closed or open chamber head for lpg?

[Anonymous]

Just wondering what would be the best head open or closed chamber for a straight gas 250 crosslow. I currently have an zk fairlane efi motor with an open chamber head running straight gas using the gas research setup.

[/img]

 

[xctasy]

Frankly, I'd use what is there if I didn't have the choice.

The later head is better suited to an EFI petrol engine.

The XF on-wards head is not a better performance head, it is the electronic control of the igntion system which allows the later engines run better than the earlier ones. As an LPG engine, as long as the ignition is optimised, that's the key. The head is a two percenter. The only difference between an closed chamber, hi swirl 1985 4.1 efi and a 1986 4.1 efi is the engine management side, and the power levels are within coee of each other. The earlier XE engine was down 10 kW on power, because the intake valves were smaller, and the ecm wasn't a feedback system like the unleaded ones.

The earliest alloy heads are the best ones to modify becasue they can take later valves with no swirl inducing, valve shroading ramp around the intake valve.

 

[Anonymous]

got some more info about this ? straight gas ?

 

[addo]

http://www.gasresearch.com.au/ is a good place to start looking.

If you go to http://www.fullboost.com.au/racing/drag ... meets.html you will find some turbo cars running LPG only.

Adam.

 

[Anonymous]

thx addo , there are not much cars here running straight gas , always a normal feul carb wit an extra gas plate onto ore into it , did not see many cars here with straight gas carb ! happen to be you now somebody who is selling a straight gas carb ? 1 for my turbo engine ! a used 1 ?

 

[addo]

They are popular second-hand (the good ones) and sell fast, so unfortunately I don't know of any. "buickroadster" has made his own TB's from old carbs to run LPG. His car has triples and runs straight gas with water injection.

Adam.

 

[Anonymous]

If one of these earlier XE heads was to be installed with the bigger valves instead of the 1.75s and it improves it substantually why not go bigger than the XF valves. How big is still ok without unshrouding.
I cant be certain but I think Ive heard of a 2 inch valve installed in Crossflow.

 

[xctasy]

http://fordsix.com/forum/viewtopic.php?t=8130 affirms what you've said Tim.

The biggest valves that fit without shrouding, and focus on the 85% diameter rule, where an exhast valve should be at least 85% of the size of the intake, and the port flow should suit the cam profile. All that stuff about the exhast flowing 80% of the intake figure is important only if you don't have a split duration cam. Where there is the same or nearly the same lift and duration at the intake and exhast, its important.

With LPG, the head modification rules change, with a wider lobe centre and a reduction in exhast flow over certain lifts being important to stop the light propane flowing right on out the exhast. Reading any good camshaft or gas-flow book will give you some idea of the modifications, but the real experts are the cam grinders and cylinder head machinists. The LPG is missing a bunch of practical people who are able to break ranks and share the information. Gas Reserch, C.O.M.E , Ford and Holden are possibly on the cutting edge, but the info is locked up in Leigh, Sam, Geoff and Peters heads, and not for us unwashed. Leigh at GRA has been an awesome ambassador for the LPG cause, but he knows a good deal more than what is feed into issues of Performance Street car, Street Machine or Automotive Enginering. One other source is Impco USA, but they are going to an information lock-up due to the big dollars involved, and don't advise on head modifications, although I'm certain they know what works for power.

All gets jolly confusing.