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914World.com _ 914World Garage _ Bore & Stroke discusion

Posted by: KenH Feb 5 2006, 09:59 PM

Assuming all the "other" parameters will be optimized for the B & S.

What are the Pros & Cons between 103mm x 71mm and
96mm x 78mm. Cost factors, reliability, ease of doing, etc.

Any comments on any other combinations??

Ken

Posted by: Mueller Feb 6 2006, 12:06 AM

Ken,

from what I have observed from Jakes engines on what he has published, second combo seems to be the better choice since it seems that the increased stroke allows for a more ideal rod ratio...also, "I" think the second combo is better since the additional stroke gives the cylinders more time to breath in the a/f and more time to exhale the exhaust....

Posted by: Cloudbuster Feb 6 2006, 12:35 AM

If I understand correctly, the T4 heads are more amenable to being optimized for 96x78 than for 103x71. Something to do with intake velocity and boring old volumetric efficiency.

Yet, the latter is more easily accomplished.

Posted by: KenH Feb 6 2006, 01:01 AM

Some where it the past I heard that the longer stroke may be less reliable due to its "mass/velocity" ratio??

Ken

Posted by: Mueller Feb 6 2006, 01:11 AM

QUOTE (KenH @ Feb 6 2006, 12:01 AM)
Some where it the past I heard that the longer stroke may be less reliable due to its "mass/velocity" ratio??

Ken

the longer rods are actually lighter !!!!!

(correct me if I'm wrong, but I think I'm correct on this)

the smaller bore pistons should be lighter as well....

Posted by: Joe Ricard Feb 6 2006, 06:01 AM

Stroke = Torque
and
Torque is GUD.

Posted by: bd1308 Feb 6 2006, 06:20 AM

which two engine combo's are we talking about?

b

Posted by: crash914 Feb 6 2006, 06:23 AM

don't forget the machine work for the 103 combo...with both cases, you won't need to work on the case...

Posted by: Jake Raby Feb 6 2006, 06:45 AM

78X96 is BY FAR the best combination, if you use the right combination of compatible components to comprise the engine. If you want to make this job so simple that a 15 year old can do it successfully, grab one of my engine kits! The second best solution is grabbing the parts from me individually as this guarantees that all the parts will be compatible and will only effect ease of assembly a tad bit since you won't get the "Support" that we give to full kit customers.

The 2270 (78.4X96) combo is the best for many reasons but primarily for the cost Vs. HP and the fact that this combo has been my most researched and has the highest build concentration here, because its just so damn perfect!

The 103mm bore size, IMHO requires Nikies cylinders to remain free of head leaks and associated problems with the HUGE bore size. These issues are not present with the smaller bores up to 96mm and only become apparent after reaching the 100mm threshold. (do searches for more info)

Also the 103mm bore size requires serious and expensive cylinder head modifications to sustain the huge bore size without sacrificing RPM range or power output. If you don't have 2K+ for a set of cylinder heads the 103mm bore will more than likely COST YOU USABLE POWER!

I do not have much time at all to go over this right now, as this week I'm building a 2270 engine while a writer from Hot VWs does a comprehensive story on the build up...

Posted by: KenH Feb 6 2006, 06:37 PM

Thanks for the comments.

Jake, your comments on problems with the 103 setup was what I was looking for.

This is a motor for the track and while I do not have any problem re-building it from time-to-time I still want as much life from it has possible.

Ken

Posted by: Jake Raby Feb 6 2006, 06:44 PM

2316cc absolutely...

I have a combo that literally falls together as a kit and makes 183 HP and about 175 torque... last week this combo with one alteration made 202HP on pump gas!

My kit will yield these types of results for LESS money than you'll spend buying the parts individually to end up with a non balanced, non engineered or proven combination.

I had several versions of this engine in my 914 and it's enough to eat a six for breakfast any day of the week.

Posted by: Carlitos Way Feb 7 2006, 12:19 AM

And at what cost does one get to eat 911's for breakfast?

I've been thinking about rebuilding my 2.0 (spare) into a larger engine. I know I need to have the heads re-done, perhaps opened up... but I'm about as ignorant as anyone could be.

So... back to the question... how much is one of those kits?

Posted by: alpha434 Feb 7 2006, 02:04 AM

QUOTE (Carlitos Way @ Feb 6 2006, 10:19 PM)
And at what cost does one get to eat 911's for breakfast?

914-6s were faster then taildraggers in the same time period. Thats why they stopped making 914s. Same deal with the new cayman. Porsche deliberately limits perfomance by (a) engine restrictions (b suspension

They don't want anything to be faster then their flagship 911. So, eating a 6 for breakfast is not a laughing matter.

Posted by: Aaron Cox Feb 7 2006, 02:07 AM

QUOTE (alpha434 @ Feb 7 2006, 01:04 AM)

QUOTE (Carlitos Way @ Feb 6 2006, 10:19 PM)
And at what cost does one get to eat 911's for breakfast?

914-6s were faster then taildraggers in the same time period. Thats why they stopped making 914s. Same deal with the new cayman. Porsche deliberately limits perfomance by (a) engine restrictions (b suspension

They don't want anything to be faster then their flagship 911. So, eating a 6 for breakfast is not a laughing matter.

no offense here dude.

some of your fatcs are wrong. not here to bust your balls....

im out for the nite...

'think before ye speak'