Good match up? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Doc Harrel · 11-10-2009, 01:36 AM

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?

1968SWBBigBlock · 11-10-2009, 10:51 PM

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

Doc Harrel · 11-11-2009, 01:35 AM

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?

PhilaTruck · 11-11-2009, 09:47 PM

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

1968SWBBigBlock · 11-11-2009, 09:57 PM

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

Doc Harrel · 11-11-2009, 11:06 PM

Quote:

Originally Posted by PhilaTruck

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

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.

Doc Harrel · 11-11-2009, 11:23 PM

Quote:

Originally Posted by 1968SWBBigBlock

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

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.

BossHogg69 · 11-12-2009, 12:23 AM

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.

11-10-2009, 01:36 AM	#1
Doc Harrel Registered User Join Date: Feb 2009 Location: Tucson, Az Posts: 25	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?

11-10-2009, 10:51 PM	#2
1968SWBBigBlock Active Member Join Date: Oct 2006 Location: Ohio Posts: 1,643	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 __________________ 1968 SWB 454 + .040, 490HP x 540 FT pounds of Torque 10-1 Kb Forged pistons, recon rods w/ ARP wave loc bolts 781 heads Ported with 2.19/1.88 SSTvalves Lunati 60204 cam, Micro Trol lifters, Ported Edelbrock Performer Rpm manifold armor coated, Pertronix Triple Strike Ignition Holley 770 Street Avenger carb,Headers armor coated Built by Watson Ruppel Performance in Sarahsville Ohio. Hardshift Tranny Built Turbo 350,TSI 10" 3000 stall 12 Bolt Eaton Posi 4.10 Richmond Gears moser axles 18.5" x 31" Hoosier Pro Street Radials ET Classic 5 Wheels - polished Power Steering, Power Brakes,Disc Brakes,Tach & Gauge Dash, Tilt,Factory Air (gone) Custom Paint & Body Work Special thanks to my wife, my son and my money tree

11-11-2009, 01:35 AM	#3
Doc Harrel Registered User Join Date: Feb 2009 Location: Tucson, Az Posts: 25	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?

11-11-2009, 09:47 PM	#4
PhilaTruck Right on the line, baby! Join Date: Oct 2003 Location: Phila, PA 19130 Posts: 1,486	Re: Good match up? What kind of numbers are you trying to turn? How much do you want to spend? __________________ 83 GMC 406 th400/3.73 Eaton Truetrac posi, headers, x pipe, & racePros. Tubular control arms, lowering rear springs, caltracs. Still ugly, but getting built right, although slowly Click and scroll down for site vendors! Subscribe here!

11-11-2009, 09:57 PM	#5
1968SWBBigBlock Active Member Join Date: Oct 2006 Location: Ohio Posts: 1,643	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 __________________ 1968 SWB 454 + .040, 490HP x 540 FT pounds of Torque 10-1 Kb Forged pistons, recon rods w/ ARP wave loc bolts 781 heads Ported with 2.19/1.88 SSTvalves Lunati 60204 cam, Micro Trol lifters, Ported Edelbrock Performer Rpm manifold armor coated, Pertronix Triple Strike Ignition Holley 770 Street Avenger carb,Headers armor coated Built by Watson Ruppel Performance in Sarahsville Ohio. Hardshift Tranny Built Turbo 350,TSI 10" 3000 stall 12 Bolt Eaton Posi 4.10 Richmond Gears moser axles 18.5" x 31" Hoosier Pro Street Radials ET Classic 5 Wheels - polished Power Steering, Power Brakes,Disc Brakes,Tach & Gauge Dash, Tilt,Factory Air (gone) Custom Paint & Body Work Special thanks to my wife, my son and my money tree

11-12-2009, 12:23 AM	#8
BossHogg69 motor exploder Join Date: Mar 2009 Location: Pittsburgh, PA Posts: 2,346	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. __________________ Adam 1969 Chevy CST/10 stepside, DART Big M/TREMEC Magnum Extreme/3.73's w/Detroit Truetrac 1965 Chevy Bel Air Wagon (daily driver), 327/TH350,10 bolt w/3.08's 1961 Chevy Bel Air Sport Coupe, ZZ454/M21/9" rear w/3.50's & Detroit Truetrac 2005 GMC 1500 ccsb 2wd, 6.0L/4L65e/3.73 G80 2006 GMC 2500HD ccsb 4x4, DMax LBZ/Allison 6spd/4.56's w/Detroit TrueTrac Use the SEARCH function on this forum - it is your friend!!

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