Running 11-Second 1/4 mile with 2.56 gears, stock stall, and 225/70-15 Coopers

[MC1of80]

Yeah, it's called rot. Mother nature's personalization of the car. Same tire combo came off 2 other, virgin metal and trim Monte Carlos with the same "no issues" whatsoever. 

[Dragginwagon467]

Looking forward to the 2025 season…car is still sporting the 2.56 gears, factory converter, but the engine has been swapped for a BluePrint 632. 
 

Now, I know what you’re thinking, “how does a tall deck BBC fit in a First Gen MC?” The answer is it’s complicated. 
 

There are a few initial challenges:

1. Hood clearance - I wasn’t willing to give up the factory hood, and the Dominator-flanged 632 intake is tall, very tall. To get around this, I sourced a rare intake, casted by GM back in 1969 for tall deck Mercruiser boat engines. Now, even though the spread bore intake is made for tall-deck engines, it wasn’t a bolt-on deal for the cavernous rectangular intake ports on the 632. After epoxying the upper bolt holes closed, the intake fit well. This video explains the intake and modification well.

2. Header fitment - Hooker 2455 are the go to header for many when running a standard deck height Big Block Chevy in the First Gen MC, and I didn’t opt to spend big money on anything else. Now, what that means is, the driver’s side header has been modified (dented) to fit the steering shaft, lower rear control arm mount, and column shift rod. Both headers were dented to accomadate the angled spark plugs for boot and socket clearance. Of course, the taller and wider deck mandated chopping off the head pipes and fitting new collector extensions  

3. Engine accessory brackets - The standard deck height power steering brackets swap straight over to the 632. Try as I may, I could not find a stock-appearing alternator bracket set. So, I did what any proper redneck would do…I used the standard deck height lower bracket as a pattern to make my own custom lower bracket. For the upper alternator bracket, I was able to slot the lower hole at the water pump, which allowed the bracket to raise straight up, as needed.

 

All this being said, we dropped it in the weekend before the First Gen Monte Carlo Takeover at Norwalk last year, and didn’t have it street ready until 2AM, the first day…only to find that I had a coolant leak due to cylinder head/intake gasket mismatch. I spent the first day pulling the intake back off, luckily the problem was obvious (now) and I already had an intake gasket that fit much better. By Friday afternoon, the 632 was running again. With only limited street time on the new combination, I chose to trailer the car to the event…and it was a good choice.
 

Day 2, the 632 made its maiden voyage down the track, and it was anti-climactic. In the burnout box, the engine gained rpm at an alarming rate, so much so I had to let off the gas abruptly - it was plainly obvious this wasn’t a 496 or 510. Not knowing what 632 cubic inches was going to do to street tires on a mildly prepped track, I left the starting line cautiously, and rolled into the throttle. Within a split second, it became clear the tires were holding all the torque the massive engine had to offer, so I rolled into full throttle. Acceleration was brisk, and when I slid the column shift into second gear, the TH350 declined the command. Second gear exited the chat somewhere between the burnout box and about 200’ out. That was disappointing, yet probably the best thing that could’ve happened in my situation that weekend.

in the end, I made several more passes, with 2.56 gears, factory converter, and without the benefit of second gear, and ran a best of 12.52 @ 112 mph. 


I drove the car the rest of the season without second gear (what can I say, I missed driving it the first half of the season). The 632 is not for the weak of heart, it has about 8” of vacuum (compared to 15” @840 rpm for my 510), and the cam is so large that the engine doesn’t really “smooth out” until 2500 rpm…meaning if you’re driving slower than about 65 mph, the engine is happier in second gear (which is there, but only slightly above idle power). The 632 is happy enough to idle down to 450-500 rpm, but it’s really choppy (honestly, it’s choppy at 1000rpm.)

All things considered, this won’t be my car’s final form. It’s fun, no doubt, and you better have the car pointed in an appropriate direction before applying significant throttle when driving on the street. The engine is just too much, and requires too many sacrifices for a street cruiser.

That’s it for now, hope to see a few of you at Norwalk (OH) in July.

Edited March 9 by Dragginwagon467

[jft69z]

Any thoughts on changing the rear end gears?

[Dragginwagon467]

On 3/9/2025 at 2:53 PM, jft69z said:

Any thoughts on changing the rear end gears?

Not really interested in changing the rear gear, as the 2.56 are great compromise if your engine has the torque pull from the dig and enough hp to pull through the traps in second gear. 
 

I don’t plan on running quicker than 11.50, but love a smooth idle and being able to drive my car anywhere. As well, the 2.56 gear, combined with hard street tires, protects the factory axle shafts from breakage. With a functional second gear, this combination is easily capable of 11.2 @ 128 mph on 225/70-15 Cooper Cobras. Should be able to run 11.50s with a friend or two in the car 😁

[DragCat]

Thanks for the post and updates 

[420ponies]

Good friend of mine has a 496 w/6-71 blower (600 edlebrocks),Turbo 400, ford 9" with 2:50 gears (21.5"x 33"tires). It's a smoke show until you let off the throttle, but can cruise anywhere. It went 11.90's at 112.00 mph, spinning in second gear. You could upgrade the transmission to a 400 and get a lower 1st gear for it like mine. You will like it with that mammoth BBC!!  I do like the "sleeper "look. You do know that motor is going to find a "weak link", and start breaking things in the driveline( like 2nd gear). Do you have pictures of the motor in the car? I'd like to see how high  the headers are in the engine bay.

[Dragginwagon467]

On 3/18/2025 at 7:36 AM, 420ponies said:

Good friend of mine has a 496 w/6-71 blower (600 edlebrocks),Turbo 400, ford 9" with 2:50 gears (21.5"x 33"tires). It's a smoke show until you let off the throttle, but can cruise anywhere. It went 11.90's at 112.00 mph, spinning in second gear. You could upgrade the transmission to a 400 and get a lower 1st gear for it like mine. You will like it with that mammoth BBC!!  I do like the "sleeper "look. You do know that motor is going to find a "weak link", and start breaking things in the driveline( like 2nd gear). Do you have pictures of the motor in the car? I'd like to see how high  the headers are in the engine bay.

 

Here’s the incorrect, in multiple ways, “396.” I hope to get back to a more stock appearing package at some point (after seeing this 632 run 11.2 @ 128 mph 🤣)  

 

 

 

 

[420ponies]

Lookin' Good !! Headers are a little tight.