Very interesting.... so in reading that I've learned that: 1. The 'Other Head Company' publishes results that you could never replicate in a VW 4 cylinder engine, because it's rare to get one over 83.5mm, even with oversize pistons. This might be to get comparisons between different head types in by controlling the other parameters in the experiment, but chances are they're just doing it for the flow numbers to stick on the ad. 2. Your porting job is probably better than theirs, if you left the ends on the valve guides, rather than shaving them off flush with the ports, and got similar results. The other possible explanation is that shaving the guides off doesn't make that much difference, but I'd be surprised if that's the case. Top work, again. I expect you'll get a load of orders by PM, especially if the dyno results align with the flow bench figures!
I think I gained 7.4 cfm by withdrawing my guides, i.e, removing the standard ones completely. They definately make a significant difference. I would not shave them, but radius the ends to reduce the intrusion. Yes you will lose a little flow, but your valvetrain and seat combination will last longer!!
That's looking good, effective with standard cam as well as higher lift ones then! Hmmm cheating then or "spin" as "new labour" would call it, BS whichever way you look at it... But interesting as it pretty much proves that you need as much bore as you can get, or put it another way, increasing the bore will increase your CFM (all things being equal). Personally I think it would (will?) be hard to beat the Jenvey DTH design, maybe same design but with slide's or barrel but how much work/expense for little real world gain Have to agree, for a road engine maybe chamfer or bull nose, I don't agree with chopping em off either Have to agree, one of the things that's kept me from paying for someone else to do a (16v) head in the past has been the lack of hard data they provide, I like this "open", "honest" approach! Cheers Simon
I feel I should stand up for CNC heads at this point - to their credit, they are one of the VERY FEW head modifying places that actually state what flow increases you will get.....and yes it seems they have been a bit cunning using a 100mm bore....but thats a damn sight better than Stage 1 or Stage 2 etc whatever that means.
Very interesting reading. Certainly explains why 'big valve' 16v heads are known to have such shrouding issues, looks like even the standard is marginal. Is it even possible to quote a figure for a 'product' like this when each head has hand finished ports? I would have thought you could quote rough figures for a particular type of headwork in advance but specific values would have to be for a specific head, each one is going to vary isn't it? - like the original castings do. Most punters want to know 'how much power increase in bhp is it going to give me?' which encourages suppliers to quote figures that end up being at best misleading. When I had my head done the company that did the work didn't quote specific figures, they simply took my standard head and applied their headwork knowledge to it (which seemed to be mainly bike heads), at the time I went on a recommendation, and like a lot of people, had very little knowledge of what they were actually going to do. I'm pleased though, looking back, that the work they did follows most of the 'best practice' that seems to be true for these 16v heads, especially looking at the finish, the amount of porting, where the most work went into it and attention to detail around the head material around the guide protrusions and the end of the guides themselves. I've seen a fair few 'worked heads' that just have the end of the guides cut off flush and the 'lumps' for the valve guide protrusions removed too, that's a lot of guide surface area gone
Indeed, there are advantages in a bigger bore, I had no problems with sealing on the 93mm bore I tried, I'll have a look at that though, good point.
A lot of work indeed. I doubt I'll get the chance to dyno this particular head as I'm not building the engine, just supplying the head/pistons/rods/inlet manifold... but if it doesnt make 200+ hp I'll be mighty miffed. There's no polished ports here, I even went back over the throats/seats after blending as I thought they looked a bit too smooth. The final flow rate is a bit over 20cfm more (110 to just over 130cfm) than the standard head at the cams peak lift, with an increase at every lift point straight off the seat.
Look's about that way around peak, though in fairness, theirs is better in the mid lift points, but mine is better at the low end straight off the seat, though mine is tested on the correct bore size. It's difficult to tell exactly like for like as even when I tested on a 93mm bore, that was still 7mm smaller than their own bore adaptor.
The guide's are already bulleted in my head. Yes indeed, though possibly +2mm (32-34), though my machinist thinks 35mm maybe pushing it a bit ! Thanks.
Looks that way Mike. I've since looked back and all their heads are tested on a 3.9 inch (100mm) adaptor, no wonder when I said to a friend they claim 190+cfm from an atmo Cossie head he said "absolutly no f%$*ing way"! Forgot about that, I do indeed have full length guide protrusion, just bulleted ends. The PM box has space..
Who mentioned CNC.... ... opp's Though yes indeed, but it is a bit of a glairing mistake. My flowbench partner (not knowing the company at all) said "they probably do a lot of V8 stuff and thats the only bore adaptor they have"... well oddly enough...
Agreed, this should hit 200bhp with an optimised inlet and exhaust system. I have seen CFM numbers around 5% lower hitting a genuine 200bhp number. Not on a VW head, but airflow means fuel, and fuel should indeed mean power at the end of the day...
That is a valid point, though all ports, seats and throats are measured and sized the same (or as close as feel with internal calipers will allow), not just by eye. Power figures are a difficult thing to estimate, as thats the best you can do.. estimate. A lot will depend on so many factors, bore size, cam, induction & exhaust will all play their part as you no doubt know... only a "potential" gain can be estimated with all factors being to at least a "good" standard.
Thats what I'm working on. The engine in question is a 2ltr ABF with 45's, Supersprint manifold & system, sub 280/11.3mm cams, 11.5:1 etc, so I've nothing to hide (and there's certainly no hiding now! ) by saying the head will go under severe evaluation if it does'nt do what I expect it to do.
I'm happy to be corrected if I've got it wrong, but I thought there were a lot smaller as standard, from the vauxhall heads I've seen.
I hope you (and the forum) get to hear the results. It would be great to see how the results on the dyno compare to the flowbench.
No correction needed.. I took it you meant in modded form.. as standard some of the Vauxhall's are certainly smaller (Ecotec's), though port size is'nt the biggest contribution to flow, it's getting the air to turn the corner and escape through the valve opening thats the tricky bit.
Well, here's the final tally on the inlet flow for a ported 16v ABF head... or at least my version of it. I have to put my hand up and say I made a small error on the first couple of tests, it took my friends apprentice to point out that " did you know the plastacine ring has dropped a bit"...doh! I in fact carried out the final test last Friday, but as it was higher than previous tests I was uncertain about printing details, so I had my flowbench partner run a completely seperate test yesterday, which came up with identical results. So, here goes... and all tests in this chart are carried out using the correct adaptor with an 82.5mm hole as per a standard 2ltr 16v. P.S.... if someone can tell me how to load a word doc on here i can load up the chart. This'll do for now...
