Some on here have played with increasing rod length on a standard 2055 build (96X71).
I'm hoping they will share their experiences/ problems with this idea.

It appears that you can fit a 5.5" rod to a KB stroker piston (1.11 comp height) with a .070 lower cylinder shim pack and end up with a deck height of .035-.040

From Jorge@europeanmotorworks

"KB 034-100B 96 x 80 22mm pin has a pin height of 1.110" weighs 494 grams w/pin and 391 grams w/o pin."

A stock 73 2.0 piston and pin weighs 680 grams.

The rod (aftermarket H beam) should weigh somewhere around 600 grams.
I could not find a weight but my 6" chevy H-beams weigh 630. My Miata H beams (133mm length) weigh 570 grams.
The stock 73 2.0 rods are pushing 800 grams.

So, in weight reduction alone I can pull 53.6 oz out of my reciprocating assembly.
This is the highest weight reduction I've ever come across. This is MASSIVE!
I improve my rod/stroke ratio from 1.845 to 1.967.
I increase my piston dwell time at TDC.
I reduce side loading on the pistons as well.

All of these are "for the better" in my book.
The weight reduction is un-believable. Porsche/VW went HEAVY for these parts.

Am I missing something?
Are there reasons not to do this?

I don’t think there is anything outright bad there.

However keep in mind T4 limitations - especially as you try to increase crank speed and HP:

T4 heads and ports have limited ability to mod - therefore limit airflow to a degree.

T4 crank is effectively a 3 bearing crank that is susceptible to crank whip, and pounding out the center bearing. The small 4th bearing in the crank nose really only supports the fan and does little to support the area of the crank that is subject to flex. Remember your crank forces increase as the square of crank velocity. It’s easy to lose sight of the fact that increases in RPM can generate force more quickly and than forces can be reduced by lightening reciprocating mass.

More HP = more heat. Air cooling makes it harder to get rid of “extra” heat from hot rodding.

There is some case relief when stroking a tyoe4 but nothing huge.

Please explain how a longer stroke reduces side load on the piston?
Maybe I’m just missing something, but it seems the angle increases, and adds more load as the crank comes around from BDC…that angle would be even steeper?

Root cause question.
On the Porsche m96/97 motor that experiences bore scoring, is a long stroke contributing to the failure of the cylinder coating?

Rich

My understanding is that he is increasing the length of the rod with standard stroke (71mm). Longer rod, smaller rod angle, lower piston side load, lower piston acceleration, etc...

Gotcha,
Thank you, it was confusing

Longer RODS reduce the angularity of the crank throw to the piston pin.

You've got a super tight engine where the crank throws get deep into the pistons (most modern engines) the total angle the piston sees to the rod is very large (20degrees maybe)

Now make the engine case so that the piston is way up.
For sake of argument let's say 3 feet...

3 feet away that crank throw only causes 2 or 3 degrees of angle in the rod and the side loading on the pistons drops to almost nothing.

This is SO important that innovations are still coming to market.

These are weird but I understand "the why" of this design.

https://newatlas.com/automotive/two-piece-con-rod-thunder/

Jury's still out but those significantly reduce piston rock and increase piston dwell at TDC better than anything else I've seen.

I just noticed R_towle's questions are mentioning longer stroke.
Yes, longer stroke ALWAYS increases piston side loading. Sometimes to the reduction of piston life. Chevy small blocks have a piss poor rod/stroke ratio stock.

I'm not talking about stroking this engine at all.
I'm increasing rod length alone.
I'm not talking about trying to run higher rpm either.
I'm out to maximize torque through the entire RPM range if I can.
Running high rpm or large stroke requires heads that can flow.
I'm trying to use fairly standard AA heads to their maximum potential.

Since you seem to like less reciprocating and/or valvetrain mass, you can get stronger I-beam Rods that weigh less (about 564 g):

https://empiparts.com/products/empi-empi-pr...bolts-00-8347-0

Make sure to get the ones that matche your crank's journal (VW, Chevy, etc.).

You can also sleeve the lifter bores and run type 1 lifters that are a lot lighter (53g versus 136 g).

If you go with the longer stroke, remember the calculations for the spacer under the cylinders (always measure)...your engine width increases and that can create problems. My current/next engine project is using the EMPI 5.5" I-beam Rods with a VW Journal and an 80 stroke (78 wasn't available) along with type 1 lifters.

Best wishes for your project.

Parameters for this engine include staying close to standard width.
No large cylinder base extensions this time around.

I prefer lower weight within reason.

I also will run tighter quench than many on the forum would, thus the hyper-eutectic pistons and the H-beams are intentional for rigidity and lack of expansion.

I cannot stand the weight of the standard lifters. Those critters are some of the heaviest lifters I've seen. I will be looking into lighter weight options, but I recently bought a NOS (from 1986!) webcam set up that includes new webcam lifters.

The budget fairy says "the lifters don't move that far anyway".
The engineer fairy says "The lifters could be 1/3 the weight".

Titanium retainers and lighter weight valves may be incorporated.

How are you going to pack the long rods AND an 80mm stroke in a type 4?

It looks like you need pistons with a compression height of 22.8 mm.

Or 6mm thick cylinder spacers.

And now the cooling tin doesn't fit anymore, and you need longer push rod tubes.
Carb linkage or FI manifolds have to be lengthened.
And the cooling tin is too large for the hole in the car and the edges have to be re-bent.
Exhaust doesn't line up anymore either.
Lots of width issues.
I want to avoid that type of BS...

I think the only thing that is to gain from this is the weight savings and the easier adjust ability of the quench and compression since you have to add a bunch of shims to make it correct (if i read that correctly)

All others are negligible/nothing gained.

Raising the rod/stroke ratio is actually WORSE for this type of engine. 1.8xx is already way too high.

Look at any production high revving 4 cylinder from the 80's to today. The r/s ratio is between 1.5x-1.6x.

I do remember some guy did a test on this with a 4age. OEM r/s ratio is 1.58. He raised it to 1.78 with some custom rods. I think it net him 5 hp and that was ONLY at peak of 8K RPM and that could be accounted by the change in weather between swapping all the parts over.

Please expand on why you think a r/s ratio of 1.8 is way too high.

I personally want to understand your viewpoint.

Why would lengthening the r/s ratio make things WORSE?

What would it make worse?


Thanks
Rick

*from here on out i will refer to rod stroke ratio as r/s

Most of the number is from looking at other real world examples. Mainly look at an ej20/ej25. They have a r/s of 1.75/1.65 and they spin higher than a T4.

You are correct that as you raise the r/s the rod angle gets smaller and tdc dwell time is longer. But you will only see the benefits from those effects when you start spinning at 9K RPM and above (2.0 r/s is around liter bike territory)

And, as with everything, there is no free lunch. A lower r/s provides one very large benefit. The downward acceleration of the piston (intake and combustion stroke) increases as the r/s decrease. This helps the intake stroke greatly at lower RPMS (<7K RPM). Creates a larger void in the cylinder quicker making the suck, suck harder.

From what I know a longer rod is happier at lower rpm's and a shorter rod is happier at higher rpm's.

Good luck with your build

Here’s the funny thing: r/s ratio is like debating Porsche vs Ferrari. Beer vs wine vs Tequila!

There are plenty of engines out there that range from less than 1.0 to way greater than 2.0. All of them are pretty cool. It’s not like there is a singular answer.

Ogdouhy has a good point about reduced vacuum but will it really matter moving 0.1-0.2 one way or another seems like the induction systems just get tuned accordingly to accommodate.

I should preface this whole post by saying I’ve spent my career as a chassis engineer so not a Powertrain guy. However I have spent a bunch of time working with the powertrain guys as well as having spent time around race engine builders competing at international levels. The debate never ends . . . And it never gets old listening to it as I hope to learn more.

But I am curious - if not trying to increase crank speed - why bother with the long rods and all the internal component lightening. Yeah - I get reduced piston side loading, reduced friction, etc but the delta is minimal without making drastic changes to the engine design. OEM components are heavy - mostly to insure durability at an affordable cost. The usual reason for going light is to free up HP and increase crank speeds but doing so at the expense of durability.

So why take the trip for a mild(ish) 2056?

Don’t get me wrong - Looks like a fun excercise. But now I’m curious what the end goal is HP & torque wise?

The EMPI I-beam rods are both lighter and stronger than OEM Rods. Sure there's a $ cost for them, but even if you buy refurbished Rods, bearings & bushings, you'll spend $ and time on OEM.

Why take the trip? Because we can.

A 2270 is a known engine. New versions will perform while running heat exchangers. Wrinkles ironed out. Why did you decide on a 2055 displacement?

I have most of a 2055 now.

I'd rather have a 2256 or 2270 but the extra cost associated with stroking the engine
might not be worth it for this application.

Staying "standard 1st upgrade engine" and making the power I hope for is far more challenging with a 2 liter than a stroked engine.

I'd be hunting 180/200 on a 2270 and that would require heavily worked heads and serious exhaust.

Heat exchangers might actually work but I would expect they would be a restriction at these power levels.

Tangerine racing sells appropriate exhausts for such an engine, but they are not inexpensive. There might be other options that are more budget friendly.

The car I'm putting this into will stay narrow and I'm using 914 drivetrain parts so limiting total power is probably the wiser choice.

I'd like to build the highest compression attainable with true flat top piston and piston to head clearances as tight as possible. I'm a huge believer in quench and want to maximize the phenomena. My target static compression is 10:1 and I'd be hitting that with a stroker.

It looks like I can fairly easily hit 9:1 with a 2055 and although that's not what I'd prefer it's probably enough to reach my power goals.

I'd like to double power at the rear wheels over the stock 1.8 the car came with.
I'm guessing a stock 75 1.8 should show 60-65 hp at the wheels and I'd be ecstatic with 120 with an emphasis on low and midrange torque.

Higher compression, maximize quench, reduce reciprocating weight, mildly ported heads, moderate cam, ceramic coatings, bespoke intake, most modern FI and ignition tech available, E85, non-restrictive exhaust, light flywheel is the basic recipe at this time.

If I run into a good deal on a stroker crank this might change as the benefits of the e85 fuel are more significant with increased compression.
If I had an easy way of hitting 10:1 on a 2055 I'd look into that with vigor.

Super tight quench requires a hyper-eutectic cast piston for both the lack of expansion and the tight P-W clearances that are possible with a hyper piston.