Monzallac 425 Lives!

[v8astregt]

Damn, I kind of want to build a big inch Caddy motor now!


I did do all the research at one time a while ago, but I just moved onto other projects.


I would consider it for my Monte, but I would think an 8.2 liter Cad motor would kill all chances I had for fuel economy.

[HI WINDING MONZA]

Go for it Josh , It would be a smooth weekend stealth driver. Doug in Az

[HI WINDING MONZA]

Took it for a ride today, I mean ,it took me for a ride today .

Man this car cooks!!!!!!! Give it a touch of throttle , and the tires break loose . Shift it at 1/2 throttle, same thing.

Had it up to 5000 rpm ( 400 over redline - no problems) Never got over 180 degrees.

Yeah , I broke something Shread - an exhaust hanger!

Got to take out the 4.56's next because it done at 700 feet !

I'd love to see what a 500 would do...........................

Got to get my pilots license now cause it flys!

Doug in AZ

[spyder_xlch]

I can tell you what a 500 in a 6" lifted Chevy shortbed with 33" tires does. Smokes all 4. In an H body with full frame and probably a full cage and a proper set up suspension, that would be brutal. I've often thought about doing a 500 swap but since I already have a 400 and the ease of it I'm gonna just stick with the 400. On the other hand, if I could trade even up for a 500 I'd like to do that.

[danfigg]

I hope your taking it to the track soon. I cant wait to see time slips. I think you should go with 3:08's or something like 342 no more than that--------------Danny

[v6buick]

Man that sounds like a fun ride.

Ben

[HI WINDING MONZA]

The guys at the Cadillac web site recomended that I go with a 2.73 - 3.08 gear with the 13" rims and tires since it is a stock motor and not to over rev past 5000 rpm at the end of the 1/4. Thats whats next to do and add a driveshaft safety loop before a test and tune session.

Doug in Az

[PeerStalkHawk]

Good to hear you got the car going hard already Doug! Sounds like the torque is quite instantly available and that's always a good thing . I think it will probably do quite well with even a higher gear like the 3.08 in this case because of all the torque it makes. Especially with the 13 inch wheels already adding to the ratio. It is actually quite interesting to hear your progress on such a unique choice of engine. And it seems to be working out very well for you so far Doug. Thanks for the update and good luck on your test and tunes...........Dean.

[HI WINDING MONZA]

Dean , they were telling me that there is diffrences in gear also when using a 22 " tall tire compared to " standard size" 28" tall tires.

Most gear they said is based on a 28" tall tire. A 22" tire multiplys that by + .90 or so! ( 3.08 = 3.92) (3.42 = 4.32) ( 2.73 = 3.5) or what I have in now............ ( 4.56 = 5.76! )

Most equations I read about are + or - .06 for each 1 inch of tire diameter . ( ex.- 22" tire to a taller 23" with 3.42 gear -.06 = 3.36) or ( a 23" tall tire to a 21" with 3.36 gear + .12 =3.48 )

Any thoughts?

Doug in AZ

[spyder_xlch]

With those "5.76" gears it might make a good 1/8 mile car. Or a good burnout contest car. Do you plan to go with a bigger tire or keep the stock look? I'd be afraid those 13's would be hard to hook up even with a spare Caddy motor in the trunk.

[bill1978v8]

doug,

I would just go find a "junkyard" 7.5 with 2.56 or 2.41 gears and put a mini spool in it. With the short tires, low weight and all that torque you can get away with it. The added bonus is the lower the gear the beefier they are in the pinion gear (not the shaft). Glad to hear it's running, now we need video!!

Bill

PS - How's the 4.56 gears holding up? (Cut pinion, that torque sure would test them!)

[HI WINDING MONZA]

Bill , No problems with those gears you cut for me, tested the
Cadillac motor with them.

They will go in the Astre when I start on that car, but I just found out today its got a 6.5 in it .

I searched my gear stuff today and luckly I still have the original 2.73 gears that the Monza came with.

Doug in AZ

[PeerStalkHawk]

Doug, I would think that because the motor is close to stock and has a huge low-rpm power band, that using a higher gear which keeps it there for a while would actually get the most out of it. Too much gear like the 4.56 you tried first would only help the launch and then the engine would soon be revving past any useful power a few seconds later. If you plan on keeping the engine pretty much stock, then about 3.08, or even the original 2.73 gears would actually work best with the smaller 22 (or so) inch wheels. That big engine has the torque to move the car initially with higher gearing and higher gears would even help to give you higher mph up top too, by keeping the engine in the most useful rpm range. It might even help your 60 foot times too because you might not spin as much initially and actually get traction and pull out harder instead. The really low gear you first tried(4.56) would super multiply the gobs of torque that engine already makes and make traction very difficult. It would be a different thing if you modified the engine quite a bit to make higher rpm power and/or lost some lower rpm torque. But in this case, the higher gear would work best all-around. I found the converter and gear choice really makes a big difference and even more so on a smaller engine like my v6 because you want to use every bit of the available power band and keep it there as long as possible. If that engine is good about 5000 rpm, use your 2.73 gear, and if you modify it to work up to 6000 rpm, then I would put in a 3.42 or so. Even with the torque converter, going conservative on a high-torque engine can actually work pretty well. I think the higher gear will match your engine much better. Actually, I'm sure of it Doug. ......Dean.

[454spyder]

How are you making the exhaust work. Especially the drivers side. The rear exhaust port exits right in front of the steering shaft at the firewall.

I'm asking because about 6-7 years ago I started a 500 in a monza swap. Had the motor mounts, but abandoned the idea, because of the extreme mods required to fit headers (or even stock manifolds). Those of you that have been around for a while might remember, I have detailed pictures somewhere.

Maybe you found a fit that I missed?

I thought the 425 was physically the same size?

[HI WINDING MONZA]

Todd, I just ran the steering shaft along the fenderwell with Flaming River joints , 3/4 DD shaft and a helm joint to hold it to that side + a Borgenson joint to the steering box

The pic is in my garage. .

I used stock manifolds ( 425 RWD) and made my own pipes by cutting up scraps and rewelding.( 2 1/4 -2 1/2 )

No difference in size of those and the bigger motor other than slight indentations near the fronts of each....................same goes for the motor other than it weighs about 100 lbs less .

Doug in AZ