6.5 Rebuild Project

[kyelectrical]

About to begin the rebuild project on my 96 6.5. But I'm not sure which way I want to go to get more power. As I tow trailers on the interstate in the hilly areas of Appalachia, I believe I need a lot of low-end torque and much better hill climbing power. I know there's a lot of guys installing the low compression pistons and turning up the fuel and boost pressure. That route sounds ok but it gets pretty expensive when you figure the cost of marine pistons, pumps and bigger turbo. I was wondering if anyone had tried or had experience with going the old-fashioned route of achieving higher compression by over-boring the cylinders and shaving the heads and/or deck. The latter route sounds better to me as I believe it will produce more exhaust pressure, therefore allowing the turbo to boost up faster per given engine speed. I do plan to go full manual controls on my engine using Bobbie Martins' method of replacing the DS4 pump with the DB2-4911 pump. Any serious suggestion out there?
Thanks

[john8662]

Pull a head and take a look, they're FLAT, nothing to take out to drop the compression without seriously compromising the strength of the surface and coolant passage clearance.

The 6.5 can safely be overbored to .040", that's really not much, considering that's only .020" on each side. I don't feel that this is really enough to drop the engine even a whole compression point.

Where are you getting your price for 18:1 pistons?

There are several options...

Peninsular 18:1 - reduced pin height cast into piston, STD thickness top.
Kennedy 18:1 - dished out piston crown, waiting to be tested (eventually).
Diesel Depot 18:1 - Full Topping of piston, shaving then re-coating.

Other machine shops are doing similar things to that of Diesel Depot, pretty common practice to drop c/r.

Besides that there is a .010 thicker head gasket, which I hear isn't the most reliable way of dropping a point.

IMHO, if you're not pulling, and are going to be keeping the 4911 IP close to the 6.5 specifications, then the 21:1 c/r ain't bad.

J

[kyelectrical]

Actually I am planning to do a complete tear down and rebuild. I always thought that overboring and of course going oversize pistons and rings would increase compression. So far the least expensive set of Marine pistons I've found was around $650.00 just for the pistons. That don't include the rings. Pen Diesels' seemed to be the highest at around $1100.00 for pistons and rings. Then you have to add another $1000.00 for the marine grade high pressure I/P and another $400.00 or better for Marine Injectors and finally another $1000.00 for a higher output turbo. That don't include gaskets, seals rings lifters and bearings

My thoughts were that if I did go the overbore route that I could go with standard OEM grade pistons that were oversize. I've not seen the underside of the head or the deck top. But I was actually thinking of boring over .060 and shaving .060 off either the heads and/or deck. I'm not a great mathematician but I think that should get her up to around 24 or 25:1. With that kind of natural compression instead of induced compression from a bigger turbo I should (theoretically anyway) get higher exhaust pressure at lower RPM's. That should in turn allow my standard turbo to spool up faster. Hopefully creating much more torque. I'm looking for at least a 50% improvement in torque at idle speed and hoping for at least 350 to 400hp at top end.
The only problem I see with this approach is it will be generating more heat per cycle due to the increased compression. But my engine does already have the high flow cooling system which I was hoping could handle the extra heat.

[Heartbeat Hauler]

Have you considered just buying one of Pen.Diesel's 300HP crate engines? That should be plenty of grunt. The other thing you might do is just do a stock rebuild nothing fancy and put your money in a set of deeper gears, say 4.56 and an aux. OD trans. Best of both worlds, you'll have good reliability from engine because you aren't pushing it to the max, and you'll have gear-splitting on a deeper axle rear gear to keep that engine in the power band, not to mention a double overdrive. More than one way to skin a cat....just no way to make him like it. :D
JP

[john8662]

No way would you be able to raise the compression ratio, the piston already comes very close to the cylinder head and valves at TDC.

Even if you could rase the compression, you'd face catastropic failure due to bottom and (casting) and crank limitations.

Stick with the stock C/R.

You can raise the C/R slightly by decking the block and getting your piston protrusion a little higher, but at what cost?

Neat to consider though, I understand your thought process.

[kyelectrical]

Are these 6.5's really that flimsy where you can't bore and stroke 'em? I mean that's standard procedure on gassers (plus a cam). I would have thought that Detroit Diesel would have built a better block than that.

[DmaxMaverick]

Increasing the CR will give you more exhaust pressure, but not from more air. The air will just be expanded more, from more heat. That translates into excessive EGT. Under the best circumstances, 25:1 would be catastrophic, as John said, but I think you'd have a meltdown before the hardware went south. The engines aren't weak, just misconfigured, IMO. There is a way to get monster power from them, and keep them together. Just ask 6.5 Nova. They are running a 6.5 with twin turbos and twin IP's in a Massey for tractor pulling. Awsome! Newer video to come shortly.

Make a choice. Increase high end performance, low end performance, or a medium of both. You won't get both with a single turbo. The turbo will either spool quickly to give you low end, and dump EG's at the high end, or spool slow, and give you higher RPM performance.

[ogrice]

What is your pocket book look like.? If you want more power, then get your paychecks up. I spent over 6k to make when I rebuilt my 6.5 2 yrs ago. It was either build up my engine or buy a newer truck. My final additions are a very large intercooler, HX35w turbo and a crankcase evac system. It has 25k miles since completion and I am very pleased with how it runs compared to how dreadful it used to run.

[ronniejoe]

You need to read the articles in my signature...especially Part I and Part II. That will help answer a lot of questions.

[More Power]

I've not seen the underside of the head or the deck top.

Need to get out more... :D A new article was uploaded to the web site last month concerning Fuel Economy (http://www.thedieselpage.com/features/65fueleconomy.htm) that includes a photo of the underside of a cyl head.... ;)

Higher compression pressures raise combustion temperatures. Fueling increases raise combustion temperatures. EGT is a big factor in limiting power.

Jim