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Rwolfejr 01-04-2013 11:12:15 67.163.184.160 Report to Moderator	Quoting Removed, click Modern View to see My head was worked and ported out some and now has 3-1/16" diameter intake valves and my old intakes are now the exhaust. The folks that did this have some sort of gadget that shows the flow? I was just ball parking the 4" but it should be around that I'm guessing. Factory hole is about 3" which would be about 7 square inches. 4" would be about 12-1/2 square inches. The shop that did the head work suggested removing the original intake and whipping something up but I didn't have time when I got the thing put together. I'm not hard core and can live with guesstimates... I had a couple thoughts to come up with roughly 4" One was at 780 cubic inches I'm about 173% of original and intake wise... to go from roughly 3" to 4" would be about 178% of original. Close enough? The other thought was measure the new opening for the pair of intakes and try to roughly match it's opening size to same cubic inch tube. Because anything beyond the size of the opening at the top of the head would seem to me to be an error to the safe side? But when you say ... want to maintain velocity... I'm not sure how bigger from the head out could effect that anyway? Wouldn't the velocity of the air being sucked in be dependent solely on the speed that the piston retracts and its volume vs. the size of the smallest cross sectional area of any part of the air path? Unless maybe you're thinking gasoline and carburetion etc...to help atomize the fuel? This is diesel and I'd think that jamming as much air in the holes as possible with the least amount of restriction would be the most desirable scenario. Denser cold air as buickanddeere mentioned and lots of it to make heat and give the air needed to burn possibly more fuel. Then the injector tip and its spray pattern and maybe the shape of the head of the piston would be the factor for the swirl or some turbulent action for a more complete burn. I'd like to know more about the velocity thing if I'm mistaken. I sure don't want to bother with this if there's nothing to gain or even worse... if it'd create losses. I'll have to get measurements in the spring when the tarp comes off the thing. In the meantime I might try to ballpark the offset required and lay something out in cad to see how sharp the bends would need to be to fit in my envelope of trying to use the same hood hole. I'll have to check but I'm pretty sure our biggest conduit bender here at the shop is probably under about 2". More I think of it probably not gonna be a hand bender for the big stuff. I'll need to ask around and see if anybody I know has access to something that'd bend something like this. And I'll check Summit to see if I could piece something together. Appreciate the ideas and any further input you might have... Bob [Reply]   [No Email]
gtx1967jewison 01-04-2013 18:28:01 174.225.129.153 Report to Moderator	Re: 2 cyl 820 intake in reply to Rwolfejr, 01-04-2013 11:12:15   Bob, a smaller diameter intake pprt inncreases the velocity of the air entering, and by changing the length or diameter you can 'tune' the intake to actually ram air into the cylinders at a slightly positive pressure. Google intake tuning, ram air etc. There are several calculators you can use. Input bore, stroke, rpm, valve size, runner & plenum size etc. This works on direct injected engines also, both gas & diesel. Great stuff! Good luck [Reply]  [No Email]
buickanddeere 01-04-2013 15:09:34 216.183.133.196 Report to Moderator	Re: 2 cyl 820 intake in reply to Rwolfejr, 01-04-2013 11:12:15   Flow disturbances such as bends, ledges, lips, edges,port bowls,valve stems, valve seats and valves are the primary restrictions. Overall diameter of the straight sections of flow is much less important. The transittion from intake pipe to head port will be vital. Without a flow bench every step of the way and trying dozens of different port shapes. Guessing fluid dynamics can be hit and miss at best. Sometimes an odd shaped kink will assist flow. [Reply]  [No Email]