Q&A / Tech

Mailbag: How to Get 400+ Horsepower from a Chevy 400 Engine

Got questions?

We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re looking at ways to make over 400 horsepower from a small block Chevy 400.

B.B. Hastings, NE

Q: I have a 400-cubic-inch small block Chevy. I would like to be able to get 400-plus horsepower from this engine while maintaining my car’s drivability on the street. The vehicle currently has a Powerglide transmission and 3.88:1 gearing. Do you have any suggestions for parts combinations that might help me achieve this goal?

A: Obtaining the 400-plus horsepower you desire should not be a problem. Achieving more than a horse per cubic inch from most engines by using stock cylinder heads is almost counterproductive, though. An aftermarket cylinder head is almost a necessity—1966-69 Corvette “camel hump” cylinder heads being the rare exception. In addition to aftermarket cylinder heads with 2.02/1.60-inch valves—or very well-prepped OEM castings at the very least—here are some guildelines for achieving 390-415 horsepower at 9.5:1 compression:

The combination of these parts should develop peak horsepower in the 5,500-5,800 rpm range and peak torque around 4,400-4,700 rpm. You didn’t mention torque converter or drive tire diameter, but factoring in the Powerglide and deeper 3 series gear, you should consider a torque converter with a 3,000 rpm stall rating and a maximum tire diameter of 25 inches. You may also want to consider 4.10-4.11:1 or 4.32-4.33:1 differential gearing.

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  1. Pingback: Monday Mailbag: How to Get 440+ Horsepower from a Chevy 400 - OnAllCylinders

  2. Lonnie Elverd says:

    I just aquired a 400 sbc,out of a motorhome,,,511 casting,,3 freeze plugs…..every thing i google says 4 bolt main…its a 2 bolt!! Any one ever see one of these.the old dude i got it from scraps vehicles for a living,,,said he got it started,,for the hell of it ,he floored it…said it boiled all 4 back tires!!.i gave 650 clams for it ,with the heavy duty th400 tranny,6 bolt converter.its fresh built,,,,060 over.gonna drop it in my 90 sportside chevy,,any ideas or comments???,,,L.A Elverd,evansville,in,812 454 9018

  3. Excellent recommendations for a 400 build, I stumbled right into that parts list almost on accident and made 518 tq & 435 hp with ported camel hump heads

  4. From the research I have been doing if you have a 511 casting block and it’s a 2 bolt main block it was a factory replacement engine

  5. larry meyers says:

    i have a 511 casting 4 bolt main block missing 1 piston. should i junk the block?

  6. here’s a question I understand 400s in motor homes and heavy trucks had a steel billet crankshaft stock vs after 84 it was cast. comments? how to identify?

  7. how about pistons and rods? getting 9.5:1 is perfect. with the variety of rodas at 5.75′ and 6″and pistons from dish to dome to choose from which set up did you choose? the wrong one gives over 12:1 the wrong one 8:1. that’s my question, which set to use to get the 9.5 CR.

    steel billet vs forged? my info says not so. all forged cranks. my block is a ’71 hi nickel content and double hump heads. I’d like to port the heads a little thinking of just smoothing the ID only.

  8. I have a 1970 Monte with a 400 and will be installing NKB heads 274-SH and a crower cam (hydraulic roller with lifters). I will install a scat crank with 5.7 rods. This with the Edelbrock Performer RPM and a edelbrock 625 elect. choke AVS-2 and Hedman shorty headers will ensure on badass 400 with about 450HP. Topped off with a aluminum radiator and detailed, painted and Moroso dress ups. Plus a 700R stage 2 and 2500 stall with a 12 bolt 373 setup. Pretty nice street rod, and completion date is set for March 2022. The car is immaculate and original at 57k miles. Just needed some balls. Hot August Nights Reno, NV. 2022. Nicest shadow gray monte in the USA.

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