Ok... 1st post in the diesel forum. (Update: Think I've decided which engine to get)

[jonrpick]

My plans for my "build" have changed permanently. Now that I know what I want, I'm looking at options to get me there.

The Blazer will return to it's status as a DD, and as such, one of the things I'd like most is to maximize my fuel economy. Now, I don't want to sacrifice everything just for better numbers (If I was willing to do that, I'd buy a hybrid! ) but I would like to get a good idea of what I can expect with a diesel. I know I'd definitely get better fuel economy numbers, but what about power?

I've been glancing over some of the options.

• 6.2L
• 6.2L with turbo
• 6.5L
• 6.5L with turbo
• 4BT
• 6BT
• Some Isuzu motor that was retrofitted into some Chevy step vans (edit: the motor I'm referring to is a 6cyl, not a 4cyl. The models I'm referring to are the 6BB1 and 6BD1T, 5.4L and 5.7L respectively)

Are there any other options that are worth mentioning???

As far as I can tell, the 6BT would be at the top of the power spectrum, while the 4BT would be best for economy. Am I correct? The 6.2 and 6.5 would be the easiest in terms of conversion/installation, correct (although that Isuzu motor apparently isn't that bad, and parts are supposedly available from GM dealers in a pinch).

I'm not looking to break any speed records. I'd like something comparable to a decent 250-300hp 350ci/5.7L gasser in terms of power. I plan to keep my 3.73 axle gears and 31" tires, so I know that probably won't be best for economy (I've read that 3.08's seem to be best with the 6.2's for economy), but it will give me a little more pulling power. I *am* willing to run a narrower, more street-oriented tire rather than the typical "AT"-type that most of us use, seeing as how I don't plan to be in dirt or snow any time soon.

What are the best numbers attainable in a street-driven, non-lifted K5? I've heard of 30mpg+ in some scenarios, but I believe those were 2WD trucks on 29" +/- street tires.

I would like to be able to pull a small/medium equipment trailer from time to time, but not often. I regularly drive 75-80mph on the interstate while traveling. I don't know if you all would consider that relevant info...

Anyway... school me...

 

[Russell]

6.2L / 6.5L will not satisfy your power demands, it'll do everything you ask of it, but you won't get 250 hp like gasser performance out of a 140ish horse engine...

The 6BT is not an easy install, and the 4BT will rattle your teeth out. The little Isuzu engines get the best mileage of any of the above, but again will not satisfy your power demands.

Your best bet will probably be to run a modern gasoline engine and sacrifice a few MPG

 

[Mikey von]

I disagree. 6.5l TD's will easily hit 250 horse. Check threads over at thedieselpage, dieselplace, and thetruckstop. 300 HP is a little tougher, but still doable.

I think a 6.5TD with a mechanical pump will be the easiest way to get what you want. It will give up some fuel economy over a 6.2L though.

 

[jonrpick]

Understand that the 350 in my K5 hits peak "horsepower" (which is a term I avoid using) at around 5000rpm. I don't believe I've EVER revved the motor that high, so I've never experienced the full power of my engine. What I'm looking for is torque I can feel.

I just want enough power for decent acceleration (in case I NEED to get out of the way quickly) at lower speeds, and enough pull to pass someone on the interstate. My top speed is usually 80mph, rarely above that.

 

[jonrpick]

Oh, and what of the turbo option on a 6.2L?

 

[longbedder]

I love my turbo 6.2. I've also got a milsurp 6.5L in a crate waiting to go in my next project.

It was capable of 24 MPG when i had 33"x9.5" pizza cutters, 3.08 gears, and overdrive in it at stock height. It also had enough torque and power to cruise around on the highway and in the hills (I don't believe it would have without the turbo).

It's now in my garage, but is soon to come out with a 4" lift, one-ton axles geared at 4.10, and 35" tires. That combo will put it at its peak efficiency RPM (1800 RPM) at 65MPH. We'll see what happens with the mileage. I'm not at all worried about power, and certainly not worried about torque. Around idle I've got gobs of torque, and at highway speed it behaves sorta like a stock TBI 350 gasser. Given proper maintenance the 6.2 will last a looooong time.

Bhays (see GMOTM vote thread) stuffed a 4BT in his and did a great job, but it took a long time with LOTS of custom fab work. I personally don't think it vibrates too bad, but those engines are also not cheap anymore. I got my 6.2L cheap with the Banks turbo and it bolted right in lickety-split.

Whatever you end up with, I believe a turbo is the single best thing you can do to any diesel by far.

 

[jonrpick]

I love my turbo 6.2. I've also got a milsurp 6.5L in a crate waiting to go in my next project.

It was capable of 24 MPG when i had 33"x9.5" pizza cutters, 3.08 gears, and overdrive in it at stock height. It also had enough torque and power to cruise around on the highway and in the hills (I don't believe it would have without the turbo).

It's now in my garage, but is soon to come out with a 4" lift, one-ton axles geared at 4.10, and 35" tires. That combo will put it at its peak efficiency RPM (1800 RPM) at 65MPH. We'll see what happens with the mileage. I'm not at all worried about power, and certainly not worried about torque. Around idle I've got gobs of torque, and at highway speed it behaves sorta like a stock TBI 350 gasser. Given proper maintenance the 6.2 will last a looooong time.

Bhays (see GMOTM vote thread) stuffed a 4BT in his and did a great job, but it took a long time with LOTS of custom fab work. I personally don't think it vibrates too bad, but those engines are also not cheap anymore. I got my 6.2L cheap with the Banks turbo and it bolted right in lickety-split.

Whatever you end up with, I believe a turbo is the single best thing you can do to any diesel by far.

I assume that 1800rpm is where the 6.2L makes peak torque, naturally aspirated???

What's interchangeable between the 6.2's and 6.5's? Anything? What can be done to mod/hotrod the diesels aside from adding a turbo and turning up the injector pump? I would assume that aftermarket support for these motors is probably non-existent, or close to it, given the limited use and short production run (in comparison to a SBC, BBC, etc...).


BTW, Russell, the Isuzu engine I was referring to is a 6cyl, not a 4cyl...

 

[longbedder]

The torque peak on the N/A version is just a little bit higher than 2000 RPM. 1800 is where the 6.2L has the best specific power (power per unit mass of fuel). Here's Banks' chart.

A lot of the parts interchange between the 6.2 and the 6.5 (the difference is .080" in the bore). The 6.5L has a bit less compression initially and is therefore more conducive to putting a higher-boost turbo on. There were year- and model-specific kinks that got worked out through the years in both.

As far as hotrodding the diesels, it's all about cramming more air in (and then the fuel to match). The trick is getting longevity as power levels go up. With the 6.2/6.5 there are some well-established reinforcement tricks that can work (head studs, main bearing web reinforcement, forged crank) but if you're set on a monster that you want lots of miles from the Cummins is a better starting point.

Short of getting a modded 6BT, don't be fooled into thinking that any of the engines you mentioned will be in the same class as a modern Powerstroke, Duramax, or Cummins. That being said, I'm a big fan of the 6.2/6.5 - learn the tricks and you've got good power, torque, and reliability in an inexpensive and low-maintenance package.

Also keep in mind that the 6BT is a BIG, HEAVY bastard and while conversions are done, care must be taken not to break your truck with it.

I don't know jack about the Isuzu you mentioned...it's probably a decent engine, though.

 

[tRustyK5]

The power you get from a diesel is just different than a gas engine. The tq is more noticeable, and more immediate...but the max rpm's are considerably lower. I don't feel hard done by in my NA 6.2 pick-up, and can keep up with everyone else no problem. It's happy putting around town from light to light, and it's equally happy running down the highway at 75 mph.

A turbo is cool, and it's certainly faster with one, but I don't think it's a mandatory mod.

1800 rpm is the magic number for fuel efficiency. The rest of your build should revolve around that number. Tire size, tranny, gearing doesn't matter, as long as you're running as near to 1800 rpm at 65 it'll turn in some very impressive fuel economy. I've seen a steady 25 mpg out of my pick-up...and that is pretty easy to live with for a full size pick-up.

I'd go with a 6.2 that's a good runner and swap it in without a turbo...then run the truck for a while. Low initial investment, and you can take your time evaluating, then upgrade later if you want.

Rene

 

[MaxPF]

A bit more info is needed. Do you want to run an automatic or a stick? What does your K5 have in it now?

6.2/6.5 swaps are by far the easiest. They literally bolt right up to your existing motor mounts and trans (with the diesel specific flywheel or flexplate). Good low mile 6.2's are getting very rare these days. The best bet, IF you can find one, is a good used honest-to-goodness AMG Optimizer 6500. Pickups and step vans with 6.5's that had their engines replaced after 2001 or so with a new "GM" crate engine will most likely have one of these. Look for the International/Navistar "Diamond" logo in the lifter valley. Occasionally you find one in a truck or van that has ended up being wrecked or scrapped. Not often, but sometimes. Other good options are the early 90's mechanically injected 6.5's, although like most 6.2's you see they will probably have a lot of miles on them. While these engines are generally reliable, high mileage is not good for the longevity batting average, and the IP and injectors will likely be pretty tired. You can get 250ish HP with a proper turbo and IP, but your best to stay around 200 on a stock engine.

Cummins swaps, both 4 and 6BTs, are a lot simpler than they used to be thanks to vendors like Crewcab59 that offer complete motor mount kits. Beyond that, ease of the swap (or lack therof) is dependent on what you want to use for a trans. Costwise, 6's are almost always cheaper than 4's, and of course they have more power capability. 4's can still make 250HP quite easily, and will give you the best fuel economy out of all the engines (well, a 4BD1T Isuzu is probably a tie). The 6 should still do a tad better than a 6.2 or 6.5 since their direct injection architecture has less heat and pumping losses than the indirectly injected 6.x. The P7100 pump on the 94-98.5 Dodge Cummins (and later industrial Cummins) will usually last the life of the engine without a rebuild. The rotary VE's in the earlier engines usually last a long time as well, but they aren't as durable as the P pump. Weightwise, the 4 is similar to a 6.x, while the 6BT is pretty porky, weighing 905lbs dry (no flywheel, starter, accessories, or fluids) and 1050+ ready to run. How long a stock K5 frame will last under one is debateable - I am ending the debate by grafting a 1 ton front frame section onto my K5 If you want the ultimate, the 6BT is it

The Isuzu's are the most complex to swap, both because of lack of kits and difficulty in adapting many common transmissions. Still, many guys do it and they are good motors. For more info on them I would check out the Isuzu section over at 4BTswaps.com.

 

[jonrpick]

I'm liking all the info, guys...

The K5 currently has a 700R4, but if I end up swapping engines I may end up switching to a manual tranny. Nothing is set in stone right now. I'd definitely want something with an overdrive if I did make the switch.

BTW, I ran the numbers on the RPM calculator on Randy's Ring & Pinion's website. With my 700R4, 31" tires and 3.73 gears, 65mph would be 1839rpm. That's PERFECT for the 6.2!

Rene, you said to gear it to run at 1800rpm @ 65mph... Is 65mph your typical highway speed, or is that just a good compromise for overall fuel economy in mixed city and highway?

 

[tRustyK5]

That is my typical cruise speed, I know in a lot of places the average cruise speed is nearer to 80 mph...

Remember that the more air you're trying to move the more power and fuel it'll take to do so. 65 mph and 1800 rpm is the sweet spot.

My pick-up has the 235/75's, 3.42's and the 700R-4. 1830 rpm at 65 mph.

Rene

 

[sixb]

If my CUCV 6.2 gives up I will seriously consider the Isuzuswapper kit. Hopefully that will be years away and there will be lots more info or documented swaps by then.

 

[jonrpick]

SixB, which Isuzu motor are you looking at specifically? Is it a 4cyl or 6cyl??

 

[sixb]

Jonrpick;
The 4BD1T/2T but would also not overlook the 6BD1T but know nothing about it. If a 6bt cummins fits in a my k5 I'm sure a 6BD1T should also but for a trail/crawler rig I'd want the lighter one.

Here's a link to some good info;
http://www.4btswaps.com/forum/showthread.php?t=7348

Personally for a dd I wouldn't go with anything less than a 6bt, those 4 bangers would have to be turned up way to much to be at 250/500 where as a 6bt would be easy. My personal experience with a 02 Cummins I had was that the edge juice with attitude was great fun but after it failed a year later and I drove without it for a couple weeks while edge was replacing it under warranty I realized that I was beating the hell out of that truck. Without the chip my oil leaks went away and the truck was still plenty powerfull. The extra 100 ponies was missed but the truck was much better off without it.

My k5 swap is EXPENSIVE but in the end I hope it's worth it. I plan on beefing up the frame as much as possible and tieing in a full cage to the frame also. I am also looking for 250-300 hp which should put me at 600-750 tq which is a mild tune for the ve and shouldn't be to smokey. Mine won't be a dd but will be used as hunting and fishing rig with some dd on the nice days.

 

[jonrpick]

Jonrpick;
The 4BD1T/2T but would also not overlook the 6BD1T but know nothing about it. If a 6bt cummins fits in a my k5 I'm sure a 6BD1T should also but for a trail/crawler rig I'd want the lighter one.

Here's a link to some good info;
http://www.4btswaps.com/forum/showthread.php?t=7348

Personally for a dd I wouldn't go with anything less than a 6bt, those 4 bangers would have to be turned up way to much to be at 250/500 where as a 6bt would be easy. My personal experience with a 02 Cummins I had was that the edge juice with attitude was great fun but after it failed a year later and I drove without it for a couple weeks while edge was replacing it under warranty I realized that I was beating the hell out of that truck. Without the chip my oil leaks went away and the truck was still plenty powerfull. The extra 100 ponies was missed but the truck was much better off without it.

My k5 swap is EXPENSIVE but in the end I hope it's worth it. I plan on beefing up the frame as much as possible and tieing in a full cage to the frame also. I am also looking for 250-300 hp which should put me at 600-750 tq which is a mild tune for the ve and shouldn't be to smokey. Mine won't be a dd but will be used as hunting and fishing rig with some dd on the nice days.

The 6BD1T is a 5.7L engine, which has my curiousity peaked. I'd like to find something with around 5.0L displacement, just because it makes sense most logically in my mind (granted, my logic assumes all things being equal, which they clearly are not...) because it's close to a stock gas engine in size.

Still, a 6BT is out... that's too much time and money for overkill. I am curious how the 6BD1T stacks up against the 6.2 and 6.5 though, in terms of both power and efficiency...

 

[MaxPF]

Still, a 6BT is out... that's too much time and money for overkill.

Nonsense. It's only 5.9 liters. That's less displacement than the GM diesels As far as time and money, you might be able to get an Isuzu 4 cheaper, but Cummins 4's pretty much always cost more than the 6ers.

 

[jonrpick]

Nonsense. It's only 5.9 liters. That's less displacement than the GM diesels As far as time and money, you might be able to get an Isuzu 4 cheaper, but Cummins 4's pretty much always cost more than the 6ers.

Yeah, the displacement thing... That's what I meant by all things not being equal. In terms of cubic inches, the 6.5 should be a beast!

I dug up some info on the 5.7L 6BD1T... looks like it weighs in at over 1,000lbs DRY.

It's funny to think that the 6BT is ONLY 359ci.

I really wish there was a 5BT...

The Wikipedia page on the 6.2 and 6.5 indicates that the turbo 6.5 had considerably more power than the N/A 6.2... 257 lb·ft @ 2,000rpm vs. 440 lb·ft @ 1,800rpm...

 

[Russell]

My Turbocharged 6.2L will slightly pull on a TBI 350 powered truck with similar driveline specs.

Personally, I am very pleased with it, and have no intention of changing that engine out to anything else in the future. However, when you compare it to my LBZ Duramax, it is a seriously anemic engine, haha

 

[MaxPF]

Yeah, the displacement thing... That's what I meant by all things not being equal. In terms of cubic inches, the 6.5 should be a beast!

I dug up some info on the 5.7L 6BD1T... looks like it weighs in at over 1,000lbs DRY.

That's what a Cummins weighs. After seeing what happened to my frame after wheeling with a 350 and then a 6.2, I decided more beef was needed. My solution was.... interesting.

It's funny to think that the 6BT is ONLY 359ci.

I really wish there was a 5BT...

The Wikipedia page on the 6.2 and 6.5 indicates that the turbo 6.5 had considerably more power than the N/A 6.2... 257 lb·ft @ 2,000rpm vs. 440 lb·ft @ 1,800rpm...

Yup. The turbo 6.5's actually got up to 210HP and 520lb-ft. That is pretty much at the durability limits of a stock 6.5 though. With some bottom end reinforcement you can go higher, say, 250HP or so, which pretty much maxes out any standard DB2 pump. If that power level suits you, then it is a hard combo to beat from the standpoint of cost and swappability... as long as you find a good one. If you want much more than that, you will find as I did that it is cheaper to swap in a Cummins than to get something like a P400. It really all boils down to what you want and what you like.