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Bear with my I don’t know **** but trying to learn. I’ve seen coefficient of discharge used as an explanation why the 706 heads work as well as they do. By both Brian Tooley and Richard Holdener
In my trying to understand why the 706’s make more power than 243/799’s 99% of the time I’ve started to consider this COD.
I have a set of 799’s and 706’s.
I’m considering having the 706’s Cnc ported but keeping the stock intake valve.
I don’t see the point of the stage 2 setup on the truck heads because if I did go that route I’d have the 799’s ported and save money.
Any of y’all care to talk about coefficient of discharge? What can you tell me?
When bolting on the smaller chamber 706 heads to a larger 4" bore 6 liter block you will have lots of chamber over hang in bore, so you remove this over hang to unshroud valves. This raises low lift flow numbers, plus smaller chamber raises compression of larger cubic inch motor. Hand porting the 706 chamber and ports and then bolting them to larger bore is a verygood affordable idea. Maybe this is what they mean by coefficient of drag?
When bolting on the smaller chamber 706 heads to a larger 4" bore 6 liter block you will have lots of chamber over hang in bore, so you remove this over hang to unshroud valves. This raises low lift flow numbers, plus smaller chamber raises compression of larger cubic inch motor. Hand porting the 706 chamber and ports and then bolting them to larger bore is a verygood affordable idea. Maybe this is what they mean by coefficient of drag?
This maybe of interest there a lot of good info on the site below. Also several charts with flow data etc. I think the 706's sort of fell out of favor as the 243 castings became plentiful. The 706 stuff can rick in many applications. Definitely a fan of the TEA 706/5.3's Stage 2's I ran.
AI mentions 500+ whp with fully ported 243/799's on 3.9 bore. AI says the 706's require more work (cost) and on 3.9 bore capabilities for 480 whp.
Per AI's site on 706 - Note: Over the years we have found these castings tend to require more time in regard to quality checks/corrections on our end. They also must be run with a larger aftermarket intake valve. Due to this, the cost is higher when using them as a base for work compared to the more common GM 243 etc.
The 706 stuff can rick in many applications. Definitely a fan of the TEA 706/5.3's Stage 2's I ran..
I just flowed a set of those. They where nice. They where the 2" ones tho.
706s besides a little lore comp .also have a more compact chamber, bigger squish pad.
this increaes the squish velocity. Forget about shrouding. Look at the red circle.
that is a stock 706 . That's terrible.
because lack of a valve job,because its seat % is so big . Sometimes a pic is worth a 1000 words. But also think about reversion.
You can throw chamber shape into that vj term if u want to . I think thats a 243 next to it in pick. Idk.cant remember.
I have a set of 799 heads on my '01 Camaro and I'm porting a set of 243 heads for a C5 while I also have a set of 862 heads in my garage. The 862 heads I use to try new things as far as porting. That should give you an idea of how I see 706/862 castings.
Discharge coefficient of a
1.89 valve @ 237 cfm is better than a 2"
valve at 250 cfm .
But 706s dont flow 237. Never seen it. Even with huge radius inlet they dont
in that article they did. Maybe he had a leak. Idk . The 250cfm on there 799 seems right.
down at 220cfm where most 706s flow the discharge coefficient is worse than the 799s. The tea's that where here went exactly to the cfm they advertise. Lots of variables.
regardless, neither of those heads in that test, the coefficients are not that good.
When bolting on the smaller chamber 706 heads to a larger 4" bore 6 liter block you will have lots of chamber over hang in bore, so you remove this over hang to unshroud valves. This raises low lift flow numbers, plus smaller chamber raises compression of larger cubic inch motor. Hand porting the 706 chamber and ports and then bolting them to larger bore is a verygood affordable idea. Maybe this is what they mean by coefficient of drag?
04-22-2020, 01:23 PM
Coefficient of discharge 706/799 stock bs ported 
