[81ElCamino]

I am having a 400 block, crank, rods, and heads givin to me. Block will most likely need 30 overbore. Crank looks perfect.

First question is rod length. I thought I wanted a 6 inch rod motor (must think in budget terms!!!)
A buddy laughed off 5.7's, saying no difference from the 5.656's the 400 came with.

But that leads to question 2, pistons. KB hyper pistons for stock rods, flat top or dome. For 5.7 a selection of dishes, flat, and domes.

Which starts question 3, heads. The small chamber heads on the current motor would do for now, the large chambers with the 400 could be done cheaply enough too. ( some day HOPE for decent aftermarket heads!!)

Will I have a hope of 350+ hp, and 350+ torque???

Any thoughts???

Dave H.

 

[lindsay]

I think the 406 is the best small block you can choose. I have one in my car and love it. 350 horsepower is about where you will end up with stock heads with pocket porting and 2.02/1.6 valves. Torque should be closer to 400 ft/lbs. I built one identical to one I personally saw dynoed at just over 400 horsepower and about 430 ft/lbs of torque. I went with slightly more cam though. I would go with the 5.7 rods. Every little bit helps. They will broaden yor power band instead of making it so "peaky". I put a 406 6 inch rod motor together for dirt track racing in a IMCA modified. Way too much work. I used 403 olds rods used pistons out of a sprint car, solid lift cam etc, etc. You will have to have the pan rail ground on to clear for 5.7 or 6 inch rods. Be careful you don't hit the water jacket, especially on the 6 inchers. Make sure the oil pan clears the rods before you start it up or you could end up with holes in your pan! What block casting do you have? Some are better than others for grinding for rod clearance. 511 casting for 4-bolt, 817 casting for two-bolt are the best but others do work.

 

[Philip]

I'm building one right now so I can't tell you how it will run. Before I took it all apart I drove it. It was in a 72 Impala 4 door. About 5000 lbs of car, 122k miles, low compression, no tune up, timing gear shot and had been sitting in a field for 9 years. Well it would still pin you to the seat!!! That was enough for me. I pulled it out and am going completely thru it. It will have 9.5-1 compression using a .030"over Fed-Mog piston # H601P (which are dished) with the block decked .020", a Comp Cam XE262H cam, stock heads with hardened seats and resized stock rods. I chose to stay with the stock rods so as not to have any clearance problems. As the figures show it will be a low rpm, high torque engine. My very old version of DeskTop Dyno says a little over 300 horse at around 4000 rpms, but 447 ft lbs of torque at 2000 rpm's. Gotta love them cubic inches.

With me doing the assembling total cost after balancing will be around $1600.

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Philip Valentine
Gold Member #42
"Perseverance is not a long race; it is many short races one after another."
[email protected]

 

[68chevelle]

81 Elco, in my opinion (for what thats worth) i would go with the 5.7 rods. i would also go with kb dished pistons but find yourself some small chamber heads - Better flame efficiency. if possible 2.02/1.60 would help - your going to have plenty of tourque at the bottom end so help out the top end a little.,.... Ever thought of vortec heads? Little more work but they flow good.
As 64elco mentioned, keep compression to around 9.5 to 1 and that the comp XE cams are a good choice. 110 deg lobe sep on all of them i believe. balance it all and have fun. Remember the balancer and the flywheel are going to be different than a reg small block.

 

[81ElCamino]

Thanks for the info so far!!! I don't have it in my possesion yet for casting info. Some combos would be like 10.5 compression, so 5.7 rods, and dished pistons looks like the way to go.
Heads will certainly be the weak link at first...
I need steam holes don't I??

Thanks again!

Dave

 

[32767chvl]

Yep, steam holes are the must on the 400's. Be careful with your overbore, and extra care with the break-in of the motor. Check the cooling system often, as the 400's had a habit of running excessively hot. Don't forget your externally balanced harmonic balancer and flexplate. (I've had friends who had success mating a 454 flywheel to a 400, because Chevy always mated the 400 with an automatice trans.) Great torquey motor, though. Great smokey burnouts.

 

[lindsay]

I forgot to tell you my motor is running 5.7 rod flat top forged pistons. I would use the keith black hypernetic pistons unless you plan to give it a shot of "the Juice". I was told the high silicone content produces a hotter/faster burn which produces more power, and they are cheaper than forged pistons. I would go with the flat tops as I did producing a compression ratio just under 10 to 1 with 76cc heads, which is probably what the heads are that you were given if they came off of the same motor. At first I did have "pinging" problems with the pertronix ignition but not once I switched to a Davis Unified Ignition HEI distributor. Make sure you don't go with too big of a cam as this motor produces power in the bottom to mid range RPM bracket. Depending on gearing I'd choose something like Cam Dynamics 272 or 278 cam.

had the 278 in my car for alittle bit smaller high stall convertor would nice but not necassary. 272 should be good without one. If your gears are 3.73 plus maybe Something like a Crane 284 cam, convertor a must in my opinion at this stage. This does assume your running an automatic. Yes do have the motor balanced, as mentioned the 400 is a externally balanced motor which means this is a must.

 

[Dwayne Martin]

I recently built a small block 400 for my chevelle. I used flattop pistons and 76cc heads that were milled so that they had 74cc chambers. This netted out to around 9.8:1 compression ratio. Remember that you can use a little more cam in a high displacement motor and still be streetable. I would definetly go with the 5.7 rods.

 

[plain 69]

My 406 uses the TRW# 2467 and has 11.1 to 1 compression with sportsman II 64cc heads. That piston is a flat top with 2 valve reliefs and is forged. That is with the stock 5.65 rods. I used the Comp Cam 274 Extreme Energy cam plus a Performer RPM Q-jet intake and Carb Shop 800cfm Q-jet. I'm looking at the Dyno sheet right now and it says 375hp at 5,000 rpms and 475 ftlbs of torque at 3500rpms. It had a 102% Volumetric Effeciency at 4200 rpms. With an avg. Air/fuel ratio from 3300-4100rpms at 11.75. I can't wait till later this year to put the Malibu on the chassis dyno. It ran a 12.89 at 104 mph.

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69 SS 454
69 Malibu 406
ACES Member #3635

[This message has been edited by plain 69 (edited 02-01-2000).]

[This message has been edited by plain 69 (edited 02-01-2000).]