KB 107 pistons

[Bad Sport]

I do intend to balance it. I was hoping there would be a stock bore piston that I can use that would give me a point bump in compression. I really don't want to mill the heads unless it's the only option. I intend to get a valve job done and some mild porting to increase flow.

Ideally I would like to come in around 9.5 to 1.

 

[fishy68]

I do intend to balance it. I was hoping there would be a stock bore piston that I can use that would give me a point bump in compression. I really don't want to mill the heads unless it's the only option. I intend to get a valve job done and some mild porting to increase flow.

Ideally I would like to come in around 9.5 to 1.

When I used KB107's in my 360 with X heads (66 cc chambers) the compression came out to about 9.65 to 1 with no block milling. The heads were cut .010 to clean them up. When I was looking for pistons the SP's were in the low 9's on compression using the same figures

 

[RustyRatRod]

There is a stock piston. The 1971 360 piston, IF you can find it. Since it was one year only, the industry pretty much went to the 72 and up and eliminated the 71 piston. It had a higher compression distance and more compression than any other year. So far, I have never been able to find them.

 

[DaveBonds]

My truck had them '72 model year. I still have them. Stock bore and another block that is less than .007" taper and no ridge. I'd have to look at the skirts, but if they're nice, it would be a good runner with some new rings and a hone.

When I used KB107's in my 360 with X heads (66 cc chambers) the compression came out to about 9.65 to 1 with no block milling. The heads were cut .010 to clean them up. When I was looking for pistons the SP's were in the low 9's on compression using the same figures

That is exactly what I'm getting, static with mine in the .030" 318.

302 heads, .010" to square them up 9.65:1 on a 3.310 stroke. 61cc. The 360 X head combo having the longer stroke and open chamber coming up with the same static number.

I've got .011" from zero at the deck, stock 9.600" height. I used Mr Gasket 1121G .028" head gaskets and ended up with .039" quench distance.

The engine is torn down now, due to a faulty torque wrench and a main cap coming a touch loose (no crank damage, thankfully.)

but when the cam broke in, you could hear it running, but you couldn't feel it or see it. Super smooth on the factory balance.

You could grab a few more points on the high end if you were going big on your cam, if you balanced, but it's not necessary at all.

They are awesome slugs. Did exactly what I wanted them to do.

 

[moper]

So - just so I'm clear - you didn't balance it, you couldn't feel anything, and one main cap out of 5 torqued with that wrench came lose? Which cap was it?
Food for thought - it takes a tremendous amount of imbalance to "feel it" especially mounted in the car. But feeling it is not the first sign of trouble. When you can't feel it, it's still generrating damaging harmonics. Harmonics that can damage parts and loosen bolts all through the driveline. I'm not saying your engine has this issue but i'm saying it's far more plausible than a momentary loss of torque wrench accuracy.

 

[Bad Sport]

When I used KB107's in my 360 with X heads (66 cc chambers) the compression came out to about 9.65 to 1 with no block milling. The heads were cut .010 to clean them up. When I was looking for pistons the SP's were in the low 9's on compression using the same figures

So did I do my math wrong, or am I confused on the difference between static and dynamic?

The 107 show a static of 10.44 to 1, which I thought would be 8 to 8.5 to 1 dynamic. Now I'm cornfused.

I am just planning to hot tank, check for damage hone and run stock bore at the moment. I need to end up around 9.5 to 1 or close.

:banghead:

 

[MopaR&D]

So did I do my math wrong, or am I confused on the difference between static and dynamic?

The 107 show a static of 10.44 to 1, which I thought would be 8 to 8.5 to 1 dynamic. Now I'm cornfused.

I am just planning to hot tank, check for damage hone and run stock bore at the moment. I need to end up around 9.5 to 1 or close.

:banghead:

Yes you are confused I was about to ask that lol... 8 to 8.5:1 dynamic is pretty high, close to the max for pump gas depending on what kind of heads/chambers are going on. Dynamic compression depends on cam profile, air pressure (altitude), etc

 

[NC Engine Builder]

There is a stock piston. The 1971 360 piston, IF you can find it. Since it was one year only, the industry pretty much went to the 72 and up and eliminated the 71 piston. It had a higher compression distance and more compression than any other year. So far, I have never been able to find them.

Yup, one year only, but also no valve releifs. Herb Mcandless used to sell a cast flattop 360 piston very similar to those years ago, probally a 9 to one ratio in a undecked block. Cheap too, at 150 a set IIRC. KB pistons are a perfect budget piston. I have a 365 circle track motor that has over 100 races on it, and spun to 7200 very often sitting in the shop floor right now. Very worn, but never failed...Its all in the proper prep, and ring gap.

 

[fishy68]

So did I do my math wrong, or am I confused on the difference between static and dynamic?

The 107 show a static of 10.44 to 1, which I thought would be 8 to 8.5 to 1 dynamic. Now I'm cornfused.

I am just planning to hot tank, check for damage hone and run stock bore at the moment. I need to end up around 9.5 to 1 or close.

:banghead:

Someone correct me if I'm wrong but I think your math was off. To end up at 10.44 to 1 static with KB107's I think you'd have to have the pistons sticking out of the hole a good bit and have some small chambered heads along with pretty thin gaskets. Gasket bore also affects compression. I didn't deck my block and the pistons were about .015 down in the hole so I'd think yours should be close to what mine was. The cam size along with a few other variables determines the dynamic compression

 

[Bad Sport]

Someone correct me if I'm wrong but I think your math was off. To end up at 10.44 to 1 static with KB107's I think you'd have to have the pistons sticking out of the hole a good bit and have some small chambered heads along with pretty thin gaskets. Gasket bore also affects compression. I didn't deck my block and the pistons were about .015 down in the hole so I'd think yours should be close to what mine was. The cam size along with a few other variables determines the dynamic compression

Thanks Tracy, yeah I did some more reading and finally came to that conclusion.

I have put stock engines back together which doesn't require a bunch of forethought. This is the first time I have started from scratch to actually custom built one, sort of anyway.

I'm quickly learning that there is some home work to do.

 

[fishy68]

Your welcome Bruce. Good luck with the project

 

[Bad Sport]

I'm sure I'll have a bunch more brain pickin' to do.

You can read until your mind is mush and it helps some but listening to others that have done it sorta helps put it perspective.

I'm trying to do as much of this as possible to keep the cost down, and to get a feel for it. I know some of the basics but when it comes to picking parts and putting them all together for optimal results, my grey matter starts oozin' out my ears, lmao.

 

[Bad Sport]

Are there specific rings for the KB's, or can I use Hastings Moly rings that are pre gapped. Or should I use the file fit??

Any opinions on the Hastings rings??

The reason I ask is I can get pistons and rings for under 300 bones.

 

[txstang84]

You'll need file fit rings because KB require special ring end gap measurements...generally accepted ring end gap is 0.004" per 1" of bore (e.g., 4" bore would equal 0.016" end gap), KB on the other hand requires minimum of .0065" per 1" of bore, in that case a 4" bore would require a .0265" ring end gap. And that's minimum measurements for N/A engines. Power adders are more due to the increased heat soak in the top of the engine.

The brand isn't as important...if KB has a recommendation, use them, but I believe my brother bought a set of Sealed Power file fit moly rings for his 340 build with KBs

 

[Bad Sport]

You'll need file fit rings because KB require special ring end gap measurements...generally accepted ring end gap is 0.004" per 1" of bore (e.g., 4" bore would equal 0.016" end gap), KB on the other hand requires minimum of .0065" per 1" of bore, in that case a 4" bore would require a .0265" ring end gap. And that's minimum measurements for N/A engines. Power adders are more due to the increased heat soak in the top of the engine.

The brand isn't as important...if KB has a recommendation, use them, but I believe my brother bought a set of Sealed Power file fit moly rings for his 340 build with KBs

Thanks, so I need to get file fit then.

 

[Woods74]

File them to the wide spec, in case you want to blow nitrious on them down the road. It won't affect performance or make it burn any oil.

 

[RustyRatRod]

Bruce, get the Speed Pro pistons. They are coated plus you don't have to worry about special ring gaps. They drop in.

 

[70aarcuda]

Bruce, get the Speed Pro pistons. They are coated plus you don't have to worry about special ring gaps. They drop in.

you still need to check the ring gaps....and if you buy file to fit...you still gotta file rings...

even the non file rings..I put them in the bore and check their gaps..

 

[Bad Sport]

Bruce, get the Speed Pro pistons. They are coated plus you don't have to worry about special ring gaps. They drop in.

I think I will go that route, I can get the Speed Pros and ring set for just under 3 bones.

you still need to check the ring gaps....and if you buy file to fit...you still gotta file rings...
even the non file rings..I put them in the bore and check their gaps..

Sounds like good advice will do.

I wonder if they include ring gap measurements in the kit.

 

[70aarcuda]

the rings will have a instruction sheet that shows the "normal installation"....the KB 107 require a larger gap due to the placement of the top groove...

 

[80fbody]

Hastings makes good rings. I would think that you'll be fine with the standard ring set as you'll need to open up the top gap anyways if using the KB's. I'm betting the file fit sets are just a little tighter so gaps can be set. It's not like it's a different ring material or anything.

 

[RustyRatRod]

you still need to check the ring gaps....and if you buy file to fit...you still gotta file rings...

even the non file rings..I put them in the bore and check their gaps..

Well no kiddin. But it's no guarantee that you WILL have to file them.

 

[Bad Sport]

The kit pistons/rings has Hastings Moly rings with it.

 

[80fbody]

They're good for our use. My last couple sets were Hastings Moly. Again, I would buy the kit & check the ring gaps in the bore. You'll most likely have to open them a bit anyways due to KB specs. Not a big deal. Check first & if so pick up a ring filer for $50 & make 'em nice. I wouldn't really recommend hand filing as it can be tough to keep the ends square.

 

[Abodybomber]

Bruce, get the Speed Pro pistons. They are coated plus you don't have to worry about special ring gaps. They drop in.: Quoted by RustyRatRod.
AGREED! Seriously . Seen a dippy doo ,whack these piston 7000+ on N20,Bruce. Never checked ring end gaps. They lived through 150 N20 hits,for three years.(he couldn't shift or tune...)Speed Pro,please....