Moparts Tech Archive
Cylinder heads/Flow numbers....etc
ive been doing a little prep on a customers W2 heads, and its reminded me of how inconsistent cylinder head castings can be and how much they can vary in terms of flow, fit and finish, and the surface finish of the castings in general.
i guess what i'm trying to say is, dont assume that because you read a magazine article on a particular head, or were looking at some slow results on a manufacturers website that thats what you'll be getting when you buy a set of those heads.
i havent tested a large number of W2 heads, but over the years ive had several sets come through the shop, and they have all made it across the flow bench. ive had some out of the box W2's flow as much as 260cfm. of course, another port on that same head was in the 240's.
this set im working on now i believe was cast in 1997. they are the newer style with the stiffening ribs next to the outer head bolt holes, and i cant recall exactly
when that upgrade happened....but there is a "97" cast into the top of the head, which i believe is the year of the casting.
so, i decided to test one of the ports in the "out of the box" configuration to see how it stacked up. in the past, the port that would be the #1/#8 cylinder has been the best, or one of the best ports in each head because of the way the core shift usually is.
this head didnt have much core shift, but i flowed a cylinder in that position anyway so it would be a more direct comparison to the other W2's "better" cylinders. this one peaked at 235.3cfm@.550 lift on the intake, and a measly 136.9@.450 lift for the exhaust. from there, the intake went into turbulence and the flow decreased. on the exhaust, further opening of the valve showed no increase in flow. the port had stalled.
yes, this head will still work fine, and will still be able to make plenty of power.....but it will take a little more time, and a bit more $$$ than had the head flowed in the 250+ range to begin with.
the bottom line is, the only way to know if the heads youre buying/bought are going to be everything you're hoping they are, is to have them checked out by someone you can trust.
im more talking about bare castings, or the true "out of the box" type heads(like Edelbrock) that dont recieve any kind of "real" prep.
when it comes to published flow results....i think there should be a disclaimer....
HA HA HA!!!!! Welcome to the wonderful world of the New W-2's Dwayne. Yep, the ones with the Stiffening ribs..... I have now had about 5 sets in my hands, and 3 of the 5 were BADLY shifted exactly like you are describing. The set I had on my Dart and the Square ports were not that bad. The other 3 sets, were piss poor for flow. Well I should'nt say piss poor, but they were not as good as the "better" castings..... So they just along with most other heads are hit and miss for castings. That's why I like the new Commando heads, I've had two sets now and every freaking cylinder puts up nearly identical #'s It's uncanny. I've seen the wild variation in #'s in the E heads you reffer to also.
BTW: You having fun grinding Iron? God I hate it..... 6 hours today, all covered in cast iron dust. The graphite stains your skin.... What a PITA.
--------------------------------------i guess the main theme of this topic was to try and shed some light on the whole "flow number" thing. with the wide range of flow numbers that one could get from testing a bunch of the same type of cylinder heads, on the same test equipment....its pretty easy to imagine that testing a bunch of different castings, on a bunch of different flow benches, would almost certainly end up yielding a bunch of different results. even doing "before and after" tests arent going to tell the whole story. some ports will just respond better to a given level or rework than others of the same type. for example, if you spent 20 mins doing a basic bowl blend to one of these 235ish CFM W2 ports, it might be worth 20-25 cfm. if you did the same amount of work to one of the 260cfm W2 ports it might only be worth 10cfm....but you'd have a 270cfm port instead of a 255-260cfm port. so even though it didnt respond as favorably as the poorer port....its still a better port in the end. what im getting at there is, comparing before and after numbers still doesnt necessarily mean that two sets of heads that were tested at different facilities, that both saw the same amount of increase in flow from the porting work, flow similarly even when tested on the same piece of equipment. the bottom line is, its nearly impossible to accurately equate flow numbers gleaned from one piece of test equipment, to numbers from another piece of equipment. however, what doing a before and after test does do well is show the amount of improvement thats being made on that particular head. and if the numbers youre looking at are from your heads....thats what really matters to you. if the place thats doing the flow testing has previous data that was taken from the same equipment your heads are being tested on....then those numbers can also be compared with yours.....apples to apples. the other thing that should be apparent is, since the heads can vary a significant amount in their unported form, they can also still vary when ported. especially when youre buying a porting/prep "package". this package type of prep is good for both the head porter, and the customer since they each know up front what the cost will be, and basically what they'll be getting. the package's include a specific amount of prep, and will generally provide a given level of performance. sometimes the heads will flow really well, other times they might be slightly below the average....but youre buying time...and thats how much time the dollar amount you payed for will buy. in most cases, if youre looking for a specific amount of flow, then the job would get billed hourly. in that case the price for the work can only be estimated.