Let's spitball... 7.3 with shorter stroke?

[C'roy78stroker]

Just something that came across my mind. I was try to think of a negative to this hypothetical scenario. The ones I could think of would be a drop in torque, added expense for a longer rod, or block deck machining depending on the amount of de-stroking. What drew me this direction was if we had a smaller displacement engine but fed it the same fuel, for sake of max effort, 400/400's and then also ported the cylinder heads... Would the HP numbers go up any higher? Or would we still be breaking even do to fuel and air remaining constant? Just a thought, but I'd like to hear some speculation.

 

[ja_cain]

Just something that came across my mind. I was try to think of a negative to this hypothetical scenario. The ones I could think of would be a drop in torque, added expense for a longer rod, or block deck machining depending on the amount of de-stroking. What drew me this direction was if we had a smaller displacement engine but fed it the same fuel, for sake of max effort, 400/400's and then also ported the cylinder heads... Would the HP numbers go up any higher? Or would we still be breaking even do to fuel and air remaining constant? Just a thought, but I'd like to hear some speculation.

HP is a function of torque/RPM. I would think that unless you are getting significantly more RPM out of it, then you are taking a step backwards. I could be wrong in my assumption, but I feel like the RPM is limited more by how fast the injectors can operate than the stroke on the 7.3. Destroking it could improve rod to stroke ratio which would increase the longevity of the rods and less stress on the block too.

 

[Petro]

If less cubic inch was what you were after, I would think sleeving down the size of the cylinders would be a simpler way to go about it. I'm very curious to see where this discussion goes. Seems like I remember Morgan saying something about removing cubic inch from a 7.3 in a discussion a few years back. It was all hypothetical but I thought I remembered this conversation happening on here. Good topic by the way.

 

[ja_cain]

If less cubic inch was what you were after, I would think sleeving down the size of the cylinders would be a simpler way to go about it. I'm very curious to see where this discussion goes. Seems like I remember Morgan saying something about removing cubic inch from a 7.3 in a discussion a few years back. It was all hypothetical but I thought I remembered this conversation happening on here. Good topic by the way.

I vaguely remember that discussion too. Sleeving down should strengthen the block due to thicker cylinder walls. Rotating assembly would be lighter too due to smaller/lighter slugs.

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[morefuel]

From what i remember somebody, Morgan or HotRodTractor I believe, said the best from a performance aspect would be a large bore and short stroke. The big bore allows for a larger valve area to get the most air in. I believe it was in a discussion on stroker kits for 6.4's and that for strictly adding cubic in. that adding bore was more effective than stroke because of headflow/valve area.

And I think that the 7.3's main issue is the injectors aren't fast enough for high rpm so to make horsepower they are forced to make gobs of torque.

I'd be curious to know if block weakness is more relative to cylinder pressure or from actual engine torque.

 

[ja_cain]

Increases in cylinder pressures will most likely track increases in torque or vise versa.

Good point about a large overbore and the ability to run larger valves. 7.3 could probably benefit from this, but not sure how it's open area scales from say a 6.0 or 6.4.

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[superpsd]

How about a Big bore short stroke engine with commonrail kit. Sounds expensive.

 

[psduser1]

Sounds fun!

 

[JDelaney]

Probably be cheaper to punch out a 6.7L to 7.3L.

 

[Petro]

I believe the discussion on removing cubic inch was strictly to deal with the limitations of heui injection system like the OP suggested. Basically making the most of the fuel the 7.3 is able to inject in the given window. With a common rail Injection system, I don't see any reason to eliminate cubic inch when you would have basically unlimited amounts of fuel flow. Head flow would be the biggest limitation after that. That's the way I see it, but I could be wrong.

 

[psduser1]

Just something that came across my mind. I was try to think of a negative to this hypothetical scenario. The ones I could think of would be a drop in torque, added expense for a *shorter* rod, or block deck machining depending on the amount of de-stroking. What drew me this direction was if we had a smaller displacement engine but fed it the same fuel, for sake of max effort, 400/400's and then also ported the cylinder heads... Would the HP numbers go up any higher? Or would we still be breaking even do to fuel and air remaining constant? Just a thought, but I'd like to hear some speculation.

Fixed. The expensive part would be the machining on the crank for the different throw travel. Then youd still run into fueling limits with the heui system.

At which point, you'd be money ahead to look into a different platform. Maybe somewhere along the lines of jdelaney' s post. 6.7l is probably about where you'd end up in a destroked situation with a 7.3 block anyway, lol.

 

[superpsd]

The limitations with heui to move mass amounts of fuel is trying to actuate them quick enough to hit an ever shrinking injection window as engine speed increases. Where was commonrail does not rely on moving high pressure oil to inject fuel. With a big bore engine you can put in bigger valves and let it breathe and with short stroke you can spin it faster. However swamps has already had their commonrail 7.3 past 6K rpms if i remember correctly.

 

[Petro]

The limitations with heui to move mass amounts of fuel is trying to actuate them quick enough to hit an ever shrinking injection window as engine speed increases. Where was commonrail does not rely on moving high pressure oil to inject fuel. With a big bore engine you can put in bigger valves and let it breathe and with short stroke you can spin it faster. However swamps has already had their commonrail 7.3 past 6K rpms if i remember correctly.

Yes there's nothing keeping a 7.3 from spinning rpm other than the ****ty heui setup. The mechanical and common rail guys are spinning them as fast as any other motor.

 

[ja_cain]

The limitations with heui to move mass amounts of fuel is trying to actuate them quick enough to hit an ever shrinking injection window as engine speed increases. Where was commonrail does not rely on moving high pressure oil to inject fuel. With a big bore engine you can put in bigger valves and let it breathe and with short stroke you can spin it faster. However swamps has already had their commonrail 7.3 past 6K rpms if i remember correctly.

This is precisely what I was trying to say. P-pump will solve this problem.

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[ja_cain]

Yes there's nothing keeping a 7.3 from spinning rpm other than the ****ty heui setup. The mechanical and common rail guys are spinning them as fast as any other motor.

Exactly! I think Cory at CNCFab has kits in the works.

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[C'roy78stroker]

And if you sit down and compare prices between a mechanical and top end heui build, almost everything offsets each other until you get to the front cover. Those suckers are very pricey.

 

[JDelaney]

Well, the 7.3L is already pretty square and has a pretty good rod ratio so I don’t think decreasing displacement is going to help a whole lot. Air flow and HEUI limitations are roadblocks. Maybe a 4 valve cylinder head and higher volume HPO system would yield greater returns?

 

[PsdPullerJr]

About halfway thru this thread, Morgan answered my question about changing the 7.3 stroke. http://powerstrokearmy.com/forums/archive/index.php/t-55394.html

 

[ja_cain]

And if you sit down and compare prices between a mechanical and top end heui build, almost everything offsets each other until you get to the front cover. Those suckers are very pricey.

I bet there is a lot of maching on that bad boy.

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[ja_cain]

About halfway thru this thread, Morgan answered my question about changing the 7.3 stroke. http://powerstrokearmy.com/forums/archive/index.php/t-55394.html

Good thread. I remember reading it back in the day. Basically confirms everything I understand about destroking. The part about shorter dwell time on the destroked motor was a good revelation too. All that back and forth about head flow numbers and then Dave blows it up at the end. Lol! I plan on visiting their shop one day for sure.

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