[1979Formula]

Hey guys, I'm starting on my 400 build for my Formula. It's a '71 481988 block bored .040"over with the dreaded 8VR 411np pistons. I have a set of '71 96's and '76 6X-8's on the workbench now. Seeing as my compression would be quite low, would it be worth to find a set of 62's or 670's, or just invest in better pistons? My goal is to be able to run 92 or 93 octane, and 95% street driven with an occasional run at the strip. Thank you in advance

[steve25]

Besides lowering the stock 8.2 compression that your 71 400 had, your pistons are covered in sharp edges due to all of those 8 notches that make detonation and ping issues far more likely once a certain level of cylinder pressure is reached.

Get new slugs with only the needed 2 valve notches then fully rebuild your 96 casting heads and Mill them .045” on the deck and Intake flange while your at it.

If either set of heads you have might already be rebuilt , then sink as much money into the short block by getting the factory rods out of there!

It’s real nice to know you have a short block that is built better then you need so that down the road and with confidence you can up grade the heads.

You might have the option of selling both sets of your heads you have now to possibly fund getting a set of just about any set of pre 1971 heads with screw in studs which could get you to the needed 9.2 to 9.5 compression that you want for a 400 .

[unruhjonny]

it really seems to me as though not too ago those 1971 #96 heads demanded a premium;
iirc they are something like 8.3:1 compression;
If you pay attention to deck height and other details when changing slugs, it probably would be too tough to be closer to 9.0:1 or better.

I'd vote for those.

I also think that these days the 1971-96 & 1972-7K3 heads are virtually ignored.

[Dragncar]

Get some real pistons and find some 13s or 62s. I would not run the 670s.
You could mill the 96s with a nice set of 2 valve relief pistons, one for exhaust and one for intake( not the Butler generic Ross) and a .027 Cometic and get the CR to 9-1.
Might not even need the .027 head gasket.
And you get a much better piston with thinner rings and less drag.
Get some 4340 rods while you are at it. Do your basic oil system mods.
i would not waste my time with those pistons.

[74Grandville]

if your budget allows, get a 4.25" rotating assembly. compression and piston issue solved... =)

[Cliff R]

Team the #96 heads up with a stroker crank would be money well spent.

If you stick with the 400 build they don't make enough compression even with flat top pistons and tight quench. Even milling them pretty hard and using a two valve relief piston at zero deck height and .039" head gaskets you are still pretty "low" for static compression. This limits cam choices and power output.

Even with that said 400's can be made to run very well. We helped a customer with a 400 build a few years back, he had KRE port a set of 62 heads for it. With the Crower 60243 cam, stock intake and 1968 factory Q-jet the car runs high 11's. I know folks who build bigger engines and put them in similar weight cars that don't run nearly that quick.

Nothing really fancy going on with the rest of the car either, 3.73 gears, DOT's, and a TH350 (prepared here) with a custom built torque converter we spec'd out for it.......Cliff

[turbo69bird]

I have three suggestions

Turbo it
Turbo it
And turbo it!

Seriously, low compression tons of power runs like a regular low compression engine when not in boost what’s not to love.

Any car I’d build/ drive I’d turbo unless it was some type of rarity.

[DaleO]

I had the opportunity to drive an older 930 Porsche once with "only" one turbo.....wow!

[locomotivebreath]

Cliff , what is the fuel system on your customers car with the 400/ 68 jet ? Was there any trouble with the early carb ?

[Formulabruce]

Originally Posted by steve25

Get new slugs with only the needed 2 valve notches then fully rebuild your 96 casting heads and Mill them .045” on the deck and Intake flange while your at it.

If either set of heads you have might already be rebuilt , then sink as much money into the short block by getting the factory rods out of there!
.

So make a 1 OFF engine that can ONLY use a Majorly milled Head, AND intake , and just deal with the manifolds closer to the block? Factory rods gone too? Why, for his application? Never seen factory rods do " occasional " track time?
IMHO, get some #13 's and be done with it. Drive it, don't feed the parts cash cow.
Even 8.3:1 is fine with gobs of factory Low end torque.