Connecting rod length

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JimmyC
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Connecting rod length

Post by JimmyC »

I am playing with some calculations that are supposed to tell me the optimal intake tract length. It is asking for connecting rod length, which I do not know. Does anybody have one they can measure center to center for me?
Jim Chance
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idstitch
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Re: Connecting rod length

Post by idstitch »

I don't of recall offhand but look in the manual. Whatever the stroke is should be the length center to center I believe.
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Hotzenplotz
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Re: Connecting rod length

Post by Hotzenplotz »

idstitch wrote:I don't of recall offhand but look in the manual. Whatever the stroke is should be the length center to center I believe.
wrong ! The stroke is the distance the piston moves between top and bottom dead centers.

The only relevant info i could find originates from the Austrian Army maintenance book. There they state on page 10-33:
Achsabstand bei der Pleuelstange : 156 + 0,05 mm . That looks like a plausible figure...

Hope that helps
Cheers
Albert
========================
My Pinz has NEVER been with any army
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Jimm391730
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Re: Connecting rod length

Post by Jimm391730 »

The piston stroke is defined by the crank diameter; the length of the connecting rod does not affect the stroke. It seems strange that a calculation about intake runner length (dealing with the flow of air) would want information about the connecting rod length. The displacement of the engine, the number of cylinders, would be crucial but connecting rod length? Hmmm.
Jim M.
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kdiqq
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Re: Connecting rod length

Post by kdiqq »

Rod length shouldn't matter. As its been stated, displacement (of fuel/air) is determined by bore and stroke. Your rod can be 3ft long, but if your stroke is the same, your displacement isn't affected. Which standalone are you using if I might ask?
1977 Austrian 710M
GRCameron
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Re: Connecting rod length

Post by GRCameron »

The Rod to Stroke length ratio has a significant effect on piston acceleration and peak piston speed. How quickly fuel/air mixture can be delivered is important for high piston acceleration conditions. See this article http://www.epi-eng.com/piston_engine_te ... basics.htm for a pretty thorough analysis of piston motion.

Whether it really means much on a Pinz engine which is tuned to produce low end torque over a relatively wide rpm band (primarily by cam profile, duration, and overlap) remains to be seen. In specific high output conditions, i.e. race motors, intake runners are tuned to work best with radical cams at specific (read HIGH) rpm ranges. Most of those engines can't idle below 1000-1200 rpm. They may sound "cool" with the loping idle and they may burn rubber like crazy with the pedal to the metal, but their driveability suffers in the real world. Reliability is also an issue in most race motors. The extreme is the top fuel dragster motor that is torn down and parts replaced between runs, but it produces more than 8000 HP for several seconds from 500 cubic inches - some of the time. The rest of the time these motors spit parts out like bullets. They're sure fun to watch!

Why mess with a Pinz?

Please, no flames. It's just my opinion.
George Cameron
Yarnell, AZ
1979 Pinz 710M
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JimmyC
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Re: Connecting rod length

Post by JimmyC »

I did some crude scaling on a picture in the manual and 156 mm is close to what I guesstimated.

I think the Pinz has an amazingly good engine, but the fundamental definition of an engine is "a machine that makes too little power"! I am also sort of fixated with exhaust odors since that is what my GF likes least about the truck.

Part of me just really wants to understand the engine better. I am pretty good at diesels but this is the first gas engine I really get interested in. I find the whole throttling issue fascinating. I can't get over the fact that at idle you are supposed to purge the gas out of the combustion chamber while you have more pressure in the exhaust manifold than the intake.

Part of me thinks things could be improved. I suspect the compression ratio is low for the type of gas that is typically available nowadays. I wonder if a longer intake tract would bump things up and help with the exhaust reversion at idle speeds. I also wonder if a bit of a step going into the headers would help with reversion. I wonder if triple cutting the valves would keep the torque from falling off at high(er) RPM. If I was president I would put the National Research Council to work on these issues.

I think the reason the piston rod length is in the intake runner length is that it determines the crank angle for maximum piston speed.
Jim Chance
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Profpinz
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Re: Connecting rod length

Post by Profpinz »

If you want to improve the original motors performance your best way, in my opinion is to go for a 2.7 litre conversion......It increase the compression ratio and obviously the power output.
It was one of the improvements the factory made to the last air-cooled Pinzgauer's produced.
Peter

1974, 712 6X6 Pinzgauer
1983, 710-1.6 4X4 Pinzgauer
1997, 718 6X6 Pinzgauer (in pieces)
1971, 700 Haflinger
1974, 703 LWB Haflinger
2001, Range Rover

http://www.ozpinz.com
kdiqq
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Re: Connecting rod length

Post by kdiqq »

JimmyC wrote:... I am also sort of fixated with exhaust odors since that is what my GF likes least about the truck...
When I first met my wife, she commented on how my Trans Am smelled like a boat. I just let her know it was a stipulation of the relationship. :lol:

You may be chasing the smell forever. It's the nature of a carbureted engine. The carbs are constantly giving off fuel vapors and the never running 'perfect'. EFI and modern ignition are going to get you as close to a modern engine as possible. The smell of a 70s carb'd military truck can be chalked up to 'character'. I'm worried that if your addition of a cat didn't fix it, you might just be chasing your tail over something that only modern engine controls can help alleviate.
1977 Austrian 710M
JimmyC
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Re: Connecting rod length

Post by JimmyC »

ProfPinz, that is neat to know. Are the factory parts for the 2.7 L available? Is this the same kit Jim L sells?
Jim Chance
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JimmyC
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Re: Connecting rod length

Post by JimmyC »

Kdiqq, Touche on both points. Last week the GF was discussing an indoor air problem caused by someone striking a match some hours before.

I probably am mostly chasing my tail, but I like doing it. I retired about 9 months ago and am having fun doing it. The cat had a positive effect and so did regular tuning, but neither is 100%. The "exhaust smell" is real close to 100% cured but I am still getting noticeable eye-burn. I thought the burn was from NOX, but now I am thinking it might be aldehydes.

My fuel air mixture varies too much for any cat to work well. The kind of cat I have is about as good as you can get for a poorly controlled mixture. It oxidizes hydrocarbons to the extent oxygen is available and then reduces NOx once the oxygen is depleted. When it reduces NOx this produces oxygen that is then available to oxidize more hydrocarbons. It can store oxygen when it is plentiful but not much.

My mixture is too rich on power and (i think) too lean on trailing throttle. I think to make a cat work I would either need to stabilize the mixture, which I do not think is possible with a carburetor, or try to run it always a bit rich and have a second catalyst with air injection.

When the stench would get truly horrible (which it no longer does) it is always related to poor combustion at high manifold vacuum. At high vacuum there seems to be too much exhaust gas mixed with the mixture for it to burn well so I get misfires and poor combustion. This is how I got fixate on the intake and exhaust - trying to limit exhaust reversion - but that got me thinking about the power aspects.
Jim Chance
710M

All my post fully incorporate the Dunning-Kruger effect
kdiqq
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Re: Connecting rod length

Post by kdiqq »

JimmyC wrote:Kdiqq, Touche on both points. Last week the GF was discussing an indoor air problem caused by someone striking a match some hours before.

I probably am mostly chasing my tail, but I like doing it. I retired about 9 months ago and am having fun doing it. The cat had a positive effect and so did regular tuning, but neither is 100%. The "exhaust smell" is real close to 100% cured but I am still getting noticeable eye-burn. I thought the burn was from NOX, but now I am thinking it might be aldehydes.

My fuel air mixture varies too much for any cat to work well. The kind of cat I have is about as good as you can get for a poorly controlled mixture. It oxidizes hydrocarbons to the extent oxygen is available and then reduces NOx once the oxygen is depleted. When it reduces NOx this produces oxygen that is then available to oxidize more hydrocarbons. It can store oxygen when it is plentiful but not much.

My mixture is too rich on power and (i think) too lean on trailing throttle. I think to make a cat work I would either need to stabilize the mixture, which I do not think is possible with a carburetor, or try to run it always a bit rich and have a second catalyst with air injection.

When the stench would get truly horrible (which it no longer does) it is always related to poor combustion at high manifold vacuum. At high vacuum there seems to be too much exhaust gas mixed with the mixture for it to burn well so I get misfires and poor combustion. This is how I got fixate on the intake and exhaust - trying to limit exhaust reversion - but that got me thinking about the power aspects.
As long as you're happy doing what you do,keep doing it!!! :)

It's interesting to say eye burn. I've only experienced that on pig rich cars. I left garages essentially crying when a friend didn't both correcting the jetting in his new carb haha

Try a carb rebuild by some reputable, have them synced, and put your Pinz SSI on. If you're getting eye burn, I'd bet money that it would be fixed after that. If that doesn't fix it, you're looking at EFI.

Keep on trucking though. A cat doesn't need consistent AFR, I've logged my EFI stuff and even on stock motor cars it bounce like crazy. What you do need is heat though. You may need to move it before the muffler. I think that's sucking up a lot of heat. Try to get a cheap IR temp sensor and see what the temp of the pipe is going in to the muffler and going out. I may be just blowing smoke!

Ha. Haha... I know, too funny.

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1977 Austrian 710M
JimmyC
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Re: Connecting rod length

Post by JimmyC »

I have rebuilt the carbs and synced them. There was a lot of wear in the throttle linkage which effected the airflow at idle. Combustion at idle is very sensitive to the throttle setting. I think that was my biggest problem.

I bought a bung for each exhaust tube and will check the mixture on each cylinder.

I have a pretty good infrared thermometer and am amazed by how quickly the exhaust pipe cools as it gets further from the head. It looks like it drops like 100F per foot in the tube and a bunch going through the muffler. The cat needs higher temps, but I need to figure out how that will effect the exhaust tuning before I do anything.

The Pinz SSI is going on right after I Dyno it. I want to Dyno it with the stock distributor and try a couple of different ignition timings before I put in the PinzSSI.
Jim Chance
710M

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ako
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Re: Connecting rod length

Post by ako »

If you want to get heat to the cat you could try ceramic coating the manifold and exhaust system that is in front of the cat.

Not sure how much of a good idea this is on an air cooled engine though.

Other options is the thermal wrap which is at least easily reversible. But it can trap moisture in and promote corrosion.
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