Alright guys/gals,

I'm gonna be re-building my ABD bottom end soon as I'm going to be doing a full balance and lightening on the rotating parts...

I'm also going to be raising the compression ratio. Some of you know i've got all the tools, but i've never done it before so I'm just wanting some more information on the matter.

The standard C/R of an ABD is 8.5/1 (if i remember correctly), but I'm hoping to get it up to around 10.5/1. But it all depends on the lift from my 268* "Newman" camshaft as obviously i run the risk of collision between the pistons and the valves on the exhaust stroke.

Now, my choices are fit a different set of pistons, but 3F components don't fit, and any other will leave me with the same comp ratio...

Another way is to deck the block, but this will require the pistons decking to accommodate it, this sounds like the best option to me?

Has anyone got any more information?

Cheers,

Edited 29 December, 201114 yr by MaxMax

Use the thinner steel head gasket and deck / pocket the pistons accordingly. I have the numbers somewhere. I want to do this sometime and was also going to deck the head to unshroud the valve seats. This will lower the valves by a couple of mm and also require a vernier pulley to correct.

I want to do this sometime and was also going to deck the head to unshroud the valve seats.

Personally I think the best way to go would be totally in the other direction.

Do you have a copy of four stroke performance tuning? Read the section on Heron design combustion chamber.

Basically he says it's rubbish and the best way to get performance is to sink the valves 1.5mm into the head.

I've though for a while that the AEE head with its small chambers may flow better than the flat head 8V design. I've never flow tested one, but maybe someone has some numbers.

I don't know the chamber volume, but a relatively small chamber volume would be okay with the 1.0 and 1.3 engines as they're only small displacement.

ABD is 9.5:1. With this knowledge, is it still worth the effort for you to go to 10.5:1? Maybe just a generous skim of the head?

ABD is 9.5:1. With this knowledge, is it still worth the effort for you to go to 10.5:1? Maybe just a generous skim of the head?

As always, thanks for your hearty reply's guys. Probably the 3 people i was hoping to get a reply from.

@Chris - Are you sure thats the correct compression ratio? I've read that its only a moderate 8.5/1 or somewhere there abouts...

If that is the case i may have a re-think, but whilst its dissassembled, i may aswell improve the engines efficiency in every way possible.

I'll probably end up working the C/R out myself, it seems the most reliable way.

Use the thinner steel head gasket and deck / pocket the pistons accordingly. I have the numbers somewhere. I want to do this sometime and was also going to deck the head to unshroud the valve seats. This will lower the valves by a couple of mm and also require a vernier pulley to correct.

Thats a good idea to use the thinner headgasket, instead of decking the block which will take time...

What would be the advantages of decking the head though? The space around the valve face and cylinder head face is very small?...

@varnish

I haven't got a copy but i will be sure to purchase one, maybe a good christmas present for myself

I'm aware the heron design isn't very efficient in terms of flow, but now that i've put a lot of work into it already, i'm set on using it.

Also, fitting an AEE head on the heron design orientated ABD bottom end may require a lot of calcuations to get it to run efficiently. Be good to see someone do it though...

ABD is 9.5:1. With this knowledge, is it still worth the effort for you to go to 10.5:1? Maybe just a generous skim of the head?

As always, thanks for your hearty reply's guys. Probably the 3 people i was hoping to get a reply from.

@Chris - Are you sure thats the correct compression ratio? I've read that its only a moderate 8.5/1 or somewhere there abouts...

If that is the case i may have a re-think, but whilst its dissassembled, i may aswell improve the engines efficiency in every way possible.

I'll probably end up working the C/R out myself, it seems the most reliable way.

Compression ratio is 9.5 according to VW Max, cheers Mark

As always, thanks for your hearty reply's guys. Probably the 3 people i was hoping to get a reply from.

@Chris - Are you sure thats the correct compression ratio? I've read that its only a moderate 8.5/1 or somewhere there abouts...

If that is the case i may have a re-think, but whilst its dissassembled, i may aswell improve the engines efficiency in every way possible.

I'll probably end up working the C/R out myself, it seems the most reliable way.

Yeah, you're right, skimming the head will only get you minimal gains in compression ratio - I suggested it really just as an idea. As Mark confirms, it's definitely quoted as 9.5:1, but hats off to you for going to the effort of properly measuring it when the time comes - it will be interesting to see the results.

Cheers mark, your always there with the hard to find intel!

Chris, The head has already had a moderate skim to get rid of what looks like a good battering from a foreign bit of metal entering the combustion chamber. It must be down ~1mm already.

I did have the idea of machining in some properly calculated combustion chambers, around the valves and using some flat pistons from another engine (HK etc) but its a lot of work and i need the engine in ASAP.

Seeing as its been confirmed to have a 9.5/1 compression ratio, its not going to take a lot of machining to get it to around 11/1. I'm going to do some calculations, maybe using the thinner metal HG, and removing some material from the pistons.

Cheers everyone!

I want to do this sometime and was also going to deck the head to unshroud the valve seats.

Personally I think the best way to go would be totally in the other direction.

Do you have a copy of four stroke performance tuning? Read the section on Heron design combustion chamber.

Basically he says it's rubbish and the best way to get performance is to sink the valves 1.5mm into the head.

I've though for a while that the AEE head with its small chambers may flow better than the flat head 8V design. I've never flow tested one, but maybe someone has some numbers.

I don't know the chamber volume, but a relatively small chamber volume would be okay with the 1.0 and 1.3 engines as they're only small displacement.

u asked me to do this a while back, i completly forgot! if your still interested in the outcomes mate send me a pm. and ill try and get back to you with the results.

@varnish

I haven't got a copy but i will be sure to purchase one, maybe a good christmas present for myself

I'm aware the heron design isn't very efficient in terms of flow, but now that i've put a lot of work into it already, i'm set on using it.

Also, fitting an AEE head on the heron design orientated ABD bottom end may require a lot of calcuations to get it to run efficiently. Be good to see someone do it though...

It's a really good book.

It's not too technical (it's not full of scary looking equations) but has a wealth of information, and its broken up with the authors anecdotes which makes it which makes it, imo, more rewarding to read than an engine text book.

It would be cool to fit a chambered head, and its something I'd like to do. But at the end of the day its all about horse power per pound spent. So going for a proven combination is really the way to go unless you're very curious or have deep pockets.

@ captin_urbis

That's alright mate.

If you get a chance post the numbers them up here. There might be some other interested people.

Well one of the mechy headed engines, maybe the hk and gk? Have the combustion chambers in the head, which is more than likely the reason (or a contributing one) they deliver ~5hp more than the hyrdo equivalent.

A good combo would be a bottom end from said engines, and a aee head? Giving you a non heron design cylinder head and the ability to run a high lift cam. Or maybe a AEE bottom end with a hk head for revs?

Anyway on topic, Chris ill get a copy of that book, be a good read. I was going to work out how much material I need to remove off the combustion chambers to reach a c/r of 11:1 but I'm too tired

When i built my ABD a couple of years back, had the pistons and block decked, then pockets put into the pistons for valve clearance, CR was taken up to 10.5:1. 85bhp@5800 and 92lbft@3600 on a DMTL, very torquey, driveable engine but ran out of breath early being undersquare and tad lame on the cam. Its been said before i am aware, but on paper the oversquare 16v 1400cc engine with a half decent CR and set of cams makes alot more sense for a N/A application, regardless of any blinkers you might be wearing.

What happened to the plans for forced induction?

Have you got £500 to spend on an afh and a set of decent cams? I know i haven't! A bit irrelevant too.

Thats a great figure from a standard abd with a dmtl, I'm hoping to get around 100bhp.

I'll be aiming for a slightly higher comp ratio aswell , wether or not my Newmans lift will allow it I don't know.

I dont have £500 spare, nor is it necessary, the AFH cams are sufficient for a road tuned engine in an 86c chassis.

The £300 i spent on an ABD, gaskets, bearing, rings, bolts and a little labour would have easily covered a donor AFH if they were as readily available back on 2007/8 as they are now. Not going to groan on about it, you've still got your 8v spectacles on i see.

If you have the parts to hand, i'd do a trial build with some plastercine to find for what the standard valve-piston clearance is like with OE parts. You've got a reference then for what the ABD will take in terms of Cams and therefore what piston pocketing is required. I have no experience here, my cam was reprofiled and the valve seats recessed, then head skimmed to account for the reduction in base circle. What little was gained in lift at TDC was given to the piston pocket.

Edited 12 December, 201114 yr by polopete

Seems like an awful lot of work for not a lot of gain...

you get 100 standard with an AFH,

why waste time mit das 8 Valve.

you get 100 standard with an AFH,

why waste time mit das 8 Valve.

Well that's one way of looking at it. But for some the end result may not be the main objective.

I know the 8V engine is not the best engine design. That's why I like it.

I like the idea of taking an inherently bad design and improving it to perform above and beyond what it was designed to do.

Taking enjoyment from designing, planning and making the modifications is a lot of what I like about this hobby.

I would get a lot more enjoyment from designing and building an 8V engine with a baffled sump, modded rods, different pistons, radical cylinder head, and some fun homebrew turbo or bike carb set up then just bolting in a more powerful engine.

Then looking at it, I could think I designed, made, and built that whole engine myself.

Which to me would bring a lot more enjoyment then just going fast.

That's what Nitrous is for :-D

homebrew turbo

then it makes perfect sense. but the standard AFH will be more economical (when driven conservatively), rev higher (if you like that sort of thing) and be quite a bit easier than a modded 8v to the same power.

What are the benefits of raising the compression ratio? I will have all the bits at ky disposal to build a high comp 1.6 afh when I finally get round to pulling my car apart, just wondering if its worth doing?

"my" lol, and the car should be being pulled apart over Xmas

The cr of the engine I'm building should be 11.5:1, using the afh pistons should give me a comp ratio of 12.3:1. Knowing very little about this subject could any one that has any idea about it let me know if it will make much difference and what would be the benefits/drawbacks of it?

You could make a 1.0L 8V rev its tits off. Its very under square, it has the same dimensions as Yamaha's R1 engine.

By increasing the Compression ratio you increase the thermal efficiency of the engine. Basically you increase the amount of usable energy exacted from the fuel. But with this you get an increase in combustion temperatures, which could push the engine into detonation if you increase the compression ratio too much, or don't use a higher octane fuel.

there are some pikey ways of increasing CR I have seen people using weld to make the combustion chamber smaller, filling out the bowl in pistons etc. but realistically maximillion its piston design that can be most effective domed pistons with valve cutouts are a good way or custom designs for bowl in piston jobbies.