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rileyp

400 head on a 426?

10 posts in this topic

Hi my 426 head is dead.. I can get 400 head nearby possibly at the right price.

1 Will it fit ?

2 Do I need a 400 or 426 gasket?

3 will it effect compression ratio ?

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Yes it will work, I'm running that set up right now. The hot start sys. is different so there is a hose barb on the back of the head, that you can just use a vacuum plug on. The gasket i used I can't remember if I used the 426 or the 400. I have been running this setup for about a year and a half with no problems.

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Yes it will work, I'm running that set up right now. The hot start sys. is different so there is a hose barb on the back of the head, that you can just use a vacuum plug on. The gasket i used I can't remember if I used the 426 or the 400. I have been running this setup for about a year and a half with no problems.

Thanks for responding :)  Does it affect compression ratio?  The 400 head has a smaller diameter machined out section. So it would increase compression i would think...

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Using the 400 head on a 426 cylinder should raise the compression to about 13-13.2:1, due to the smaller combustion chamber volume.  That's a rough calculation, but it should be pretty close. 

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Will increasing the compression ratio have any ill effect and would I need to do anything to to compensate for it?

 

Ive read a little and I would need to run higher octane fuel is this correct?

Normal fuel in Aus is only 91-93

Edited by rileyp

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Is that 93 Research Octane, Motor Octane, or the US "anti-knock index"  (an average of both methods)?  The manual requires 95 octane by the Research Method.  That's about 87 Motor Octane, and about 91 on the US AKI. 

 

If you ran OK at the stock CR, you'll probably be alright at 13.2, but pay attention to it at lower RPM at first. 

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Thanks for your help hooliganone and greyracer :)

In Australia

 

"Australia: "regular" unleaded fuel is 91 RON, "premium" unleaded with 95 RON is widely available, and 98 RON fuel is also reasonably common.    

All fuel in Australia is unleaded except for some aviation fuels."

 

http://en.wikipedia.org/wiki/Octane_rating

Edited by rileyp

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