My Compression test results are all over the shop

**stirlsilver** · 8th June 2008, 10:50 PM

My dad came up with an interesting suggestion to explain why the cylinder pressures are all over the shop. Since the engine is a high CR engine, the volume that remains when the piston is at TDC is very small so any imperfections in the chamber result in varying pressures. Since we manually seated the valves using grinding past the valves all sit at different heights resulting in varying cylinder volumes. I know for a fact that we had issues with number 1 where we had to grind it a long way to get rid of a score in the seat and it is one of the lower results. Number 5 is possibly in the same boat.

This is probably not the only reason but i'm sure it could well be a contributor.

**rovercare** · 8th June 2008, 11:03 PM

Originally Posted by stirlsilver

Would love to build something electronically controlled. Something with the megasquirt ecu or something. Electronically controlled fuel and ignition. Ohhh that would be a cool project. Maybe... one day, I would probably try to get an LPG injection kit in there too Oooooo. Ok now i'm talking big bucks. Dreaming... again maybe one day.

And your worried about changeing the mech. advance on a dizzy?

Just sort the timing out and stop it pinging already

**rick130** · 9th June 2008, 08:54 AM

Originally Posted by rovercare

Just need various springs and wieghts and a timing light, then play around, if no vac advance, which you disconnect to set up mechanical advance anyway, you just change the springs and wieghts, then rev it and check the timing with the light

That's all I did years ago with my 351C on LPG and 302 2V quench chambers (4V valves, approx 11.75:1 CR)
And I was even cheaper, just kept shortening the OE springs on the stock dizzy, watched the tacho and hammered it at 500RPM increments till I got a feel for what it wanted, then sent a fax to Performance Ignitions/Scorcher in Melbourne to build me a Bosch electronic spread cap dizzy with my curve.

It was the prefect solution for LPG.

Although the only time I could run it on petrol was Avgas out of the race car

(or octane booster on Optimax)

**stirlsilver** · 9th June 2008, 04:42 PM

Originally Posted by rick130

That's all I did years ago with my 351C on LPG and 302 2V quench chambers (4V valves, approx 11.75:1 CR)
And I was even cheaper, just kept shortening the OE springs on the stock dizzy, watched the tacho and hammered it at 500RPM increments till I got a feel for what it wanted, then sent a fax to Performance Ignitions/Scorcher in Melbourne to build me a Bosch electronic spread cap dizzy with my curve.

It was the prefect solution for LPG.

Although the only time I could run it on petrol was Avgas out of the race car

(or octane booster on Optimax)

Rick, I would be interested to see the results you got as the general profile should be similar for my engine.

When I did build the engine, I had about a week before the LPG conversion was to be done. 98octane and octane boost wouldn't stop the detonation in mine. Runs very well on LPG though (except when the mechanical advance gets in there and ruins the party).

**rovercare** · 9th June 2008, 05:05 PM

Originally Posted by stirlsilver

Rick, I would be interested to see the results you got as the general profile should be similar for my engine.

When I did build the engine, I had about a week before the LPG conversion was to be done. 98octane and octane boost wouldn't stop the detonation in mine. Runs very well on LPG though (except when the mechanical advance gets in there and ruins the party).

Even simpler solution, lock the dizzy and run high static timing, real drag car stuff

**LOVEMYRANGIE** · 18th June 2008, 05:01 PM

Just another thing I noticed on my plugs. 1 to 7 all had this brittle white material buildup on them which had a very rough appearance (number 7 had very little of this buildup). Number 8 was very clean with a slight brown tinge on it.[/QUOTE]

This will be your mysteriously disappearing oil.
Think you will find it is only burning in small amounts and is burning off cleanish with gas and high compression/combustion temps.
No 8 sounds like it should be running fine.....
i presume as you did little to the heads, you probably didnt use new valve stem seals?? If you take the heads off, check your intake valves and guide clearances also. This is usually the way in for oil.
in a new or recon engine, If the wrong oil was used in the initial run in period or if rings dont bed properly, the engine will constantly have oil consumption issues.

**stirlsilver** · 28th July 2008, 10:52 PM

Hmm, I think I see a pattern here!

1- 157psi 2- 174psi
3- 174psi 4- 167psi
5- 148psi 6- 181psi
7- 162psi 8- 203psi

Cyliders 1 & 3
157psi & 174psi

Cylinders 5 & 7 (7 leaking into the water jacket)
148psi & 162psi

Cylinders 2 & 4
174psi & 167psi

Cylinders 6 & 8
181psi & 203psi

All the cylinders are badly glazed too.

**RaZz0R** · 29th July 2008, 07:41 AM

puck! They have seen better days lol

bore or just piston & rings needed?

**rovercare** · 29th July 2008, 08:34 AM

Ahhhh, the consequences of bad timing and high CR

**stirlsilver** · 29th July 2008, 09:14 AM

Actually, I think what has happened here is that the 3rd row of bolts (the ones closest to the Exhaust ports) were torqued up too high. Because the RH bank doesn't have any leaks.

My problem is now that I bought tin head gaskets again and that I might not get them to seal properly in the areas where there was leaking previously.

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