im sure im missing something.
Turbo Mini Forums

so. im thinking of this 998 turbo engine and well im a little baffled

Bore 68.1 mm Fill in the Yellow boxes
Stroke 76.2 mm
Compression Ratio 8.04 :1
Gasket Volume 3.40 cc
Ring land Volume 0.78 cc
Piston Volume 0.00 cc
Head Chamber Volume 30 cc
Deck Volume 5.25 cc

Swept Volume 277.55 cc
Chamber Volume 39.43 cc

thats cant be right without dishing the pistons i can get to 8? btw this is on +80 pistons.

http://www.afracing.com/cr.xls

Edited by AlexF2003 on 3rd Oct, 2007.

AlexF

Well most 998 pistons have a 6cc dish (if dished) BUT they have zero deck volume. You seem to have this the other way round, so you will get the CR you have calculated.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

30cc is a big head for a 998.

It's a 1080cc though tom, +80 overbore

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

True, but it is still a big cyl head, the swept capacity is only 85% of the typical 1293 engine that would use a 30cc head.

I understand what you are saying, my hillclimber for instance has 24cc chambers and 6cc pistons (8.5CR). but my road 998 has 28cc chambers and flat top pistons (9.1CR) , which is why I thought that 30cc was not all that massive (especially if you start with 28cc as standard!).

Remember you'll have 15cc dishes in a largbore piston, this isn't possible in the small bore engine.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

am i still right in asumeing the exaust valve extends out past the bore of the cylinder even tho its a +80 thou?

was going to get it pocketed anyway as the ones ive seen pocketed before seem fairly big however people say +80 thou is fairly big and i may be able to get bigger valves.

i also want to see how big i can go on the valves even if i have to get them at a silly offset.

also i have abit of a weird question, are there any low rotation scatter cams about?

Edited by Sam on 5th Oct, 2007.