Ok we finished up the new 383 and it shakes pretty bad, thought it was just the cam. Took it for an easy tour down the road, and it starts to shake, REALLY shake. Bring it to 3000RPM and the shake is enough to throw the T5 out of gear. Thought it might have been something in the tranny to the driveshaft or back from that. Parked it in the driveway, left it in neutral and started bringing the revs up and it still shakes like hell. We think we're gonna need a new harmonic balancer. The one on the engine now is from a stock 350. Since there's an aftermarket "400" Eagle crank, and the original 400's were externally balanced, does this mean I'm in need of an externally balanced Fluidamper. (Thats what i'm getting is a Fluidamper.) Do you think this will solve the problem? Do you think the fluidamper will work well enough that i won't have to take out the flywheel and have it balanced? Can a fluidamper compensate enough to solve this problem?

Thanks

 

Uhhhh... You didn't externally balance the engine? With a 400 crank? I'd not run it again until you do.
I would've thought that everybody would have understood that 400 cranks need to be externally balanced, by now.

 

since you bought an aftermarket crank is it internal or external balance? is your flywheel and dampner external or internal balance? the all need to match, plus the rest of your rotating assembly. if you don't know you shouldn't run the engine till you find out what you have.

 

the crank itself was balanced and the pistons were weighted.
the engine shop that sold the engine kit said it would use a stock 350 dampener and flywheel, but he was obviously wrong. I even asked him if I would need a special dampner and he said the 350 would work.

 

and of course he's hoping you're the one you'll bring your car back to work on when **** really hits the fan....something i learned, unless you personally know him, never trust a mechanic.

 

Yeah, I understand that it should have gone with a different dampner in the first place. What i'm asking is if you guys think that the Fluidamper will be enough to fix this problem without having to remove the flywheel. The flywheel by the way is from an older pre 87 car due to the different bolt pattern of the back of the crank.

 

If you change the balancer you HAVE to change flexplate or flywheel depending on automatic or straight drive. Every engine I have had balanced the shop always wanted everything that would be attached to the crank, pulleys,balancers,flexplate or flywheel w/pressure plate,all bolts that would be used to hold these parts to the crank.

 

I'll bet the motor was never balanced at all. I'll bet they weighted the pistons and assumed it would be ok. Other wise they would have caught it.
You can try replacing the flywheel and balancer with ones
for a 400. (external balanced) but I'll bet the motor will still be some what out of balance. Good Luck to ya.

What shop was that anyways?

 

if it was my motor, i'd start dissasembling it now to have it balanced.

if the shop didn't have a harmonic balancer and flywheel to balance with the rotating assembly, then it's not balanced at all.

good luck!

 

Well, before you take it apart do a compression test. I have seen engines jump all over the place because of the valves out of adj. Tight.

Auggie

 

yeah, that could happen (valves out of adjustment) but the point is, this is a (now known to be) completely unbalanced motor. the labor and $ to tear it apart and get it balanced correctly isn't much of a big deal compared to scattering the entire thing on the highway.

first things first- call the guy who did your crank and find out whats up!!! I suppose it's possible he did a really expensive "heavy metal" balance job so that you could use a 350 flywheel and balancer, but i really don't know what the point in that would be (waste your money?). but call him and find out whats up.

 

Well, good advice.

Auggie

 

I put the fluidamper on and the shake has decreased considerably. You can only feel the shake inside the car. You could put a full glass of water on top of the engine at all rpm's and not spill a drop. This weekend I took the flywheel off to take it and have it balanced for a 400. The guy I bought the engine kit off of is ancient and said the kit would work with 350 balancer and flexplate. he was full of ****.

 

they can't just balance your flywheel for a 400. If they tell you they can, they are lying. The entire reciprocating assembly (pistons, pins, rods, rod bolts, crank, harmonic balancer, and flywheel) must be balanced as an assembly.

You have an unbalanced engine. You can take it apart and balance it now, or hope you're lucky enough that it won't scatter itself all over the road later. Even if it doesn't scatter, the imbalance will surely reduce the life of your entire bottom end.

good luck.

 

Tell me what the reasons are that a 400 or 383 can't be balanced internally. Please.

 

Well, there are none!

Auggie

 

nother good point to balance it is it will also trash all the bearings in the bottom end because of the inbalance.

 

This thread explained it very well.

https://www.thirdgen.org/techbb2/sho...hreadid=119003

Here is a quote form that thread:

I was going to paraphrase but couldn't do it justice. HTH

Jim

 

Well, I am building a 400 right now and here is the way I am going to do it. Stock 400 block (9.025") decked to 9.010". Stock 400 crank (3.75"). Eagle 5.7" rods. Stock Manley .030" over forged pistons with a 1.560" comp. dist.

5.7" (rod)
+1.560" Piston comp. dist.)
+1.875" (1/2 stroke)
--------------
9.135"

The pistons will be out of the bore .125" (9.135 minus 9.010 = .125"). I will machine .125" off of the top of the pistons for "0" deck clearance and a new piston comp. dist of 1.435". This will move the top ring from .263" to .138" from the top of the piston. This will also require a top ring end gap of .025". The comp. ratio will be adjusted (not decided yet) by machining a "D" shaped dish into the top of the pistons. I will use a Fel-Pro .041" head gasket for a tight squish to make the eng. less prone to detonation. 10.5 to 10.8 to 1 on 92 oct. fuel with steel heads.

Auggie

 

wow, are you kidding? you are going to machine 1/8 of an inch off the top of the piston?!?! Uhm, pistons aren't that thick, and you will be (in my opinin) critically weakening the top of it. You are probably going to be taking 1/2 the entire thickness of the center of the piston away.

Why don't you just get some pistons set up for 5.7" rods with 400 stroke. KB Silvolite makes hypereutectic pistons for this purpose, in lots of different dish sizes, and i'm sure lots of other manufacturers make these pistons too. They just move the pin up a little in the piston. which is far prefferable to a paper thin piston top. One bout of detonation and your pistons are going to have big holes in them. I've seen unmodified pistons with holes in them because of detonation, let alone thinned ones...

Shaving 1/8 off the top of the piston is VERY scary to me. Talk of machining a dish into the pistons after they have been shaved is even more scary.

At the very very least, call the people who make the pistons and ask them if this is OK. Remember, they don't load these things down with tons of extra metal that you can machine off, because extra metal is extra weight and extra weight on a recip. assembly is HARD on everything (and a pain to balance).

 

Well, very good observation but I already have built such an eng. in July of "93" and its still running strong. Has many, many hard miles on it. Dyoned out at 422 hp @ 5150 rpm and 465 lb. ft. of torque at 4000 rpm. 10.5 to 1 comp. ratio on 92 oct. with steel heads. Installed in a 1987 Monte Carlo Aero Coupe using a 750 mod Q-Jet with ccc and sails right through emissions. Oh by the way the stock piston head thickness in the center is .280" .280 minus .125" minus .030" (dish depth) = .125".
I quote from Pro Engine Blueprinting Magazine: The thinnest point on the head of the piston is usually in the center and should not be less then .080". I will also be useing a 100 hp shot of N02. Because these eng's are installed into cars with ESC they are safe from deto because of the knock sensor. Wish me luck.

Auggie

 

Auggie:
You're going to a lot of trouble just to burn some holes in those too thin piston domes. Trouble is engines that have to operate
on knock retard most of the time while at full throttle to stay out of detonation, don't make as much power as a motor that runs with optimin power timing and a little less compression ratio.

There is just no benifet to building a motor like this and then crippling it with knock retard and or rich fuel mixtures to keep it out of detonation. ESPECIALLY with NOS
I'd really rethink this.... You can easilly exeed 422 hp
with more reasonable compression of 9.8 to 10.2:1 and run
full timing.

We won't even go into the different operating conditions that the motor will see "in the car" as opposed to "on the dyno".

 

Well, like I said I already have one out there with many miles on it. I wanted to buy a custom set of pistons from Ross, which I can but they want $587. So I bought a set of stock 400 pistons for $180 and had my machinest buddy do all the mods on them at "0" cost. I did all the carb calabrations on the Monte using an Air/Fuel Monitor (did not want to remove computer and wireing from the car for the dyno runs) so I know what to do to my Q-Jet. Also like I said these cars have ESC (knock sensor) to protect the eng. from deto.

Auggie

 

And how do you think the knock sensor protects the motor from detonation? By reducing the timing. Once detonation is detected by the computer, it has to knock back the timing quite a bit just to kill the detonation.

You may have gotten 422 hp out of it on the dyno under a one time flash reading but in the car (Typically higher air inlet temps and block temps) you need considerable knock retard to keep it out of detonation. This REDUCES POWER.

When it comes to Nitrous motors a thinned piston dome and a high ring placement are definatly not the way to go.

What cylinder head chamber size are you using?

 

Well, exceding 422 hp is very easy to do but I am after driveabilty not max hp. I do not want my eng. to idle rough or have a high idle to keep it running. You are right about running high comp. ratios and retarding the timing. Retarding timing is not necessarly a bad thing but dosn't make sence. In this case the total timing the eng. liked was 32*. Also one of the key things you are missing is the squish clearance. Engines with tight squish clearances will tolerate higher comp. ratios because of the comb. chamber turbulence. A second flame front has a hard time to lite off because of the violence in the com. chamber. Anyhow after we got the eng. running and the carb done we disconnected the knock sensor and the eng. did "not" ping or deto. So we set the timing at 4* btc for a total timing of 32* at 4000 rpm. He did call me a month later and said that the eng. started to ping slightly when it shifted from first to second and was getting worse. I asked what was the last thing he did to the car. He said that he fillered her up with 92 oct. I told him to drive it easy and run that tank down to 1/2 full and go to another station and add some 92. The pining went away. He stopped and fillered her up at one of those stations that puts 87 in the 92 pumps.

Auggie

 

Well, 75cc #3973493. Int. flows 222.4 Exh flows 172.4. Int valve = 2.02 Exh. valve = 1.60. Int port = 168cc. Int manifold = Weiand Team "G" 360*

Auggie

 

I'm not big on huge lumpy cams that eat gas either.

I get a calculated cr of 10.25:1 with 75 cc heads
a .030+ flat top at O deck height with a felpro .041" 400 gasket
Allowing 6 cc's for valve reliefs. (typical)

That should be ok on 92 gas. Compression is funny, you're all right, right up till ya got just a little too much for the gas you can get. Then all hell brakes loose.

I had a .060+350 I build to 10.34:1. it was ok but could be touchy on any thing but sunoco 94. It had nice tight quench and cool (-2) street plugs also.

Once they get some miles on 'em the octane requirement seems to go up. carbon, oil in chamber.

 

Well, actually the comp. ratio comes out to 10.89 to 1 because when I cut the .125 off of the piston top the dish and valve reliefs are gone. Now of course I can dial down the C/R to what I want when I have the "D" shaped dish machined into the top of the pistons. I got to tell you man, I would like to give you a ride in that Monte. It really rocks!!

Auggie


PS: I know what your next question is going to be and yes the valve to piston clearance is OK. I like talking to you because it is hard to find someone who knows what their talking about.

Auggie

 

well, i'm totally suprised to hear about a motor with such thin piston tops lasting like that, but i guess ya year of something new every day.

I'm building up a 406 (actually a 404.8 as i'm only 0.020 overbore) with the KB silvolite pistons and 5.7" rods, the pistons have the higher pin to handle the extra rod length. they have a partial dish design that matches the chamber in my fastburn heads, so it has a good quench area like you are talking about to increase turbulance and decreate detonation tendencies. The block was decked a few thou so that the pistons were only about 0.005 down in the bore, and with a thin 0.038 head gasket, the quench area should be pretty good.

anyways, didn't mean to flame you, just didn't believe it was possible to take that much off the top of the piston and be successful. way back when i worked in a shop, i saw a ford 302 piston that had a quarter size hole punched through it due to uncontrlled detonation in a totally stock motor..

 

Well, I never felt the least bit flamed, just a good old discussion on differant ways to build the same type eng. Good luck with that "404".

Auggie