Good match up?
 

I have a bone stock 400 sbc in a 68 stepside. The truck has a 400TH tranny and 4:11 rear diff. I would like to drive it to work, about a daily 6 mile round trip, but still be able to turn some good times on the track. I was thinking about boring it out to a 406, and maybe changing the gears ratio in the diff. What kind of suggestions do you guys have? Should I leave the differential gearing alone? Should I leave the engine alone? What would you do, or what have you guys done with similar setups?

Also...what kind of peak rpm can I expect to get out of a 400? 406?

Re: Good match up?
 

Doc - I would leave the gears alone they will work for your trip to work and the track
Boring the engine would be fine but a question if it is worth 6 cubes
The 400 is a good motor I would keep stock configurations below 6K

Re: Good match up?
 

I suppose the extra 6 inches isn't really worth the work. I see that you have a a 4:10 rear end yourself, what kind of top speed can you get? My biggest concern is that the engine will reach its peak rpm range before I'm anywhere near the end of the track. I drove on the highway, and I felt like 70 mph was my top speed. My truck is still in Texas right now so I can't really go find out what rpm it was at. Should I drop it down to like a 3.73 or so?

Re: Good match up?
 

What kind of numbers are you trying to turn? How much do you want to spend?

Re: Good match up?
 

I twist 3350 @ 65 MPH
You should have plenty of motor and rpms left at the track
I would wait to think about changeing gears

Re: Good match up?
 

I would like to get a 12-12.5. If I could get a new rear end for around $200 I think it would be worth it, if I can still turn that kind of time. I wouldn't have any reason to go on the highway, all of my driving would be in town stuff. But I will be driving this truck to work a lot, so I don't want absolutely horrible gas mileage.

Re: Good match up?
 

What is your top speed with your current setup? Have you taken it to the track, if so what is your average time? I have a 400TH, compared to a 350TH, how much different do you think my truck would respond? Sorry for all the questions, I'm obviously a noob,.I just want the best setup for what I want to achieve. Good times on the track, and as good gas mileage as I can get.

Re: Good match up?
 

not to rain on anyone's parade, but mid 12's, good gas mileage and a stock 400sbc are things that won't coexist. Especially with the 4.11's. You'll need around 500hp to run that number, but you'll also want to keep those 4.11's and the th400 to do it. And a posi, some good heads, cam, headers, carb, intake, stall converter, shift kit, the list goes on and gets expensive quick... Things is 500hp is totally doable with a streetable 406, it just takes some money and a good combo of parts. I don't know if you could expect much more that 10mpg with 4.11's, a three spd auto and a 500 horse motor, but I could be wrong.