AndyGT6 Posted February 11, 2009 Share Posted February 11, 2009 As I said earlier in this thread, I was very interested in what the outcome would be, as the compression values on my 2.5L are lowish. Today I dug out the cylinder head that was fitted to my GT6 when it was 2L with dome top pistons. This head is in serviceable condition but it had .055" skimmed off it. I thought I'd do a rough measurement of the chamber volume today using some small plastic syringes I have ( I've got a burette on order from a local Lab supplier ). I know the chamber volume is somewhere between 35cc & 36cc. I don't know the deck height neither so I have assumed between .010" & .020". These figures give me a possible compression ratio of between 10.9:1 and 11.6:1 if I fit this head to my car. I know GT & GT5R have stated a CR this high wouldn't be a problem but years of conventional thinking still sets off alarm bells in my head. I am running a 25-65 Vitesse cam and Megajolt. All thoughts welcome. Andy Link to comment Share on other sites More sharing options...
gt5r Posted February 11, 2009 Share Posted February 11, 2009 conventional thinking Thats the problem - conventional thinking doesn't work on a 6 cyl Triumph Link to comment Share on other sites More sharing options...
Mother Teresa Posted February 11, 2009 Share Posted February 11, 2009 Andy, is that piston height above or below deck height on yours? I'm wondering what difference/benefit there is in letting the pistons 'pop-up' above the deck and to what level can we get away with before it presumeably becomes counter-productive? Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 11, 2009 Author Share Posted February 11, 2009 No stress for me to hack that water area out Bruce and increase the size to match the gasket, I haven't done it yet cause I have yet to get the butchery tools out. Tomorrow should see it done bar the rockers. Few hours here and there keeps me happy. I really do hope the thin area holds. Let's call it "needs must". I reckon it will be ok. I jet washed the head under 200psi of pressure and blew out some silt. That was the first job to remove the "tonic". I'd stick it back on as is Bruce. It's only a head gasket... We'll have to chat about the pushrods. I haven't looked at the position of the "balls" on the rockers, if they are bit a low, no problem...It's only 0.045-46" thou anyways. If they are already "high" I'll drill out the top few threads and make clearance. We will be over budget anyway I think on labour anyway due to the complications, but it's been a nice thread, or will continue to be. I don't mind, you owe me some espressos for the forseeable future, I'll let the rest go Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 11, 2009 Author Share Posted February 11, 2009 Pop-up, 0.010" max? Those rods are made of rubber and the compressed payen gasket is just 0.0315". Link to comment Share on other sites More sharing options...
gt5r Posted February 11, 2009 Share Posted February 11, 2009 I know GT & GT5R have stated a CR this high wouldn't be a problem GT's results are pretty well documented in his manuals and backed by race proven results - basically it does what it say's on the tin - there is no dought in my mind that his advice is second to none. And believe you me I've followed a few!!!!!!!!!!!!!!!!!!!!!!!!!!!(Quote 'Life of Brian') My advice again has come from many years on the track trying to extract power for a 1950's cast iron boat anchor Don't take main stream advice as you will end up with a sack of shit that produces less power and torque than a 1.1 Nissan Micra Bin the idea of logic and trust the advise given here - it works and it wins races - not the I've got a bigger willy than you contest :o High compression also requires long duration cams with lower lift Link to comment Share on other sites More sharing options...
Mother Teresa Posted February 11, 2009 Share Posted February 11, 2009 You're a gentleman Dave . Pm with whatever sum you feel is appropriate and I'll get the funds ready. I've thoroughly enjoyed this whole exercise 8). Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 11, 2009 Author Share Posted February 11, 2009 Lapped all the valves in this evening, took a while as the new exhaust valves are gas nitrided I think, hard as nails, darker colour to them, much harder than the seats! Recut inlets lapped in well, as I said these weren't cut right before, or central as when they were recut there was run-out on them. I used diamond paste to lap them in first, then finished with "chemico" fine, I like this Chemico paste. Relieved the sharp reface edges from the chambers and smoothed them up. Last job tonite is to just to radius the exhaust valve edges... So, grinding the seats back is next, grinding out some extra room for the pushrod channels, as there are some rubbing marks, cut out the rear water way, clean up the water holes in a few places...have a quick grind on the short radius. Then I can wash it again, degrease it, paint it and assemble it with the freshly sonic washed parts. Leaving just the rockers to have a gander at, also check the rocker geometry on the bench with just the inner springs fitted. Link to comment Share on other sites More sharing options...
AndyGT6 Posted February 11, 2009 Share Posted February 11, 2009 Once spring arrives I'll swap the head over and see how it goes, only going to cost time and a head gasket set. MT: I'm fairly sure my block hasn't been decked, so I'm assuming the pistons are below the top of the block. GT5R: Are you saying I need to change the cam as well, mine is only 270 duration, or just suggesting I go for a longer duration sometime in the future to get the full benefit of an increased CR?. Andy Link to comment Share on other sites More sharing options...
logicaluk Posted February 11, 2009 Share Posted February 11, 2009 just wanted to say that looks well nice dave, i look foward to reading how good it is. Dan Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 11, 2009 Author Share Posted February 11, 2009 I don't take any credit for the main work Dan, as it was done before by Gardius, I am just trying to sort the issues caused some communication break down? There are actually a few issues I haven't listed yet that are minor but still a detraction. I'll take credit for the details I'll post later on though. It's just a shame we can't pump up the compression to the desired level and make these new exhaust valves really "work". I think the exhaust valves will be an improvement, often overlooked and too much time spent on the inlet at the expense of the exhaust? What goes in, must go out! I think on my K-series I put a bit more effort into the exhausts?! Link to comment Share on other sites More sharing options...
logicaluk Posted February 11, 2009 Share Posted February 11, 2009 thats why i love this place, thanks dave if only sales men were as honest as engineers. Dan Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 12, 2009 Author Share Posted February 12, 2009 Rounded a bit, mainly to just remove any excess material right at the edge of the valve seat. However to my mind, gas has to go out the exhaust port, not in So a smooth edge to the valve may help, do they do reverse flow benching? Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 12, 2009 Author Share Posted February 12, 2009 opps...misfire. Easy enough to do this, a drill piece of wet and dry paper (400grade) and some lube. Link to comment Share on other sites More sharing options...
Mother Teresa Posted February 12, 2009 Share Posted February 12, 2009 8) Link to comment Share on other sites More sharing options...
gt5r Posted February 12, 2009 Share Posted February 12, 2009 As I said earlier in this thread, I was very interested in what the outcome would be, as the compression values on my 2.5L are lowish. Today I dug out the cylinder head that was fitted to my GT6 when it was 2L with dome top pistons. Andy Andy - is your GT6 2.5ltr ??? if so high compressions don't work - this thread has followed 2.0ltr - so quotes of 12.5:1 are only applicable to the short stroke units If so I found the TR5 profile cam with a bit more lift worked well on the 2.5 - limit comp ratio to 10.75:1 using normal pistons - you need to spend £££££££££££££ on pistons if you go more radical and don't expect it to last long Link to comment Share on other sites More sharing options...
AndyGT6 Posted February 12, 2009 Share Posted February 12, 2009 gt5r: My engine is 2.5L, I received my GT Tuning Manual yesterday ( Thank you Dave ), and bedtime reading last night was tuning the six cylinder, I realised then that the cylinder head on my work bench will not be going on this engine. I will however get my current head skimmed and plan long term for a 2L high compression engine. Andy Link to comment Share on other sites More sharing options...
Mother Teresa Posted February 12, 2009 Share Posted February 12, 2009 Spoke to Cometic today, the gasket may be £100. It would have to be made in the US and shipped over, 6-8 weeks. I'll email him the spec of the engine/bore size and CR etc and see what thickness they can go down to. I'm thinking that whilst there is potential for a thin gasket to offer some improvemnt: unless I go for super-skinny gasket, it wouldn't be worth the expense. Realistically, that money may be better placed put toward making a long term solution, rather than short term improvement. Anyone got a good bare old mk2 GT6 head going cheap.... ;D Link to comment Share on other sites More sharing options...
spitNL Posted February 12, 2009 Share Posted February 12, 2009 Spoke to Cometic today, the gasket may be £100. Anyone got a good bare old mk2 GT6 head going cheap.... ;D I was afraid the gasket might be expensive, but I didn't expect it to cost this much, shame. I'm sure everyone will keep their eyes open for a mk2 GT6 head. Frederick Link to comment Share on other sites More sharing options...
gt5r Posted February 12, 2009 Share Posted February 12, 2009 Spoke to Cometic today, the gasket may be ?100. It would have to be made in the US and shipped over, 6-8 weeks. I'll email him the spec of the engine/bore size and CR etc and see what thickness they can go down to. I'm thinking that whilst there is potential for a thin gasket to offer some improvemnt: unless I go for super-skinny gasket, it wouldn't be worth the expense. Realistically, that money may be better placed put toward making a long term solution, rather than short term improvement. Anyone got a good bare old mk2 GT6 head going cheap.... ;D You'd be better off spending £100 on some 5 star petrol It gets expensive with custom gaskets especially if you want to whip the head off between practice and race time - been there done that - quite honestly the power it will produce doesn't warrant it - put your money towards a set of 77mm pistons (which you can use a std gasket with );D ;D ;D ;D ;D ;D ;D Link to comment Share on other sites More sharing options...
JamesR Posted February 12, 2009 Share Posted February 12, 2009 http://www.rimmerbros.co.uk/bargains/spitfire.html Hmm. KD engine £75 plus carting it about, just ask for the head maybe? Or buy and get built keep the current bun. Or am I'm barking up the wrong tree with this engine. (Hijack) Actually are any of those 4 cylinders engines any good on there? small crank, useful block. Link to comment Share on other sites More sharing options...
gt5r Posted February 12, 2009 Share Posted February 12, 2009 I received my GT Tuning Manual yesterday Here Andy - does GT's new manual cover 20v Volvo heads :'( :'( :'( :'( :'( :'( :'( :'( :'( Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 12, 2009 Author Share Posted February 12, 2009 Here is the problem, check out how badly the unleaded seat inserts line up...obviously as bad before on the old valves! Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 12, 2009 Author Share Posted February 12, 2009 Link to comment Share on other sites More sharing options...
DaveNotSoSideways Posted February 12, 2009 Author Share Posted February 12, 2009 Be gone! Steady hands needed, best to stick to two double espresso's in the morning. Just need to go over then with a finer grade of band once all 6 are "roughly" done, as these 2 are. Link to comment Share on other sites More sharing options...
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