83 replies to this topic

[Calver ST]

Just to clarify from liirge's comment - the standard 998 I ran on the rollers before the modded one was a late high compression A+ one. KC

[liirge]

I would still have thought that adding the 940 head would add compression, as i have always been led to believe they have a smaller combustion chamber than any head of the Small Bore series.

[lrostoke]

According to another article by KC the 940 as a lot smaller combustion chamber

940 21.4cc

295 28.3cc

typical 998 A+ 25.5cc

[Calver ST]

They do liirge - typically the small bore heads are 23.5 to 24.2cc (the later A+ ones vary considerably). Most 940s are around 21.4cc. Modded as I did in that project build I think the chamber was nearer 22cc. I'd have to go back through the article/notes top double check. But yes, as such there is a compression increase - but not to the point that makes a HUGE difference in performance. Though likely over one of the older/earlier very low compression engines as you pinted out. I'm not sure I'd want to run those old 8.5CR pistons at 10:1 CR though..... KC

[liirge]

If you modded the head to get a 22cc chamber, then you have modified the combustion chamber shape, so surely its not a real fair test is it.

[Nightrain]

You can't help but laugh

it looks like somebody needs to use the spelling checker more often. Either that or a good dictionary.

engines as you pinted out.

[benb12]

It's not really funny, I'm not interested in petty spelling mistakes and I doubt the OP is either - can we drop it and get back to engines?

[Nightrain]

Yep good point well put............

[Calver ST]

Liirge - the only mods were to give the exhaust valve clearance to the block. Many believe you absolutely have to pocket the block to fit a 940 head. The project was done to show that it was not necessary yet still get good performance using a sports type cam. The only mods were to recess the exhaust valve far enough in to the chamber to achieve that goal. I also flow tested the heads before and after to show that recessing the valves didn't hurt flow. Otherwise the chambers were standard. You can just about get a 940 head to fit with no mods providing a standard-lift type cam is used with standard rockers. Also - 940 heads are relatively abundant in comparison to 295 heads, and are way cheaper than decently modified 998 heads at around £450 a go. KC

[liirge]

They do liirge - typically the small bore heads are 23.5 to 24.2cc (the later A+ ones vary considerably). Most 940s are around 21.4cc. Modded as I did in that project build I think the chamber was nearer 22cc. I'd have to go back through the article/notes top double check. But yes, as such there is a compression increase - but not to the point that makes a HUGE difference in performance. Though likely over one of the older/earlier very low compression engines as you pinted out. I'm not sure I'd want to run those old 8.5CR pistons at 10:1 CR though..... KC

you state modified, and then state a slightly higher than usual Chamber size, this would led one to believe that slight chamber modifications were made, am i right here?

Liirge - the only mods were to give the exhaust valve clearance to the block. Many believe you absolutely have to pocket the block to fit a 940 head. The project was done to show that it was not necessary yet still get good performance using a sports type cam. The only mods were to recess the exhaust valve far enough in to the chamber to achieve that goal. I also flow tested the heads before and after to show that recessing the valves didn't hurt flow. Otherwise the chambers were standard. You can just about get a 940 head to fit with no mods providing a standard-lift type cam is used with standard rockers. Also - 940 heads are relatively abundant in comparison to 295 heads, and are way cheaper than decently modified 998 heads at around £450 a go. KC

A Decent 998 Head is a 295, that you can pickup for just under £100. To be honest to get the full potential from a 940 head on a small bore you need to compliment it with a decent cam, otherwise in my opinion it's not really that effective. On top of that no one seems to state the machining costs of recessing Valves, i bet its equal to having the block pocketed.

[Calver ST]

The extra capacity came from recessing the valves and thinning the valve seat margins down a little. Otherwise the combustion chambers and rest of head was untouched, so no - you are not correct in that way. This would be a heap easier if you could see the article first. Otherwise we are likely to be re-producing the whole thing that was covered across two magazine issues here. The cost of recessing the valves is nowhere near as costly as pocketing a block. Not even close.

On the 295 head front - if you are getting them in good working order that does not need any re-conditioning for £100 - that's pretty good. You should buy 'em up and store them/sell 'em on. All the ones I've seen or had through my hands in the past decade or more have required full re-furb, which sensibly includes converting for lead free fuel. Just a standard lead free converted re-furbed head is around £150...

As for your opinion - it is just that. And my opinion is just that, based on all the testing I've done over some 30 years. I am not trying to be offensive, but I do not know who you are or your experience as I have not been on this forum for a very long time - just offering up my shot on the deal. KC

[liirge]

The extra capacity came from recessing the valves and thinning the valve seat margins down a little. Otherwise the combustion chambers and rest of head was untouched, so no - you are not correct in that way. This would be a heap easier if you could see the article first. Otherwise we are likely to be re-producing the whole thing that was covered across two magazine issues here. The cost of recessing the valves is nowhere near as costly as pocketing a block. Not even close.

On the 295 head front - if you are getting them in good working order that does not need any re-conditioning for £100 - that's pretty good. You should buy 'em up and store them/sell 'em on. All the ones I've seen or had through my hands in the past decade or more have required full re-furb, which sensibly includes converting for lead free fuel. Just a standard lead free converted re-furbed head is around £150...

As for your opinion - it is just that. And my opinion is just that, based on all the testing I've done over some 30 years. I am not trying to be offensive, but I do not know who you are or your experience as I have not been on this forum for a very long time - just offering up my shot on the deal. KC

No need to start making it personal...may i remind you on a regular basis your "30 years of experience" is called into question especially your pontifications based on these tests you have done, but lets not turn this into a cat fight.

On the unleaded deal there aren't that many 940 Heads that are unleaded, you say it, as if it was nearly all of them are unleaded...there not.
And once again...no one who has done the valve recession bodge, can quote me a price.
And David Vizard seems to agree with me on where the torque comes in on a 295...

Edited by liirge, 25 September 2009 - 06:26 PM.

[Calver ST]

What is it with everybody copying and pasting previous posts in to their replies????

Liirge - like I said - I was not meaning to be offensive, blah blah blah (read relevant post). So obviously I was not trying to get personal... As for my '30 years of experience'... seems to get called in to question with a similar flavour to a similar few posters. Particularly as I am not around often to 'defend' myself. Which becomes very tiresome when folk take a great deal of what is said out of context. And how well do you know David Vizard to say that he agrees with YOU? I know David very well. And he is the first to admit that NOW what is written in TBASE is very ancient indeed...

Not that many 940 heads unleaded? For the past, what, decade?, I have been getting deliveries of 30 to 50 head castings some 4 times a year for modification for various customers. I would say that in the early years of that 20 to 25 % of those were already unleaded. Latterly that is more like 55 to 60%. That is fairly significant in my book.

Valve recession 'BODGE'. Have you read the article, seen the pictures? What constitutes it as a bodge? Have you really tried that hard to get a quote? Taking the article along to an engineering comapny to show them what is required since it is not something they would normally do in the way of a head re-con? You think I do not know how long it takes (and therefore costs) to do the valve recessing/block pocketing - bearing in mind it is what I do for a living?

You are starting to sound a lot like my other best mate/confident/stalker Tony Smith, Sorry - Nightrain.... it's not a wonder the good and truly knowledgeable stay away from forums these days...

Edited by Calver ST, 25 September 2009 - 11:27 PM.

[minispecial]

I may be missing the point here. Is it you want more power out of the 1098 engine or is it you just want more power in the car.

If it you just want more power in the car then why not just drop in a 1275 or if you can get hold of one a 1275 turbo engine out of a metro. To get a 1275 engine for £200-300 should be easy enough to do and may be possible to get a turbo lump for that. This way just seems a lot less hassle to me.

fair comment mate im also looking into that. All good suggestions. cheers

[valve bounce]

i will be using a 295 head on mine because the head cost me nothing and already have it in the shed, and the other reasons are
1. easier to fit (no need to resess valves, pocket blocks etc etc)
2. from what i have read it will produce the same power on a low reving 1100

thats my opinion