Pro Stock Heads

[john]

Why not make a titanium piston then if weight is an issue . Someone will say cost but in a class like pro stock where they will spend thousands just to make 1 or 2 extra horsepower and its not like they are going to be replaced all the time . Infact I wouldnt be suprised if Titanium engine components like rods and pistons arent allready out there in pro stock .

Weren't exotic materials banned?

 

[Nick Name]

Not sure you could call titanium an exotic these days.

 

[Bill]

Jay,
I couldn't remember when the dual plug version of the 426 head was released, but I did find this, with a picture, at AllPar.com:

>>>"A small number of special twin-plug heads were produced for the 426 Hemi, long before Chrysler engineers started using dual plugs on the 5.7 Hemi. James Schild provided a 1970 press release showing the twin-plug heads; engineers managed to insert the extra spark plugs (shown on the left-most cylinder below) without interfering with the rocker arms or pushrods. He wrote, “I found a part listing in the 1973 Mopar Performance catalog for a dual plug head, Race Hemi, P3690038, and aluminum valve covers with part number P369232 for the 8 or 16 plug heads.”

This information can be found at Hemi Overview
along with the picture.

Bill

 

[70AARCuda]

Mopar's Infamous Hemi - Notable Hemi Vehicles

Looks like the D5 hemi heads in 1973 were first with the dual plugs

 

[john]

James Schild provided a 1970 press release showing the twin-plug heads; engineers managed to insert the extra spark plugs.

They started working on them in 1969.

 

[Mr. Fix It]

If the Hemi engine has so many HP making issues, why does/did it dominate so many classes? Why was it so strong in other forms of drag racing?

 

[john]

If the Hemi engine has so many HP making issues, why does/did it dominate so many classes? Why was it so strong in other forms of drag racing?

It has a huge chamber to fill with air and fuel, that makes a lot of power. Pro stock tech has come a long way and the current designs put most of the combustion chamber into the cylinder, not the head. It is doubtful the design will fall from fuel racing as that huge chamber has a bigger advantage in blown applications. In normally aspirated engines, the wedge refinements are getting ahead of the Hemi in volumetric efficiency.

 

[Nick Name]

If the Hemi engine has so many HP making issues, why does/did it dominate so many classes? Why was it so strong in other forms of drag racing?

In supercharged applications where high static compression ratios are not used, the hemi has the advantage of the large valves, etc.

My wife's newer Charger has a dual plug hemi. Altho not a full hemi for the reasons we have discussed, Chrysler calls anything with the valves opposite each other a Hemi. Even Harley Davidson moved away from the full hemi design.

 

[tcrawf]

What do the pistons for the IHRA Hemi engines look like? Are they pretty flat or do they have a small dome?

flat . . . looks like a size 12 boot stepped in wet cement.