so I think this means the Pontiac (Japanese) 4-speed auto DOES NOT have a lock for 4th gear. Still I get about 24 mpg with the Sunfire, but the performance with a 4 cyl 110 H.P. engine is just slightly better than pathetic! I recall in an old Thread Don Meyer mentioned obtaining a 3.27 rear gear but I don't recall if that was for a 9" rear or and 8". The gear selection seems to be much more readily available in a wide range of ratios for the 9" rear but there is a gap between 3.00 and 3.55 for the 8" rear. I would welcome references to a site for a reasonable price for a 3.27 ring and pinion set for the 8" Ford rear. Thanks Henry, it looks like at least you have ruled out the 3.70 gear if I want to get at least 20 mpg.

Don Shillady
Retired Scientist/teen rodder

Don,

If this makes you feel any better, 3.55s with a 700-R4 are the equivalent (in first gear) of 4.27's in a Muncie wide-ratio 4-speed.

(3.55 x 3.06)/2.54 = 4.27

That's a pretty hairy drive ratio in a light roadster.

Guessing gas mileage on your roadster vice my Vette is chancy at best. Bear in mind that the Vette has a 350 LT-1 with a pretty decent fuel injection system on it. A carbureted 350 of the same hp isn't likely to get the same mileage. I don't even begin to know how to compare. Also, keep in mind that the Vette weighs about 3300 lbs. The roadster would be much lighter.

However, I'm guessing that if I get 20 average in that car, you should be able to get a similar number in your much lighter roadser with the same gearset. Besides, if it gets 19 instead of 20, that's 16 miles less on a 16 gallon tank. In 5000 miles, that amounts to $25.00 with $1.90 gas.

If you drop down to 3.00 gears, you've got the equivalent of 3.60s in my Muncie comparison. Not bad, but not enough to put a grin on my face. In your shoes, I'd go with the 3.55s. Good punch, decent mileage.

Originally posted by Streets
Dan ... The "Granny Tranny" talked about here is NOT what you'd use fer Draggin material.. 1st gear would getcha 6,000 RPMs at a speed of 10 MPH with the standard 4:10 rear gears usually found in trucks with this tranny..(And the engine would blow up before the 60 foot mark) It weighs in the neighborhood of 300 pounds and is a top shifted tranny, MOST everyone that has a big heavy truck or a heavy load to pull uses these trannys if they like sticks.. When just cruisin' around town you start out in second gear.. saves on the killer engine rpm's!! It also has a PTO drive on the passenger's side AND a bolt-on u-joint assembly!!

I knew that a sm420 was not suited for drag racing and, I just wanted to see if anyone would catch on.

Streets, you are a kidder! With VWs and my MG Midget it was fun to give away mpg with performance improvements and still stay above 20 mpg while with these V8s you have to be careful to get above 20 mpg. Thanks to Henry Rifle and Tech1 I saw the light and got a 700R4, now I can hopefully get performance and good mpg cruisin'. Anyway what I really want is to get back to the performance of my Dad's '69 Chevelle in a Model A body. Today I found a site that offers 3.25 rear gears for 8" Ford rears for about $200 so with bearings and labor adding up to about $500 maybe I now have to worry a little over 3.25 versus 3.55, although the 1600 rpm full converter lockup at 55.3 mph argues for a 3.55 for sensible driving where I get into 4th soon and easy and then run in overdrive with occasional blasts staying in low and second longer. Thanks for your suggestion for the stainless flaring, I will take my bent tubing to John York tomorrow for double flares. He is building some beautiful Cobras in his shop and you can have one for a mere $35-40K, I am still hoping to build my roadster for under $20K, but we will see how it goes.

Don Shillady
Retired Scientist/teen rodder

Don,

I don't understand the 1600 rpm lockup you mentioned. How is that accomplished? Just based on converter stall?

The reason I went with Bowtie Overdrives was the positive electronic lockup in 4th gear. As long as the car has shifted up to overdrive, the converter is locked, and the manual switch allows the same in 2nd and 3rd. As I understand it, if the RPM drops below the stall of the converter, the transmission still stays locked. It will downshift and unlock if I hit the loud pedal, or if I move the shifter lever, but otherwise, stays in high gear and locked.

Henry Rifle, Well I had a long chat with the Tech guy at Megamonster and maybe the difference is that with the hydraulic switch I won't be able to stay in the fourth gear as with the electric lock. As I understand it (?) it will down-shift just like a third-to-second with a TH350. As I calculate it I will be able to stay in fourth longer and get to fourth sooner with the 3.55 rear gear and so get better mileage with an effective (0.7 x 3.55 =) 2.485 drive ratio as compared to my present 2.79 in third gear with a TH350, but I need to get to that gear at a reasonably low mph for "normal driving" so I am using the 1600 rpm stall speed to estimate when the lock might down shift. Estimating roughly with the 1600 rpm value the down shift might occur at 55 mph (?) so this will be great on the Interstate but I will still have a 3.55 gear for city driving. I may make more rapid progress on the roadster buildup now that I have found John York's Cobra shop just a half mile away and maybe the electric switch is better, but I did not want to get into a situation where I had to worry about the wiring. Maybe I will just spin the wheels with the low gear and not get 20 mpg after all, but it looks to me that the 3.55 rear gear will get me into OD sooner at lower mph and that will help the mileage; especially since a lot of my driving is on Interstates. Then again, comparing a full-fendered '29 body to a Corvette body surely will lead to a need for more gear once the air resistance builds up at 60-70 mph speed so I will just have to wait and see. On the other hand maybe someone on this Forum can tell me how much the shift points can be changed so as to make sure I can get to fourth gear at maybe 50 mph with a 3.25 rear gear????? Then the problem is to ask whether the engine woud pull a (0.7 x 3.25 =) 2.275 OD below 2500 rpm?? I am sorry to bother you guys with my worrying, I guess I will just put it together and take what I get within reason. Another way to look at this is that my '98 Pontiac Sunfire has a Suzuki 4-speed auto and the gears are nearly identical to the 700R4 in the trans and the rear (FWD) is 3.60 so the 3.55 gear with the 700R4 should be streetable although maybe with a V8 instead of a little 4 cyl. engine the mileage will have to be lower than the 24 mpg I get with the Sunfire. Of course auto engineers can try various combinations on a test track while I am trying to learn from the collective experience of Forum members; it is like choosing a cam with the same sort of possibilities for guessing wrong.


Streets,

Now you tell me you get 31 mpg with a 2.79 rear in your T-pail? I thought you said in an earlier thread that you got 18 mpg with the blower turned off? Gee you could have really got me going if you had told me 31 mpg earlier! Anyway I got the 700R4 now and hopefully I will get a tire burner in low gear and good mileage in fourth gear. Maybe you could define your actual mileage with what engine, what rear and w/wo the supercharger. My understanding was that you got 18 mpg with the supercharger mounted on a 383 but the clutch to the blower drive disengaged. Of course many of us were impressed with the clever clutch on the blower drive but I was more interested in estimating the mileage as compared to the Magoo '29 which claimed 18 mpg with a Hi-Po 327, TH350 and a 3.08 rear gear. Can you tell us/me how you got 31 mpg with what engine, what trans and what rear gear?

Don Shillady
Retired Scientist/teen rodder

Don- I belive that there is another wiring set-up for the 700r4 that may be the one that your looking for, I know that there's one for it to go in the other direction to raise the shift points- if you will call Emanuel Zavackis shop there in Richmond, or Paul Scott's Speed Shop in Chesterfield I think they MIGHT have something to help you.

Don,

Here was my thought pattern with the electrical control.

- The wiring isn't difficult at all. Plug in the trans, connection to hot, connection to the brake switch.
- I always have the trans in lockup in OD.
- My trans only downshifts when I make it downshift.
- The stall speed of my converter doesn't matter.
- I have much less worry about burning up a $1000+ trans.

There is a wiring setup that uses a stock GM brake pedal switch instead of the Bosch relay.

http://www.bowtieoverdrives.com/cata...php?ITEMID=332

Guys this a great thread, I really appreciate all the input. Thanks to all the contributors, both those asking and those answering!

Pat