bighammer
Well-Known Member
I found an interesting read on the internet in regards to head work. I always thought the larger valves was something I needed (or at least really wanted) but according to this machine shop (they specialize in mopars) the larger valves may tend to hinder performance on a street car. Here is a link to the page: http://www.bjrracing.com/small_block_heads.htm
I will copy and past the info here as well:
"The 340 and 360 will be covered together just as the 273/318 engines were. Once again the same will apply for the 340 engine just as the 318 mods applied for the 273 engine. A good 340/360 engine shouldn't need more than 160/168 cc's of intake port volume and 250 cfm's of air flow. More airflow is a plus but not at the cost of a larger port runner.
Even though the strokes are different in the 340 and the 360, the rod length is the same. The piston speeds are different but the port can remain the same and this is why. On the 340 engine you should use the 1.88 intake valve to keep the port velocity up in the larger runner. The same modifications that were done to the 318 heads will apply here also. A good 340 head with the 1.88 valve should flow in the 235/240 range @ .500 lift and 160+ @ .200 lift if the port is properly done. The same air flow will apply to the 360 engine. The specs stated above would be a very good street/strip head and would satisfy most 340/360 engines.
There is no need for a 2.02 valve until you're racing at high RPM's above 6500. The valve size is just too large for any low RPM engine, and bottom end TQ and throttle response will be suffer.
With the air flow stated above, the 340/360 should be capable of making over 550 HP. The need for more than this will result in you spending big $$$$ and won't be very streetable. Anything more than this would be considered race only.
Just for reference for stroker engines, a 318/349 engine would use the 160 cc 1.88/1.60 valve 340/360 head. And the 360/408 engine would need a 180/185 cc head and air flow in the 280/290 range or more with a 2.02 intake valve and a 1.625 exhaust valve.
In any case, the intake to exhaust port flow ratio should be kept to 70% for best results. Superflow states that anything above 60% won't really be noticed in a street or drag engine. Ratios above 80 and 90% have been seen and only help high RPM engines like NASCAR where high efficient exhaust flows are needed to make HP at 9,000+ RPM's. Obviously heads like this aren't cheap or useable for street use."
I found this info to be very interesting. I realize that there are quite a few owners of 'full on' drag cars, but I think the majority of members drive their street mopars, and maybe an occasional trip to the track.
What do you guys think about the above info? Has this been the general consensus here? The author seems to be very knowledgeable.
I will copy and past the info here as well:
"The 340 and 360 will be covered together just as the 273/318 engines were. Once again the same will apply for the 340 engine just as the 318 mods applied for the 273 engine. A good 340/360 engine shouldn't need more than 160/168 cc's of intake port volume and 250 cfm's of air flow. More airflow is a plus but not at the cost of a larger port runner.
Even though the strokes are different in the 340 and the 360, the rod length is the same. The piston speeds are different but the port can remain the same and this is why. On the 340 engine you should use the 1.88 intake valve to keep the port velocity up in the larger runner. The same modifications that were done to the 318 heads will apply here also. A good 340 head with the 1.88 valve should flow in the 235/240 range @ .500 lift and 160+ @ .200 lift if the port is properly done. The same air flow will apply to the 360 engine. The specs stated above would be a very good street/strip head and would satisfy most 340/360 engines.
There is no need for a 2.02 valve until you're racing at high RPM's above 6500. The valve size is just too large for any low RPM engine, and bottom end TQ and throttle response will be suffer.
With the air flow stated above, the 340/360 should be capable of making over 550 HP. The need for more than this will result in you spending big $$$$ and won't be very streetable. Anything more than this would be considered race only.
Just for reference for stroker engines, a 318/349 engine would use the 160 cc 1.88/1.60 valve 340/360 head. And the 360/408 engine would need a 180/185 cc head and air flow in the 280/290 range or more with a 2.02 intake valve and a 1.625 exhaust valve.
In any case, the intake to exhaust port flow ratio should be kept to 70% for best results. Superflow states that anything above 60% won't really be noticed in a street or drag engine. Ratios above 80 and 90% have been seen and only help high RPM engines like NASCAR where high efficient exhaust flows are needed to make HP at 9,000+ RPM's. Obviously heads like this aren't cheap or useable for street use."
I found this info to be very interesting. I realize that there are quite a few owners of 'full on' drag cars, but I think the majority of members drive their street mopars, and maybe an occasional trip to the track.
What do you guys think about the above info? Has this been the general consensus here? The author seems to be very knowledgeable.
