thoughts/questions on swapping from 350 to diesel..

[william_7900]

I'm thinking of swapping my 350 in my 71' Blazer for a 6.5l. Any reason I shouldn't do this?

I have a few of reasons for wanting to do this:
1. More fuel options with diesel than gas
2. More torque with diesel than gas.
3. Better gas milage

I have an NV4500 tranny and get tired of running at 2700
RPM's and/or having to downshift on hills.

I'm i thinking correctly about the benefits of swapping?

Thoughts?

William

 

[imiceman44]

I'm thinking of swapping my 350 in my 71' Blazer for a 6.5l. Any reason I shouldn't do this?

I have a few of reasons for wanting to do this:
1. More fuel options with diesel than gas
2. More torque with diesel than gas.
3. Better gas milage

I have an NV4500 tranny and get tired of running at 2700
RPM's and/or having to downshift on hills.

I'm i thinking correctly about the benefits of swapping?

Thoughts?

William

If I had time, I would put a diesel in every vehicle I have, and I already have the engines waiting.
I did however find a better way, now I buy diesel vehicles.

 

[kennyw]

I put a 6.2L in place of the original 350 in my '79 when it was due for a rebuild. Since I was doing the work anyway it was worth the effort.

Since you can't buy a '71 K5 with a diesel I'm sure it will be worthwhile if it meets your needs. You will need to pay attention to tire size and gear ratio however. The power band on a diesel is lower than the gas motor.

 

[william_7900]

I put a 6.2L in place of the original 350 in my '79 when it was due for a rebuild. Since I was doing the work anyway it was worth the effort.

Since you can't buy a '71 K5 with a diesel I'm sure it will be worthwhile if it meets your needs. You will need to pay attention to tire size and gear ratio however. The power band on a diesel is lower than the gas motor.

My blazer currently has 4.10 gears, NV4500 tranny and 35" tires.

My hope is that i get more torque from the diesel - especially in overdrive...

I'm currently running 2600 +- RPM's at 65 mph. I would like to lower that if possible.

Thoughts?

William

 

[kennyw]

The diesel is going to want to cruise at 1800-2000 RPM at 65. With the NV4500, 35" tires and 4.10 gears you should be there already. Are you sure your speedo is accurate?

 

[william_7900]

The diesel is going to want to cruise at 1800-2000 RPM at 65. With the NV4500, 35" tires and 4.10 gears you should be there already. Are you sure your speedo is accurate?

Yes, I've checked it against my wife's van. 65 mph is right around 2600 RPM's.

Any idea what RPM's the 6.5 diesel will be in my truck at 65 mph, given my setup - (4.10's, 35" tires and the NV4500) is running 2600 RPM's at 65 mph?

William

 

[kennyw]

www.4lo.com has a gear ratio calculator.

 

[tRustyK5]

Yes, I've checked it against my wife's van. 65 mph is right around 2600 RPM's.

Any idea what RPM's the 6.5 diesel will be in my truck at 65 mph, given my setup - (4.10's, 35" tires and the NV4500) is running 2600 RPM's at 65 mph?

William

The math says your setup is turning at 1867 rpm at 65 mph. Unless you aren't using 5th gear...

All the calculators out there are set-up for a 1:1 final ratio.

65 x 4.10 x 0.73 x 336 / 35 = 1867 rpm

Unless you have an SM 465 and not an NV4500?

Rene

 

[william_7900]

The math says your setup is turning at 1867 rpm at 65 mph. Unless you aren't using 5th gear...

All the calculators out there are set-up for a 1:1 final ratio.

65 x 4.10 x 0.73 x 336 / 35 = 1867 rpm

Unless you have an SM 465 and not an NV4500?

Rene

Something is wacky here because I'm pretty sure of what I have. I purchased the NV4500 new. I know I have 4.10's (purchased new from Randy's ring and pinion) and pretty sure I have 35's... :-) I guess my RPM gauge could be wrong but it seems to work flawlessly (I never pay attention to the odometer in my Blazer - used my wife's van to know I was running at 65 mph).

Will putting a 6.5 diesel run at about the same RPM's as the 350? I would hate to go to the effort of assembling a 6.5 and shoehorning it in my Blazer only to not get much benefit. It will be fun to build this with my kids so that will probably be benefit enough to justify the effort, still i would like to see a marked improvement in torque in OD and offroad.

Thoughts?

William

 

[kennyw]

I think you may have a problem with the tach... could be as simple as a 6 cyl tach being used on an 8 cyl motor. That's happened before. What kind of tach are you running?

Your tires are probably closer to 34" tall than 35", but it doesn't account for that big of an error. The RPM will be the same for both a 350 and a 6.5L at 65 when you keep the tires, gears, transmission, etc the same.

Your set up well for a diesel motor, but it may be simplier just to regear to 4.88's and you would now be better setup for the gas motor already in the rig. Right now your pulling a load at the low end of the power band due to the taller tires and 4.10 gears. OD in the NV4500 is basically useless to the gas motor for anything other than flat ground with no load.

 

[william_7900]

I think you may have a problem with the tach... could be as simple as a 6 cyl tach being used on an 8 cyl motor. That's happened before. What kind of tach are you running?

Your tires are probably closer to 34" tall than 35", but it doesn't account for that big of an error. The RPM will be the same for both a 350 and a 6.5L at 65 when you keep the tires, gears, transmission, etc the same.

Your set up well for a diesel motor, but it may be simplier just to regear to 4.88's and you would now be better setup for the gas motor already in the rig. Right now your pulling a load at the low end of the power band due to the taller tires and 4.10 gears. OD in the NV4500 is basically useless to the gas motor for anything other than flat ground with no load.

KennyW,

Thanks for the help on this. The tach is factory and "sounds" about right at an idle... 800 RPM's.


Yes, the OD in the NV4500 is basically useless in the gasser except on relatively flat ground - is my hope unfounded that all things being the same, the 6.5L will solve this problem because of the increase of the torque?

William

 

[imiceman44]

KennyW,

Thanks for the help on this. The tach is factory and "sounds" about right at an idle... 800 RPM's.


Yes, the OD in the NV4500 is basically useless in the gasser except on relatively flat ground - is my hope unfounded that all things being the same, the 6.5L will solve this problem because of the increase of the torque?

William

The 6.5 or 6.2 will definitely feel better at lower RPM's than your gasser which means the OD will be useful to keep you going with less fuel.
As noted in another post if you don't want the 700 because it's auto, I would stick with the NV4500, I would buy it from you if I wasn't broke and selling everything

 

[kennyw]

KennyW,

Thanks for the help on this. The tach is factory and "sounds" about right at an idle... 800 RPM's.


Yes, the OD in the NV4500 is basically useless in the gasser except on relatively flat ground - is my hope unfounded that all things being the same, the 6.5L will solve this problem because of the increase of the torque?

William

The tach could be close to accurate at idle but be way off once it goes up. But yes, the low RPM torque of the diesel will be better suited to the tranny, gear and tire combo you have.

 

[Russell]

Just keep in mind that unless you actually run a 6.5L turbo diesel, you will not see any power gains, and will have to continue downshifting on hills. My naturally aspirated 6.2L won't even touch the power of a stock 350. The turbocharged 6.2L will keep up with a TBI 350 though.

 

[william_7900]

Just keep in mind that unless you actually run a 6.5L turbo diesel, you will not see any power gains, and will have to continue downshifting on hills. My naturally aspirated 6.2L won't even touch the power of a stock 350. The turbocharged 6.2L will keep up with a TBI 350 though.

I'm hoping to get a 6.5 turbo charged diesel, and I'm hoping it won't just "keep up" with my 350 but surpass it.

Should i not expect that?

William

 

[imiceman44]

I'm hoping to get a 6.5 turbo charged diesel, and I'm hoping it won't just "keep up" with my 350 but surpass it.

Should i not expect that?

William

A turbo 6.5 stock might be slightlt better than the 350, it will have more low end torque, but the top end might be close, if you get a Banks Turbo diesel, then you could expect to well surpass a stock 350
I had a Banks turbo 6.2 and I loved the power and still getting 20MPG. Too bad I needed the money and had to sell.

 

[kennyw]

All of my stock 6.2L NA's have been slightly better than any stock 350 I've had. More low end torque when you need it. I've borrowed a friends '95 K2500 with a 6.5L TD many times and it is way better than a stock 350 for pulling a load up a grade.

 

[william_7900]

A turbo 6.5 stock might be slightlt better than the 350, it will have more low end torque, but the top end might be close, if you get a Banks Turbo diesel, then you could expect to well surpass a stock 350
I had a Banks turbo 6.2 and I loved the power and still getting 20MPG. Too bad I needed the money and had to sell.

I want to make sure I'm understanding... A very nice option is to have the 6.5l with the stock turbo that came from GM but with additional Banks add-on's? Or are you suggesting I use the 6.5L but put the Banks turbo instead of the GM stock turbo?

I plan on putting in the aftermarket head bolts and the girdle as well... any other bolt-on's i should consider?

Thanks for all the help.

William

 

[imiceman44]

I want to make sure I'm understanding... A very nice option is to have the 6.5l with the stock turbo that came from GM but with additional Banks add-on's? Or are you suggesting I use the 6.5L but put the Banks turbo instead of the GM stock turbo?

I plan on putting in the aftermarket head bolts and the girdle as well... any other bolt-on's i should consider?

Thanks for all the help.

William

Yeah usinf a 6.5l engine that was turboed, but using the Banks turbo setup will net you more power.
Not that in my opinion the stock setup is bad, I would take it anyday, but for people that want more, the banks will get you more.

 

[Russell]

Just don't overboost it, good way to destroy your engine. Keep a close eye on your EGTs and keep your boost at reasonable levels.

In my experience a 6.2L is not as quick of an engine as a 350 is by any stretch. What they have going for them is fantastic mileage, and despite being slow all the time, the torque they produce makes sure that you don't go any slower when loaded.

If you are looking for a go fast engine, or are looking to improve acceleration, a 6.2L / 6.5L is not going to impress you regardless of how well geared it is. My 6.2L powered offroading truck has to be decelerated then downshifted to climb up hills all the time. Thats with 4.56 gears and 33.5" overall diameter tires. With the 2.73s and the same tires I was hardly able to maintain 65 mph, literally drove it in 4th gear (1:1) with the pedal on the floor the whole way, shifting it into O/D (I have a 5 speed manual trans) would result in a loss of speed. With the 4.56 gears I am able to cruise at 75 mph in 5th gear on flat ground, but definitely not in hilly areas.