#'s Matching 340 build
6500rpm is way higher than I have seen with manifolds but.... different builds. How high would you expect that build at 418 cubes to peak? Asking for a friend. J.Rob
That cam advertises 300 duration and he was a hair light on gear at 3.55 but you can stretch rpms with an auto in 2nd. lol
That combo, identical, with the exception of 4" stroke...probably about 5600 and done, no more hp...tapped.
I ported those in the bowl, did not do any guide work or roof kink...just a gasket match and bowl work. It was like you're doing...on a tight budget.
I just wanted an honest 350-65hp for him and I didn't think the cam on stock x heads would do it alone.
What the others don't realize is that you can get a production head to flow pretty decent ..like close to/about 250cfm without ever touching the guide, roof kink, without gasket matching or back cutting...works great on a 340-367cid ,but it's still a small port volume for 408+.You can remove the kink, do the guide profile, gasket match....nothing else ...and only find maybe 10-12 cfm, but the volume gain can open the window rpm wider. Volume is how how the rpm window is, smaller is lower...bigger is higher. Stock 155-160cc heads need to be a minimum of 15 cc bigger to make it into the 6000 rpm playground with a 4" stroke.
For everybody else ...
a good example is a 340 built with ported 273 heads, 188 intake valves, a .470 lift solid cam with 223 at 50 on a 110, with .029 quench distance
That engine , although making more power than a stock 340, was done around 5500ish rpm...like horse powered out, breathless.
305hp @5400 375lbs@3800-4000rpm
The heads had a final port come of about 137cc, that is too small for 340cid, 145 is too...that's why a stock j or x will support 6800 rpm and a 675/315 273/318 head flowing the same and actually a hair better on a 340/360cid is a rpm limiter/choke because the volume is short for the cid.
Port volume IS important.
If you want a factory head to support 4" stroke, you will have to spend a lot of time simply making the port bigger, walls, roof, guides...'bowl' most dont have the money to pay for it...or the time. I wouldnt pop heads out like this in a week, or 2 or 3, more like.. I'll call you when they are done. Labor of love or a sadists dream come true. Lol