720 Diesel

Dan Davidson · Dec 27, 2014

I'm going to open up my diesel motor on the 720 and freshen it up. I'd like to make a few more hp. Its original now. Whats my best bang for the $$? I will do the valves anyway and possible bore if it needs. Also a check of the fuel system/injectors. Thinking since I'm doing this I could make a few improvements. Not looking to spend 20K or go pro. Just have some fun. Thanks

buickanddeere · Dec 28, 2014

To burn more fuel, more air is required. More lift and duration via a re-ground cam. Multi angle valve job. Clean the rough edges out of the ports. Will 80/820/830/840 intake and exhaust manifolds bolt on? New valve springs to allow some rpms. Dry air filter conversion. Put 830/840 tips on the injectors.
Figuring a typical natural aspirated diesel will make approx 0.25HP per cubic inch at 1800rpm and is starting to smoke at that level. This puts a 720 at about 63HP at 1200rpm. Higher rpms are of little gain when the engine's breathing is limited.
Maybe 75HP if built and tuned right at 1200-1500rpm ? It's going to lug down to about 900rpm for the last 20-50ft of pull. It's not going to build up speed to help coast the sled and weight with built up inertia when in 1st or 2nd gear.
The first three components to work on first when pulling are traction, traction and traction. The add HP afterwards.

showcrop · Dec 28, 2014

I know a guy that does well at the pulls with one. It really rolls the coal! I asked him about it once when there was no one else around, and he said that it was injector work, but I expect that at least there was some pump work and probably some advanced stuff as B&D suggested.

BushogPapa · Dec 28, 2014

Making Smoke with these is not really necessary if a better Cam and larger injector pumps (at a Higher cracking pressure) are used, along with a REAL Intake clean-up...

Most beautiful sounding one here in Ohio (Plain City), idles and has throttle response like any healthy Gas 620/720 but pulls seriously HARD and I have yet to see it spew Smoke...

Ron.

Dan Davidson · Dec 28, 2014

Thats what I am after. There is a guy here pulling with a 70 diesel that is all smoke and no go. He must have done all the fuel work needed but non of the air modifications or head work/valve work.
I've watched a couple clean burning 730 diesels tear up 4020's and even a couple 820 and 830's I intend to pull heavy and remove no weight at all on this tractor. Any recommendations for rear tire size? currently 15.5-38. I 'd like to go to 16.9

buickanddeere · Dec 29, 2014

(quoted from post at 01:40:56 12/29/14) Thats what I am after. There is a guy here pulling with a 70 diesel that is all smoke and no go. He must have done all the fuel work needed but non of the air modifications or head work/valve work.
I've watched a couple clean burning 730 diesels tear up 4020's and even a couple 820 and 830's I intend to pull heavy and remove no weight at all on this tractor. Any recommendations for rear tire size? currently 15.5-38. I 'd like to go to 16.9

Check the local pulling organizations if they have tire rules. It's no fun getting DQ'd before unloading the tractor from your trailer.
Forgot to add that some super keeners will shoehorn 830 valves into a 70/720/730 head. No idea however if the flow increases on the test bench. The top of the bore has to be relieved to provide intake valve clearance.
The cam is everything. When we rebuilt the 70D the factory cam looked tired and anything from a salvage yard wasn't any better. We had the cam re-ground and they must have improved the specs. She easily dyno's 63HP at 1250 rpm on the belt pulley with very little smoke.Factory narrow spray pattern 720 tips to match the 720 pistons and 70's small 10mm pumps.
The 720/730 had the larger 13mm injection pumps from the factory as did the black dash 820/830/840. The 720 tips were smaller. The blackdash 820,830 & 840 tips having six orifices at 12 thou dia iirc.
I could never understand somebody tearing an engine down , bringing everything else up to new spec or better. Yet leaving the worn cam and followers untouched ???

gpuller · Dec 30, 2014

(quoted from post at 22:40:56 12/28/14) Thats what I am after. There is a guy here pulling with a 70 diesel that is all smoke and no go. He must have done all the fuel work needed but non of the air modifications or head work/valve work.
I've watched a couple clean burning 730 diesels tear up 4020's and even a couple 820 and 830's I intend to pull heavy and remove no weight at all on this tractor. Any recommendations for rear tire size? currently 15.5-38. I 'd like to go to 16.9

What trans do you have in your 720? Is it a creeper gear with 1st gear above reverse? If it does I would say run 18.4-38's if the rules allow. If your pulling heavy your going to need them. I run 18.4 Firestone Field And Roads mounted on pressed steel rims on my 720.
Pull from 7500 to 10,500. Does the best in 85 and 9500, run second gear up to 10,500. Depending on track conditions I have run 2nd gear.
If you want someone to work on your fuel system I would recommend Garry Power. He checks in here or if you are on Facebook he's over there in the antique pulling group too.

720 Diesel

Dan Davidson

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buickanddeere

Well-known Member

showcrop

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BushogPapa

Well-known Member

Dan Davidson

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buickanddeere

Well-known Member

gpuller

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