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Old 23-03-09
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Head performance modification.

I have to redo the head on my S2 Spider.
Checking for required parts,I had the idea of fitting larger intake valves,racing cam chain and kent lifters etc.
I want to keep the standard cams..
Is that a silly idea?
Do I need to put bigger jets in the Weber carbs?
I am already running a semi freeflow exhaust.
Will their be a significant improvement in torque and top end?

The engine lasted for 15 years,until I decided to mess with it

By changing the specs in the head,does it not have an adverse effect on the engine,shortning it's lifespan?(metal fatigue etc.)
I am not planning to use my car on the track,only on the road.
I would appreciate your opinion
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Old 24-03-09
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Re: Head performance modification.

I think with head work there is no single thing which makes a humongous difference, but lots of little things which add up. Have a chat to any of the specialists and they will probably give you good advice. And I'm sure there will be a few more expert than I along soon here.

But my two pence worth is that if you are having new valve seats & valves there's an improved valve seat angle which gets you about 3bhp free (well, free if you're replacing valves & seats anyway).

A bit of head work and gas flowing will get you another 5hp or so I'd have thought. So with your freeflow exhaust you are probably getting an extra 12-15hp with those mods. I'm not sure bigger intake valves by themselves will help, hopefuly someone else can advise.

A good pair of cams will give a worthwhile boost, but don't go too crazy or it will be all top end (not a cheap mod this). Traditionally this would be one of the easier ways to get more power. And I am probably thinking you won't get your money's worth out of the kent valve lifters & springs without a better cam. So maybe it's worth considering? Why did you want to avoid cam change (cost? Yes they are v expensive).

I found a new tubular 4:2:1 exhaust manifold freed up the engine letting it rev nicely and giving a bit of extra top end. But others say that the standard manifold is pretty good and doesn't need much upgrading. Maybe my original one was duff.

For the classic car mileage you will cover I don't think there will be a noticeable effect on life. They are strong engines which can reasonably reliably be tuned to 150hp, and more if you are prepared to trade reliability.

You shouldn't have to rejet the carbs, though a rolling road tune will do that for you and get the most out of your other mods.

The bible on head work for nord engines is the Jim Kartalamakis book 'Alfa Romeo DOHC High Performance Manual'. All above my head but it gives loads of advice on head work and what mods give what effects. If you are getting a local shop or engine builder to do work then a copy of this with the relevant passages highlighted will be an excellent 'to-do' list. If you are doing work yourself the same applies.
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Old 24-03-09
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Re: Head performance modification.

If you don't want to part with too much cash, follow Pat Braden's advice and alter the cam timing via the verniers. (It's in his book, I won't pretend I am able to recite it here). As Harry says it doesn't seem worth making the mods you suggest with standard cams. Just make sure everything goes back together well - check the manifolds and gaskets match the ports in the head closely. If you are skimming the head you will get a slight compression increase anyway.
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Old 24-03-09
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Re: Head performance modification.

Standard valves are ok until you get into the upper reaches so I wouldn't bother with oversizes ones. Or the Kent springs unless you're going for high lift cams.

Porting works but is very labour intensive and bear in mind that unless you do it right you could end up with LESS power than you started with.

Keep it stock for now and fit some better cams (C&B do some nice ones) if you want a bit more oomph.
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Old 24-03-09
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Re: Head performance modification.

If you are skimming the head, make sure there is enough to skim off!
You cant skim these heads for ever, eventually they reach a minimum height and that is that, no room for further reworking....nobody really wants a head under say 111-112 mm thick.
Check liner protrusion too, if it isn't to spec you will have to remove these and fit new O rings under the liners.
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Old 24-03-09
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Re: Head performance modification.

Thank you for the advice people,it is much appreciated.
I think I should buy some literature before diving in,as advised.
What worries me about a performance cam is the rough idling,couple that with a relatively worn carbs and linkages you have a party..
Am I wrong with saying this?
I don't think I want to do this job myself.When last have you removed the head off a 105?Not an easy job when the engine was last overhauled 15 years ago.Rather make it the mechanics problem
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Old 24-03-09
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Re: Head performance modification.

Or...... fit a twinspark engine from a 75. I am advised this is now a cheaper option than a full nord engine rebuild. An easy 150hp, no carbs to worry about, more torque at the bottom end. Better breathing head as standard. Non original of course and you'll lose the wonderful sound of those carbs sucking and gurgling. And you may not have an experienced specialist local.

I know you started out with the idea of some low cost head tweaks while doing a little top end rebuild, but God, I just love spending other peoples money with suggestions like this.
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Old 24-03-09
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Re: Head performance modification.

I looked some time ago at a GTV with a twinspark injection engine.Not for me thanks,the noise from the carbs are a must for me.
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Old 25-03-09
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Re: Head performance modification.

Originally Posted by garry-graig View Post
What worries me about a performance cam is the rough idling
Unless you go for some manic race cams, you'll be fine. I've got 12mm cams in mine and I use it mainly on the road and it's fine pootling to the shops, sat in traffic etc.
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Old 25-03-09
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Re: Head performance modification.

Rick's right, the whole "lumpy idle" thing is a throwback to the 60's and 70's when people used to throw a full race cam in their mini then wonder where the idle went.

Cam design has come a long way since and it's quite possible to get decent gains without the old compromise of losing the bottom end completely.

The Alfa Nord engine has bags of low end power anyway so you could afford to lose a bit if need be.

As for the TS conversion, I don't see how it'd be cheaper than a Nord rebuild. Assuming that you'd rebuild the TS anyway, all the gaskets, pistons/liners and bearing wills cost you about the same and you have to add the cost (say £200) of a scrap 75. You wouldn't really just throw an engine from a banger in without rebuilding it would you?

OK, so you end up with 150 bhp not 130 so it would be cheaper overall if that was your end goal but if you just want a rebuilt engine you're probably better rebuilding the one you already own.

A head skim on your engine is worth it, I got the wife's Punto one done for £25 cash so it's practically free horsepower, even if only a couple.


Jim Spackman
Alfaholics.com

Alfa 75 TS LE Veloce
Fiat 125 Abnormale
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