906 head porting Dart short turn
Just wondering how much exactly did you increase the cross sectional area of the port?
The pushrod pinch is the limiting cross section, and was widened only enough to clean up casting errors. The pinch height did not change, and the finished width is slightly less than oem Eddy heads. So very little change to the cross section area. I was trying to keep the limiting port velocity UP. The bowl area was increased, but only to that equal to Mopar templates...research said a 75 degree bowl cut (what I did) removes the same material as the templates.
ssba:
The engine is street performance, a 383/432 stroker going in an Ebody. There are several really good engine builds on this forum....IQ52 has listed several, and Chally340 also. In every case improvements in cylinder head flow translated to increased engine TQ & HP.
MRL performance had a good comment...you can either increase compression or cylinder head port flow to gain TQ/Hp, or DO BOTH and really gain.
So I'm going for the increased port flow, and moderate compression... for a "general high performance street engine".
Would they work well on any big block standard port build? I think so; MRL has it right. IQ52 listed his 'pops' engine build in this form (big block Abody)...very impressive LOW compression engine.
These 906 open chamber heads really limit the compression ratio for pump gas...both static and dynamic, because of the risk of detonation if you go too high on either ratio without the correct camshaft choice and near perfect tuning.
My build will be 9.8 static and 8.0 dynamic. You could go higher on both with a good quench style cylinder head such as the Stealth or Eddy RPM.
This stroker build I'm doing with flat top pistons at zero deck will work with either iron or aluminum heads...just have to do your homework on the static and dynamic compression ratio. The alum heads would require reducing the combustion chamber cc's to make the best ratios...milling the heads is no big deal, just needs to be done the right amount, and pick the correct cam (intake valve closing angle).
I stayed with the iron to be more street friendly at my 5200 ft elevation. Even in the summer the morning temps can drop to near freezing and without a heated intake manifold there are times where the engine can barely pull the car down the road. I had switched my old work truck to all the alum parts...and ended up going back to all oem iron...it runs so much better all day every day. So I'm going the same route with this engine build.
I'm an ASE certified mechanic, have been since 1978. I just like to work on cars. So the idea of studying cylinder head porting and doing the work myself is part of what I like to do.
I have just under $1000 into these old iron heads, with all new parts, and hard exhaust valve seats. Most folks would say its a waste of money. So unless it fills a personal requirement (like my cold summer days), I would really suggest aluminum heads if it is in your budget, mainly for the quench benefits AND the nice out of the box port flow. If I really did my port work correctly I MAY be close to the OOTB flow of the alum heads I suggested.
A bowl cleanup on either of the alum heads would up their performance that much more. Some have room for unshrouding the valves in the combustion chamber too for yet another gain. JMHO.
On the other hand...I used to have a 68 GTX with factory 440 4spd dana60 with 4.10 gears, ALL stock. It ran really strong, won many street races, even against the big motorcycles of the time. It had iron heads and ran great. The body twisting was enough that the windshield was cracking apart more and more every day. I suppose it wouldnt run with todays big strokers, but so what if you don't need it.