View Full Version : Valve sizes.....?
Started my project engine last month, after receiving a doner at the begining of. (pix will start to follow shortly)
Now, the engine is a meggy F7R engine (one of the later ones with a more robust head and plastic cam cover). Destiny for this engine is undecided yet as to wether to go forced induction, or stay NA. Either way i figure, if i make a fit NA, i can always breath a little boost down it at a later date.
I'm currently in the process of rounding as many parts up as poss and have a number of kinkey bits in stock already.
Increasing valve size is a deffinate, and was looking what would fit. Currently 33mm Inlet & 28.5 Exhaust. Ive heard people have opted for 35's before & exhusts unchanged (seems a little rude though considering the size of them!). Ive got a bunch of 36's out of a Scoobey WRC with a nice 6mm stem & flat back to the valve which could squeese in, but am worried about bore shrouding & wether it would be counter productive (always the option of machining them down i suppose). Another possibility, which a few of you might consider: Pug 306 GTI6 Valves & guides. 35.4 on the inlet 6mm stems and the guides press straight in! bonus.
Any experiance/suggestions on the matter would be greatly excepted.
Cheers, Jonny
think you can run 36.5 mm peugeot valves in this head. speak to ben r or stan on here either will be able to point you in the right direction. also i think you need to decided on turbo,s before the build. not worth the expense in my opinion unless you run the high boost conversion. in which case you need to build the bottom end with low comp pistons.
as above, if ur gonna go pressure, do it properly.
as for inlets, im running 34.6mm from an mi16.
i think ben has done work with 35.2mm. but that will be the max. you wont fit 36mm's in there, thats for sure! in either case you need new seats.
the thing is aswell, its realtively easy to get a machine shop to fit new seat inserts, but thats not the end of it. there is then extensive port work to be done to match the throat, and aid flow to match the valve head. unless ur handy with, and have, the appropriate tools/burrs/abbrasives/points, i really wouldnt do it.
its not as simple as a basic port job.
I know, Ive got all the kit i kneed available to me, I am the machine shop!
Was going to 100% CNC Combustion chamber & ports for consistancy and control of shape.
You heard of a grade of bronze that can be used for valve seats (read about it somewhere and can't remember what it is or where i read it) perculiar name...
Be very careful when going for valves that are as large as you can, in most cases, too big is just that...too big. I have come to 35.2mm inlet being the largest i will support on upto 84mm bore. There is just no point going any larger IMO. Shrouding takes great detail to overcome and with valves as large as mine will take some serious development, even larger and i cannot see it really working as you will have a horrible intersect between the 2 valves not just the chamber and bore.
When it comes to picking valves out of other cars, stem dia is the last concern, look at overall length, collet groove size and height, and nose height. Then weight becomes an issue when you start looking at valvetrain harmonics and seat/nose pressure required.
CNC'ing the chambers, like i mentioned, is a fantastic idea, but you will have to hand finish it after (which goes back to hand grinding and the accuracy required, especially in regards to keeping seat heights consistant to a thou), i've not seen a CNC profile finish of quality to support decent combustion. Have you thought of spark erosion? Either way, you will need a chamber, and especially a throat/seat/chamber flow profile that will actually allow the valve area to work. Just having 36mm valves doesnt mean you will flow more than 33's. One problem with the 710/714 series heads is the bifurcation is in such a horrible position and really doesnt help. If you cant make the head flow on 35+mm valves, i dont see a point.
On the case of seat material, are you planning on running Ti valves? I dont see a point running the more expensive ally/bronze seats, they are a little softer and wont last as long in the long run.
If you must, there is Trojan CoNiSi Bronze, or Ampco 45 etc.
Copper beryllium if your feeling frisky and dont mind the radiation.
And if your going to be running a std inlet type, i really dont see a point at all.
Have fun!
Cheers Ben,
Was looking at the bifurcation, and could see a lot of potential for improvement. You suggested it was in a horrible position. You thinking it starts too far down the port?
One aspect of the port design i was looking at, was to perhaps increase the angle of the port it self. Probably leave the floor where it is and try bring te roof up slightly. Now i know this will probably reduce my tumble and hence thermo-dynamic efficiency, but was wondering wether the increased volumetric efficiency would compensate enuff at the lower engine speeds. Idealy i would like to retain a torquey motor & just fatten the curve all the way up.
Valves: I would like to stick to the scoobey ones as they've got a really flat back and thin head to them (and i've go a set free). They are 36's, but could easaly bring them down a bit and re grind the angle's. The stem length is .8mm shorter so clearance needs to be adjusted there. If the .8 was the only descrepency i would be tempted to take that up when i spec the cams (obveiously would'nt want to do this to the excess though!).
What tends to be the standard practice for exhaust valves? They seem really close to bore. Tempted to suggest moving them closer to the centre a mill each and upping to 30 or 31.
Cheers again, it's all learning at the mo i'm affraid.... :D
The bifurcation position isnt the be all and end all, its more how it actually blends into the port itself, its just crap. The port floor upstream is crap, the roof is fine.
In regards to making the port itself more downdraught, its alot of effort and you'd be reconstructing it. If you left the floor but raised the roof, you'd need to build a new inlet manifold. You'd shear the flow with differing roof/floor length ratios and induce turbulace in the port. If you want to do the whole thing you'll have to strip it of all steel, weld, normalise, align every face relative toto the cam bores which you will have to align hone again.......then after that you might aswel of bought a 172 engine if you want a higher included angle. I dont personally see a point, all my highest flowing heads are hondas, with valves that are smaller and ports which have next to ne included angle....and i'm talking some serious outflowing!
If you want to retain torque, keep the 33's........concentrate on reaching their flow capabilities first. Too big a valve and you will drop velocity in the bowl drastically as you have to open it up a massive amount, and all inertia energy will be lost for stagnent low lift slow low rpm events.
If you must use the scooby ones. The hyro tappes have 2mm uptake, so you cna increase the BCD of your cam by .8mm to account for the shorter stem. Or go solid and just use your shims.
If you move the spacing of the ex valves, you will have to do the same for all guide bores, lifter bores, spring seats, cam lobe positions etc....waste of time. And when you do, you'll be left with a stagnent pocket on the outside of the bowls, which will make for a horrible port shape with no welding.
If your not planning on making 270bhp, i wouldnt bother. If you want to do it as a pure machining exercise, no need to ask us ;).
Cheers for your help again mate!
I'll keep you up to speed with progress + pix
:wink:
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions Inc. All rights reserved.