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Do you guys like KB pistons for a street motor....

bandit67 said:
Guys, found myself needing to rebuild a 440 , a 76 block, for my 73 B body. Time to purchase internals and looking at KB 237 flat tops. Plan is to use the 452 heads for a mild rebuild. So, having not yet ran any KBs, I understand they are a decent replacements rather than twice the price custom pistons....any opinions.....thanks....
Click to expand...

I dunno why every Piston thread gets into a piss'in match around quench ?
It's overblown if you ask me if you are NOT exceeding the Fuel's detonation capacity.
and.....
Depending upon Bore Size and Cylinder Head Intake/Exhaust Flow ratios we've witnessed HUGE gains on the Dyno with BB Mopars by INCREASING quench distance to up around .075" to .080" from sub .050"

Anyways,
back to the regularly scheduled programming, and given this is a mild build using 452's considering KB237's..... they work fine, we've used them..... but given the special ring end gap requirements we find the ICON 9953 Forged Pistons for only $30 more to be a wiser alternative ?
https://www.summitracing.com/parts/uem-ic9953-040
 
Wasn't trying to cause a problem, just point out that to get the desired results of that quench piston design takes a bit more planning, measuring and maybe machining. In my 360 the results were good. Got 9.5:1 compression for my truck 360 engine that runs really strong on pump swill. One note is these "magnum" pistons require the LA rod pin ends to be narrowed to magnum pin width. Not an issue with the Big Block, just noting if someone with a small block is interested.
One issue may be that if I ever want to use closed chamber heads, the quench dome would need to be removed.
When I looked back at it, I could have gotten the same compression ration with a flat top, but have no quench with the stock iron heads. Not sure if the engine would have been more sensitive to fuel octane though? On the other hand, I could have just put aluminum closed chamber heads on to get quench and more compression if I decided to use the engine for a higher performance application.
 
We all come here to get and give information. Some of us, ME, ME, can be a bit slow at retaining this info and do appreciate all who have patience with us slow pokes..me, me, me again. Knowledge can be more valuable than gold and folks here with first hand experiences save me time, money and MISERY many times. 340 got a great point, forged for only a few bucks more surely sounds the way to go....much thanks...yall keep batting those thoughts and ideas around, my bb is bound to fall in its slot sooner or later.....lol
 
I'm not going to disagree with Challanger
keys with open chamber are fuel and timing
you may make more top end hp with an open chamber over a 915 - at the top end- like super stock
on the street- never
with a closed chamber and dish to get the cr you want or a FT if you want a lot of compression you can make that work very well also
but here we are not talking about 915 or AL heads
there is just no way to light off a plug low on one side of the chamber and expect an even flame front to way over past the valves
If that area lights off first bad things happen fast
you retard the timing and you build heat
you lower the piston further down the hole you build more heat and less power and way worse mileage
We did a lot of work to develop that piston,, before that we were welding up the chambers- or expensive custom pistons and both worth it
you get the torque with the cam and being able run optimum timing
 
wyrmrider said:
Squish and cam (reduced overlap and opening ex later and closing earlier (closing the lca and reducing ramps)
can reduce EGT by 800 degrees
Click to expand...

Not a BBM, but
That must work for SBMs too. It seemed to me that the HE2430AL Hughes cam I once installed
(270/276/110;223/[email protected]) in at 0 advance (180psi cylinder pressure, .034Q;
Ran nearly as good as the Hughes HE3038AL
(276/286/110;230/[email protected]) in at 4* advanced, with same pressure and Q.

For those that might want to know, this was a 4.04 bore 360.. Yes with Hypers; KB107s.
Initially I installed the KB107s at .0025skirts, with a gap-factor of .0065......... after weeks of heating issues, I pulled the engine out, and opened the skirt clearance to .0035, and the toprings to .008 factor or about .030/.032
Since I did both at once I cannot say which/or both was/were the trouble maker. I suspect it was the gaps and not the skirts. Cuz, .0025 was already generous for a streeter.
After that, I threw away the 180stat, and now run her at 207 full-time. No more heat-issues.
If you guys are worried about .0035 skirt clearance, I'm gonna say don't be. The skirts only rattle when the temp gets down close to freezing, and it only lasts a few seconds. On a hot LeakDown test with a New Plasma-Moly ringset, the LD was so small in the freshly honed cylinders that My gauge could hardly read it. And the engine now has over 100,000 miles on it.
A few weeksafter the changes, the 68 Barracuda went 93mph in the Eighth with 3.55s and a 4-speed, at 3467 pounds and 900ft elevation.
Not a BBM
 
Last edited:
Challenger340 said:
It's overblown if you ask me if you are NOT exceeding the Fuel's detonation capacity.
and.....
Click to expand...
Maybe, but over 100,000 miles I have run 87E10 the whole way, having saved thousands and thousands of dollars. This in an 11/1 Eddy-headed, 230*cam 360. Not a BBM I know, but thousands of dollars, to me is a really big deal.
Not to mention the 367 went 93 in the Eighth,@3457 pounds and 900ft elevation, with a 230/237/110 cam.... and a Q of .039..... and 34* timing, with 3.55s and a 4-speed. It was the only completed run of 4 starts.
If the engine is already tore-down,and it's a streeter, Quench is fairly easy to engineer.

The cost savings in the fuel is a quadruple bang.
>Up here 91 is our top grade fuel and is more than 12% more costly than 87E10
>Being able to run 11/1 ( or even 11.3/1 in a former iteration) means I can drive more hiway miles on the same dollars.
> And I can run less cam for the same street performance......
> and I can run less rear gear, with the slightly stronger bottom-end torque.

I cannot say if Q is overblown or not.
I just know, that I will never again not have a tight-Q, nor 150psi cylinder pressure; those days are history.
 
Last edited:
Ok from Down Under,
New guy to V8's, we have a local Mopar guy in his 60's,
First time I met him for a met n greet, he gave me an almost hour long talk about how the engineers in the 70's ruined the motors by going open chamber, lots of talk about spark plug location and detonation etc.
Anyway 440 build,
Now 0.60 over, its very hard to get blocks here, originally a.30 block in pieces when I got it , however with .10 wear 0.40 wasn't an option
Going with KB184KTM. its for a street car, maybe not a big Hp car , but great torque :)
 
I built a 78 440 using the KB 237 with 915 heads and a small cam. Went 12.80 @ 108 with a stock iron intake and 750 AFB in a 4000 lb B Body. I was happy.
 
Gary Jenkins said:
Ok from Down Under,
New guy to V8's, we have a local Mopar guy in his 60's,
First time I met him for a met n greet, he gave me an almost hour long talk about how the engineers in the 70's ruined the motors by going open chamber, lots of talk about spark plug location and detonation etc.
Anyway 440 build,
Now 0.60 over, its very hard to get blocks here, originally a.30 block in pieces when I got it , however with .10 wear 0.40 wasn't an option
Going with KB184KTM. its for a street car, maybe not a big Hp car , but great torque :)
Click to expand...
Open vs closed chambers is always a great debate.
:bananadance:
 
Got my engine and parts to the machine shop this morning and got the bad news straight from my machinist, he said he would not be able to TOUCH my stuff for two months, they are that far behind. Dang the bad luck. He said he don't go home till nine pm every nite....some things never seem to change. Guess this China virus thing has got you guys busy out workin on our clunkers.....
 
rumblefish360 said:
Open vs closed chambers is always a great debate.
:bananadance:
Click to expand...

The factory big block heads also have poor spark plug placement. And both factory chamber types (open or closed) still require quite a bit of ignition timing.
The Stealth head is more like a factory closed chamber head with the stock plug location. Most of the aftermarket big block heads seem to try re-locating the plug in the chamber. Anyone know how much improvement the heart shaped closed chamber is compared to the D style closed chamber in the heads?
 
i would think lots
dyno work with closed chamber passabger car heads like 915 and earlier and truck heads with the ford FE /sbm spark plug loction showed the truck heads could use 5-7 degrees less timing this was in the 60's
both had d-dish pistons both had good quenchnand both better than 68 and later
you have several sbm examples open chamber vs late heart chamber or Magnums
big difference in advance requirements
what rumble says below
but you have to have the piston/ quench right to get all the benefits
although just changing the spark plug helps even with the pistons down the hole like a late 440- get amatching piston to really help
 
Last edited:
451Mopar said:
The Stealth head is more like a factory closed chamber head with the stock plug location. Most of the aftermarket big block heads seem to try re-locating the plug in the chamber. Anyone know how much improvement the heart shaped closed chamber is compared to the D style closed chamber in the heads?
Click to expand...

Does it make a difference, certainly. Does it make much difference, probably not in most cases, IMO. Also, not all relocated plugs are created equal, and not all "D" or heart shaped chambers are created equal. And then imagine all of the other variables you'd need to hold constant to even do a test. About the only comparison that would be close to apples to apples would be the Mopar Eddy straight plug head to the regular Eddy 84 cc angle plug head. I guess if you changed pistons between tests to correct the compression ratio, you could test the 84 verses 75 cc Eddy heads.

The TF 240 chambers look a lot better than the Eddy 75 chambers even though both are heart shaped, sort of.
 
I'm not sure what power difference the chamber design makes? I do think the closer quench distance does help prevent detonation, and I also don't need to use as much ignition advance with the more heart shaped, re-located plug heads (B1 B/S, Victor MW, TF240.)
 
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