Darling - so thoughtful as ever! Tidy looking work... maybe you should go into business as a cylinder head man ;o) Did you do the flow testing with or without guides? I'd have thought they'd make a difference It's probably not a linear relationship, but I wonder if a test at an 'average' valve lift for a given cam might not give a meaningful number of what an engine might flow on that cam. Just as a really rough example, a KR inlet has 9.6mm max lift, so maybe 7mm would be a good number to test. It would be interesting to try it on a stock head, and see how the numbers relate to the standard power output. Or does the calculation you're doing already factor that in?
Can you post up your final results when you have finished the seats and valve combo, I think that will make interesting reading
I dont think it is either, though obviously the whole intake set up really needs to be flowed to get a closer picture. I have the 8v hillclimb engine coming back today (compleat with inlet manifold & 45's) for more power, I know it's current output, so guess what's going on the flowbench soon...
My pleasure. Aw shucks, thanks. Well I sort of have really, (though not full time) this is one of 3 current customer projects, and the idea behind the flowbench, rather than just grind away (ooh err) without having a clue as to whats going on. With the guides in, or the valves would be a bit of a bugger to seal ! (but you knew that really )I had 4 of the old guides turned down so they would push in and out so I can swap them around to whatever cylinder I want to test. At some point (when the decks are clear) I'll do some before and after testing with bulleted guides and various seat shapes & valve sizes on both an 8 & 16v head, and with manifolds. This current head will obviously be getting the seat work and guide treatment, the seat's should bring up the low lift flow and add a touch to the top flow too... we will see in the nxt couple of weeks. I have a full lift curve of both standard and modded ports. Both ports increase flow up to 500 thou, though only in steps of a couple of cfm after 400 thou in the case of the standard head (.400 = 108cfm, .450 = 110.3, .500 = 110.9). Either the valve caps hit the top of the guide or the inner spring went coil bound at .500 as it was impossible to lift the valve further (did'nt look to see). The standard cams lift to a bit under .400 dont they ? so it's even worth lifting road cams to .450 to take advantage of the heads peak flow area, just keep the duration down.
I wasn't sure how you'd manage to test it without the guides, but the picture didn't show them, and there's always lumps of plasticine! Interesting illustration of the law of diminishing returns in valve lift... isn't there a rule of thumb that with lift over 50% (or is it 60%?) of a poppet valve's diameter, that you don't get any more airflow? It also suggests that there's a real tailing off at higher lift. I suspect that reprofiling the valve and recutting the seats should move that curve a bit. Interesting to see what you find. A standard KR inlet cam lifts 9.6mm, measured from the cam. I think you lose a bit for the hydraulic lifter though 9.6/25.4 = .377" A stock ABF is 10.8mm as far as I remember 10.8/25.4 = .425"
Yeah, it's been a busy time lately. The ABF has responded well to some more simple mods, backcutting the valves in the standard port brought flow up from 21.3cfm to 27.4 @ 0.050 (i.e just off the seat), and on a modded port flow came up from 20.6 to 27.6. My thinking is modding the port has allowed more air to bang into the poor standard seat and cause more turbulance, thus less flow. At higher lifts the effects are less, though still up at all but two points (the difference between two different ports anyway?) The modded 16v ports flow better at every point now except .200 (0.8 down) & .250 (0.3 down), as an example, at 0.450 it's gone from 110.3 standard to 112.2 modded to 121.5 with the valve backcut. Peak is still 125 as the backcut has'nt helped up the top but the 3 angle seat in the head is'nt done yet, plus the tapered guides. We tested a race Pinto head last week from one of the best (allegedly) around with raised ports big valves etc, that made 103cfm (twice, as we thought something may have been wrong with the first test.. it was'nt), so like for like on THIS bench the ABF looks to be going in the right direction. The 8v hillclimb engine has indeed landed back with me, so that'll be coming apart soon for flow testing, maybe bigger inlet valves (subject to results) and a better cam (304 Schrick to my 318 profile) with more c.r (12:1's for wimps ). And a 1300 8v Mk1 Golf road/track day package is coming together ok so far, though with tiny 34mm inlets flow is a bit down on the 16v, but a sensible gain so far for what it is and needs to be. As soon as I get some ink for the printer (Epsom printers wont run with low ink apparently) and with the owners permission, I'll hopefully get the graph up for the 16v.
Mr Hillclimber, this is absolutely awesome work you have been doing. Looking forward to seeing the graphs. Gurds
OK. Interesting work you are doing there. From all the you work you have done here, you are demonstrating that with the correct porting methods, the cylinder head ports subjected to a test pressure will more more air than STD for various valve openings found on a typical set up. Using a rule of thumb for CFM or lb/hr it is assumed that airflow by a factor = BHP. What I am interested in is how these mods would modify the STD engine torque character. So the best bet here to complete your study is to optimise a STD engine and run on an engine dyno to log EGT, AFR, Torque at WOT. Then fit the head with improved cylinder head optimise agian then run up at WOT. Also how would this modiifcation improve response at load/engine speeds under WOT. You may need to find a way to measure response before and after. It is time consuming I know but at least it will comfirm your work. I am sure these mods would do something to engine behaviour but by much how long and where. Peak BHP values are only a value when the torque (drive acceleration) in most cases maybe droping off.
Saying that Toyotec, when I fitted an optimised head to my old 1.8 kr, the torque characteristics improved right across the range and therefore power too. From what I have seen, this is from improving port flow while, very importantly, mainting or increasing port velocity at all ranges of lift possible to improve cylinder fill. I think I am correct in thinking that if this is what Mr Hillclimber is aiming to achieve, then his headwork will improve the torque along with peak power. Gurds
I believe that it would G. And as someone who has been messing around these engines I am really interested in any graphical plot that shows how the engine torque increases, where from and how long would it hang on for staying fairly high. I am not really interested in actual corrected BHP value, just a back to back comparison for stock optimised engine vs optimised engine with headwork.
This is why I gave the suggestion. As a BHP measurement by itself really does not say much unless you assume that the vehicle in question has a typcial engine torque curve that is unchanged from car to car.
I dont think theres been much talk of bhp, apart from suggested power from flow. But even this, as I have said, does'nt "always" add up, but it appears to be close more often than not.
