I found a great deal on a fresh 406 that's been internally balanced. I have a T-56 and a resurfaced LT1 flywheel. I read a post that said I can have the flywheel bored and holes drilled to use on the older style block. I have a few questions about this motor before I buy it:

1. The post I mentioned said the flywheel had to be neutral balanced to use with a normal externally balanced 400. Does internally balancing the 400 mean it will use a 350 flywheel (& harmonic balancer?) with no other balancing considerations? The guy who has the motor says it has a new Fluidampr.

2. Any issues with boring & redrilling the flywheel to fit the older style block - will it weaken the flywheel or are there any concerns with doing this? This is intended to be a daily driver, no 6500rpm clutch dumps with slicks.

3. He told me the motor has a Comp 268H cam in it (the lifters & valve springs come with it too!!) I'll be running Sportsman II heads and complete Super Ram induction - heads, base, runners & plenum all ported & matched, with the stock computer (or switch to SD), 58mm TB & 1.6 rr's. I noticed the cam has a 110 lsa, will this cause problems with the computer? If 110 is too low is 112 the lowest lsa that should be used? If the cam is not the XE series or if I have to replace the cam because of the lsa I've considered similar duration as the XE268 (224/230 @ .050) with the appropriate lsa. I welcome any recommendations on a cam, from what I've read I'll likely be replacing it. I probably won't go retro roller cam on this iteration, but have not completely ruled it out.

Thanks in advance & sorry for a long-winded post.

 

If a 400 is internally balanced, then it uses non-400 externals. So a 350 balancer and flywheel would work.

The computer will definitely not be happy with that older design cam.

I'd suggest getting a custom grind, about like a XE268, except ground on 114° lobe separation.

Look carefully at the valve springs you have. If they are 1.25" oute rdiamter, they will not work with a XE268 and 1.6 rockers; or any other combination that produces more than .500" of valve lift. I would strobgly recommend stepping up to 1.45" diameter springs, which the heads may already be cut for.

 

Thanks RB. I think the heads are already setup to accept the larger dia springs so I should be ok.

 

Actually, the 110 LSA is the minimum you would want...the next big question is how do you plan to TUNE the combo? TRAXION on this board has gotten cams with 110 LSA to work well with an EFI setup, but I think that was with a lot of tuning (you may want to PM him to verify this)

If you are going to burn your own chips and keep the MAF setup, then that cam CAN work for you...however, if you would like to switch to a SD setup, then certainly get a cam with at least a 112 LSA, preferrably a 114 LSA...

HTH,

 

Hey Shawn,

I was the guy that posted about the T-56 Flywheel, because I did it to my car.

RB is right that you need non 400 external parts, which means neutral balanced. The one piece rear main seal LT1 moves the little counterweight on the rear end of the crank to the flywheel. So all LT1 flywheels have a chunk of mass cast into the inner (engine side) of the flywheel. To run this flywheel on an internally balanced engine, you need to remove that extra material, and make the flywheel neutral balanced too.

As for drilling the holes and strength. I had the machine shop drill my flywheel to match a 2 pc RMS flywheel I gave them as a template. They did, but they drilled the new bolt holes directly outside the ones! The difference in bolt pattern diameters was clos enough that the old and new bolt hole actually intersected each other slightly! This was extremely bothersome to me, but I went ahead and installed it anyway and it never gave me a bit of trouble. Now, I didn't run a sbc 400; it was just a little 305. But I did run it at the track ALOT, launched as hard as the car would (1.9 60') and powershifted every gear. Never had a probem. After two years, I pulled it out and gave the T-56, clutch and flywheel to a friend. When we pulled the flywheel it showed NO signs of stress or cracking in the flange area, and it now sits behind a 7000 RPM, TrickFlow headed 350. Still no issues.

SOOO, I think it's safe. And even safer if you have the machine shop drill the new bolt hole STAGGARD to the old ones! I'd have total confidence in that set up.

One ither thing that needs to be done; the inside dia of the flywheel flange needs to be bored out to fit over the centering flange on the 2 pc RMS crank, which is larger than the centering flange on the 1 pc RMS crank. Hope this info help your project.

 

I'll burn my own proms, I have everything at my disposal and was just starting to get into it when the 700R4 let go one morning when it hit second gear at ~5500 rpms...

Thanks for the info regarding 114 as the preferred lsa for SD. I am leaning more and more toward making the switch to SD so it would be best to plan for that.

 

I just spoke to the guy who has the motor and he described the internal balancing that was done. He said the machine shop told him he could use a bolt on weight at the flexplate - he was going to run an auto tranny - to save money on the balancing by using less heavy metal. So as it was described, the motor would balance like a 350. My question is will I be able to use my LT1 flywheel? Based on the description Tom 400 CFI gave I should be able to if I get the new holes drilled in the proper orientation based on the location of the weight that is cast in the flywheel. Can someone verify this or fill me in on how this can work? I'm supposed to go up to look at the motor in ~3 hrs.

Thanks, Shawn.

 

O.K. I'm familiar with the Bolt on weight he is talking about. You can buy them from Summit for about $30 bux, and they sandwich between the flywheel/flexplate, and the crank. Some things the guy with the motor said don't quite make sense to me.
1) The "bolt in" weight is meant to use a neutral balanced flywheel/flexplate, on a stock, 400 sbc cranked engine (334, 383, or 400). this weight essentially adds the missing weight to the neutral (265, 283, 302, 305, 327, or 350) flywheel/flexplate, that a 400 unit would already have to balance the 400. So if you're engine is TRUELY internally balanced, it shouldn't need ANY weights to balance it. It should have a perfectly neutral balanced wheel in it's tail. If it's balanced to be like a stock 400 crank (which doesn't sound like the case) then you can just balance the LT1 flwheel using a stock 400 flywheel/flexplate as a template and forget about adding the bolt on weight.
2) As I see it, a 265, 283, 302, 305, 327,350 etc isn't REALLY internally balanced because the end of the (2 pc RMS) crank has a counter weight cast into it. On the newer 1 pc cranks, that weight is not there, so it is moved to the flywheel. Which is why the LT1 flywheel/flexplate has the weight cast into it. So if he really ZERO balanced the rotating assy (minus any type of flywheel) then you need to ZERO balance the LT1 flywheel.
3) So how did this guy really balance this motor?
*Total zero balance? You need to neutral balnce the LT1 flywheel.
*Balanced to still require a stock 400 crank's flywheel? Get your LT1 flywheel balanced using a Stock 400 flywheel/flexplate as a balancing template.
*Balanced "like a 350"? Well that would be pretty much like "total zero balance". Your old 2 pc RMS crank has the little balancing weight on it already so again, you'd have to zero balance the flywheel.

You have to find out how this engine was balanced. To what standard or measurement? Any way you slice it, the LT1 flywheel will work, you just need to figure out where the engine is at right now.

 

Thanks for the reply, Tom. The motor has a small diameter Fluidampr on it and the seller reiterated that it was set up to use 350 externals, plus he gave me the bolt-on weight that the machinist supplied with the motor. This is a thin stamped steel piece that feels like it weighs about an ounce and has "400" ink-stamped on it. I'll take the motor back to the machine shop to identify what was done and have them modify the flywheel accordingly. I'm guessing based on all this that they'll neutral balance the flywheel and I'll use the bolt on weight.

 

Yea, it sounds like it, but there's still that conflict about it
"that it was set up to use 350 externals"
which implies that it is neutral balanced, and then
"plus he gave me the bolt-on weight....it weighs about an ounce and has "400" ink-stamped on it""
which would imply that it was balanced to a standard 400 and needs a 400 only flywheel(or a cheapo after thought bolt in weight). Again, that is the same cheapo balance plate I used when I put a SBC 400 in my TA, with a T-5. i had a standard (neutral balanced) 350 flywheel, so I took the cheap way out and bought that cheesy stamped tin balancer and slaped it in there.

If your engine turns out to need that plate, instead, get your hands on a 400 flywheel or flexplate, and have your machine shop balance your LT1 flywheel to match the 400 one. Then you can forgo the crappy tin weight.

 

I wondered about being able to do that, especially with the flywheel having a weight cast in it, but I figured that would be too good to be true. That's what I'll try to do, I would rather not use the stamped steel weight if I don't have to. I wonder if he just meant the motor was dynamically balanced to a stock 400 configuration. I'll report back once I find out. Thanks again.