does anyone know the flow results of a standard abf head and what a good modified flow rate should be?? cheers
It just so happens... I flow tested a standard ABF inlet port today, it flowed about 110cfm (left the results behind in the workshop! ). If I can get the pc to communicate with the printer tomorrow I'll print off a graph. Modded ports appear to range anything from 120-140cfm, depending on who's head and flowbench. I'll flow my current version of a modded inlet port tomorrow and if time permits the exhaust as well. The CNC HEADS website has various graphs to help as a guide.
how does that relate to a theoretical BHP increase? obviously it would depend on nothing else becoming a restriction. i might have this completely wrong, but if you work back (and i am literally making an educated guess here!) does 130cfm equate to (theoretical) 177bhp?
cheers for the results. what valve lift was that at??? ill get my results up soon when ive flowed my head. ill try n do it next week. as for the direct correlation between bhp n flow. its far from accurate and if it flows too much then u can hav major issues with torque loss.
good info ! what do the following heads flow as standard ? and ported & Polished ? KR 051 ALLSTAGE HEAD KR 027 - Cheers
I've spoken at length with a competition engine builder regarding this and cfm data isn't directly proportional to output. Just because the head is flowing more volume doesn't mean the mixture is doing the right thing internally. He regularly sees higher output from lesser flow on a wide range of engines.
Is Allstage "the shed"? On a Superflow SF120 bench a standard ABF flowed 121 cfm on the inlet side bare port flow, i.e without any valves in. No idea on the 027, I would like to get one tested on the same bench, just to see what the difference is. Regarding flow bench numbers and bhp output, they are not proportionally linked, for example making ports too big will ruin the incoming air velocity, but...a head that flows sod all air will not make any real power. As with so many things regarding engine development there are always so many different factors to consider
Yes ALLSTAGE is the man in the shed. i have a flowed 027 & 051 in my workshop would be interesting to see the difference.
Well, an Allstage 051 head flows 124 cfm bare port flow in the inlet. A whole 3 cfm (2.5%) more than a standard ABF head. Tested back to back on the same flowbench (SF 120)
From memory 450 & 500 thou were largely the same... I'll try and bring a copy of the chart home tomorrow printer permitting. You can never really have too much flow, but a compromise between flow and velocity (air speed) is what you need to look for. If you make the port size too big in relation to the valve size used then torque can indeed suffer. We will be able to take port velocity readings in the not too distant future.
Thats true to a point, I know engine builders that have also seen flow go up but power has'nt, it could be that velocity has been lost and thus mixture aggitation and combustion can be effected. Flow benches are like rolling roads, and to a lesser extent engine dyno's, sometimes, the numbers dont tell the full story, but, unless the flow is fairly good on a flowbench and power is good on a dyno, power and perfomance just wont happen.
I flowed both standard and modded ports last week bare..i.e no valves, and saw 115.6 for the standard ABF and 137.5 for my modded port, which I think is a resonable increase compaired to some, I think the CNC heads are claimed to be 140cfm with guides and seats finished. I made a fixture to open the valves and carried out several full range of lift flow curves yesterday (to check for repeatability) and saw peak readings of around 110cfm @ 500 thou. I'll be running the modded ports tomorrow (well later today!) with valves fitted, but still with final detail stuff like seat angles and tapered guides to do. The standard peak flow of the ABF head I have looks a little low but the rest of the range is'nt far out, it may be that the head I have is not as good as it should be from the factory, it can happen with casting differences. I have possible access to a standard KR head and a tsr head (I believe it's based on a KR casting too) so will flow them at some point, so at least some back to back testing on the same bench will be available... at some point.
Once ported, there shouldnt be a huge difference. That's the thing with hand ported heads, there will always be subtle differences from head to head, and casting to casting, you cant do anything about a casting if the ports in particular head are too big "as cast" for example.
In fairness, sometimes (so i'm told) a good head will flow better with the valve fitted, but we'll find out in due course.
I have seen documented evidence of this with some heads - honda vtec for example(not VW - there appears to be a real shortage of reliable data for all VW stuff). I believe it is more down to the head design and the valve shape rather than the work which is subsequently done on the head, either way, as you say, a loss is a loss, and these need to be minimised.
cool, will be keeping an eye on this thread... Mr. Hillclimber: it would be super if you could do a thread on diy flowing a 16v head afterwards, like you did for the 8v
Well, the inlet results are in, and... From 350 thou lift to 500 thou we have gains between 5.1 and 14.8cfm, peaking at 125.7 cfm, up from the standard head's 110.9. I also carried out some tests with an unmodded Dbilas inlet manifold, the type many just buy and bolt on to suit Weber or Dellorto carbs. On the standard port, the manifold lost between 2.6 cfm @ 150 thou lift to 6.1cfm @ 500 thou, with the biggest loss of 6.9cfm @ 450 thou. On the modded port the losses were even greater, rangeing from 1.7cfm @ 150 thou to 10.2cfm @ 500 thou... not what you'd want when adding performance parts, and the reason why so many have poor results when fitting twin carbs. Note, these results are with valves fitted, not an open port. The inlet valve has taken off 4.7cfm from the bare port flow I did last week on the standard port (115.6 down to 110.9), with the modded port dropping from 137.5 to 125.7, an 11.8cfm loss for those without a calculator to hand. These tests are also without any valve seat cutting or valve back-cutting or guide tapering, something which I expect to help with flow right through the lift range, and certainly help in the case of the modded port where the losses are much bigger... I'll keep you posted. Exhaust port testing tomorrow.