Compression Ratio

[Eddie DVK]

I need some info.
Can you bump compression ratio for every cam?
Why I am trying to say, is it related to lift, duration or lobe centre?
Is there somewhere a limit?

I know it is related to the octane in gasoline.

Thanks

[Udo]

Yes , comp. ratio depends on the cam - with more duration you can have more cr

Udo

[Eddie DVK]

Ok Udo thank you.

You know type4 engines, I want to push a little more HP out of my engine. (a sort of 2.0 version of my engine)
Have some upgrades laying around, like lighter rods, lighter pistons and go from 40 webers to 45 dell.
My compression ratio is a bit on the save side 9.5 and want to bump it to 10 + range.
I Have the 316 schleicher cam with a lot of duration.
I now have a deckheigt of 2.0mm, so I can easely go to 1.2mm which would give me around 10.4.
So can I bump it to 10+ range?

Thanks

[Dougy Dee]

You seem to be started on the right track to answer a lot of your own Q's.
Playing around with a DCR calculator, like the one at Wallace Racing, will help.

[Udo]

The 316 Schleicher does not have much degreese . But 10,0 should work . i like the pauters more or webcam

Udo

[Eddie DVK]

Thanks Udo,

You know my engine, which Pauter cam would you suggest?

Regards Edgar

[Udo]

Do not know the spec of the engine right now ..2, liter ...

Udo

[Eddie DVK]

Ok Udo,

This is it:
- 71 mm crank balanced with 200mm flywheel (6.0 kg)
- Now standard, New h-beam rods Standard size (300gr lighter, with piston oil squiters groove)
- 94mm type 1 pistons (total seal rings), New lighter piston pens
- Head 42mm x 36mm, 44cc chambers (done by Udo) 10mm rockers
- 316 schleicher, HD type 4 lifters, HD alu pushrods
- Now Deckheight 2.0mm - 9.5:1 compression want to go to Deckheight 1.2mm - 10.5:1
- 26mm type 1 oilpump, New 30mm type 4 oilpump (for squirtes and maybe extra oilcooler)
- No extra cooler just type 4 in type 1 shroud.
- 41mm Turbo Thomas Header with single quiet pack muffler.
- CJ 2.0 liter case (a lot polishing/mods done for better internal air flow)
- Now 40mm Idf, New, 45mm Dellorto s
- CU TSHD distributor

Was pushing 125HP @ 6000RPM (180NM) with the 40mm Idf's.

But gathered some new stuff over the years (H-beams, carbs, thruogh bolts, porsche swivels, oilpump)
I just want to make a upgrade this winter to push a little more HP / 7000RPM's out of it.
And learn some more enginebuilding skills/tricks  .

Regards Edgar
 

[Torben Alstrup]

With that powerrange there is no need to go 45 Dells. 40´s will keep up to 140 easy and close to 160 if pushed a bit.
Also you will not increase the rpm range much even though you raise the CR. Maybe 100-200 rpm. 6000 rpm for 125 hp is a lot in the first place, but that´s typically what the Schleicher cams do.
A 30 mm oil pump will rob about 2 hp compared to now. So the hp increase may be minor. The usable torque will most likely increase due to a much better burn if you reduce the deck, and you may be able to pull 2 degrees out of the ignition advance. That will aid in torque, as said, and much better cooling capabilities.
T

[Udo]

Eddi
You can use a 324 Schleicher or Pauter in the 286-290 range like M5 and with the 45 carbs you can get soemthing about 160 - 170 hp

udo

[Eddie DVK]

Thank you Udo and Torben,
Ok know a little more now.
Udo I think going to mail you soon for a cam.

Torben, so I would only increase the RPM s bij 500 (so 6500 max for testing).

[Eddie DVK]

With that powerrange there is no need to go 45 Dells. 40´s will keep up to 140 easy and close to 160 if pushed a bit.
Also you will not increase the rpm range much even though you raise the CR. Maybe 100-200 rpm. 6000 rpm for 125 hp is a lot in the first place, but that´s typically what the Schleicher cams do.
A 30 mm oil pump will rob about 2 hp compared to now. So the hp increase may be minor. The usable torque will most likely increase due to a much better burn if you reduce the deck, and you may be able to pull 2 degrees out of the ignition advance. That will aid in torque, as said, and much better cooling capabilities.
T

Pulling this up again.

Torben, what do you mean by this.
I now have about 31 degrees at 3000 RPM, do I go to 33 at 3000 RPM or 29 at 3000 RPM.

Thanks Edgar

[Airspeed]

The usable torque will most likely increase due to a much better burn if you reduce the deck, and you may be able to pull 2 degrees out of the ignition advance. That will aid in torque, as said, and much better cooling capabilities.
T

Pulling this up again.

Torben, what do you mean by this.
I now have about 31 degrees at 3000 RPM, do I go to 33 at 3000 RPM or 29 at 3000 RPM.

Thanks Edgar

As Torben mentioned, less timing because you made a more efficient combustion chamber by having less deck height. So, 29 degrees is usally/probably better then 31 in that case.
These timing tests are however best done on a dyno where you can exactly see which timing gives best hp at what rpm ;-)
Maybe Fred at HRengineering holds another of his dyno days this year..?

[Eddie DVK]

Walter,

Thanks for explanining.
I think I get it now.

A dyno day would be nice, always thinking of going, but was somehow always busy.

Regards Edgar