Armond

what's the avantage of using a longer con rod to a M10

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I have no experience on this subject at all but heard that you can replace the stock M10 connecting rod to a 5 series rod which is longer and will supposedly get better performance. The crank will remain stock. What are the benefits to go this route. TIA

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There are a few good reasons for longer rods.

One the load is reduced on the skirt of the piston as the wrist pin is higher in the piston. Makes the piston lighter as the pin boss can now be shorter.

Second and more importantly the dwell time at top dead center is reduced (in minutes and seconds not usually even a whole degree) and this improves intake air flow a slight amount and cuts down reversion a slight amount.

These changes effect the torque curve of an engine and can influence the durability in high speed operation.

This subject is covered in detail in Bill Jenkins 70's era book on the small block Chevrolet. Required reading for anyone wanting to learn about modifying any type engine.

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Armond,

Remember that simply changing the con rod to a longer version is just the beginning. The piston will need to have a shorter distance from the wrist pin to the top surface. Otherwise you will only make 1/4 of a turn on the crank before noticing a slight interference when the piston contacts a valve or the head. While aa/fd has an excellent point regarding dwell time this is a performance upgrade that needs thorough examination.

What else do you have in mind?

Todd

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Thanks for filling in the blanks,

Sometimes I forget to mention the obvious and leave out fairly important stuff like "you will need a set of custom pistons to use longer rods"

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There are a few good reasons for longer rods.

One the load is reduced on the skirt of the piston as the wrist pin is higher in the piston. Makes the piston lighter as the pin boss can now be shorter.

All good info. I'll add to it the following FYI from my recent experience:

During side-by-side M10 race engine builds, there was an opportunity to compare the weight of stock length Ireland H-beam rods mated with forged pistons versus longer rods (again, the H-beam) with a shortened forged piston. The result? The weight of each combined rod-piston assembly was nearly identical (meaning the weight lost in the piston was gained back in the rod).

Whether the same with be found with stock rods and cast pistons I don't know...

-KB

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Armond,

Remember that simply changing the con rod to a longer version is just the beginning. The piston will need to have a shorter distance from the wrist pin to the top surface. Otherwise you will only make 1/4 of a turn on the crank before noticing a slight interference when the piston contacts a valve or the head. While aa/fd has an excellent point regarding dwell time this is a performance upgrade that needs thorough examination.

What else do you have in mind?

Todd

I plan on getting JE or IE pistons with this set up and 284 cam.and I plan to match the KF pump to the compression ratio. As far as performance, where would you feel the power? Top,mid or bottom range?

the goal is to give my Tii motor a little more or moderate umph and I'm seeking ideas to accomplish this w/o totaly making this a stroker.

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Guest Anonymous
I have no experience on this subject at all but heard that you can replace the stock M10 connecting rod to a 5 series rod which is longer and will supposedly get better performance. The crank will remain stock. What are the benefits to go this route. TIA

The are many variables that some have touched. In theory, the longer rod, will create more displacement, at the cost of higher revs. Torque vs. Horsepower, a la Grumpy Jenkins and just about any diesel engine. How that translates into better performance depends upon who you ask and the tasks to be performed.

If things were as simple as you ask, doing this would be a forgone conclusion. Sometimes, but not always, there is an advantage to a higher spinning smaller displacement engine (for example the 1600 versus 2002).

More displacement usually means adding more seafoam. D. Regan?

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Armond. You mention you're going to get a 284 cam. What is stock, do you know? My recollection (but I could be wrong) is that a 284 cam won't buy you much more performance vs. stock, and many go with a 292 or something. Just food for thought. See you in Brisbane, I trust?

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Alright, well I'm trying to answer my own question here and I can't seem to find the stock cam size. However, from Mike McCartney's book:

"A 284 give only a mild improvement over the standard cam. Good low end torque characteristics, no loss of driveability...." "A 292... Excellent mid range performance (3,500-5,500 rpm). Performance improvements are obtained throughout the rev range. Top end performance benefits from the extra breathing capabilities of the twin side-draft carbs (NA in your case Armond) and 140-150hp is possible with such an installation. Low end performance is still impressive....."

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Tom,

I believe the stock cam is a 264. Call me when you can.I'm on the road.

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Lots of stuff to think about in all the previous reply posts. Good info. But all missed the most fun part,........................ you get to spend LOTS more money. And that helps us all in these dire economic times. Your own economic stimulus package. ............We 2002 owners never forget to help our fellow man. LOL.

mac.

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Armond,

Remember that simply changing the con rod to a longer version is just the beginning. The piston will need to have a shorter distance from the wrist pin to the top surface. Otherwise you will only make 1/4 of a turn on the crank before noticing a slight interference when the piston contacts a valve or the head. While aa/fd has an excellent point regarding dwell time this is a performance upgrade that needs thorough examination.

What else do you have in mind?

Todd

I plan on getting JE or IE pistons with this set up and 284 cam.and I plan to match the KF pump to the compression ratio. As far as performance, where would you feel the power? Top,mid or bottom range?

the goal is to give my Tii motor a little more or moderate umph and I'm seeking ideas to accomplish this w/o totaly making this a stroker.

So, how are you going to go about modifying the injection pump to match this exotic motor build? Inquiring minds would love to know who is modifying Tii injection pumps for modified motors.

The Tii injection pump is tuned for a very specific application and does not take to modified camshafts well at all. Almost every time I have seen a camshaft in a tii motor the pump leans out dangerously at high RPMs due to the different flow characteristics of the cam profile. They are never as smooth in all driving situations as one with a stock cam. Lean/rich and flat spots abound. If you have ever ridden along with Sean Casey when he is trying to tune a hot cammed tii with his wideband O2 sensor setup you would understand better why he and I hate cams in Tii motors.

There are the pumps that were for the early euro 10:1 motors but beyond that there is no real way to modify a tii injection pump for modded motors (especially hot cams) that I know of unless one obtains an Alpina pump or cone. There were Alpina pumps modified for using the factory 300deg cams and then the A4S motors. I have heard of European sources having made modified cones, but those may still be just copies of Alpina or similar.

Think of a Tii K-fish as a multi million dollar German engineered dyno tuned fully sequential fuel injection. Meaning that each injector fires at a very specific time and flow rate for each cylinder based on the air flow characteristics of a specific cam.... etc. I.E. in the firing order of 1-4-3-2. Even the '80s 6 cylinder BMWs with Bosch Motronic Injection fire their injectors in banks of three. That includes the V12 750i too! Really only in the '90s has electronic computer based fuel injection been successful in fully sequential operation.

If you really want a modified Tii motor than I wholeheartedly suggest you talk with and listen to Sean Casey and Bill Holmes. I have heard of Holmes building dyno proven 170hp Tii motors. Sean's Malaga Tii makes around 150hp without long rods or a performance cam!

I also suggest you talk with any of these places about modified Kugelfisher Fuel Injection Tii injection pumps. http://2002tii.org/phpmyfaq/index.php?sid=857086〈=en&action=artikel&cat=220444&id=434&artlang=en Of these, Precision Automotive Research is known to be the best and is who Sean Casey uses. www.precisionautoresearch.com/ Pictures and more info here....

http://www.bmw2002faq.com/content/view/66/32/

A great article and Interview of Gus Pfister of Pacific Fuel Injection here. With pictures and VIDEO.

http://www.bayarea02.com/features/pfister-interview/index.html

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Longer rods = less angular movement at the piston pin and crank. So less friction, less energy loss.

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Longer rods = less angular movement at the piston pin and crank. So less friction, less energy loss.

Lee,

other than the Pistons and e28 con rods, is everything else pretty much a m10 "standard" rebuild? I'm having a machinist do all the work with the help of my local mechanic

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Give it some more thought. If you change the offset of the crank, you'd get more displacement. I don't think longer rods will increase the displacement.

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