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MG Midget and Sprite Technical - Head modifications
| Gents Purchased a partly ported/machined large valve Metro turbo head recently and currently working on refining it further to gain the optimal performance from it. Been following Des Hammill's advice which seems sound enough, but one or two points..... Cast bosses surrounding exhaust valve guides. These have not been removed - though inlets have. I have rounded them off a bit....will it make much difference leaving them basically as cast? Inlet ports - grinded out a little further to about 28W by 30H approx - sufficient or more required? Exhaust ports approx 25x25 tapering gently towards throats - is this adequate? Throats themselves have been ground out as per Des Hammill - anything to note particularly here? Looking to mate the thing up with a Unipart HP gasket/LCB/RC40.....mmmmmm! Cheers Mark |
| Mark O |
| We always remove the exhuast bosses, good for flow and haven't found any negative heat effects. |
| Paul Walbran |
| Paul Yes, understood that it is probably desirable to remove them, but as I have no machine shop and limited tools/facilities, would leaving them in situ be a particularly bad move? |
| Mark O |
| That just sounds scary mark... Your doing head work and yet have no machine shop or tools Id stay close to the basics and not get to wild. Take off only what you need from the ports, the bigger the hole the slower the air moves...think shop vacumes, and careful around those port dividers As to the valve guilds, normally id say pull them....but with the limit resources avialable to you id say leave and re-ream them unless there is something telling your gut and neck hair differantly Prop |
| Prop and the Blackhole Midget |
| Prop Shut up Cheers Mark |
| Mark O |
| Prop - read the posts BEFORE commenting, luv David |
| d brenchley |
| Mark By far the most important is three angle valve seats, blend the throat in and a 30 degree cut blended on the back of the valves. The short side of the ports is vital to flow and needs to have a generous radius. Basic work on the port sizing has minimal effects apart from very fast road/track day/ race use. Remember the port is always there but the valve is shut mostly, then open just a bit. The name of the game is to keep the airflow on the valve seat and back of the valve for as long as you can to encourage good cylinder filling. Has it been fitted with larger than standard turbo valves? I am not too sure Des has tons of experience with all the different engines he writes about. Peter |
| Peter Burgess Tuning |
| On 2nd thought mark, Grind the jesus out of the ports, bigger the better it can handle alot of extra air...dont worry about those port deviders, grind those out to, those are just blocking air Prop |
| Prop and the Blackhole Midget |
| Prop! Knowledge speaks, but wisdom listens! |
| Steven Devine |
| Steven Shut Up! Cheers Prop |
| Prop and the Blackhole Midget |
| If I was going to work on an A-series cylinder head I'd read Peter Burgess book and David Vizard's book. |
| Daniel Stapleton |
| Peter Cheers for that - seems to make good sense. Trouble is I have no vertical miller or whatever to cut the seats with any degree of accuracy. I could do a spot of valve grinding/lapping though I suppose... Head has 35mm Inlets - non std for MG turbo I think - and standard outlets. Head looks like a MG turbo as raised faces on stat and elsewhere, blanked off take-off port for heater, and no water pump bypass. Alot of work has been done - ports, throats, inlet valve bosses, so I am titivating a little really, to Des Hammill and the link below - which seems useful http://www.specialistminiforums.com/heads.htm It also only has single valve springs. Not sure of their provenance - what say you to that arrangement? |
| Mark O |
| Hi Mark, my MG Metro (non turbo) head has the raised faces, blanked off heater port and single valve springs. The inlets were 35.6mm IIRC. I think the way to tell if its a turbo head is with the exhaust valves having wider stems. Thanks Mark |
| Mark Whitmore |
| Prop shutting up now.....cheers! :-) |
| Steven Devine |
| Steven....hahaha Prop |
| Prop and the Blackhole Midget |
| Raised faces are just a sign of the age of the head (from end of 1979 I think) The turbo head only differs in the dimension of the exhaust valve stem (8mm) to allow for the sodium filled exhaust valve. Vizard is the book to read if you want to mod your head. Some comment that it is a bit out of date and chamber shapes etc can be improved upon but the basics are correct and it explains a lot of principles. And it always helps to understand what you do and why you do it (more power is not the complete answer ;) ) |
| Onno K |
| Chaps Further to this, assuming I fit the head, mate up to an LCB and RC40 zorst and keep the HIF44, would a different needle for the HIF44 be desirable? My thinking is that the engine will be able to suck in more mix, more fuel, and thus perhaps a slightly slimmer profile needle than the current standard Metro BDL needle currently fitted will be required. Was the needle for the MG Metro any different? Note slightly hotter cam fitted, standard block/pistons.... AFAIK! Cheers Mark |
| Mark O |
| Being blunt but if you don't know what is in your engine how are we suppose to know what needle you need? it's all trial and error until you put it on a RR |
| Onno K |
| Hi Mark, I have an MG Metro head, Titan inlet with HIF44, BDL needle and K&N, Maniflow exhaust and manifold, +30 overbore and Piper 270 cam. When I took my car to be Peter Burgess rolling road he tweaked the needle a bit by filing it back in the appropriate place. I would imagine that the BDL is not too far off the mark for my engine spec otherwise he would have fitted another needle. The MG Metro was fitted with BDL as standard and IIRC ran 10.5:1 compression with larger inlets. So our lower compression engines should cope fine with it. A rolling road set up would be the only way to be 100% sure to get it spot on. Thanks Mark |
| Mark Whitmore |
| Mark Spot on, just the info I require. Many thanks. I too believe a little tweaking would be required, but just needed to be reassured I was not too far off initially. I too would be down to pay Mr B. a visit - were I not residing in the Arctic and thus many miles distant. How does yours run now? - just to get my juices flowing.... Thanks Mark |
| Mark O |
| If you need a BDL Needle, i have several available for the Cost of the Postage |
| dominic clancy |
| Hi Mark, she runs great, very responsive with 93BHP at the flywheel, although for the past year she has been off the road due to a clutch replacement which has lead to a few 'whilst the engine is out I'll just do......' jobs!! A Youtube clip speaks a thousand words!!! https://www.youtube.com/watch?v=JCi9UYBuEkw Thanks Mark |
| Mark Whitmore |
| http://www.youtube.com/watch?v=JCi9UYBuEkw |
| Prop and the Blackhole Midget |
| Thanks Prop, wasn't sure why it wasn't a clickable link (copied and pasted as usual) Mark |
| Mark Whitmore |
| Mark Truly orgasmic...I do like the popping on the overrun. Must return to garage forthwith and wield some spanners..... Dominic...grateful thanks for the offer...will advise... Cheers Mark |
| Mark O |
This thread was discussed between 06/11/2014 and 13/11/2014
MG Midget and Sprite Technical index
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