Combustion chamber mod

[eracers999]

This is a idea only.

Why couldent you fly cut or broach 6cc out of the combustion chamber to lower effective compression.

With the Mahle piston that is .010 down and 5cc removed from head comes out to 18.35 comp.

With 6cc out if head makes it 17.98

Please chime in here on this. Seems doable.

Kent

[arrowheadracing]

While I havent personally looked at a 6.5 head,yet, internally. I would say that enlarging the chamber by strategically removing material in the chamber could be very beneficial to the motor. Unshrouding the intake valve ( which most heads are not too good around that area ) would definetly help low lift flow. I would recontour the chamber more then just enlarging the chamber itself. I just worry knowing that the motor could make more power, but then the trans and torque convertor might not be up to the higher outputs. I easily see being able to push 300 rwhp with the correct mods, but how driveable and how long would it last ? Or how much more work would the trans and convetor need ( transfer case aswell ).

Good idea Kent
Todd

[grape]

Originally posted by Kent:
This is a idea only.

Why couldent you fly cut or broach 6cc out of the combustion chamber to lower effective compression.

With the Mahle piston that is .010 down and 5cc removed from head comes out to 18.35 comp.

With 6cc out if head makes it 17.98

Please chime in here on this. Seems doable.

Kent what diameter head gasket did you use, and how thick was it? Where was the piston in relation to the deck surface, and how many cc's did you measure in the dish of the piston. I've been measuring a few things on engines I've taken apart, and so far what I've measured stock, they are below what the gm book says they are.

[Kennedy]

There is no "chamber" to speak of on a typical diesel head, but the idea is definitely not a bad one. Problem is you'd run into trouble at the precup. From there, I'm not sure how much thickness we have left to give in the head. Specs don't allow for much decking at all which could be a valve height issue, or thickness. You'd have to go a lot deeper as you wouldn't be gaining from area occupied by the valves and the slight recess around them.


http://www.kennedydiesel.com/images/combustchamb_cc_sm.jpg

[Kennedy]

Allowing overbore and not counting the area above the top ring between the piston and cylinder, I figured in the neighborhood (I worked it all in a spread sheet when I did my piston design) of 14ccs is necessary IF the piston still pops out .005" or so...


Using a 20/20 pushing on the small end, you can shorten the rods a few thousandths also.

Don't forget to allow for decking...

[arrowheadracing]

I would say that would definetly be a job for a cnc setup. After seeing that picture, I would also conclude that the intake valve is severly shrouded. But with as much as might be necessary to unshroud the valve, you would run out of material before you would be able to really make a difference. Which would second my opinion that all port work on heads should be directed towards low lift flow. Not increasing the port, but reshaping it to promote better velocity , not more volume. As the engine doenst see enough rpm to really risk losing valuable low end power, in search of 5 hp at the cost of 20 ft lbs down low.

These diesel engines interesting me more and more with every modification I do.
Todd

[eracers999]

Grape: Im using performance trends compression calculator and just figured the compession using the mahle .010 lower piston, stock deck heith, that alone lowers the compression a full point. Then playing with chamber cc, i kept adding cc to the combustion chamber figure, and it only takes 6cc to get it to 17.98 from there. 5cc brings you up to 18.35 and looking at 5cc in the burret doesent look like much.

JK: I dont think there is 14cc in the head, for some reasone my block is very flat on the deck. So i get the benifit of the .010 lower piston.
Now for the shape of the combustion chamber, draw a imaginary line across the chamber, staying .250 below the pre cup, rounding just around the valves out in to the quench staying about.125 away from the fire ring contact area. Starting at the depth of the cut between the valves and tapering up. Seems safe enough??

Arrowhead: Definatly a job for cnc, but if you were to have a junk head and did a cc measure and then took a carbide to it to see how much was there i think the head would be totally fine.
The rainbow would be unshrouding the intake valve and obtaining a lower comp ratio with out a major rebuild.

Kent

[BUZZ]

This may sound a little extreme, but in the gasser area it is common to fly cut pistons to allow for greater piston to valve clearence. Could this be done to achieve the 5 to 6 ccs? Big question is how would you monitor the cut?
Buzz

[Kennedy]

I keep scratchin my head wondering where I saw the odd shaped fire ring. I don't think it was the 6.5 now. I wonder, was it the old 6.2 (Victor?) gasket that was out of round on the one end?


The pic is a bit deceiving as for valve shrouding. We did not find it necessary when we did the heads for my 96 which is what I have pictured.

As for flycutting the piston, looks like we'll have to do some more soon. This is what I do:

http://www.kennedydiesel.com/images/lowcomppist_sm.jpg

[gmctd]

I tend to wonder what there is about a flat head surface that would 'shroud' an open valve.

Iirc, 'shrouding' occurs when the opened valve is surrounded over a major portion of the circumference by the walls of the wedge-shaped combustion chamber, which is a pocket in most gasser-type heads.

Dunno - maybe it's the new math, or something...........

[eracers999]

JD: I see your point, however the int valve is recessed .090 in the head and these dont have a very hi lift profile on the cam. The intake valve is shrouded by the cyl wall pretty good cause it is so close to it.

There is no new math just ideas floatin around.

Kent

[grape]

I'm curious about getting tulip shaped valves made, lighter and more CC's in the chamber.

[gmctd]

Most Diesel combustion chambers are in the piston crown.

The slight depression for the valves in this indirect injected head is to keep the flat-top piston from cramming the valves further into the ports at TDC.

3500rpm Boosted engines do not much care about valve shrouding, at any rate, where the fuel is injected into the cylinder, and not part of the intake 'charge'.
The fuel cannot be separated from the mixture by inlet path turbulence.

360cuin naturally aspirated small blocks, however, running 8500rpm with a restrictor plate preventing that big Dominator from doing it's job, need all the help they can get.

Not too sure of the total effect in the pistons JK pictured, where the Comet chamber was almost totally eliminated - it is part of the indirect injected Ricardo Comet Combustion Chamber system.

(Most folks seeking 18:1cr 300hp aren't really after fuel economy, are they?) ;)

The Bohn pistons, oem for GM 6.2\6.5, have a lowered crown for 18:1cr, maintaining the flat top and the ~0.055" deep Comet two-leaf clover, from examples I've seen.

IMHO, the Mahle or Silvolites, with .010" wrist pin offset, with relieved crowns, as in JK's offering would be most practical and economical, with the Bohns as best choice.

BTW - hard anodizing is technology NASA employs on the shuttle surfaces to deflect intense heat of re-entry.
It is extremely heat-insulative thru-barrier, yet the barrier evenly deflects, transfers and distributes heat along the outer surface.

Bohn, Mahle, Silvolite, and others use the same technology on these and other offerings, and modifications can be re-processed.

IMHO - don't mess with the heads - the Isquared Csquared system already causes much problem with manageable heat transfer in the very area proposed to be modified.

That's my story, and I'm stickin' to it.......

[ 01-12-2005, 07:44 PM: Message edited by: gmctd ]

[gmctd]

FYI, Kent - the Troublshooting\Repair section in Member's Area has cross-sectional view of a 6.5L head, sliced thru the problematic water passage, if you or any have not seen it..........

[Jim P]

When I rebuilt my motor, I did a lot of machining on my heads. I was told by somebody on another forum that it was not possible but I am here to tell you that it is.

I wish I would have taken a picture of mine but I did not.

If you look at the first picture that JK posted you can see that the two valves are recessed into the head. From the valve seat, out to head surface has a 45 degree bevel. I increased the angle of this bevel to 60 degrees and it significantly unshrouds the valves. The only problem is you can't do it all the way around the valve. You will cut into the head gasket sealing surface.

In his picture you can also see a radiused depression in between the valves. I used a horizontal mill with a huge flycutter to cut this deeper and wider so that it is as wide as the circle that is formed when cutting the new 60 degree bevel.

[Kennedy]

I think the Comet chamber recess doohicky was designed for a piston that was coming much closer to the head than the 18:1 "redesign" that the marine guys came up with. My 96 has been running these for some time now. Mark Bajus has a set in his along with my splayed caps, and probably has the most miles of any on my pistons. By the time I machine, and coat the new pistons, it is more than the marine versions, but better IMHO.

[gmctd]

That appears to be a very well thought out modification to a design requirement necessary to channel and distribute a very narrow pressure front out of the pre-cup, where the piston crown is in close proximity to the head surface.

Supposedly exists an N\A 25:1cr all fuel, all weather stationary service 6.5, requiring the slightly depressed valve-in-head location.

While the original design lends itself to n\a and lower Boost pressures, it is remarkable that the identical size, shape and location of ronniejoe's failure is duplicated in several 'over-Boosted' 21.5cr engines, where some previous overheating was 'allowed', BG (Before Gages).

Sustained Boosts claimed from ~17psi to ~20psi, with 'no damage'.

Not pointing any finger(s) here, folks - merely noting remarkably coincidental coincidence.

That's four I've seen, two down here, two up north, maybe five, counting what appeared to be the start of a second failure in adjacent cylinder on the same truck - all but rj's with wastegate spring-jacked to attain the high Boost, all on passenger-side, adjacent turbo, cyls 4-6-8.

It would appear that the writing is on the wall for sustained Boosts over 15psi with 21.5cr engines - possibly even occasional excursions, as is my wont......

While the failure quantity (I've seen) is far from remarkable, the size, shape, and location of the wound is, imho.

Counterpoint(s)?

[rjschoolcraft]

See my comments in the other thread.

One time, I calculated the overall cylinder pressure ratios from compression and boost for my 21.5:1 cr engine and 18 psi boost vs. John's 18:1 cr engine and 25 psi boost... His pressure ratio was higher than mine. I don't think it really matters how the pressure ratio gets there... but it does matter what it is.

MP wrote about peak flame temperatures and cr in an article for the Power Project Truck series some time ago. I would think that should be born out in higher egt. I guess my question is, what about high boost and high compression ratio is inherently bad, if the overall pressure ratio is less than another application?

[ 01-12-2005, 06:35 PM: Message edited by: ronniejoe ]

[gmctd]

I had just been sitting here thinking about that, when it 'dawned' on me - the other similarity was that none of the trucks had a charge-air cooler.

My bad.... redface.gif

My isp has been giving some connectivity problems, or I had intended to strike and correct that part of the above post, hopefully before many read it.

Iirc, JK's 25psi was testing, only, not sustained operation when towing or hauling, but in that case, I think it would be head-clamping forces that would fail, not those pistons.

Also iirc, 10psi Boost at 21:1cr is equiv to 16psi at 18:1cr, or there abouts, pumping pressure, which would give similar overhead for increased power

[ 01-12-2005, 07:36 PM: Message edited by: gmctd ]

[rjschoolcraft]

No, JK's truck would pull 25 psi running solo on hard acceleration. He ran 25 psi most of the way up the hill in the Pull-Off event. It was quite spectacular to hop in his truck, roll down the road and smash the accelerator...and see the boost gage swing round to 25 psi. :eek:

[Spindrift]

JD,

Am I reading you correctly? Four trucks runnin' 17-20 psi with no charge air cooler! What EGTs had they reported for cryin' out loud.

[cruzer]

GMCTD, I had same failure as RJ except crack went all the way across piston, of course I did drive it for 200 miles after failure, so crack may not have extended all the way across intially. The crack was inline with and directly above wristpin. It was #3 hole. All other cyldrs were in great shape, you still could see honing cross hatch and all other cyldrs were to std spec.

The mods were only the Banks Stinger system, which increased boost to about 10psi & spike to about 12psi. 6 months earlier(5000mi)the engine did get hot a couple of times going out west. EGT's were kept in check. The hottest EGT's I ever saw was
about 900*post turbo climbing the west side of Loveland pass. I purchased the truck w/75000mi and failure was at about 127000mi. Stk old style cooling.

FYI

RJ, sorry for your loss.

Ken

[ 01-13-2005, 06:12 AM: Message edited by: cruzer ]

[Kennedy]

I was going to say oil spray would help, but RJ's should be so equipped although the cooler lines are the small ones IIRC...

25 psi to the speed limiter on my '96. It didn't spool as rapidly as I would have liked, but once it got rolling...

[rjschoolcraft]

Yes, the oil cooler lines are the small ones...should I be upgrading to the larger cooler and lines?

I've thought all along that the oil spray jets are what saved me in these overheating events.

[arrowheadracing]

Doesnt seem like unshrouding the valve would be a very easy task. Especially since the chamber ( or lack of in the head ) is spaced as such. Is there any room for larger valves ? And also I would be concerned of tulip valves , with the extreme heat you would be seeing. I dont think the extra cost of having a set made would counter any added benefit in performance , and would possibly hinder longevity. Now dished piston design, there is a whole new discussion. While I am not familiar with all the dimensions of the 6.5 deck height and everything, just from looking at the pictures I see there would be quite a bit of thought process involved to really see any noticeable improvements but at what $ cost?

I guess its like when I was running old pontiacs. No one made anything for them , you wanted to go fast you sat down and thought about it and made your own parts. With trial and error came to a conclusion of what worked and didnt. It seems like the 6.5 is the same way. Maybe its time for me to buy Dmax and leave it alone ?? Like that would ever happen.

Todd

[gmctd]

You know one of them, Spin (sorry 'bout that Spin, Andy!), as does ronniejoe.....

And another one up in Canada - Wester flashed, 20psi Boosted, 0-60 in 10 seconds, no c-a cooler - well on his way to achieving the same end, I'd say.

[ 01-13-2005, 02:29 PM: Message edited by: gmctd ]

[grape]

Originally posted by arrowheadracing:
I guess its like when I was running old pontiacs. No one made anything for them , you wanted to go fast you sat down and thought about it and made your own parts. I take it you've knocked some lifter bores out of some 421 blocks.

[arrowheadracing]

Yeah and quite a few cracked cranks. Most of the stuff in stock form lasted up to about 575-625 hp or so ( no nitrous of course ).

I am just suprised to hear about some of the explosions and stuff here. But alas, I ve only built two turbo cars in my time.

Interesting topic though. I ve picked up quite a few good ideas here.

Todd

[Billman]

This thread is scarin' the crap outta me.

Boost it 'til ya break it and then back off a psi.


Dually for sale.....

[patrick m.]

im running 15psi max now, no way to increase boost....no wastegate. i've had JK's big cooler for around 16 months and i drive it like i stole it (most of the time).
so there is a year and 1/4 of a 6.5 living at 15psi.
Maybe the mark is 15-17 psi at stock compression.
above that, 18:1 is required.

I have found a new wastegated turbo, VERY similar to the GM-8, only slightly more efficient turbine and exducer, along with a 70 trim two stage compressor wheel (i hope i wrote that right).

If this turbo hits the "sweet spot", i'll be preparin for 18:1s

get a set ready for me JK ;)

[rjschoolcraft]

I went 63,000 miles in a year and a half at 15+ psi including 20,000 miles in 7 months with 18 psi while towing. I was not interested in any more boost without lowering compression. I stilll think if I hadn't pre-stressed the pistons with over heating, I would have been OK there. All the other cylinders look great. Can still see the cross hatching from the hone...

I will not go back together without 18:1 pistons.

[rjschoolcraft]

Originally posted by Billman:
This thread is scarin' the crap outta me.

Boost it 'til ya break it and then back off a psi.


Dually for sale..... :D :cool: