Forged are a lot of money and I can get a good set of hypereutic for a good price.

My question will they be alright with a 125hp shot of NO2? I would like to go with the nice cheap pistons and I don't think they are that bad.

thanks for help.

 

I would not use hypers on a 400 or stroker motor if I planned on using NOS. Not worth the cost savings. A good forging will run approximately 225 more than a hyper.

 

You'll be fine with cast or hypertectics at the power level
as long as you use the best available pump gas. 92/94
octane to avoid detonation. And under 10.0:1 cr. You can open up the top ring gap a little too. If you are using KB's follow their recomendations for ring gap closely. Go easy on the ignition advance and be sure to provide enough additional fuel for the Nitrous injection.

 

hypers really hate NOS i would say 75, 100 shot TOPS otherwise get some forged units, there not all that expensive,...

 

They are not all that expensive but I just saw a set of Hyper's for $155. I want around 10.5 compression ratio so maybe I will go with the forged.

 

I wouldn't run N20 with hypertec pistons. In fact I wouldn't run a hyper piston in any high performance application. I bought my forged pistons from jegs for $216. Forged pistons arn't that expencive you don't have to buy ross or JE pistons to get a good set of forged pistons. I purchaced speed pro #L2256F40 and they only cost $27 each. You could look into speed pro or TRW pistons they both are good.

 

yeah thats a good price. But I have a 400 SBC. it seems that for only a .125 inch bigger piston the price jumps an easy $100

 

Since you plan on pushing the compression to the limit 10.5:1
Nitrous or not I'd go with forged, cause you'll be detonating
some times.

If the extra cost of forged pistons bothers you, what about
the cost of quality fuel. At 10.5:1 you will have to run at least
94 octane all the time.
I would build a street 400 with 9.5/9.8 cr for cast iron heads
and 10.0 to 10.25 with alumium.
The bigger bore of a 400 makes it more detonation **** than
A 350. (more surface area to volume). Deck the block for proper quench height and you'll have lots of power at 9.5 to 10.0:1
And be able to run a nice 125 to 150 shot reguardless of piston.
There is way more power in improving the head/induction system
than getting the last little bit more compression.

 

hypers really hate NOS i would say 75, 100 shot TOPS otherwise get some forged units, there not all that expensive,...



Hypers hate detonation Hypers have different thermal properties than cast or forged and must be set up differently.
(different clearances, slightly less compression, slightly less ignition timing)

forged pistons hate detonation too, but will take the abuse a
little longer.

It is false economy to design a motor that will detonate
cause you built in too much compression for the available fuel
or won't run the nessessary fuel for the compression you have,
and then depend on the forged pistons to save your a**.
Cause they will soon fail too. (Crushed ring lands Pinched piston
pins, loss of ring seal, melted piston{they all melt at the same temp}
I've seen cast , hypereutectics and forged fail, all only
when the motor was set up wrong. (lean afr, lack of octane, over boosted, improper nos setup,over advanced timing. over reved.
I've never once seen a motor fail; because of the type of piston in it. I've also never seen a crank fall out on the ground on a two bolt block. Ever, but I'm still watching for the first one.

 

the less expensive ones are just basically a forged version of a stock piston. It is extremely heavy.

There are other issues that come into play with NOS with hypers. The top ring gap (while less than KB used to recommend) ends up almost being doubled. Your talking about a top gap of about .028". In some cases over .030". Not only will you spend a long time gapping rings but even after you will loose some compression to the leak (even after warmup).

Its one thing to build a 400 that will take a little (100-125 shot) spray. Just regapping rings (even on hypers) will be sufficent. But, if your shooting for something in the 650+ hp range, (200shot or so), you really need to approach the motor with NOS being fundamential to the use at all times. By that I mean that the motor should not be thought of as optimized when not on the spray. The cam duration and valve timings will be much more oriented to take advantage of the NOS as will the exhaust system and portwork. Different bottom end parts should also be associated with the full-time NOS combination.

The 650Hp route will also require that a whole lot more work have been done in the suspension area or you will not take advantage of it. Rearend gearing will also need to be raised by at least 10percent to prevent the motor from being over-reved at the topend.

Actually, I know someone that has used stock 400 bottom ends and 200+ shots on a 80Z for along time. Every now and then he will cough up a single piston or something.. but he just goes and gets another. . I don't really agree with that logic but it can be done.

 

The cost of gas doesn't bother me at all. I wasn't trying to complain about the cost of forged. Its just that the price of these Hypers looked real good compared to the forged prices. I don't want to run nitrous all the time just have it there just in case. I am definately not looking into as big a shot as 200 I was thinking 150 at the most.

So what are hypers good for?

 

The original concept was for slightly higher performance rebuilds than stock. I don't think NOS was ever really considered. There are some good ones out there now.. they have teflon to reduce scuffing.

Its really a personal thing with me.. if I am going to lean on it hard enough to need to NOS, I just feel going the extra mile for a good piston ( and rod) than stock.

Put it this way, if your planning on using a 5.7 factory rod, with a good bolt, you will probably not be anymore likely to have a piston failure than you would a rod failure. If you going with a highquality aftermarket rod, use a forged piston (and something other than a factory crank-i don't think you need a forged crank). Its just the logical combination.

 

I already have the crank. It is a scat crank. I haven't decided on rods yet but who knows what I will go with. I was leaning towards forged anyways but saw the price oh the hypers and wondered how good the were.

 

Unless your planning on putting something like 2.73 gears in this thing, you will find that the length of time you have it on the floor (even normally aspirated) is very short. My 400 (with 4.10s) revs soo fast, you could not use spray in anygear except the top of thrd and maybe 4th. Thats probably no more than about 5seconds of time. Even a old stock motor should be able to take that with proper fuel delivery.

I think the hypers would be ok.. don't go too tight on piston to wall. I don't like .002". four thousands is a little closer to what I like.

Third gens are very light and it will rev extremely quick..

 

What are you using for a tranny? I have aT-56 so it has kind of small gears. I either am going with 4.10's or 3.73's. I was leaning towards 4.10's because of the T-56.

 

Your missing the point there is no power level
or application restriction here.

If your motor is setup improperly for any of the reasons
I stated above, you will run into trouble sooner for later
mostly sooner. Nitrous will just show you the error of your ways
a lot faster. Forged piston tend to allow a little more "learning
curve" than cast pistons cause thay are stronger.
We've repeatedly run 300 hp on a cast piston motor
with no ill effects as long as detonation is avoided.

Hypertectic pistons work in stock, racing, nitrous, turbo, blown,
marine, dirt applications. As long as the motor is set up right.
And can handle all kinds of power.

 

well here are my plans in full swing:

A 406 roller motor topped off with a superram
I have Edelbrock RPM heads.
I was looking at 10.0 - 10.5 compression
a 125-150 NO2 shot
93 octane ALL the time I would even get some octane booster for times when I know I would be spraying.
The NO2 is not a full time thing only a once in a while blast. That is why I was thinking I could get away with hypers because I didn't plan on using it all the time

 

Thats my point about short term load.. I have not really ran my car in the quarter or any killer launches yet and the T5 has held up.

I will probably go T56 or tremec. The 400 has the torque to pull the gear spacing that the tremec and T5 have and the first gear ratios are much better at getting something rolling that the T56.


Your combination:
combustion pressure
First and formost I think you are really approaching some high cylinder pressures for pump gas. Even without the spray, your going to need a cam in the 224-230 degree intake duration range at about 112lsa combined with a pretty well taylored spark curve to avoid any part throttle knock. 400s are much closer to detonating that 350s bc of the bore and rod ratio reduction.

Torque and traction
With a superram, your probably talking 550ft/lbs of torque on the motor at a pretty low rpm. Thats going to take some good traction bcs it's not going to come up slowly either. Once you add the spray your going to have traction problems at 50+ mph.

airflow
If you can't afford to get a custom ground cam, (which will take adantage of the spray), I would at least fully port the exhaust (and actually, to feed even a mild 400, the performer rpm heads could use some intake work).

Gearing
I think your going to end up running over the topend on that with a 4.10 gear. Unless your going to run about a 30" tire.

6000 rpm with a 4.10 and a 26inch tire is about 114mph.,, you will have the ability to run that speed on the motor easy... and most 400s don't really turn lots of rpm. If you do want to,, you need more head than the performer rpm. Once you talk NOS you will be buzzing 6500+ a little past the 1/8 mile mark!!!. Put a 3.73 gear in it to start.

 

actually the cam I was looking at is the SLP 224/230 soemwhere in the .5xx for lift. either that or Comp Cams has a Marine cam about the same. Comp Cam also has one with 226/236 that I was looking at as well.

I plan on getting a 12-bolt and some sticky drag radials

I was thinking about porting the heads while they are off

Hey thanks alot jcb999 you have reinforced alot of things I have been considering and maybe you are right about the 3.73 gear the motor should make plenty of torque to get by with that gear ratio.

i still haven't decided on a cam you got any suggestions? HOw much does a custom cam go for and if I got what would you reccomend for duration and lift? I should go with at lesat a 112 LSA right? more would be better right? sorry for all the questions

 

Two things - 400s need air - 1.6s on the intake is often the best start.

Find something that has at least .53intake lift (and alittle more exhaust duration and lift for the spray) and then see if you can get a set of 8 1.5s and 8 1.6s rocker arms.

Most I beam rods on 3.75inch stroke cranks will require a reduced base circle cam or that the rods be stroker clearanced.

The SCAT 4340 I beams with cap screws do not have enough clearance (I know personally).

A custom design cam from comp is about $255 (they will mix and match lobes, change the LSA and even go reduced BC for that price). From cam-motion its about 295 (standard BC).

You call them, and they will ask your combination and then makeup something. Comp will make it up using some of their book lobe patterns (which you can sort of figure out your self doing mix and match).

Cam-motion does basically the same but i think they have a few more newer designed (read more aggressive) lobes than comps (and you can't look at their base lobes) But, they are very close..

I specs I got from comp were within 2 degrees of the cammotion version. When you talk reduced base circle, the smallest comp can go is like .055" smaller than a 1.1inch standard core. That would not have provided me enough rod clearance. I went with cammotion who was able to grind a hyd-roller on a .9inch core. (it was about 350bucks).

So, it will depend on the rod work you have-done/will do.. as to what physical grind you might need.

But, I would really tend to pump the duration up to the 235 range to be on the safe side.

The LSA is going to be a compromise either way: The 400 will love something in the 110 or lower range (mine is 109). But the spray will not. You will not get anywhere near the actual rating of the NOS shot without at least a 112LSA.

 

use whatever you can to get the deck as stiff as possible.

Head studs and plugging the deck holes and redrilling for the coolant size are a must on a 400with nos.