The Cal-look Lounge

Ok, maybe a bit of a trivial question, but i am weighing the pros and cons on a solid 1mm shim under the barrel or a copper 1mm shim on top between barrel and head.
which is better, are there benefits doing one or the other?

I like having a completely flat head topping the cylinder. No step, no copper gasget, nothing with any kind of edge to start pre-ignition or detonation. It should be as sano a connection between head and cylinder as possible. No tweaking, no distortion, just a completely flat and square join between the two for best results. Put the spacer next to the case. Ideally you would have long cylinders and machine them to the exact length and have no spacers.  ;)

Well there you go, I was just thinking of this the other day too.
 :)

Can I add a quick question to this too please?

Has anyone ever noticed any corrosion on the head from using a copper head gasket on a long-term street engine?
(dissimilar metals)

Lots of variables but if its a N/A street engine with sensible stroke and rod ratio? then under barrel just as its cheaper ;D 

OK, it was a NA, but will be turbo, hence the slight lowering in CR. but all very modest. engine is a 2276 with porsche length rods. as for the price, i have both options available.

I would put copper on top then to keep as much of piston as possible in cylinder at BDC

cheers Richie

thanks.

see if i can make this work.  ;D

From John C. : '69-82mm crankshafts can use the VW (5.394″) or Porsche (5.354″) length rod, IF it is made of Chromoly. Once you start using an 84mm crank, you are required to use a 5.5″ or longer connecting rod so you don’t overstress the rod and rod bolts! I recommend a 5.7″ or longer rod for strokes longer than 88mm.'
I agree with John on that one, and you're making a mistake using Porsche length rods. NOBODY does that in the automotive world, and most do the opposite and use as long a rod as possible.

Martin

So John C says use Porsche length rods up to 82mm stroke and you agree with him?  and this is 82mm stroke [2276] but you think its a mistake to run Porsche length rods? I am confused which it is?  Porsche length rods have been used with 82mm stroke in 1000s of engines over the years

cheers Richie

I'm agreeing with John that it can be done. And I'm agreeing with John with his last statement too. Name one engine builder in the world (besides us bug guys) who uses these short rod lengths, just one :)

Nissan

What rod length/ratio do they use?

Factory RB26 skyline 4.78inch rod  :o

(Stock Config "Overaquare/Short Stroke" 86mm x 73.7mm & 121.5mm):
OEM RB26DETT Configuration/Stroke.
121.5mm Rod Length & 73.7mm Stroke = 1.65:1 (1.64857530529)
30mm CH/PH Piston Used (Standard).
-----------------------------------------------------------------

I was thinking RB too  ;D

OK that's one. Everyone else uses long rods for good reason. Look at listings for rods for V8's. Stock length, or longer.

Great now I'm googling this like everyone else :o
Here's an article where they are trying longer rods on a Nissan motor (gee I wonder why ::)...

Building the Long Rod Nissan SR20VE Engine
'We researched economical ways to do this by perusing the rod dimensions from other motors. We did not want to order custom rods for cost and timing reasons so we figured we could find a rod/bearing combo that was close and work with that. We ended up settling on the rods from a Honda H22 Prelude motor. The H22 rod is 5.630” long vs the stock SR20’s length of 5.365”. This would give a stroke to rod length ratio of 1.66:1 vs the stock 1.58:1. Not a huge difference but one that we could probably find measurable results from.'
http://www.motoiq.com/MagazineArticles/ID/2135/Building-the-Long-Rod-Nissan-SR20VE-Engine.aspx

 ;D






Later OS30 engine uses 86mm stroke[ so relevant  to our scene agreed ? ] with a 5.45 rod  :o, Now given what they were doing with these engines I am guessing they thought about it for quite a while before doing that.

Here's another one off top of my head[ yes I did check this before writing as its not something I am really familiar with, BMW 2002 M10 has 80mm stroke and 5.31 rod ratio, not as short as Nissan but still similar to our VW topic so I am guessing there are dozens, maybe 100s more out there.

All I am saying is there is more than one way to do things :)

cheers Richie

I want some of what you're on if you think short rods are the way to go in a bug engine, har har  :P

PG tips Tea  ;D Yes you should try it ;D and that's not actually what I said is it?  I said there is more than just one way to do it, and there is in my opinion, we all have different ideas and aims for our engines and what we want to achieve in performance and reliability :)

cheers Richie

1956 Ferrari 750 Monza: 90mm stroke, 142mm rod = 1.57
1959 Maserati T61: 92mm stroke, 143mm rod =  1.59
1967 BMW Apfelbeck M10: 80mm stroke, 135mm rod = 1.68

Maybe check your weed wacker engine too!  :P

To#¤ta - 1JZ Bore x Stroke: 86.0mm x 71.5mm
To#¤ta - 2JZ Bore x Stroke: 86.0mm x 86.0mm

1JZ Rod Length: 125.25mm
2JZ Rod Length: 142mm

That makes a 1JZ a 1.75 rod to stroke ratio  :)

 ;D

Virtually all of Honda's B,D,H and K motors have a rod ratio shorter than an 82/Porsche rod vw. Subaru 2.5 STI is 1.66
Unless your talking under 1.4 or over 2.2 who cares?!?

B16A1, A2, A3 - 1.74:1

http://www.superstreetonline.com/how-to/engine/0506-ht-rod-stroke-ratio/

The only 'good' reason to use a short rod is to stuff your big motor into an oval. (and that's good reason!)

Nicolas, one thing I learned about 20 yr ago was to machine the chamfer off the top of the cylinders, to increase seating area. No matter copper gasket or not.

Berg use to offer the service of honing your cylinders straight on a honing machine. More recently I had mine done locally and they said the new AA cylinders were wonky from new so it's well worth doing.

TYPE 4 engines.  ;D
Not big strokes but short rods for torque to push heavy buses.

Cool! Back to "discussing" rod lengths again.
Good fun, keep at it, I'll get the munchies.
LOL!
 ;D

Now there's a real performance engine, sheesh, VW Vans?? :-\

From CIP1 website where you can't even buy rods as short as he's using in the 2276:

'A note about rod lengths. We offer 4 different rod lengths because rod ratios are very important. Most engine builders today agree that longer rods produce more power, and less ware on internal engine components then shorter rods. Top engine builders try to achieve a rod ratio of approx. 1.6-1.8 to 1. A 82mm stroker crank should have a rod that is 145mm (5.7inches) to achieve a 1.76 rod ratio.' http://www.cip1.ca/ProductDetails.asp?ProductCode=C13%2D8310%2DARP

Why don't you build two engines.  One with the recommended 5.7" rod and one with the Porsche length rod. dyno them and show everyone your results?

That would be a good magazine article. Most people already have their mind made up by the time they start paying the engine shop for machining, etc. For myself, I went with what my engine builder recommended.  8)

If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth. Back in the days when Buddy Morrison and I built dozens of small-block Modified motors, we earnestly believed that an engine needed a 1.9:1 rod/stroke ratio. Today every Pro Stock team uses blocks with super-short deck heights, and we couldn’t care less about the rod ratio. A short deck height improves the alignment between the intake manifold runners and the cylinder head intake ports, and helps to stabilize the valvetrain. These are much more important considerations than the rod-to-stroke ratio. There’s no magic – a rod’s function is to connect the piston to the crankshaft. Period. David Reher

Wow I didn't see that coming! Totally agree about the short deck height. But I don't get your intake manifold and head port reason. I like it because it makes your engine efficient (burns everything and thus runs cool) and creates POWER without having to advance timing. The tighter the better. .035" seems reasonable for a bug motor. ;)

i could do that, makes sense as far as seating surface goes. i'll dig into this deeper.


yes, that is also an option. i am more then likely going to rebuild this thing within the next few years and if i can come up with a good set of 5.5's or 5.6's i might give it a ty. why not.
for now however i want to get this engine build and hopefully be able to taste at last PG tips turbo engines  ;D

Why not? There are a few reasons for a street engine if you want to do a proper job with the cooling system. The cylinder tin had to be extended using another set of cylinder tin as donor metal and the shroud had to be modified, stretched and tweaked to fit on the cylinder tin and not have huge air leaks. The header needs to be cut and stretched out to fit the wider motor as well as the intake manifold. Plenty of extra work is involved! Here's a pic looking very frankensteinish...
(http://img.photobucket.com/albums/v415/mschilling/Shroud%20mods/IMG_1223.jpg) (http://smg.photobucket.com/user/mschilling/media/Shroud%20mods/IMG_1223.jpg.html)

I can remember Mark Herbert was a fan of short rod motors.
The piston dwell time at TDC and BDC was less with a low rod ratio.
I think the big reason Mark liked them was that piston acceleration rates are higher with a short rod, so this will force a port to flow better than if you had a long rod.

For Nicolas' original question, go with the shim under the cylinder.  The shim on the top just creates twice as many surfaces that can have a sealing failure.

For my 2332 cc with Mahle cylinders, I used copper head gaskets for this very reason.  When checking the piston skirts, more cylinder shims wouldn't have been the best idea, as the piston would have pulled out the cylinder further.

Bruce, do you believe that? ???

Martin, you missed the most important part of Brian's quote.  The part that said it came from David Reher.  He's not talking about the space from piston top to cylinder top deck.  He's talking about NHRA pro stock V8 block deck.

Ok now that makes more sense to me. The priority for those engines is the intake. That's not the same as for a VW engine where the priorities could be increased cost or fitting the motor in the car. We're lucky that modifying the rod length, along with barrel length is fairly straightforward. You're simply missing out on power/rpm if you don't go for it. My engine builder had a one track mind and that was to build it the best with the parts I felt like paying for. He said I could easily open up / match the intakes, bolt on some dual carbs and go win some races with the engine.