upping the compression ratio

[dingo]

What is the simplest way to bump up the compression ratio...using stock pistons ?

[germansupplyscott]

on a 2 litre bus engine, the simplest method would be to use 914 pistons. there are two different 914 pistons, one has a small dish, one is almost completely flat-topped. stock 2 litre bus pistons have a deep dish.

[covelo]

This may be a stupid question, but why would you want to do this?

[dingo]

I already have the stock pistons....i was wondering if there was a way by shimming the jugs.....(i may be way off the track here)

This may be a stupid question, but why would you want to do this?

Ill preface by saying that im not an expert on this subject: I believe higher compression ratio will give you more h-p or torque or both...i already mix up my own octane cocktails, so i thought i would experiemnt on the next 2L engine i put together

[dingo]

from Chiltons VW 1970-1981 page 70

72-73 Bus w/ Type 4 1679cc CR : 7.3 : 1 HP: 63/4800 , Torq:81/3200

'71 411 w/Type 4 1679cc CR 8.2: 1 HP 85/5500, Torq: 99.5/3500

'72-'73 914 w/Type 4 1679cc CR 8.2:1 HP 76/4900, Torq: 95/2700

'73 914 Calif. " 1679cc CR 7.3: 1 HP 69/5000, Torq: 87/2700

[Bleyseng]

I already have the stock pistons....i was wondering if there was a way by shimming the jugs.....(i may be way off the track here)

This may be a stupid question, but why would you want to do this?

Ill preface by saying that im not an expert on this subject: I believe higher compression ratio will give you more h-p or torque or both...i already mix up my own octane cocktails, so i thought i would experiemnt on the next 2L engine i put together

You can just have the head decked to raise the CR but what cam are you using? The stock cam barely works with the stock CR of 7.3 to 1 as is causing high cylinder head temps under load (375-450F) which kills the aluminum head over time. Raising the CR will result in higher temps...so have you done you calculations to determine what you have now. Measure the deck ht, CC the heads and piston dish etc to figure it out.

BTW I am running USA914 94mm pistons but with 1800 heads and keep the CR at 7.5 to 1.

[dingo]

What is the best way to CC the heads ?

[bottomend]

Wow. Bleyseng, I would've thought your CR was higher.

Dingo> go over to westy78's thread and look at the pics of him CCing the heads and pistons. He made a disc of plastic that fit's into the bore of the head and seals it with a little grease.

There is a small hole drilled in the center of the disc in order to inject colored liquid ( easier to see againts the aluminium head) into the space now created by the disc, which acts like a roof. The syringe used is graduated so he can observe exactly how much liquid it requires to fill up the void. This # represents the volumn of the space. Most heads should be around 50-55cc. Most piston dishes are around 12-15 cc.

All the numbers need to match between componants or the combustion chambers will be uneven in size, which in turn causes an unbalenced engine. If the chambers are even and the rotating parts of the engine are balenced the sukka should purr like a kitten.

I've got to get over to Sluggos house to record a snippet of his engine. We didn't balence the rotating mass but we did balence the recipocating parts and CC'd the chambers and pistons. They were EXACT... and it produced really sweet results.

[dingo]

cool...thanks for the info