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Wed Mar 01, 2006 3:53 pm

In my research for building up a high power engine, I am finding that some setups rely on piston size for power and some rely on stroke. i.e. Berg kit comes with smaller pistons and longer stroke.

What are the advantages of one vs. the other. I know about cylinder walls being thin, and more heat in the heads with larger cylinders. I've also heard some bad things about stroking.
Would a stroked kit like the Berg setup run cooler than say an engine with larger pistions?

Who can give some knowledge here. THANKS

Wed Mar 01, 2006 4:57 pm

the 1904cc is a good street engine it uses the 90.5mm pistons and a 74mm stroke crank

69 mm Stroke

83mm Bore = 1493
85.5mm Bore = 1585
87mm Bore = 1641
88mm Bore = 1679
90mm Bore = 1756
90.5mm Bore = 1775
92mm Bore = 1835
94mm Bore = 1915

74 mm Stroke

83mm Bore = 1602
85.5mm Bore = 1699
87mm Bore = 1760
88mm Bore = 1800
90mm Bore = 1883
90.5mm Bore = 1904
92mm Bore = 1968
94mm Bore = 2054

Wed Mar 01, 2006 7:45 pm

It comes down to what you intend to do with the car when it has a larger motor in it.

94 P&C can be run for a long, long time.

Berg doesn't like them. Their take is that if it doesn't last as long as stock, its crap.

I'll build and rebuild a big motor 20 times over before the P&Cs wear out.
I like to change and tweak stuff too much.

Long stroke gives you torque.

Go for both.

Wed Mar 01, 2006 7:53 pm

short stroke and big bores like to rev high and like big valves to fill the cylinders.

a long stroke and small bore likes to rev low, produce alot of torque, and can fill cylinders with smaller valves.

a 69x94 (1915) will want to rev higher and make more top end than a 74x90(1904) despite the similar displacements.

Low revving, torquey motors are more fun to drive on the street and will tend to last longer than high revving motors.

There's ALOT more to it than that, but that's the basics.

Justin

Wed Mar 01, 2006 8:05 pm

Basically, I am looking to build a disgustingly large motor for my Karmann Ghia. I will probably not drive it more than two or three times a week as my Beetle is my daily driver. Sounds like I need a combination of both in higher numbers to suit me. Maybe 94PnC and 84 stroke for some real haul butt. Engle 110 or 120 cam and CB heads. to get started .LOL

THanks for the breakdown on the sizes and such.

Wed Mar 01, 2006 8:28 pm

84x94 would net you a 2332 pretty strong and about as big as I would go with a stock case. There is alot of cutting that will ahve to be done and pay one of the bigger shops to do it. Go with a forged crank and a GOOD set of P&P heads. Hope you're ready for the pricetag......

Wed Mar 01, 2006 9:13 pm

Thingster wrote: short stroke and big bores like to rev high and like big valves to fill the cylinders.

a long stroke and small bore likes to rev low, produce alot of torque, and can fill cylinders with smaller valves.

a 69x94 (1915) will want to rev higher and make more top end than a 74x90(1904) despite the similar displacements.

Low revving, torquey motors are more fun to drive on the street and will tend to last longer than high revving motors.

There's ALOT more to it than that, but that's the basics.

Justin

That post is perfect, according to an old HS English teacher of mine.
It's like a woman's skirt: long enough to cover the subjectl; but short enough to keep it interesting.

Thanks Justin!

Wed Mar 01, 2006 11:25 pm

Thingster wrote: short stroke and big bores like to rev high and like big valves to fill the cylinders.

a long stroke and small bore likes to rev low, produce alot of torque, and can fill cylinders with smaller valves.

a 69x94 (1915) will want to rev higher and make more top end than a 74x90(1904) despite the similar displacements.

Low revving, torquey motors are more fun to drive on the street and will tend to last longer than high revving motors.

There's ALOT more to it than that, but that's the basics.

Justin

my 73 scamp with the slant six is a big stroke very low reving engine. 105 hp @ 4000 and 185 torque @1600. It has a stroke of 4.125!!! Why these engine live up to the "bullet proof" (besides its also a solid iron block) name is that they rev so low and that also seems to increase the engine life. i drive about 1500rpm at 25mph, and at 80 mph, it barely tops over 2700rpm.

Thu Mar 02, 2006 3:13 am

If they have to choose, nine out of ten women prefer a fat piston with a short stroke to a skinny piston with a long stroke. At least that's what I've heard.

Of course, I haven't had any complaints with a basically stock setup, myself.

Thu Mar 02, 2006 9:04 am

PierreDeKat wrote: If they have to choose, nine out of ten women prefer a fat piston with a short stroke to a skinny piston with a long stroke. At least that's what I've heard.

Of course, I haven't had any complaints with a basically stock setup, myself.

ROFLMAO damn now THAT is funny, Pierre!

Thu Mar 02, 2006 9:35 am

I know there is a simple formula for calculating displacement, can someone post it for me?

Thu Mar 02, 2006 11:34 am

(pi(r^2)(h))xc
pi=3.14159
r= bore/2
h=stroke
c=number of cylinders

To get the numbers you typically see (2332, 2007, 1915, etc) you need to convert the bore and stroke from mm to cm before calculating, but that's easy enough. All you have to do is move the decimal point one spot to the left. 69mm=6.9cm, 94mm=9.4cm, etc.

Also your bore and stroke measurements need to be in the same units. both in cm will be the easiest to work with.

As for engine life, it is definitely a function of RPM. As RPM increases, wear increases even more quickly. Of two identical motors, but one that lives at 3000 and one that lives at 6000, the one that lives at 6000 will live less than half as long as the one that spends all of its time at 3000.

The best comparison i can do for this one is this. A guy I worked with had a 78 GMC tow truck with a 350 in it. The truck NEVER went over 50 mph and probably never saw 3000 rpm in its life. It made it 586,000 miles before needing a new motor.

A buddy of mine had an 84 chevy longbed with a 350 that he drove like a racecar from day 1, redlining it everywhere he went. Made it about 120,000 before needing a total rebuild.

Both stock motors, both well maintained, just one was never revved and one was always revved.

Justin

Thu Mar 02, 2006 11:44 am

'preciate it Justin, but I just sat down over lunch and figured it out.

Thu Mar 02, 2006 6:52 pm

Great post don't ya think
I have only rebuilt two vw engines and pulled apart 5 and more to come.

sounds like i want to go with 1904cc with 90.5mm pistons and a 74mm stroke crank.

Can i run this with stock parts. or do you have to change the heads/valves , cam,

I probabbly should tap for full flow

Fri Mar 03, 2006 6:35 am

73resto, definitely go with some better heads and an Engle cam, like a 110, and don't forget the phat exhaust.

Fri Mar 03, 2006 10:45 am

73resto wrote: Great post don't ya think
I have only rebuilt two vw engines and pulled apart 5 and more to come.

sounds like i want to go with 1904cc with 90.5mm pistons and a 74mm stroke crank.

Can i run this with stock parts. or do you have to change the heads/valves , cam,

I probabbly should tap for full flow

Sounds good but let me play devils advocate for a moment :twisted: For about the same money and just a bit more machining you could go to a 78 or 82 crank. If you use one of CB's aluminum high roof cases you don't even need to machine. Forged pistons are the same price in "A" or "B" pin position so why not a bit more torque?

My plan right now it to build a 1776 with the CB case CNC heads and an FK8 with 1.4:1 rockers. I'm a couple years away from building a bug for my teenage son... When I build his motor the crank and pistons from my 1776 will go into his, and I get to graduate to an 82mm crank and "B" pistons for my toruble!

Fri Mar 03, 2006 12:56 pm

theredbarn wrote: [
Sounds good but let me play devils advocate for a moment :twisted: For about the same money and just a bit more machining you could go to a 78 or 82 crank. If you use one of CB's aluminum high roof cases you don't even need to machine. Forged pistons are the same price in "A" or "B" pin position so why not a bit more torque?

sure for "the same money" you can go bigger based on crank stroke...but that doesn't tell the entire story...bigger engines have bigger appetites, which relates to "bigger" heads, exhaust, etc.... gotta look at the entire engine not just stroke...

Fri Mar 03, 2006 4:35 pm

I have been researching all the combinations and such that one can put into the engine. I still want to know if the Berg style setup would run cooler than the larger P&C. If so I might opt for that choice.

I have an entire parts list that I am building and the core of the engine must be decided first so I know what size heads etc.......................

Fri Mar 03, 2006 5:32 pm

tornadoboy wrote: I have been researching all the combinations and such that one can put into the engine. I still want to know if the Berg style setup would run cooler than the larger P&C. If so I might opt for that choice.

I have an entire parts list that I am building and the core of the engine must be decided first so I know what size heads etc.......................

i think cylinder head temp would be lower because smaller p&c have bigger cooling fins. not sure about oil temp

Fri Mar 03, 2006 7:23 pm

tornadoboy wrote: 73resto, definitely go with some better heads and an Engle cam, like a 110, and don't forget the phat exhaust.

do i have to go with better heads.