KB hypers & timing

[77cruiser]

Do KB hypers tend to want less timing than other pistons?
Do they have more tendency to detonate due to the higher temp?

Still puzzled why a 9.7 C/R can only take 30 deg. without rattling.

http://speedtalk.com/forum/viewtopic.ph ... highlight=

[Ed-vancedEngines]

Is it possible you are inducing an early detonation by having too great of a quench distnce? With that combination using the flat tops and that head I would be doing it at .035 to .040 quench.

Are you using a thick head gasket?

Are you using a regular .040 - .042 but have your piston deep in the cylinder?

Do your pistons or your heds have any sharp edges on them?

Is your distributor giving you more advance than you think when under operation?

With that head chamber with flat tops it should be comfortable with 34 deg to 36 deg all the time and even up to 40 deg for racing with correct jetting.

Ed

[77cruiser]

Thanks Ed. Quench is fair .040 to .045, rod lengths vary a bit. Before I put it together I broke any sharp edges on the pistons around the valve reliefs. Heads are as delivered.

[machine shop tom]

From what I understand and this may be an oversilmplification (that's why I would understand it), the KB pistons are designed to increase HP by making the head of the piston run hotter. That's why they need a lot of top rind end-gap. This is also the reason they require less timing. I just sold a set of KB hypers to a customer (400 Pontiac) and there was documentation in the box that had words to that effect.

tom

[Ed-vancedEngines]

tom,
The reason we need to gap the top rings wider with the KB Hypereutetics is becuase of the ring stack. The top ring is very close to the crown of the piston so it gets more heat than if it were lower down away from the crown.

I am really wondering what his problem is because I do use several of the different KB style of pistons for street/strip engines and we just don't have these problems. We also use much more compression and much more timing in them. Shoot even my cast iron head 64 cc with flat tops do fine with 92 octane pump gas and 34 to 36 degrees of timing for street driving, and even more with race gas for racing. I am talking about 80,000 mile to 120,000 mile street engines too. I also do this with alumin head engines and have even gone as high as 11.30 -1 with the KB Hypereutetics. I never build een the engines for 87 octane with less than 9 1/2 and those are usually up to 10.00 -1 for using 87 octane regular and with timing in the areas of what I suggested.

I might add that most of the builders around here do tell me that compression ranges I do won't work though. One of them tried what I told him to do and his customer engine burned up in less than a month. So please do not do what I say I am doing. Do what works for you, not what works for me. This was added for readers who might try to do the 11.00 -1 ast iron head stuff. I do a lot also with the entire package it is more than just compression.

I still thnk you muct have other issues.
Is your exhaust real restricted?
Do you have header leaks?
Are you sure that you aare getting good fuel distribution?
Are your spark plug heat ranges too hot?
Do you have any vacuum leaks at the carb gasket or intake gaskets?

You do know that a normal aspriated engine will run hotter with retarded ignition timing, don't you?

If this is a street engine I would have ignition timing to not begin advancing until 1,700 rpm and to be fully advanced by 3,500 rpm. Any advance before an engine's fast idle speed is not good. 22 to 24 degrees of advance in the distributor and 12 to 14 degrees initial advance usually will work ok with heads and chambers like you have.

I can not comprehend it needing less than 30 deg total at full throttle at rpm.

[shawn]

I just skimmed through your other post, but i would say it has more to do with your carb then anything. Put a good Holley on there and you'll probably get ride of your problem.
shawn

[77cruiser]

IIs your exhaust real restricted?
Should be OK 2.5 Flowmaster system.

Do you have header leaks?
No.

Are you sure that you aare getting good fuel distribution?
Not sure of this never checked plugs after a pull on the chassis dyno.

Are your spark plug heat ranges too hot?
I'm using the recamended plug by AFR.

Do you have any vacuum leaks at the carb gasket or intake gaskets?
No.

Advance starts @ 1200 & in by 2800 20 deg. mechanical 9-10 initial 10 vac.

[RogerF]

Couple of things jump out at me.

1) AFR cnc chamber is very well designed (needs less timing)
2) KB pistons run hotter (need less timing)
3) Reasonably tight quench (needs less timing)

On the surface, I would expect this motor to require minimal lead for best power, and that's a good thing.

You don't say what length rod's in it, but that might also play into the timing some as well.

As for the power, I see two things specifically.

1) As others have mentioned, spread bore to square adapters are awful. Essentially trying to fit a round peg in a square hole on the secondary side. This wreaks havoc with distribution and flow. Get rid of it. If you want a Q-jet (and I like them too) put an Edelbrock 7104 intake on it immediately.

2) That cam is mismatched. If it really is 292 @ .013" and 278 @ .020" as stated, then it's probably 282 ish at the lash you're running. If so, it's giving you a dynamic CR around 7.8 (which is consistent with your compression test) and is too low for your application and converter. I would go smaller and to a split pattern. Something like a Reed Cams #T264/270 233/238 110+5 looks good to me for this motor particularly in a heavy car.

FWIW...

[machine shop tom]

tom,
The reason we need to gap the top rings wider with the KB Hypereutetics is becuase of the ring stack. The top ring is very close to the crown of the piston so it gets more heat than if it were lower down away from the crown.......
.............. I can not comprehend it needing less than 30 deg total at full throttle at rpm.

That's part of the way they make the top of the piston run hotter. By moving the ring farther up it runs hotter. Since the ring is one factor in dissipating heat from the piston, is only make sense that if the ring is hotter, then the top of the piston will be hotter. They also use a HUGE accumulator groove and space the second ring quite far from the top ring.

I'm pretty much going by what they instruct on the timing. I'm not going to try to second guess the designers. I have seen a lot of KB and Silvoite piston damaged by ring butting and preingition and detonation damage. I attribute these probems to mis-machining due to ignorance of the proper specs for these pistons and to improper tuning due to the same reasons.

I don't usually recommend K/B or Silvolite claimer hypers mainly 'cause there are too many pitfalls awaiting the "on the ragged edge" guy or the careless tuner.

And please don't take any of this personally, Ed, it's intended to describe those who don't read directions or the uniformed.

tom

[77cruiser]

I agree with the adapter prob. not the best way to go about it. I do have a 3310 I'm going to try, I had it on before but never did any tuning on it so I wasn't impressed.
I do have another adapter too, it's a little thicker so I think it might have a better transition to the plenum, with some work.

Thanks for your time
Jim

[dwilliams]

I don't usually recommend K/B or Silvolite claimer hypers mainly 'cause there are too many pitfalls awaiting the "on the ragged edge" guy or the careless tuner.

KB is serious about the extra gap on the top ring. But even experience engine builders often fail to read the directions, and they wind up with a piston that looks like the one in the little booklet that comes in every box of KB pistons, that shows a piston with the top ring land ripped off. I have one sitting on the shelf, that I picked out of another shop's scrap bin.

"Damned junk, that's what usually happens with those things."

"Did you file the extra clearance into the ring gap?"

"What? I can't waste time with that."

I've also seen people fail to notch the oil ring for the dowel pin for the pistons that bridge the lower rail across the pin bore. They'll make two or three attempts to jam the piston into the hole, then line the gap on on the dowel. That doesn't work very well either...

These are usually the same guys who hate Spirolox, because they never read the instructions on how to install them.

As they say, "RTFM."

[Cammer]

Hypereutectic pistons exhibit good strength and good thermal qualities.

Thermal stability allows for tighter clearances allowing decreased negative piston motion and longer life.

Hypereutectic pistons will not tolerate much detonation.

Ring grooves close to the top of pistons help curb detonation by limiting area of piston seeing heat and reflecting heat back into the combustion chamber. This can positively influence power levels. The piston ring package must be designed specifically for this application. Piston designers are moving top rings upward and reducing piston height to increase efficiency.

Ignition advance is an indicator of the range of limitations in a particular engine and designers try to design engines needing minimal ignition advance for the intended application

Specific applications demand unique ignition requirements and tuning. Let your engine tell you what it wants, do not just follow the crowd!

[SandRacer]

I used a set of these to race with for a couple seasons, but only ran a few races with them and did fine. !3 to 1 406 set at 34 degrees with race fuel. However I have had 5 other buddies that used them and every one blew them up! The first was a circle track 355 with the timing set to 40 degrees, lasted 15 laps till the top of the piston came off because the end gaps closed up (ruined the block and 1 head). 2 were from the same malidy as the first, too much timing and too close on the end gap. The one that really bothered me was 1 setup with everything correct and it pulled the piston pin out at 7500 rpm, can I say what was left! Another was a circle track motor done right, the pin pulled out of the piston on it too! The last one was a big block drag motor that lasted a season and a half before pulling the piston pin out!

These were all full race motors run to their limits and beyond, maybe a street strip would last better. I never had a problem with mine, but pulled them and installed some JE's just because I was scared of what happened to my friends.

Tom

[SilverFox]

Wouldn't all those pins yanked out the piston be an indicator of a piston sticking at high R's due to not enough clearance?? All those pins pulling out sends a red flag up for me.....and I'd be looking at clearance before suspecting a poor piston design.

[Ed-vancedEngines]

Maybe I am just lucky all the time then.

I have not experienced the problems with products that it seems that others experience. In a way I really don't understand. I use Total Seal Rings and have for years and love them, but I read on here mostly negatives about them. I have daily driven and raced frequently during the week and raced at the track on weekends engines that are using exactly what it seems everyone else has problems with and most of my junk I do for either normal aspirated or mild nitrous is set up with more compression than most use and the stuff just lives and lives.

The same or similar engine 385 cu in With Canfield Aluminum Heads, one of my customer's has is running at 11.30-1 measured static compression ratio, is using the KB Signiture Hypereutetic Pistons with Total Seal Gapless Rings. IT even has the piston sticking out of the hole by .005 and he sprays it with a 150 shot most times he races it, so I am pretty sure his piston tops are getting pretty hot. His timing is computer controlled but initial is close to 18 deg and it does not start advancing by rpm until 1,800 ropm, but I do have it advancing when it sees a very low vacuum signal and full throttle. It cruises at between 34 deg to up to 40 deg on decelleration and is set at a max of 40 deg until 5,500 rpm, where I cut it progressively back until max rpm which is usually 6,800 rpm. (Hydraulic Roller).

If piston pins (I assume you mean wrist pins) are coming out there has to be slack in the end play somehow. They don't just come out. Mention has already been made about the top compression ring gap. Ring gaps don't just come together, or close up.

The hypereutetic pistons were never intended as serious race pistons. They were to fill a gap between the cast aluminum pioston factory replacements and the higher costing forged pistons of all alloys.

Because many of my customers have very low budgets we do have to use these more than I would prefer but have not seen the problems I have heard that some others have had. If you are detonating enough to crack or bust the hypereutetic, I am guessing that you would also damage any forged piston as well. .

I think that the KB or Sterling/Speed Pro/Trw/Sealed Power hypereutetic pistons do very well in the use they were intended. The KB does require a much wider ring end gap though.

I will have to admit that I build very few circle track engines so most use of them is in street/race or in bracket race or daily driving. I am pretty certain that in long duration racing applications, if I did have to use them that some clearances woul be different.

Ed