HP52TA

iTrader: (4)

Hey guys, looking for some opinions on whether my current bottom end will stay together until round 2 of it's build up.

I got a very low mileage 406 sbc which I was going to rebearing/rering and run. As I want to keep the engine looking like the 305 (serpentine setup) it is replacing, I am replacing the camel hump heads as they have no accessory holes. With new aluminum heads and matching cam and valvetrain added to the current bottom end, I should be seeing around 450/460 hp. (I am not intending to spin this past 6000.)

The engine was built to a 385 hp spec previously, so I am concerned about the additional power I will be adding to it, as I feel the bottom end was built to its maximum potential already.

Here is what I got:
Crankshaft - Stock 400 turned .010 under
Rods - Stock 5.565" rods, running ARP bolts/nuts
Pistons - H601P hypereutetics, providing 10.23:1 compression with the 64cc heads
The rotating assembly has been externally balanced.

During disassembly, I have been blueprinting the as found state, and all the dimensions (even the ring gap) is looking like as new specs. I am planning to run this through my WCT5 (as the 2pc seal 153t flywheel will work with this clutch) until round 2 which would see a T56 replacing it.

The long term plan (round 2) is to intall a new rotating assembly built for 600+ hp, but only bump up the N/A power slightly and add a 150 shot of giggle gas and the T56. More saving has to happen before all this occurs though.

So,
Will she stay together, or should I be building up the bottom end now?

F-BIRD'88

There is no reason why it won't stay together for a long long time.
The stock stuff is a lot, lot stronger than you think.
Just realise that even with new, better heads etc, that motor will not want or require a lot of rpm. So no need to abuse it. Excessive rpm will kill any motor even with the expensive stuff.

Sounds like you took it apart for nothing. Make the top ring end gaps generous if you plan on a lot of nitrous.

HP52TA

iTrader: (4)

A friend was replacing this with a 572, so it has never been in my car. The engine had been built about 10 years ago so before I put it in I thought it was time for a re-ring if nothing else, besides I wanted to see what I all had inside.

Upon tear down I did find a bad cam bearing, which I found odd because the cam looked and measured out like new.

The engine came from a Sunday driver, so it has seen minimal runtime over the years.

What amount of NOS could a guy add?

AlkyIROC

With a factory cast crank, not a whole lot.

Sonix

iTrader: (1)

150hp shot should be ok. Gap the rings WIDE and make sure you have lots of fuel.
RPM's kill rods/crank more so than power.

F-BIRD'88

Have seen a factory cast 400SBC crank handle over 1300hp repeadidly.
About 600 of that was from the nitrous. other parts failed when tuning mistakes were made but the crank was never a problem.
It was cryo heat treated "iced" but other wise just a stock plane jane cast 400 crank reground for the hi perf "H" series bearings. The cast 400 crank is not a problem. I believe these cranks are more durable than the popular aftermarket cast chinesium cranks.
The motor can actually take a good bit of nitrous as long as the nitrous is not engaged at a low rpm and detonation is strictly avoided. For anything more than 175hp use 100% 110+ octane racing fuel.
Watch the nitrous/fuel ratio and spark timing. Keep it rich/safe and take lots of timing out. make sure the fuel system can keep up to demand, while maintaining pressure.
use cold non-projected tip spark plugs.

HP52TA

iTrader: (4)

I wasn't thinking of going beyond a 150 shot, so I am happy to hear this. I was more concerned about using the 5.565" rods, but no one has mentioned these yet so I assume they will not be the weak link.

I lost three rods at 5800 RPM in a vette many years ago and I don't want to do that again. It was a wild ride back down to zero without powered controls!

This is for a street engine with very limited track use, so I won't be hitting the NOS very often, more for back up purposes.

I have an MSD Digital 6 with the timing retard, so timing should be handled.

cc 82Z-28

iTrader: (7)

I talked to a guy from another forum who builds 400's and he said that the stock bottom end with good bearings, hardware, and proper clearances will hold up fine as long as you don't crazy with the rpm's. I am in the process of building a stock 400 virgin short block that has never and does not need machined. I am going through and putting ARP hardware throughout and putting in new bearings, checking clearances and throwing some Patriot Aluminum heads with a hydraulic roller cam and lifters. I plan on keeping the revs at 6000 rpms. Should be a torque monster for sure. I say go for it and fun..

1989GTATransAm

iTrader: (3)

"Pistons - H601P hypereutetics"

If there is cause for concern using nitrous that would be it.

HP52TA

iTrader: (4)

Thanks for the replies everyone.

I am heading to the border to pick up the top end today, so with not having to upgrade the bottom end, I will be putting her back together soon.

Sonix

iTrader: (1)

Aww man, do you know somebody in Montana to receive parts for you or something?!? Damn, I keep trying to make friends with someone in Sweetgrass, but no luck so far

RacerX13

The stock short 400 rods are stronger than the 5.7 rods. Keep it from detonating and you'll be fine. Your T5 isn't going to like all that torque though.