I have been offered a "big valve race" head for my 1600 HF.
I have not got any details as yet, though I believe it has been ported and skimmed to raise the compression ratio, as well as having bigger valves fitted.
I realise this is a a very vague question, but I'll ask anyway. My car currently has a standard head, fitted with Omicron "rally" cams and runs with the std 42 mm Solex carbs and a modified exhaust system (again Omicron supplied). The rallies I use it in have autotests in them which require reasonable low down torque (2000 - 3000 rpm), which my current set up delivers.
I read in one of Paul's articles on his blog, that he felt that a bit of head porting helped the torque of an engine, and from my own experience an increase in compression is also beneficial. However, I realise that the intake gas velocity is also important.
So the $64,000 question is what effect does the team think that fotting this modified head would have when running the std carbs ? Will I lose too much low end torque?
The problem is that I also have a set of 45 Webers on a Gp4 manifold that I have run when hillclimbing and I really think that this head will help me squeeze a few extra horses out in this configuration, but the main interest is in the rallying
Big valve head
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tim
Re: Big valve head
Michael
I have a big inlet valve head ported and skimmed by Paul and am running std 42 mm carbs and std cams but gp4 evolution exhaust manifold which seem fine - plenty of tourque. I have some 45 dellortos to try some time (and some 1016 holbay copy cams) and take the view if they are good for the track I will swop around for different uses - like you I am more interested in driveability for rallying mostly.
Tim
I have a big inlet valve head ported and skimmed by Paul and am running std 42 mm carbs and std cams but gp4 evolution exhaust manifold which seem fine - plenty of tourque. I have some 45 dellortos to try some time (and some 1016 holbay copy cams) and take the view if they are good for the track I will swop around for different uses - like you I am more interested in driveability for rallying mostly.
Tim
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Shaun Pond
Re: Big valve head
I don't have anything meaningful to contribute to the Big Valve head discussion, but I did come across a short video of you in your car on YouTube, at the "Irish Classic Retro 2007":
http://www.youtube.com/watch?v=FTq1SJnQ ... ed&search=
Looks like it was fun!
Regards
http://www.youtube.com/watch?v=FTq1SJnQ ... ed&search=
Looks like it was fun!
Regards
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Michael Beattie
Re: Big valve head
Cheers Shaun
Yes, Irish Classic was fun, was doing quite well until we broke a rear spring on the night section.
Those are the sort of tests we do, plus some others that have no reversing, but would have handbrake turns round pylons at intervals to slow down the average speed. Hence the need for some low range torque !!
Yes, Irish Classic was fun, was doing quite well until we broke a rear spring on the night section.
Those are the sort of tests we do, plus some others that have no reversing, but would have handbrake turns round pylons at intervals to slow down the average speed. Hence the need for some low range torque !!
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P. de R. Leclercq
Re: Big valve head
"Big valve" is a term that can practically only be used in a relative sense when talking about Fulvias - especially 1600s.
The standard valves are 38mm and 34mm diameter. The biggest inlet valve that can be fitted without a totally radical re-think is 39.5mm. LArge exhaust valves can be fitted (I have 37mm in my engine) but it's debatable whether there would be any benefit. The problem is that the ports cannot be opened up to suit - on the exhaust side. ON the inlet side it is possible to open them a bit. bear in mind that for inlet, the relationship between port diameter and and valve diameter is important. I would guess that larger inlets with only slightly larger ports would provide a torque improvement whilst I know that any work on the exhaust side does improve torque as the standard valve throat is very restrictive.
Paul
The standard valves are 38mm and 34mm diameter. The biggest inlet valve that can be fitted without a totally radical re-think is 39.5mm. LArge exhaust valves can be fitted (I have 37mm in my engine) but it's debatable whether there would be any benefit. The problem is that the ports cannot be opened up to suit - on the exhaust side. ON the inlet side it is possible to open them a bit. bear in mind that for inlet, the relationship between port diameter and and valve diameter is important. I would guess that larger inlets with only slightly larger ports would provide a torque improvement whilst I know that any work on the exhaust side does improve torque as the standard valve throat is very restrictive.
Paul
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Michael Beattie
Re: Big valve head
Thanks Paul, sound advise as ever.
I haven't been able to actually talk to the guy who has it as yet, so as yet what exactly big valve means has to be determined.
I'm using a slightly modified cams, seems to have about 0.5 mm extra lobe height and timed at 112 degrees. So I don't think the valve lift varies too much from std. Lukas mentioned the possible need for valve cut outs on the pistons, wouuld 39.5 mm inlets need these?
I haven't been able to actually talk to the guy who has it as yet, so as yet what exactly big valve means has to be determined.
I'm using a slightly modified cams, seems to have about 0.5 mm extra lobe height and timed at 112 degrees. So I don't think the valve lift varies too much from std. Lukas mentioned the possible need for valve cut outs on the pistons, wouuld 39.5 mm inlets need these?
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P. de R. Leclercq
Re: Big valve head
Hello.
Yes; I have never had a depth problem - the problem is width of the cut-out when using larger valves.
Barry Waterhouse invented a simple tool to do this. You get a suitably-sized scrap valve, and with an angle grinder turn the head into a cutter, Insert the valve into the guide, bolt the head with a couple of dowel bolts, apply a battery drill, and voila! a perfect cut-out in the right place.
I know I owe you all a picture of the special piston ring compressor - I'll try to do this tomorrow and at the same time I'll post a snap of the cutter tool. Watch the blog!
Paul
Yes; I have never had a depth problem - the problem is width of the cut-out when using larger valves.
Barry Waterhouse invented a simple tool to do this. You get a suitably-sized scrap valve, and with an angle grinder turn the head into a cutter, Insert the valve into the guide, bolt the head with a couple of dowel bolts, apply a battery drill, and voila! a perfect cut-out in the right place.
I know I owe you all a picture of the special piston ring compressor - I'll try to do this tomorrow and at the same time I'll post a snap of the cutter tool. Watch the blog!
Paul