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How do you hotrod a Detroit 6-71?

3500GMC

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So I have this Diamond T, a '67 with a 6-71N. Dunno if it's 2 or 4 valve, dunno what injectors it has.. Yet. It's just a toy. Thought I'd like yet another truck that turns diesel into beautiful noise. :D

Nobby you out there?
 

Will L.

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Now, how are you going to go and announce that with out pics?

426 Cid x 2 stroke in my book = 852 x the noise!

Are you going to keep it full size or bring it down to pickup size and rod it?
 

Will L.

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Oh yeah, the n designation is the 'newer' 4 valve. Most parts don't interchange different piston, rods, "n"needle injectors, more but cant remember. They love high rpm, so well balanced components make a difference. I worked on them, but def not an expert. Ahh, the magic of a blown-natural aspiration.

I wonder if fluid damper makes a balancer for them? The unbalanced shake was an unmistakable drawback. They are mega oil leakers thatcreated the name leaktroit. all that air blown through its no wonder. I always wanted to hook up a vacuum system to the crankcase to see how much of that it would cure. Maybe a gapless ring in #2 position could help that also? Definitely spend time on a good felt job fitment in the blower, that helps a lot.
 

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Oh yeah, the n designation is the 'newer' 4 valve. Most parts don't interchange different piston, rods, "n"needle injectors, more but cant remember. They love high rpm, so well balanced components make a difference. I worked on them, but def not an expert. Ahh, the magic of a blown-natural aspiration.

I wonder if fluid damper makes a balancer for them? The unbalanced shake was an unmistakable drawback. They are mega oil leakers thatcreated the name leaktroit. all that air blown through its no wonder. I always wanted to hook up a vacuum system to the crankcase to see how much of that it would cure. Maybe a gapless ring in #2 position could help that also? Definitely spend time on a good felt job fitment in the blower, that helps a lot.
The "N" designation means naturally aspirated, or only supercharged(no turbo). I've seen turbo'd in both 2 and 4 valve, but the 4 valve is capable of ALOT more power. I believe it was N-95's were about as big of an injector you can go without a turbo, and will put you in the low 300HP range if it's a 4 valve. If it's a 2 valve it will be quite a bit lower. You will also need the better 4 valve head to reach that HP number as there are several different heads out there for them. Friend of mine just basically gave away a brand new 4 valve 6-71 turbo head(one of the GOOD ones). He needed money, and the shop he took it to only offered him $350 for it after he had a receipt showing he had bought it 2 years before for $1100.
 

Will L.

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Oops, sorry if I misled you. I thought the n was for the needle injector change design when they went to the 4 valve, I remember reading about it but then again I have a hard time remembering what I remember.

I know the only change we would make when adding the turbo parts wise was the injectors, turbo and all the duct work. It was a kit so idk if the internals of the turbo was set up the same to run as hard as factory turbo or not. Nothing internal was changed. Don't miss my Daily Dose of Detroit. Once in a great while is fine with me anymore. Do keep us updated tho...:)
 

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Oops, sorry if I misled you. I thought the n was for the needle injector change design when they went to the 4 valve, I remember reading about it but then again I have a hard time remembering what I remember.

I know the only change we would make when adding the turbo parts wise was the injectors, turbo and all the duct work. It was a kit so idk if the internals of the turbo was set up the same to run as hard as factory turbo or not. Nothing internal was changed. Don't miss my Daily Dose of Detroit. Once in a great while is fine with me anymore. Do keep us updated tho...:)
My uncle has a pair of JOHNSON & TOWERS 6-71N's at 310HP in his boat. I went through the factory service manuals and there were about 4 different 4 valve cams, 3 heads, and who knows how many injectors. DETROIT used the last letter to designate teh aspiration system. N was natural or just supercharged(2 stroke diesels have to have a supercharger to run), T was for turbo, TT for twin turbo, TA for turbocharged aftercooled, and a few other designations. The REALLY high HP ones had quite a bit of technology in them for there day. They used a smaller port system to improve bottem end pull, but had a supercharger bypass valve that opened once teh turbos had enough boost to take over and bypassed the superchargers all together. If it is a 4 valve N engine, it can be one of about 3 variants IIRC. The base model low output, high output natural engine, or the turbo engine without a turbo. Most of the turbo engines without turbos went to companies like JOHNSON & TOWERS for marine conversions. For trucks most got the low output generator engine version(with a different governor system than the generator version).
 

cornemuse

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I used to work for a company that had a bunch of equipment with various dee-troit engines in 'em. Had some 'Koehring' excavators, (a 455 & a 666, yeah, a long time ago), & a bunch of navy surplus 'Grove' cranes with 2 & 3 cyl deets. Refered to them as 'yammers' as in 2 cycle yamahas. Anyway, what we did was we would add 5 gallons of gasoline every time we fueled the backhoes, (100 gal plus tanks). They seemed to 'push' harder against the governers & had noticeably more power, and started easier in the winter time. We only did this with the excavaters. -c-
 

Will L.

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Ferminator:
:bow:
Your like a walking encyclopedia. As soon as I read it the memory flashbulb lit up. I know there was some designation on the injectors, because we had to add a plate near the original and we had to stamp the letter for the injector based on which kit they ordered for power/mileage gain. This was on generators and trucks.

I dreamed of manuals at that dealer, but alas, they "invested" in microfiche and for those of you that remember trying to learn off that...HA! Most of the important sheets ended up in somebody else's toolbox long before I got there. Most my stuff was seat of the pants or "Hey Johnny, What's the torque on a..." Only so much is taught in the 3 day a year mandatory class to be Detroit certified. Hopefully that changed over the years. I do kinda miss that 2 stroke scream tho, those sucker sounded fast even at idle.

BTW for anyone not familiar with these engines just reading along, swapping the injectors is a pain, it's under the rocker arms, so you have to run the rack, reset the injector height,etc. - still needing that sarcasm font for my nothing internal comment- So he cant just "pop out" an injector to see what's up. Around 20-25 minutes per cylinder to swap an injector and reset it all up.
 

btfarm

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You might inquire around the Super-Semi pullers knowledgeable (where IDK) because some of those are old Detroits.
:nopics: A Diamond T? Do tell bud, Dad was a worshiper.
 

bison

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Sorry for the hijack.

I have a Cockshutt tractor with a 4-53 detroit in it, it's rated at 105 HP.
What would i need to do to get a few more ponies out of it?.
 

Will L.

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Both 3500gmc and Bison, same basic rules don't apply to 2 stroke. Add turbo, or increase turbo size and up the injectors and control bypass on the blower with turbo pressure. There is not a lot left on the table in n/a 2 strokes. Keep in mind the blower is "blowing" only, not actually "supercharging" the air pressure. These factory blowers at best can raise the pressure to 2psi, most are still at or near atmosphere. The blower just pushes the air out the exhaust to allow a good mix of new air/fuel in. . If you actually "supercharge" the air pressure by upping the gear ratio of the blower into a supercharger you can get around 4-4.5 psi. A turbo is where the magic happens. 25 psi will light these things up.

Blowers tend to wear down the lobes and score the cylinder slowly and that is a loss in power. Piston cylinder ring wear can be enough that the engine cant run without the help of the blower. I pulled a
blower and ran the engine without it one time showing a customer that his engine was ok, just his blower was wiped out.
All that aside, just pulling and cleaning the injectors and running the rack can do a lot for one that has many hours on it-out of adjustment is a good loss.

What kind of numbers are you all trying to get to?
 

bison

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I have less than 1000 hrs on the 4-53, it is in prime shape.
It'll fire up in a couple seconds without start fluid after sitting still 9 months out of the year.
I like to get 25-30 more ponies out of it so the SOB will pull my 567 baler without losing up to 500 RPM depending on the slope.
 

3500GMC

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First thing I thought of was bigger injectors and if possible, don't know if it's been done, overdrive the supercharger.. ? I could plunk a turbo on it with relative ease, it's just the bypass deal that is the missing link.

I guess first thing is to pop the rocker cover off and have a look see. The PO of the truck said it has seen an in-frame within the last 10 years before he owned it. The PO put maybe 10k miles on it in 4 years. It doesn't slobber like a typical Driptroit so it must be fairly sound.

All I know it takes some muscle to drive because it has NO power steering.

5 speed overdrive trans, air shift 2 speed rear.

She's pretty ruff around the edges. I'm posting a YT video as of this writing.
 

3500GMC

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Vid

Crank it up. This thing is a blast to drive, wish she had a Jacobs brake.
.

[video=youtube;xV5MsotqDuo]https://www.youtube.com/watch?v=xV5MsotqDuo[/video]
 

Will L.

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I have less than 1000 hrs on the 4-53, it is in prime shape.
It'll fire up in a couple seconds without start fluid after sitting still 9 months out of the year.
I like to get 25-30 more ponies out of it so the SOB will pull my 567 baler without losing up to 500 RPM depending on the slope.
You can get it with a big turbo and injectors, I am way to far out to know the numbers but 2 years ago I helped a friend drop in a 170 hp or so new one, but he was like 10,000 into it iirc.for a complete assembly. You needing turbo kit complete is probably in the range of $3000 would be my guess. Nothing high on skill level, just time and knuckle skin.

For My friend in Ohio, you can overdrive the blower, but not like it's done on a gas hot rod engine. Your only going to pull a couple pounds of boost out of overdriving it. As for the no slobbering, don't worry, that will come with the boost. By the lug it has at idle and no oil blow, I would bet you are at under 1 psi on the driven side of the blower when at 2,000 rpm. The smaller cid like Bison's can build the boost easier because the the valve size to chamber ratio is way better for holding boost- Also why they die sooner when turbo is on it, 2 strokes cant breathe good under pressure. Definitely a turbo in your future for any power gains, but your going to have to figure what exactly you have before you start trying to get any parts other than the bypass. On the truck, It looks good,but I was thinking different headlights, see there goes my memory again. Good looking rig, reminds me of a modern Pete with an 80's KW bonnet. Too much there to chop into a lil truck. Think I would add power steering.

For both you guys, I am not real knowledgeable on these, there has got to be a forum out there somewhere that has all the info. I used to work on them a bit and did some turbo kits, and swapped several worn out blowers, but that was in a kit form, and the injectors were off the shelf. Take your time setting up the bypass, not hard but makes a difference in a smooth transition into boost. One thing that I didn't mention earlier is the airfilter. Depending what you currently have the air filter might be too small for the increased airflow.

I did one 8-71 that was turbo only, and not injectors. The customer didn't have the cash yet was planning on coming back for the injector job in a couple months. It helped so little without the injectors it was amazing. It could rev quicker with no load, but under load it was almost not noticeable, except it cleaned up his exhaust some. Putting in his injectors was the last job I did there (10 or 11 hour day)and boy he was a happy camper afterwards.

Hope some of my faded memory helps. If not maybe it can give a laugh- does to my wife every now and then.:wink5:
 

btfarm

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Grinnin' ear to ear over that vid Brad. Dad would be too.

Sent from my SCH-I535
 

3500GMC

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It's one of my toys. One of those 'projects' lol.

Yeah Will it should have the round quad lamp setup. It's been messed with. Over all a lil ruff around the edges but structurally sound.

The small amout of research done, been able to determine that '67 was the last year for Diamond T as a brand. They were bought out by White and assimilated into the White/Autocar line. This is a plus in some ways as they used that particular cab for EONS like up into the 90'S..
 

bison

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Thanks for the info Will.

3 grand for just a turbo kit and 4 injectors is far more than i'm wiling to spend on this 45 year old tractor.
The complete engine rebuild kit was only in the neighborhood of $1200.
 

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From your video it looks like you have a 2 valve engine, I believe all of the 4 valve engines got the cast valve cover while the 2 valves got the stamped. From the sounds of it I would say your rack needs adjusting. You can hear in the video that it isn't idling on all 6 smoothly and a couple are pulling more than the rest. Also the buffer screw needs adjusting because you can hear it hunting some at idle.
 
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