147 replies to this topic

[N/A-PWR]

Hi All,
Just asking for advice on 14:1 compression pistons for the 202 engine.
I remember in my apprenticeship my instructors got factory XU1's and beefed them up with 14:1 compression pistons ( quote 'they said it could lose traction at 60 mph' end quote ),
I am just wondering if we can get these pistons for a 202/208 project which I would machine valve clearances into them. Dave I

p.s. I know the compression will reduce due to machining but I would have maximum compression.

[Uncle Chop Chop]

The good thing about 14:1 compression is that the methanol you need isn't all that expensive. Bad news is it needs to run a lot richer than 98 octane to run properly.


Back to reality, 14:1 would be very difficult to get even with a 161 head on a 208 CID six. They would definitely need to be custom made lumy pistons.

[N/A-PWR]

Gee's Vick,
I do have a 161 chamber in the Head that produces 250 psi with normal flat tops on a 208ci - as this is what I normally flog to smithereens. Dave I

[wot179]

How many cc's are your chambers?

[N/A-PWR]

How many cc's are your chambers?

Dont know how to get cc'c - but it is 23 grams of water

[N/A-PWR]

G,day mate,easiest way to check cc is to set the head up level,screw in a spark plug ,get a large syringe and fil the chamber and take note of how many mls it takes to fill the chamber flush with the head face. 1ml = 1cc

Thank-you STRAIGHTLINEMICK,
Yes you are right as I have been searching google over night - 1ml = 1cc of water.
And I did make a mistake with the 23mls the 186 head is 100 thou shaved and is 42cc with the spark plug.
Just had a thought that you could have a spark plug sitting further in and get a higher compression ratio. Dave I

p.s. not sure if it is correct but further reading found that compression psi divided by 14.7 = compression ratio,
where my compression is 250psi on the dot divided by 14.7 = 17.006 compression ratio which I think is wrong.
I have a 208ci block with flat top pistons which from memory were pretty level with the deck.

[N/A-PWR]

Hi All,
I found this 202ci quote ' With a 45cc head and pistons 17thou above the deck we have about 11.5:1. With a 36.5cc head we were able to achieve 14:1 ' end quote on this forum reply #12 - http://www.buga.com....2&topic=1767.10 . Dave I

[N/A-PWR]

OK,
Doing some sums and I have 1mm left on the head to the witness marks which will bring the cc's down to 36.5cc and I will deck the block 17 thou ( 0.4318mm ) which should just about do it to get 14:1 approximately depending on the Head gasket used. Dave I

p.s. this is great to know so that we don't need special pistons to get 14:1

[greens nice]

you would be lucky to get .500" lift with a 1.75 inlet valve though........

[N/A-PWR]

you would be lucky to get .500" lift with a 1.75 inlet valve though........

Thank-you greens nice,
Yep you are right about the valve clearances as a valve needs about 50 thou to the piston.
The Comp Cam involved needs the piston machined anyway because of the high intensity grind and I would need pistons that are machinable that does not get too thin. Dave I

[greens nice]

i doubt you will ever have piston to valve clearance issues with a flat top piston but the valve will touch the top of the block and .140' off the head and probably .040 off the block from standard will leave you with not much room to lift the valve.

[N/A-PWR]

i doubt you will ever have piston to valve clearance issues with a flat top piston but the valve will touch the top of the block and .140' off the head and probably .040 off the block from standard will leave you with not much room to lift the valve.

Ah Ok greens nice,
I see where you are now,
Just measured the bore side of the valve to head surface and is currently 12mm ( to see if it will hit the bore ).
I can also see the head gasket imprint ( showing the bore ) which is 11.5mm from the shut valve to the bore edge ( next would be too push the valve 0.5 inch and measure again ). Dave I

[Uncle Chop Chop]

Gee's Vick,
I do have a 161 chamber in the Head that produces 250 psi with normal flat tops on a 208ci - as this is what I normally flog to smithereens. Dave I

I was assuming a head with around 46cc chambers.

[N/A-PWR]

Bad news is it needs to run a lot richer than 98 octane to run properly.

Hi Vick,
Thank-you for your input, how would 112 octane aviation gas be for the fuel type? I remember the Williams-town Air force base guys were using it on a 202 which makes the carby go green. Dave I

p.s. I think it is ilegal to use on the street

[N/A-PWR]

it is only illegal if you get caught.

Hi ljxu1torana,
I suppose we could use octane booster instead - the old leaded super fuel was better. Dave I

[rodomo]

Gone are the days that you could tune your engine by the colour of the exhaust pipe Dave

[N/A-PWR]

Gone are the days that you could tune your engine by the colour of the exhaust pipe Dave

Yes rodomo,
Especially after a long drive and see the lean light tan look in the muffler. Dave I

[N/A-PWR]

This link to a Compression Ratio Article is interesting:-
http://www.popularho...ch/viewall.html

[Dave6179]

Now thats a good read! Something I've been thinking about this week, maybe I'm running too hot. When Cromies opens I'm going to get a thermostat that should reduce the temp by 30 degrees. The 6cyl one is the same as the 308 apparently... Holden don't stock anything for the red six anymore!

[N/A-PWR]

Now thats a good read! Something I've been thinking about this week, maybe I'm running too hot. When Cromies opens I'm going to get a thermostat that should reduce the temp by 30 degrees. The 6cyl one is the same as the 308 apparently... Holden don't stock anything for the red six anymore!

Hi Dave6179,
Yes, when I was reading the High Compression article I was thinking there is a lot of components to improve on,
and by the sounds of reducing the water temperature,
as High Compression creates Hotter water your engine should be at the right Temperature, if that makes sense. Dave I

[N/A-PWR]

e85 would be a great fuel for this

also there is more to compression than a static number

Hi gmlj6,
Yes you are right about static compression vs dynamic compression ratio's and e85 is 85% ethanol 15% gasoline.
I will have to work out the compression ratio with the modifications to be done, but I do know the Compression PSI will increase towards 300 PSI or more.
Here is a Link to an article on the Static vs Dynamic compression ratio's:-
http://classicinline...essionRatio.asp

[Uncle Chop Chop]

A couple of points:

Using leaded Avgas in an ADR 37 vehicle is illegal.
A vehicle running a higher static comp. ratio won't always run hotter. Methanol needs around 14:1, but the engine will run cooler.
The static comp. needed for 112 octane Avgas? Not sure, but it would probably be between what 98 octane and methanol needs.

This is from a bloke who used to brew his own methanol/ethanol in the garage back in the 80's. But only enough to use it as a booster.