Max RPM on mostly stock 400?

[blackhand]

Anyone have an idea of how much RPM a mostly stock '78 400 can handle?

Everything is stock on the engine with the exception of a mild performance cam (.442int, .465exh, 214* int @.05, 224* exh @.05), some long tube headers, and an Edelbrock 650cfm carb. Not sure about the valve springs, but I think that they're also stock. My main concerns are the cast, externally balanced crank, and the fact that it has a single, non-roller timing chain. The good thing is that the engine has only 60k original miles and only 400 miles on a very basic rebuild (new gaskets, seals, etc...)

The engine pulls strongly up to as high as I've been willing to take it at this point, which is about 5,000 RPM. I'm honestly surprised that I don't feel any loss in power up to that high of an RPM on a mostly stock 400, I guess it's probably just the high bore to stroke ratio that these engines have.

Anyhow, I was hoping someone could give me a sense of how much further I can push this thing.

Thanks for any help!

 

[rumblefish360]

The cast crank is good to over 500 HP and the timing chain should have been done new with the cam change. Same with Valve springs. You can push it far. The biggest draw back is the low compresion ratio.

 

[EL5DEMON340]

i would think it would drop off big time right after 5500 rpm,

 

[demon seed]

i would think it would drop off big time right after 5500 rpm,

x2

 

[daredevil]

As far as how far to push it I would say 6500 is safe but 7000 with stock rods it starts getting iffy.

 

[caferacerx]

I wouldn't push it very far with stock valve springs

 

[RustyRatRod]

But with upgraded valvetrain, a good solid or high rpm hydraulic cam and either aftermarket or upgraded factory rods and I wouldn't be scared of 7500. The 400 has a really short stroke. It's like a big bore 340.

 

[blackhand]

All good info, thanks guys. I'm glad to hear that I can safely bring the RPM's up a little higher while the engine's still pulling strong.

It did get a new timing chain with the cam swap and engine rebuild, I'm just worried that it's a single, non-roller type and I'd feel much safer with a double-roller type.

As for the valve springs, I'll probably add some stiffer springs later when I change to roller rockers. Still eying a new set of heads too though, so who knows when that will be.

Hell, I don't know, I'm still looking at the Hughes whiplash cams as well. Maybe I'll end up adding one of those with a double-roller chain and some stiffer springs. Get it done all at once that way.

 

[turbofreek]

The cast crank is good to over 500 HP and the timing chain should have been done new with the cam change. Same with Valve springs. You can push it far. The biggest draw back is the low compresion ratio.

just how far can that cast crank go? Would 700 be safe with a good set of rods and light pistons?

 

[mosleyme]

Oiling would be my biggest concern. I had a 383 that liked 7000+ but it eventually could not keep oil fed to the last pair of rod journals. My 440 has HV pump, extra capacity pan with trap doors and kick outs, and 1/2" pick-up.

440 has Eagle rods, light weight Ross pistons, 0.990" pin, solid lifter flat tappet cam. I have the 6AL 7000rpm chip installed and occasionally bump into it.

 

[RustyRatRod]

Have you had the pan off? Just so you are aware, the 400 got the steel crank LATE. I have a 77 that had a NICE steel factory crank. I know it was factory installed cause the block had the Maltese cross and the bearings were undersize still with 77 date codes.

 

[rumblefish360]

just how far can that cast crank go? Would 700 be safe with a good set of rods and light pistons?

That is a very good question.

I myself wouldn't want to try it out at that level. I myself have not been there. I feel it best answered by the been there and done that. Application for street or strip are 2 different things as well.

You could push it on a strip only car since it see limited run time, though abusive. On a street ride, I'd be more conservitive.

Where these lines can be drawn vary with equipment and parts used. If you wanna press me for an opinion, I'd leave at, "Yea, I'd guess so." Notice how I said guess, not know so.

 

[jamesdart]

im not sure id want to spin it past 5000 with stock springs and rod bolts. if you float a valve kiss your cam good bye. i dont see how the shumacher tri Y headers with 1 5/8 primary and 2 1/2 outlet are rated at higher hp than the 1 3/4 tti full length headers. i think that is misleading.