lowkeytow

I recently put a 572 ci engine in my 68. Thats the cool part. The tough part seems to be that my M21 transmission although holding up well, doesnt allow the new engine to be as fast off the line and through the gears as i would have thought. Seems like the gearing
I probably need a new transmission.

Any suggestion on a replacement?

roscobbc

Hmmmmmmm - (you won't have much of a 572 with that 'low rise' hood! ) I would have thought a M21/big block to be the perfect combo (although the longevity of the 'box will be questionable), i.e. high torque big block with a 3.25 or 3.08 rear end! what rear end ratio are you running?

gkull

With the TQ of a 572 I would use a 5 speed with over drive. You want first gear to be around 10:1 with the first gear and rear end ratio. final gearing in OD anywhere from 2.40 - 2.80 overall gearing.

So the first question would be what is your rear end ratio?

lowkeytow

That original hood has been delegated to the basement. I have an L-88 hood that i had to cut. The engine is in and done headers rear pipes and side pipes with cut outs on the side pipes.

You bring up a good point on the rear I didnt think of that. I will have to check but it was a basic 327 300Hp M21 trans hook up if that helps to give some idea of what rear I might have.

Here is a clip of what she looks like now. If you listen close (maybe not all the close is needed) you can hear and exhaust leak l had in one of the headers. It has since been welded.

http://www.youtube.com/watch?v=iorTN...e_gdata_player

Solid LT1

I would think any 572 is making north of 500HP so I would upgrade to a M-22 gear set. Auto gear has a wide ratio gear set for your Muncie case that should get you up and going. Here is the link:http://autogear.net/ag_archive/m22ratios.htm
That is the cheap and easy route. I really enjoy the Tremec TKO600 overdrive in my wife's LT-1 Vette. Cruising at 2100RPM going down the freeway while knocking down around 20MPG makes the car really enjoyable (not as comfortable as the C6 Z06 @ 28MPG.)

Rebelrob

Lowkey is the rearend stock, meaning know previous work or upgrades/rebuilds? I have read that all Vettes, came with Posi tractraction from 70 models and forward. With that being the very first C3 year, you might have yourself a one legged rear end which would not be a good idea with all that power from a 572. I am sure some rearend guys will chime in here to confirm or not.
Congrats on the new build that is very cool. I like the swapping of exhaust pipes mod you got there. I know that engine is louder in person. That video is not doing the sound true justice.
BTW- be curious to know if your keeping that thing cool enough come summer time with what looks like a stock fan and rad.

ZZ71S

http://www.5speeds.com/book.html
You might look at one of these guys Autogear super case M22Ws..
I bought one from these guys and it was a direct bolt in NO modds.

ajrothm

With a 572, your tranny gearing should not even matter....nor your rear gearing....On street tires with a stick you should be wasting 1st/2nd with wheel spin.... First thing I would do would be to check the timing, 2nd thing I would do is re-visit your air cleaner choice, that little mini air cleaner sitting only 1.5" above the carb throat is choking that 572 to death.....Also check the basics, make sure your carb secondaries are opening fully when the throttle is on the floor....you may need to re-adjust the cable..Lastly, does it run the same whether using the under car exhaust as well as the side pipes? The side pipes are likely killing 40-50hp....atleast...

That car should be down right nasty.....I think you have some stuff on that car that is killing the motor..,,

Yeah that muncie is on borrowed time....I would be looking at a TKO600 or Magnum t56 soon.... Or better yet, a t400....

Bromleys Corvettes

A 572 in a 68 thats awesome That tiny air cleaner is WAY to small for that motor. I understand you not wanting a huge air cleaner sticking up but that thing has to go lol. You should be able to start off in second gear and just ease into it and blow the tires off. I have a 565 in my 80 and even with 29.50X11.50 Hossier quick time pros it would do crazy burn outs in high gear if you layed into it at 60m.p.h lol I would put a built TH400 with a 3500 stall in it and not even worry about what rear gear you have. Even a 308 gear will be more then enough for a 572 TQ monster.

lowkeytow

Thanks for all the input.

After reading the earlier posts I am leaning towards checking the rear. I did some research at lunch and found that there is a code stamped on the rear end that will tell me whats in it. I have 20" rims and measured the hidth at 28.5 inches from ground to top of tire.

The engine seems to be running fine even with the smaller air cleaner. I have to decide what to do with that however as my plan is not to just leave as is.

Since reading some of the later posts I will add..... It definately will burn the tread of those tires even with the nitto tires on that are new and seem sticky. It actually tries to lift the front end of the ground when the hammer gets dropped. It goes from 0 -70 in the drop of a hat but then cries to be let off. (High RPM max for the speed.)

On the side pipe question .....The rears are open all the time 3" pipes with magnaflow mufflers. When I open the sides also 3" pipes hooked to short racing mufflers... Only ones we could find to fit under the covers, it seems to give a little more HP as most of the air flows through the sides given the little resistence of the side mufflers.

I am thinking 3:38 rear maybe 3:08 with the M22 upgrade in the tranny but first the Rear the go from there.

Oh one last thing the specs are 620 hp 650 torque

gkull

Both the m-21 and M-22 are junky when compared to todays equivolent 4 speeds made by places like Tex Racing/G-force.

lowkeytow

Wow just found out that I probably already have something in teh nieghborhood of 3:36 or 3:08 see post below.

Acording to my book, in '68 the 327 300hp 4 spd came with (2) possible ratios: 3.36 and 3.08 and the auto came with only the 3.08

Hope this helps

I guess I should just ask. What do I need to do to find that happy medium between good launch speed and good top end speed?

gkull

Without over drive you are kind of hosed. 3.36 good for a big motor with tall tires. I opted for 3.55 because it is good around town with the first 4 gears and I still have 5th for open roads.

http://www.secondstrike.com/Technical/GearCalc.asp

The TKO 500 first 4 gears has a wide ratio gears set like the m-21 wide ratio

The TKO 600 first 4 is like the M's closed ratio gear sets.

Ben Lurkin

Something here doesn't seem right. My LS5 454 with reworked heads would light 'em up in all four gears with 3.08's. Your engine has at least 200 hp/tq more than this. What's your initial timing and advance set at?

gkull

What kind of tires did you have on the rear?

jerome1979

i'm not an expert but as other said:

--> air cleaner too small
--> Side pipes ok but only with STS spirale baffle or w/o muffler
--> Check all your setting and if all works well(carb & advance)
--> go for an OD manual tranny (TKO,T56) only if MPEG is a problem.

ajrothm

That big motor does not need more then 3.36 gears honestly...... that is a 6200rpm motor tops.... 28.5" tires are pretty tall but I would still think the bottom end/midgrange of that motor should pull the tall gearing well.... A 3.36 and a 27" tire is a good blend of acceleration and still a top speed of 140 mph or so at 6200rpm in high gear (1:1).

You'll be rebuilding that rear end before long anyway....

63mako

I used to go through stock muncie transmissions on the order of 4 or 5 a year. This was in a 67 Camaro with a 1970 stock 350, heavy flywheel, 390 posi gear, traction bars and N 50 15 bias ply street tires. Wheelspin will save it and the rear end for a while or maybe until tomorrow. You have a 400 HP drivetrain with 620 hp and 650 tq. TKO 500 and save up for a 12 bolt conversion for the rear. Or go with the TKO 600 and look at uprading the rear to a beefed up 3.73 when it goes.

lowkeytow

The engine checks out fine. I have run it with the hood off and varios air cleaners with no change in performance. The sidepipes only allow more air flow not less. The sidepipes are 3 in with racing mufflers that are the next best thing to straight open. When sidepipe cut outs are open exhaust is flowing through the rear pipes also. Brand new exhaust sytem 2 weeks ago.

I am thinking that it may be a throttle cable issue as there is not much pedal travel.

If I am hearing what most are saying the transmission and rear end although weak compared to the 572 should not be affecting pull or top end to the degree that it is.

Obviuosly a 5 or 6 speed trans with OD would be a good fit .

The engine doesnt suputter or anything I just may not be getting wide open throttle.

I will add that when running at 75 on the freeway it has very little throttle movement from there to the floor.

I appreciate all your input as I really dont have enough knowledge on this other than I know a 572 should be a monster.

gkull

People kid their selves into thinking that side pipes are performance items. Very few side pipe systems are built with any thought as to primary size and lengths anywhere near being functionally tuned pipes.

The throttle cable is easy enough to figure out by just have a friend floor the gas and look down the throttle bores.

Motors in the 600 - 700 hp range are fun, but not a monster. Zero to about 130 mph is kind of fast like around 12 seconds and then the air barrier slows the rate of exceleration.