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  1. #1
    1000+ Posts Luca's Avatar
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    Default 205 GTI head

    How do I calculate how much I can take off my head to bring the comp up?

    Cam has been modified along with polish & port job, there's also some dekking been done but how much more can i take off before the valves hit the pistons????

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    Thanks all

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    1000+ Posts PeterT's Avatar
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    You can take up to 2mm off safely. You'll need to compare yours to a std. head to work out how much more to take.

    Don't forget you'll need to advance the cam to make up for the decking.

    You'll also need to modify the top engine mount.

    '92 205 Mi16
    '90 Mi16x4

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    Fellow Frogger! Cubits's Avatar
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    What's the gain in compression from 2mm?
    1987 205 GTI - Graphite Grey - 206k km's
    1988 MR2 Supercharger - Mica Blue - 114k km's

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    Quote Originally Posted by Cubits
    What's the gain in compression from 2mm?
    around 10:1

    '92 205 Mi16
    '90 Mi16x4

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    Gee, that's not very high. I guess some S1 pistons will help that though.
    1987 205 GTI - Graphite Grey - 206k km's
    1988 MR2 Supercharger - Mica Blue - 114k km's

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    sorry, I thought you were talking about a series 1. A 2mm cut off a S3 head will give about 11:1.

    '92 205 Mi16
    '90 Mi16x4

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    Quote Originally Posted by Cubits
    Gee, that's not very high. I guess some S1 pistons will help that though.
    Your'e joking, what fuel do you plan on using?
    My 9.6 to 1 130 hp car pings on light throttle using Optimax.
    Don't do it unless you plan to fit a knock sensor.
    Graham

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    Well i wasn't exactly going to wade in, stick the compression up to 15 and see what happens...

    But i know the compression should be raised to handle my goal power output of 150hp. I think that, along with a new ecu, bigger cam, and a ported head, should see it on regular 98.

    Of course, i'll have to experiment with the engine a bit first. :p

    BTW, is that 98E10 fuel more resistant to pinging because of the water content (than regular 98)?
    1987 205 GTI - Graphite Grey - 206k km's
    1988 MR2 Supercharger - Mica Blue - 114k km's

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    Quote Originally Posted by Cubits
    Well i wasn't exactly going to wade in, stick the compression up to 15 and see what happens...

    But i know the compression should be raised to handle my goal power output of 150hp. I think that, along with a new ecu, bigger cam, and a ported head, should see it on regular 98.

    Of course, i'll have to experiment with the engine a bit first. :p

    BTW, is that 98E10 fuel more resistant to pinging because of the water content (than regular 98)?
    I have been trying to find a good camshaft and after a search in the UK and talking to experts here I have come up with nothing, except cautions about cams that haven't worked out!
    The consensus seems to be you need to change to the Mi16 engine, the 8 valve as delivered is just about as good as you will get out of that design.
    I have decided to just freshen up a 90kw engine but run lower gearing.
    If anyone has any comments about worthwhile mods to 8 valve engines I would be only too happy to retract the above statement!
    The water content in E10 would only be present if the fuel had been sitting for a while?
    Graham

  10. #10
    1000+ Posts Luca's Avatar
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    Quote Originally Posted by PeterT
    You can take up to 2mm off safely. You'll need to compare yours to a std. head to work out how much more to take.

    Don't forget you'll need to advance the cam to make up for the decking.

    You'll also need to modify the top engine mount.
    At what stage is the advance done? Who takes care of this? How much advance is req'd?

    What mod is req'd to the engine mount and why?

    Thanks mate.

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    Fellow Frogger! Cubits's Avatar
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    There have been a couple of 180hp 8v's on this site, so i think there are some gains to be had over 130hp without sacrificing liveability. Of course, those monsters have ITB's, big valves, and run on rocket-fuel.

    I've seen 150hp pop up as a reasonable target. I think PeterT has an 8v cam profile that would yield reasonable gains.

    205 8v with quad TBs and Haltech

    Edit: Wait, you posted in that thread, and you say there aren't any decent gains to be had on the 8v? Going from 90Kw at the flywheel to over 100Kw (when it's sorted) at the wheels while staying on 98RON fuel is a pretty good gain in my books!!
    Last edited by Cubits; 16th December 2005 at 11:47 AM.
    1987 205 GTI - Graphite Grey - 206k km's
    1988 MR2 Supercharger - Mica Blue - 114k km's

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    Quote Originally Posted by Luca
    At what stage is the advance done? Who takes care of this? How much advance is req'd?

    What mod is req'd to the engine mount and why?

    Thanks mate.
    When fitting the timing belt, just enough to restore the correct valve timing.
    The timing changes due to the shorter distance between the timing gear on the crank and the one on the head. You will need to modify your timing pully or fit an adjustable one.
    The head will be 2mm thinner, therefore the engine will sit at an angle, I imagine you would have to machine the same 2mm off the engine mount somewhere.
    Graham

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    Engine Mount:
    The RH side mount saddles the head and the block. As two of the holes are now 2mm closer to each other, the bottom hole (which goes into the block) needs to be elongated.

    Ignition Advance:
    The 8V pings in the 2000-3000 range because of too much low down advance. Retarding the distributor is the not the fix, as this will remove total timing as well. The correct fix is to fit stiffer springs in the dizzy, so the advance comes in at a slower rate, but the maximum advance of 30-31 deg. is retained. The better alternative is mapped ignition.

    Cam:
    Cam design is limited by the compression ratio and the valve springs. The cam I use has 238 deg. @ 0.050" and 0.429" total lift. It needs at least 10:1 to work, but runs A LOT better with 10.5:1. The limit of the std. springs is 0.450" lift. The Group A grind is 251 deg. @ 0.050" and 0.460", so therefore beyond the safe limit of the std. springs. It does work very well however, but needs 11:1 min. CR. My advice here is to stay within the limits of the std. valve springs unless you want to spend lots of money. This point makes Mi16's look very attractive unless your class of racing demands the std. head.

    Valve Sizes:
    The biggest gains are made from 3 angle seats and porting, not the valve diameter. I wouldn't spend money on big valves again and have the flow charts to prove it. Obviously firms that make money out of big valve conversions will argue otherwise. The reality is however, their large gains are made from the 3 angle seats! I'd rather put the money towards an Mi16 engine.


    Parry's engine on 45mm TB's is a excellent example of all of the above. It makes the same hp at the wheels as an Mi16 (with 10.8:1 and Stage I cam). It doesn't ping and makes HEAPS of torque.

    '92 205 Mi16
    '90 Mi16x4

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    Quote Originally Posted by PeterT
    Engine Mount:
    The RH side mount saddles the head and the block. As two of the holes are now 2mm closer to each other, the bottom hole (which goes into the block) needs to be elongated.

    Ignition Advance:
    The 8V pings in the 2000-3000 range because of too much low down advance. Retarding the distributor is the not the fix, as this will remove total timing as well. The correct fix is to fit stiffer springs in the dizzy, so the advance comes in at a slower rate, but the maximum advance of 30-31 deg. is retained. The better alternative is mapped ignition.

    Cam:
    Cam design is limited by the compression ratio and the valve springs. The cam I use has 238 deg. @ 0.050" and 0.429" total lift. It needs at least 10:1 to work, but runs A LOT better with 10.5:1. The limit of the std. springs is 0.450" lift. The Group A grind is 251 deg. @ 0.050" and 0.460", so therefore beyond the safe limit of the std. springs. It does work very well however, but needs 11:1 min. CR. My advice here is to stay within the limits of the std. valve springs unless you want to spend lots of money. This point makes Mi16's look very attractive unless your class of racing demands the std. head.

    Valve Sizes:
    The biggest gains are made from 3 angle seats and porting, not the valve diameter. I wouldn't spend money on big valves again and have the flow charts to prove it. Obviously firms that make money out of big valve conversions will argue otherwise. The reality is however, their large gains are made from the 3 angle seats! I'd rather put the money towards an Mi16 engine.


    Parry's engine on 45mm TB's is a excellent example of all of the above. It makes the same hp at the wheels as an Mi16 (with 10.8:1 and Stage I cam). It doesn't ping and makes HEAPS of torque.

    Thanks for correcting my statement regarding the engine mount Peter
    On reflection 2 mm isn't a lot of change to the engine location!
    Reading your reply I can see why a lot of people have got poor results from the 8 valve, everything must be spot on and experience (no doubt painful) is the key to everything.
    Going back to the start again, do you think an otherwise standard engine would cope with 10.5 to 1 if the advance curve was changed?
    Graham

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    Quote Originally Posted by GRAHAM WALLIS
    Going back to the start again, do you think an otherwise standard engine would cope with 10.5 to 1 if the advance curve was changed?
    Graham
    absolutely. I can tell you what numbers to aim for if you like.

    '92 205 Mi16
    '90 Mi16x4

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    1000+ Posts Warwick's Avatar
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    Graham, it would be a waste of effort pulling the head off and decking it 2mm and whacking it back on IMHO. Spend a few hundred and make the cylinder head a better shape. I have no fancy equipment to judge, but the standard series One head looks as flowed as a garbage bin lid. Certainly by itself higher comp can only make the car nicer.
    The cam I had ground was brilliant. It was so torquey, yet great at high revs. I forget all the numbers now. Did it maybe go from 0.4" to .49" lift or somewhat? Plenty of lift anyway. Combustion chambers were beautifully reshaped to a figure 8 style of design, with no dead spots behind valves.
    The cam grind was called a 162B grind, and came from the racing Volvo Turbos of the 80's. Wade's will sort it out for you. I got bigger inlet valves in mine. Like Peter said, if the head is shaved it is closer to the crank, so it needs to be correctly timed again by a different cam sprocket.
    I lost interest in mine before I bothered doing the dizzy springs. Even then it went brilliantly, though it pinged a bit at times.
    The things that go together to produce the power are extra fuel, extra comp, extra cam duration and lift and shaping everything nicely and making sure the holes are big enough for the air to get in and out without fuss.
    Don't fart arse around buying Piper cams or name brand things like that. Sure they are probably very good, but just aren't good value.
    Mine ran at 10.6 or 10.8:1 from memory.
    Attached Thumbnails Attached Thumbnails 205 GTI head-205beforeafter2.jpg  
    "Now my dream lies shattered like the shards of a broken dream"

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    Quote Originally Posted by Warwick
    Graham, it would be a waste of effort pulling the head off and decking it 2mm and whacking it back on IMHO. Spend a few hundred and make the cylinder head a better shape. I have no fancy equipment to judge, but the standard series One head looks as flowed as a garbage bin lid. Certainly by itself higher comp can only make the car nicer.
    The cam I had ground was brilliant. It was so torquey, yet great at high revs. I forget all the numbers now. Did it maybe go from 0.4" to .49" lift or somewhat? Plenty of lift anyway. Combustion chambers were beautifully reshaped to a figure 8 style of design, with no dead spots behind valves.
    The cam grind was called a 162B grind, and came from the racing Volvo Turbos of the 80's. Wade's will sort it out for you. I got bigger inlet valves in mine. Like Peter said, if the head is shaved it is closer to the crank, so it needs to be correctly timed again by a different cam sprocket.
    I lost interest in mine before I bothered doing the dizzy springs. Even then it went brilliantly, though it pinged a bit at times.
    The things that go together to produce the power are extra fuel, extra comp, extra cam duration and lift and shaping everything nicely and making sure the holes are big enough for the air to get in and out without fuss.
    Don't fart arse around buying Piper cams or name brand things like that. Sure they are probably very good, but just aren't good value.
    Mine ran at 10.6 or 10.8:1 from memory.

    Thanks Warwick, did you have to change the valve springs? Did you change the ECU, I have a Megasquirt on the 130hp car and am building another for the project car, looks like I better get the ignition software as well!
    I won't be using the series 1 head, I have a 90 kw engine from a Citroen BX TZi to play with, this has the flywheel with timing teeth which will be handy. I'm pulling the head off the series 1 tommorrow, should be interesting to have a look at the differences.
    I'd like to drive a modified 205, I've only driven standard 75kw cars and my 130hp car plus Casnell's car which has a performance problem at present.
    Graham

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    Here's the flow chart showing the difference between 43/34.5 and 39.5/33mm valves. Notice how the intake port goes that at 0.450" anyway. The best gain from all of this was the exhaust flow, which increased to 75-80% of the intake. These graphs are before porting. The numbers below are after porting.



    Code:
    	in	ex
    0.1	60	54
    0.15	89	77
    0.2	111	95
    0.25	132	107
    0.3	148	117
    0.35	157	118
    0.4	164	119
    0.45	163	119
    Attached Thumbnails Attached Thumbnails 205 GTI head-8v_flow_2.jpg  

    '92 205 Mi16
    '90 Mi16x4

  19. #19
    1000+ Posts Warwick's Avatar
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    Yup, the springs were changed. If not, with greater lift you can get coil bind and you wouldn't wish that on the local Transvestite!
    ECU was fine. Was for me for 121 BHP at the wheels anyway.
    The 90 kw head is just shallower and with slightly gentler angles around the place.
    "Now my dream lies shattered like the shards of a broken dream"

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    Here's a picture of my chambers, but as I said, why bother?

    205 GTi Big Valve Head & Cam

    '92 205 Mi16
    '90 Mi16x4

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    Quote Originally Posted by GRAHAM WALLIS
    I'd like to drive a modified 205, I've only driven standard 75kw cars and my 130hp car plus Casnell's car which has a performance problem at present.
    Graham
    It sure does, not a lot of torque or top-end, what would people suggest-a mega-squirt with ignition or a Haltech? Or an adjustable cam-pulley?With the 1.6 head I thought it was ok without doing the cam-timing? Chris

    Seems to be hard to get timing right without pinging, even on 100 fuel...
    Last edited by casnell; 17th December 2005 at 09:57 AM.
    205gti

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    Did you check the cam timing Chris? You really need to verify what inlet lift the cam has at TDC before proceeding further.

    '92 205 Mi16
    '90 Mi16x4

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    Quote Originally Posted by PeterT
    Did you check the cam timing Chris? You really need to verify what inlet lift the cam has at TDC before proceeding further.
    What should it be with the 130 hp cam on the 1.6 head?
    Thanks, Chris
    205gti

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    Quote Originally Posted by GRAHAM WALLIS
    Thanks Warwick, did you have to change the valve springs? Did you change the ECU, I have a Megasquirt on the 130hp car and am building another for the project car, looks like I better get the ignition software as well!
    I won't be using the series 1 head, I have a 90 kw engine from a Citroen BX TZi to play with, this has the flywheel with timing teeth which will be handy. I'm pulling the head off the series 1 tommorrow, should be interesting to have a look at the differences.
    I'd like to drive a modified 205, I've only driven standard 75kw cars and my 130hp car plus Casnell's car which has a performance problem at present.
    Graham
    Well the Series 1 turned to have a series three head!!
    Big valves anyway, is there a way of telling which head it is by part number or perhaps measuring combustion chamber depth.
    Peter, can let us know the inlet valve lifts of the 75kw and 90kw engines?
    Thanks, Graham

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    1000+ Posts PeterT's Avatar
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    Quote Originally Posted by casnell
    What should it be with the 130 hp cam on the 1.6 head?
    Thanks, Chris
    I haven't set up an engine with that cam, but I would expect it to be in the range of 0.060-0.070" at TDC. I'd aim for something around 0.070". That will definitely err on the advanced side. The 75kW cam has 0.038" at TDC, so it must be more than that, and less than the 0.092" for the Stage II cam I use.

    The type of head doesn't make any difference. As pointed out by others however, milling an 8V head will retard the cam timing, giving a smaller figure at TDC. So thus it's important to check. If your engine isn't reving past 5000 it may be retarded by a whole tooth.
    Last edited by PeterT; 18th December 2005 at 03:53 PM.

    '92 205 Mi16
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