[s-cars] How many people on this list have gone the 2.6 L route?

[djdawson2 at aol.com]

OK...  I'm going to have to play a little "point - counter point" with my friend Hap.
 
High output engine in simplest terms:
Low rod ratio = BAD
High piston speed = BAD
 
A simple look at the math tells us this about the rod ratios:
 
Stock stroke = 86.4mm... rod ratio is 1.67
"Happer" stroke = 92.8... rod ratio is 1.55
Eurovan stroke = 95.5... rod ratio is 1.51
This assumes that you retained a stock rod length of 144mm.
 
Another trip to the math class tells us this about piston speed at 7k rpm:
 
86.4mm = 3969 feet per second
92.8mm = 4262 feet per second
95.5mm = 4398 feet per second
 
Bottom line... the majority of the "damage" wrt the design of a high output engine has already been done simply by going to a 92.8mm crankshaft.  Going to the 95.5 does make it worse, but by a much smaller degree than going from a 86.4 to a 92.8.  It is generally accepted that piston speeds above 4000 feet per second require significant changes to engine internals, if you expect it to hold together.
 
So, which is worse... bad rod ratio, or high piston speed?  Without question, a bad rod ratio leads to short engine life.  Piston speed, however, can be dealt with by improving the design of other internal components.  Naturally, you are going to replace the connecting rods.  We are already blessed with a forged crankshaft.  Hardware can be upgraded (rod and main bolts), and a girdle can be employed on the block and main bearings to reduce the chances of distorting the block, and bending the crankshaft.  I have yet to hear of any of our 2.5 liter brothers using a girdle... and maybe it won't be needed.
 
In the end, it is a bad rod ratio that will likely kill any stroker motor used at high rpm.  Using a 92.8 or a 95.5 is actually fairly inconsequential.  By the numbers, a 92.8 is not a good idea... and a 95.5 is just a little worse.
 
The factory, however, had different things in mind.  They used the 95.5 crank with a set of 159mm rods.  This brings the rod ratio back up to 1.667... almost identical to the ratio of our stock 2.2's using the 86.4 crank.  This isn't coincidental.
 
My expectations for any stroker using a 144mm rod would include high piston skirt wear... out of round cylinders... and a fairly short life by comparison to a factory 2.2.  With forged pistons, a bunch of boost, and a bad rod ratio, I'd feel lucky if I got 100k out of the engine before it was experiencing unacceptable blow-by.  In the end, Hap will let us know.
 
Some comparisons... the rod ratio of a typical 350 (5.7) small block chevy is 1.63... much better than either stroker option.  Honda folks are lucky... many designed with rod ratios over 1.8.
 
The numbers don't favor either stroker... but that doesn't mean I wouldn't try it as well.  However, I would certainly limit my fun to 6500rpm, and realize that the block would be scrap after one life cycle... A hone wouldn't cut it after use with that rod ratio (too out of round), and no room for more bore.
 
That's all I've got.
Dave
 
-----Original Message-----
From: CaptMagu at aol.com
To: fastscirocco_2000 at yahoo.com; s-car-list at audifans.com
Sent: Sat, 24 Jun 2006 13:45:19 EDT
Subject: Re: [s-cars] How many people on this list have gone the 2.6 L route?


There are 2 basic options when you go the stroker route. 2.5 with the 92.8 
Eurovan crank and 83 mm pistons and 2.6 with the 95.5 crank and 83 mm pistons 
and the Eurovan block. IMO the 2.6 option puts too much side loading on the 
pistons and the rings because of the extra stroke and side dispacement from the 
longer throw. You also have an issue with the speed at which the pistons travel 
within the cylinder and those inherent problems. Dave Jones would have 
severely limited my red line to under 7000 rpms if I had chusen the 2.6 route. 
With 
my current 2.5 he has imposed nothing other than a very strict break-in.

Your other requirements would be custom tuned SW/EMS, tubular EM, 3 1/2" DP, 
FMIC, Big injectors, 044 fuel pump with -8 lines, custom turbo ntake, Big Bore 
throttle body, and Big turbo to name a few. As for the turbo, the GT 35R is 
my personal choice. In the stock 2.2 litre AAN, the GT 30R is a great option 
with a tubular EM. In the 2.5 litre stroker, you'd be running out of push over 
about 5500 rpms with the 30R.

Hap, wit dakine stroker thoughts not from Evahboost, Maguire
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