New 6.7l has Siamese cylinders I see.

[fatcat]

So I read that the new 6.7l will have Siamese cylinders (e.g. no coolant jackets between the cylinders, they are all connected down the sides), which will lead to hotspots and cylinder warpage.

Now, if this is 100% true, did Cummins loose their minds or do they think the new cooled EGR will keep the cylinders cool enough?

With all the changes in this new engine, plus the couple thousand dollar cost to replace the exhaust system ... I can't see why anyone would purposely want to buy one in the first year. I would think only when you truly need to purchase a new truck should anyone buy any of the new EPA diesel trucks, and only after they have been out for a while.

 

[batfish]

My take on this (siamese cyl.) it should be a non-issue. There should be sufficient cooling around the cylinders. I would imagine the material connecting the cylinders is still allowing enough of the water jacket space to get the cooling job done due to the cylinders being round. I could be wrong but I really do not see a problem with it and it may actually be a benefit creating a stronger block design and sufficient cooling at the same time.

 

[sle2115]

I know nothing about this particular engine, but I can tell you, we steered clear of the 400 small block Chevy for that very reason. Some built'em, but most of the guys I knew would stroke a 350 to 388 and work with less cubes than to deal with such a block. I personally had one (and never wanted another) that was next to impossible to keep cool. New radiator, pusher electric fan etc. in a Blazer and any time you worked it at slow speed (read off road), it wanted to get hot. It ran great and was removed and replaced with a 388. It was put in a trans am and ran for years, may still be for all I know, as long as it was moving it was fine. Ex-brother in law had one as well, it ran hot all the time. He just tried to baby it as he couldn't afford the new radiator and such. Again, not sure how applicable this is here, but I like coolant flowing between cylinders myself.

 

[94f450sd]

i hear ya on the 400SB.but IIRC there was a way to keep them cool.ive been out of chevies for so long that i dont remember what it was.

 

[icanfixall]

Steam holes are what chevy tried to keep the 400 blocks cool. What it was is this. The blocks had 2 holes drilled down between the siamese bores. This let cool coolant in them till they "warmed up". Then it would force out the hot coolant and more "cool" would fill the holes. Sure.. Its works great. It worked so well the 502 big blocks are siamese bore too....

 

[sle2115]

Having the correct head gasket made a HUGE difference! As far as working great, if you had good luck with them, more power to you as we had little luck. At one time I could tell you where there was about 20 of them for the taking. They worked fine at speed where everything was circulating well, but once coolant temps got in the 200's, they lost their effectiveness, load one up in the mud and you were going to overheat. EVERYONE I knew that had a 400 Blazer, ditched the 400. The 350 in whatever flavor made more horsepower and was much easier to keep cool. If you got at all radical with any 400 for low RPM use, I don't think you could keep them cool - but that is just my personal experience. I know the speed shop I moonlighted at wouldn't do any build ups on the 400's either for over heating and crankshaft reasons. Of course the owner was a 327 nut anyway and if it was over 4 inch bore, he lost interest and he did hold several national titles in this dinosaur of a car with a modified 327!

 

[dieseldummy]

I've got a '76 pickup that came with the 400. Never had any problems with overheating if the radiator was kept up. I guess everyone has their own opinions about things, but years of offroading/towing have proven otherwise to me.

 

[ford killer]

the 400 was a good block for quarter mile just fill the water jacket with cement...

 

[holtzer1]

big radiators and high flow waterpumps are the key to not overheating a 400...maybe the same goes for the new cummins

 

[Cowboy2199]

If you think about it though, siamese cylinders could be good in another way too. The whole cavitation issue with diesel cylinder sleeves.. Less area the water touches, the less it can cavitate and wear through the liner into the cylinder and cause sleeve failure.

I am goin to have to ask around now and see how they are goin to fix those kinds of issues. I know someone who knows a couple of people on the Cummins RapidServe hotline.. They should know whats coming down the pipe..

 

[batfish]

I really don't see why one would compare a 30 year plus design on a chev small block siamese with the new 6.7 Cummins. Its just like everyone thought the aluminum heads would fail on the Duramax because you are squeezing together two dis-simular metals, they simply don't fail. Technology has changed we no longer can compare designs that failed over 30 years ago with todays. Won't work.

 

[92 F-350CC]

All engines are prone to cavitate, Cat, Navistar and Cummins. Seen them all leach holes in the cylinders on our farm tractors, Now some are more problems due to design, (IE 7.3L Navistar for example) and rear their heads sooner. That being said, I think Cummins might be a little further ahead of the dependability game.

 

[sle2115]

I really don't see why one would compare a 30 year plus design on a chev small block siamese with the new 6.7 Cummins. Its just like everyone thought the aluminum heads would fail on the Duramax because you are squeezing together two dis-simular metals, they simply don't fail. Technology has changed we no longer can compare designs that failed over 30 years ago with todays. Won't work.

Because a siamesed cylinder wall is a siamesed cylinder wall, doesn't matter what year it was made. Siamese cylinder walls to not allow coolant to circulate between cylinders, which causes water to flow only the length of the block, no cross flow. In essence, you create a circle of water with 4 or 6 cylinders in the middle. Technology or 30 years doesn't change that!

 

[batfish]

Siamese cylinder walls to not allow coolant to circulate between cylinders

OK sir, let me take a stab at this analogy Cummins engineers intentionally selected a 30 yr design (siamese cylinders) so the new 6.7 would automatic-leeee overheat That is a novel idea and ought to work

 

[sle2115]

OK sir, let me take a stab at this analogy Cummins engineers intentionally selected a 30 yr design (siamese cylinders) so the new 6.7 would automatic-leeee overheat That is a novel idea and ought to work

Yep, I guess I said that somewhere, but just can't seem to find it. What I said was that I preferred coolant to flow between the cylinders. Did I mention anything about a Cummins overheating? My point was and still is, that when you bog one down in the mud, just as with a 400 SM Block Chevy, they will tend to heat up quicker than an engine with coolant between the cylinders. That is all I said. If you can prove me wrong then go ahead. Personally, I prefer to not have siamesed cylinder walls, of 30 years ago or today for the reason they don't get full cooling around each cylinder. Take that for what it's worth. I will do as I have always done and steer clear of the dodge trucks anyway, cummins or no! I would assume Cummins is doing research on how to keep it cool. Steam passages worked unless the cooling system was not taken care of and they passages scaled up. Coolant technology of today is much better as well and in the long run, siamesed cylinder walls probably make for a stronger block.

Then again, you know Ford had a pretty good engine with the 7.3 power stroke as well, until they had to go and f$#% with it. If the 5.9 is all the Dodge boys say it is, why did it need to go bigger, especially to the extent of having siamesed cylinders? Are they afraid sales will go down if they don't hold the "king of the mountain" horsepower title?