9:1 compression

[rslandys3]

I'm just about to skim my 8:1 2.25 head to 9:1. Anyone have any ideas how much i have to take off and what I should be doing with timing and carb settings?

[ltwt1981]

A friend took off 60 thou and it was OK, he seemed to think it improved the power.

Don't know what the compression ratio was though, but at least its doable.

[rslandys3]

A friend took off 60 thou and it was OK, he seemed to think it improved the power.

Don't know what the compression ratio was though, but at least its doable.

I was thinking more like 90thou?

[David_LLAMA4x4]

I'm just about to skim my 8:1 2.25 head to 9:1. Anyone have any ideas how much i have to take off and what I should be doing with timing and carb settings?

I once took 165 thou off a 8:1 2.25, had the cam reprofiled and fitted an SU and it went like stink!!!!

I had to shim the rocker shaft as that was easier than shortening the pushrods...

David

[DaveSIIA]

I took off 125 thou and ended up with about 9.5:1. Worth doing a quick calculation to determine how much the clearance volume needs to be reduced.

[rslandys3]

I took off 125 thou and ended up with about 9.5:1. Worth doing a quick calculation to determine how much the clearance volume needs to be reduced.

What about timing and valve clearance?

[Tonk]

valve clearances will have to be adjusted back to standard

i'm guessing that the higher compression ratio might make it pink a bit more so u might have to retard the timing abit, more of a trial and error thing imo

[rslandys3]

I once took 165 thou off a 8:1 2.25, had the cam reprofiled and fitted an SU and it went like stink!!!!

I had to shim the rocker shaft as that was easier than shortening the pushrods...

David

Few questions;

What compression did you end up with? What did you do to the cam and who did the work? How did you fit the su? Did you make an adapter or did you buy a proper manifold? Was it all worth it? What did you do with ignition timing?

I hope i'm not asking too many questions, in fact I will re-phrase that, I hope you dont mind me asking so many questions.

Cheers.

[Daan]

valve clearances will have to be adjusted back to standard

i'm guessing that the higher compression ratio might make it pink a bit more so u might have to retard the timing abit, more of a trial and error thing imo

I doubt that very much, I have done this, and with euro95 unleaded, i never could get it to pink, I could retard it sofar that it would backfire. If you had enough material on the head, you could skim to 10:1 without to many problems I reckon (no prove for this though).

Daan

[rslandys3]

I doubt that very much, I have done this, and with euro95 unleaded, i never could get it to pink, I could retard it sofar that it would backfire. If you had enough material on the head, you could skim to 10:1 without to many problems I reckon (no prove for this though).

Daan

Thats cool. I took off 2.75mm today. Will get the head back in the truck and see how it goes.

[rslandys3]

My head after skimming 2.75mm on a pretty small milling machine. Measurement shows it's perfectly flat though.

[David_LLAMA4x4]

Few questions;

What compression did you end up with? What did you do to the cam and who did the work? How did you fit the su? Did you make an adapter or did you buy a proper manifold? Was it all worth it? What did you do with ignition timing?

I hope i'm not asking too many questions, in fact I will re-phrase that, I hope you dont mind me asking so many questions.

Cheers.

Don't know what compression it was - never tested it, or calculated it....

The cam was done by a chap who Kent Cams put me in touch with - IIRC he was called Zac or something like that...

The SU was fitted on a new manifold..

Ignition timing was done by trial and error on a dynonomet....

Was it all worth it?? Probably not! BUT it did go like stink, it was still a std engine as far as insurance ( or I suppose compoeteing class ) was concerned and it made for an interesting project......

Hope that answers your questions..

David

[rslandys3]

Don't know what compression it was - never tested it, or calculated it....

The cam was done by a chap who Kent Cams put me in touch with - IIRC he was called Zac or something like that...

The SU was fitted on a new manifold..

Ignition timing was done by trial and error on a dynonomet....

Was it all worth it?? Probably not! BUT it did go like stink, it was still a std engine as far as insurance ( or I suppose compoeteing class ) was concerned and it made for an interesting project......

Hope that answers your questions..

David

Do you know what you got HP wise?

[rtbarton]

Rule 1 of head skimming - make sure the head hasn't been skimmed before!

[hattymender]

Rule 1 of head skimming - make sure the head hasn't been skimmed before!

Now you've worried me. How thick is my head? (very, if you ask the wife ). Guess you measure from the rocker cover face to gasket face, but how thick should it be as standard?

[hattymender]

Now you've worried me. How thick is my head? (very, if you ask the wife ). Guess you measure from the rocker cover face to gasket face, but how thick should it be as standard?

A quick, and probably inaccurate, check showed 3.620" from rocker cover face to top of block. Standard? Guess the .020" is the gasket so 3.60" for head.

Any other way of telling? Minor Monthly has just run a series of atricles on tuning the A Series head, they're all different so the only way to be sure was to measure from the low point (oil inlet below rocker shaft cap) and subtract from overall thickness. Where's the low point on a LR head?

[rslandys3]

A quick, and probably inaccurate, check showed 3.620" from rocker cover face to top of block. Standard? Guess the .020" is the gasket so 3.60" for head.

Any other way of telling? Minor Monthly has just run a series of atricles on tuning the A Series head, they're all different so the only way to be sure was to measure from the low point (oil inlet below rocker shaft cap) and subtract from overall thickness. Where's the low point on a LR head?

"By Hank Rutherford, Steve Denis, Peter Ogilvie

7:1 head is 3.700 in thick, chamber volume is 91 cc.

8:1 head is 3.600 in. thick, chamber volume is 75.2 cc.

7:1 pushrod length overall, 7.300 in

8:1 pushrod length 7.175 in overall (some parts suppliers are not able to tell you the difference between pushrods, just that they are different)

Within the range of our interest, there is about 1.2 cc change in volume per .010 in. change in thickness

Milling .100 in. makes a 7:1 head 8:1. Almost exactly.

Head gasket volume and volume above the piston crown is 4.25 cc."

Hope this helps.

[rslandys3]

After milling 2.75mm from my head combustion chamber volume is now roughly 62.5-63cc.

According to calculation from this data it should be 62.2 so I assume it is about right.

Note that compression can be calculated by swept volume + gasket volume + combustion chamber volume divided by gasket + combustion chamber volume.

Swept volume = 2286cc / 4 = 571.5

[rslandys3]

Got everything back together. Managed to mash up the brass heater hose connector though. Anyone know where you can get these from?

[rtbarton]

Got everything back together. Managed to mash up the brass heater hose connector though. Anyone know where you can get these from?

Paddocks, Craddocks &c should have them. They'll need to know if the head is metric or imperial. Metrics were fitted to the 5 bearing engines. I've done away with the valve, advisable anyway if you're on LPG because you wouldn't want to stop the hot water supply to the evaporator.

[hattymender]

Got everything back together. Managed to mash up the brass heater hose connector though. Anyone know where you can get these from?

Did you keep the standard push rods? Any problem with setting the valves?

[hattymender]

Got everything back together. Managed to mash up the brass heater hose connector though. Anyone know where you can get these from?

Now come on, not fair! You've got me interested but there's no punch line! How does it run?

[rslandys3]

Now come on, not fair! You've got me interested but there's no punch line! How does it run?

Havent got the heater hose bit so ran it with no water and hadnt connected the exhaust either so its hard to say. But it does run! Valve clearances are tight now (2.75mm removed from head) so may have to shim the rocker shaft. As soon as I get the bits ill let you know how it runs.

[rslandys3]

HELP NEEDED! I have everything back together and it idles nicely. Got everything hot and adjusted the valve clearances and carb, no worries there. Although, there is a fair amount of tappet click? The problem is that it wont rev up very well. This is the first time I have ever had an engine to bit so i am worried I have done something wrong. If you rev it up slowly it is just about ok but not optimal. Have I bummed up fitting the head and now have a duff head gasket or do I have a vacuum leak or is it timing? Its now about 9.5 to 1 compression and doesn't seem to be knocking? Any help appreciated.

[Gareth Dickens]

HELP NEEDED! I have everything back together and it idles nicely. Got everything hot and adjusted the valve clearances and carb, no worries there. Although, there is a fair amount of tappet click? The problem is that it wont rev up very well. This is the first time I have ever had an engine to bit so i am worried I have done something wrong. If you rev it up slowly it is just about ok but not optimal. Have I bummed up fitting the head and now have a duff head gasket or do I have a vacuum leak or is it timing? Its now about 9.5 to 1 compression and doesn't seem to be knocking? Any help appreciated.

Have you checked the compression? (compression tester?)