To stroke or not to stroke? Maybe this will help...

[rabenne]

I have been thinking lately about adding a bit of displacement to my 4g63 6 bolt. I was considering the common 2.3 L kit that is available from many distributors. I found a couple things that I wanted to share with people who may be considering a 2.3L. I had no idea where to place this, and Im sorry if this is a bad spot.

First, one thing to consider is the piston speed increase due to the longer 100 mm vs 88 mm stroke. To find piston speed you use:

(Stroke (in inches)X Max RPM )/6= piston speed in feet per second

88 MM
(3.4646" x 7500)/6 = 4330.6 feet per second

100MM
(3.9370" x 7500)/6 = 4921.2 feet per second

What does piston speed mean?
Well the higher the piston speed the more difficult it becomes to seal your rings properly. Also, this high speed can cause piston flutter and cylinder washboarding. This additional ring to bore friction also causes lost horse power, and early ring wear.


The rod to stroke ratio is another thing to consider.

88 MM
5.900"/3.4646" = 1.7029

100 MM
5.900"/3.9370" = 1.4986

What does this all mean?
Well longer rod engines by nature have less rod angularity that shorter rod engines.
High rod angularity does provide more torque, but at the cost of top end horsepower due to losses from piston side loading, not to mention the greater intake and exhaust pumping forces (lost horsepower) caused by the longer stroke.


I dont know if this information is useful to anybody, but I thought id share it all anyway.

 

[Siral3x]

I think it's more an issue of price/reliability.
The cheapest stroker kits start from 1K+ , and the machine work is more expensive.
I'm building an engine right now; shopping and comparing tells me that 300cc is just not worth the extra 1k+, when you can stick with a high revving 2L and a sick turbo.
Indeed both of your theories are right plus it's really hard to find a good inexpensive machine shop to put your engine togheter right the first time.
Tunning a 2.3L is really hard for the average DSM'er budget.
I'm sticking with the 2L, so I chose NOT TO STROKE , but to rev hard and spool up

 

[snox135]

(Stroke (in inches)X Max RPM )/6= piston speed in feet per second

88 MM
(3.4646" x 7500)/6 = 4330.6 feet per second

100MM
(3.9370" x 7500)/6 = 4921.2 feet per second

The formula for mean piston speed is actually stroke x rpm /6 = piston speed in feet per minute

Here is more info than you probably care to know about calculating maximum piston speed, including a spread sheet.

 

[turbo addict]

the 4g61t is a 75mm stroke in my mirage turbo.
(2.9527x7500)/6=3690.944 feet per min.
(2.9527x8500)/6=4182.991 feet per min.
(2.9527x9500)/6=4675.108 feet per min.
and rod to stroke is 5.9/2.9527=1.9981
my 1.6l can spin to 9500rpm and has a lower piston speed than a 2.3 at 7500. hahaha

 

[GVR4592]

So build a long rod stroker, or a long rod 2.4 based shortblock, and have the best of both worlds.

 

[turbo addict]

long rod will help the rod to stroke but piston speed stays the same, the acceleration rates change but you still have that 100mm to travel per revolution. If you want a 2.3 or 2.4 just rebuild a little more often.

 

[rabenne]

ooopppss... my mistake... I meant feet per minute... not second... that would be over a quarter million feet per minute hahaha.... As for the formula? were you saying I am wrong about the formula? anyways... I like the 1.6L numbers, thanks for your information

 

[snox135]

ooopppss... my mistake... I meant feet per minute... not second... that would be over a quarter million feet per minute hahaha.... As for the formula? were you saying I am wrong about the formula? anyways... I like the 1.6L numbers, thanks for your information

No, just minutes not seconds. Actually if I remember correctly it's divide by 6.024 but most people use 6.

 

[GVR4592]

long rod will help the rod to stroke but piston speed stays the same, the acceleration rates change but you still have that 100mm to travel per revolution. If you want a 2.3 or 2.4 just rebuild a little more often.

Eagle and Magnus both make cranks that would destroke the 2.4 block, the Eagle is 94mm and the Magnus is 92mm. Destroke and get some long rods, you can get really close to the 4g63's R/S ratio but with 2.2 liters.

 

[Strm Trpr]

Can you use the Eagle 94mm stroke crank with 156mm rods and 2.3L stroker pistons.
With an 85.5mm bore, you'd have a 2.2L with a rod ratio of 1.66.