gasser to diesel conversion

[William@Davis]

Greetings all,
I was referred to this page by the owner of 65turbogarage. I'm not a newbie to diesel engines as I've owned both Dodge Rams 24 valve cummins and currently own a 2017 Colorado 2.8 diesel and also I was formally an engine machinist prior to moving into CNC production machining. I've owned for several years now a 1994 Chevrolet Silverado K2500 ( 14 bolt cooperate rear ) with a 7.4 liter 454 big block for pulling my hay trailer as well as hauling my lance camper. I've done a lot to this rig's drive train and interior and have no interest in purchasing another a newer truck of this caliber and paying upwards of 60-80 grand but I am getting closer to retirement and really don't want to have to feed the 454's fuel consumption after doing so but still want to use the truck for my camping and boating needs. This has brought me to where I am now, I'm interested in swapping in a diesel engine into the truck and have even gone as far as to buy Jim Bigley's Duramax 6600 diesel conversion guide. I'm still on the fence as to what would be the most feasible motor to convert to but I think I'm beginning to lean towards the 6.5 GM Detroit since it was already a factory option for this era of trucks and from what I've found in researching thus far is that the motor mounts should be the same for both the 454 and the 6.5 as well as the bell housing mounting pattern. What I'm really confused on is as to whether the diesel motor utilizes the same NV4500 five speed as my 454? I know there is a lot of other items that I will have to address including wiring harness , fuel tank, fuel lines and cooling but if anyone else on here has done a similar swap I'd be very much interested in hearing your story

 

[ak diesel driver]

What's your budget?

 

[William@Davis]

how would my budget have anything to do with the questions stated above?

 

[Paveltolz]

Welcome to the site, good luck, enjoy the project and above all else, have fun.

Budget has everything to do with a project.
Some members here are really good about suggesting courses of action that they don't have to pay for. My guess is that ak diesel driver just desired to keep things real for your sake vs. going over the top and wasting your time and sending you on paths you don't want to go down.
Such as, new optimizer vs, used motor. Rebuild the used motor, take your chances on the owner's stated history or have someone like Twistedsteel go through it. Buy a new motor; leave it as delivered or tear it down and inspect still have Twistedsteel go through and bullet proof the thing. or, ride it out with your own experience.

When WillL sees your questions he'll have a whole lot of ideas and probably answer your questions as to bell housings, transmissions etc. Hang in there.

 

[JayTheCPA]

IIRC, no differences in the hand shakers' gears. Ferd would do different gearsets depending fuel, but do not recall that GM did this. And the NV4500 should bolt-up no matter what the engine's fuel type just as long as it is from about the same era.

While there are still 6.5s out there, think hard about this engine. Some critical parts are either going unobtanium, or are not so durable anymore.

After running a 6.5 for a while, had I known then what I know now, I'd get a 6.0L gas mated to either a manual or the 6L80E. From what I have seen, the NV4500 will bolt-up to a 6.0 gas.

 

[William@Davis]

Understood, I did look at the optimizer but cannot cannot in good conscious spend that kind of money on a project. Now if I got a used motor installed and everything works as intended then purchasing the optimizer for the longevity would make sense.

In all honesty I'm still debating on which course is the best and easiest path. I think the Duramax would provide more pulling power and fuel mileage and have a better availability of parts but would also probably be more difficult to do a swap in place of the 454 and also mate to the NV4500. Still I'm going to go look at an LB7 this weekend and possibly puchase it if the price is right. Finding a 6.5 detroit is proving to be difficult even finding a reasonably priced donar vehicle in my vicinity.

 

[Will L.]

It the budget is too high for a new 6.5 - there is gonna be funny then. Not funny haha, but funny sarcastically. I will sound like a jerk but am trying to save you wasted money and aggravation. The budget question is the smartest comment on here. You answered it and either can’t afford it or won’t invest in it.

Want lower investment cost: I tell people buy a new 6.5 then rip it apart and correct a few issues from factory.

Used Dmax at this point - almost all will be rode hard & put away wet.

The transmission isn’t going to withstand the dmax long term if towing.
No one makes a good stand alone harness kit for the dmax. All the hmmwv guys learn this the hard way: buy an entire running dmax truck and drive it for a month as is to find problems the seller hid. Otherwise the problems pop up while you are working iut the conversion kinks and can’t tell which is which. The cheapest dmaxes are mid project/ 90% project trucks that usually ends up costing $5,000 to get running right without a single part purchased.

You need not just the fuel supply line but the fuel return oine larger for diesel- especially dmax. Look at the price of a FASS lift pump that you will end up buying. Thats $700 alone.

Basically:
Low investment cost
Diesel
Pick the one you want. You can’t have the other.
There is a reason new diesels are stupid money now- because inflation ruined all the prices, and the democratic party turned the screw to the diesels especially.

If you move forward, I will try to help but understand you are asking for 100 acre property with a 3,000sq ft house and don’t wanna pay over $100,000.

Put into machinist terms: I want you to turn & weld this piece of old galvanized fence post thats 6’ long into a drive shaft for a 5,000hp race car and I only wanna pay you $100 to do it.

 

[William@Davis]

It the budget is too high for a new 6.5 - there is gonna be funny then. Not funny haha, but funny sarcastically. I will sound like a jerk but am trying to save you wasted money and aggravation. The budget question is the smartest comment on here. You answered it and either can’t afford it or won’t invest in it.

Want lower investment cost: I tell people buy a new 6.5 then rip it apart and correct a few issues from factory.

Used Dmax at this point - almost all will be rode hard & put away wet.

The transmission isn’t going to withstand the dmax long term if towing.
No one makes a good stand alone harness kit for the dmax. All the hmmwv guys learn this the hard way: buy an entire running dmax truck and drive it for a month as is to find problems the seller hid. Otherwise the problems pop up while you are working iut the conversion kinks and can’t tell which is which. The cheapest dmaxes are mid project/ 90% project trucks that usually ends up costing $5,000 to get running right without a single part purchased.

You need not just the fuel supply line but the fuel return oine larger for diesel- especially dmax. Look at the price of a FASS lift pump that you will end up buying. Thats $700 alone.

Basically:
Low investment cost
Diesel
Pick the one you want. You can’t have the other.
There is a reason new diesels are stupid money now- because inflation ruined all the prices, and the democratic party turned the screw to the diesels especially.

If you move forward, I will try to help but understand you are asking for 100 acre property with a 3,000sq ft house and don’t wanna pay over $100,000.

Put into machinist terms: I want you to turn & weld this piece of old galvanized fence post thats 6’ long into a drive shaft for a 5,000hp race car and I only wanna pay you $100 to do it.

Well said, of all your input it sounds like I’d be better off keeping the 7.4 and simply applying the finances I would have put into a swap into the fuel tank instead. It is worth pondering over especially since this is not nor will it ever be a daily driven vehicle. I’m going to ponder over this further before deciding on whether or not to make the plunge. Thank you , you may have just saved my sanity

 

[Will L.]

Money spent on the 454 & truck could be things to pay off on fuel savings.
What fuel system is on it?
What compression does it have?
What transmission & gearing?

 

[William@Davis]

Currently it’s still stock with a 7:1 compression and factory TBI which with the NV4500 and 4:10 gearing yields anywhere from 9-10 mpg. I did invest in a rebuilt port matched TBI/ INTAKE manifold combination but then started considering a diesel conversion idea instead. From HarrisTuning website Brian Harris has a list of performance / efficiency upgrades to make the gen 5 454 perform better and achieve better overall efficiency but it would still not come close to a diesel in regards to raw torque and fuel efficiency. That being said the overall cost and time required to perform such a swap has to also be considered into the equation.

 

[Big T]

I just repowered a K2500 Suburban with a new long block 6.5 Optimizer. Paveltolz and I did the install. It cost me approximately $11K. If a shop had done the work, it would have been $20+K. It does run very nice. My alternative was new truck at $60K to $80K which was a big F no for my intended use.

 

[William@Davis]

I just repowered a K2500 Suburban with a new long block 6.5 Optimizer. Paveltolz and I did the install. It cost me approximately $11K. If a shop had done the work, it would have been $20+K. It does run very nice. My alternative was new truck at $60K to $80K which was a big F no for my intended use.

I can understand that completely. I have no interest in purchasing a new truck in today’s economy. My commuter is a 2017 Colorado 2.8 diesel and in that year that truck cost me around 38 thousand, I cannot fathom what one would cost now although they discontinued the sales of the babymax here in the states

 

[THEFERMANATOR]

I would keep the 454, or freshen it up, and put the money you would have put into the swap into fuel. A diesel swap can get real expensive, REAL QUICK! Your 94 454 should actually be the better tbi engine, not a vortec, but it had the better of the peanut port heads, higher compression, better intake(not the crappy carb with adapter like early TBI units), and it used high pressure tbi fuel injection(30-38 psi where 93 and older were only 9-13, this made a HUGE improvement in throttle response & atomization). If it was mine I would find a 96+ vortec 454, get a 4 barrel carb intake, carb to TBI adapter plate, long tube headers, do a cam swap while it's out, and swap it to microsquirt fuel injection for tuneability(Harris is the LAST place I would send somebody for chip tuning).

You would have a real powerhouse on your hands for not alot of money, then take what you saved, & use it for gas money.

 

[Big T]

I would keep the 454, or freshen it up, and put the money you would have put into the swap into fuel. A diesel swap can get real expensive, REAL QUICK! Your 94 454 should actually be the better tbi engine, not a vortec, but it had the better of the peanut port heads, higher compression, better intake(not the crappy carb with adapter like early TBI units), and it used high pressure tbi fuel injection(30-38 psi where 93 and older were only 9-13, this made a HUGE improvement in throttle response & atomization). If it was mine I would find a 96+ vortec 454, get a 4 barrel carb intake, carb to TBI adapter plate, long tube headers, do a cam swap while it's out, and swap it to microsquirt fuel injection for tuneability(Harris is the LAST place I would send somebody for chip tuning).

You would have a real powerhouse on your hands for not alot of money, then take what you saved, & use it for gas money.

This ^^^ is coming from a guy who did a Duramax + Allison conversion on a 1995 K2500 Suburban.