Cylinder wall thickness

[greenamex2]

How thick is 'thick enough' for a cylinder wall?

Details as follows -

- Cast iron block, no liners (Toyota 4a-ge).
- 82mm bore (currently, hence the question).
- 77mm stroke (will probably end up a couple of mm longer).
- 9500RPM.
- 220BHP (want more).

Cuurently the minimum wall thickness is around 4mm, am I pushing going out any further?

There is a bunch of stuff regarding this engine on the internet but most of it is cobblers so I tend to ignore it.

Thanks.

[terence]

Personally I,d be looking elsewhere for the extra Dennis,Cam design.Porting etc,You would only need a very slight amount of block movement to lose any potential gain,[As you are probably fully aware.]You never know,there could be gains to be had without the cost of a new set of Pistons.

[greenamex2]

I blew my engine to smithereens a couple of weeks back an need new pistons, new rods, new cranks, new flywheel, new block etc etc etc.

Just looking to maximise bang for buck.

Unfortunately the engine is full Formula Atlantic spec so there really isn't much more to be had without a capacity increase.

[knighty]

personally I wouldnt go below 4mm........if you do feel like you are pushing your luck, I'd seriously look at having all the bores fully machined out, and having a set of decent wet liners pushed in.........but its going to cost plenty.......if you want more power why dont you consider one of theose rotrex type superchargers, or just go the turbo route........seems the way to go nowdays.

[Chris Y]

Is your head/valves/inlet/etc. flowing enough to fill the existing cylinders? Would adding an extra mm or so to the bore really give you an increase in BHP? It's probably going to be marginal, and 4mm isn't really a lot to play with.

[zefarelly]

the dimensions you've given are similar to a ford crossflow, I wouldn't go below 3-4mm.

[terence]

Just one mill o/bore is possibly worth 2-3bhp,is it worth the risk?.Who built the original?

[greenamex2]

Unfortunately my series (Classic Modified Saloons) doesn't allow after market turbocharging so that is out.

The head was flowed by a ex-McLaren F1 head guy and completely outflows anything of a similar capacity that I have ever seen flow figures for so I think we have some to spare.

The only issue with the head is the ports are really too big for the capacity, unfortunately I am stuck with this as it is a defect of the original design.

Thanks for the minimum thickness figures so far, I am beginning to think any capacity increase is going to have to come from stroking, or I go to the possible grief of wet liners.

[greenamex2]

Originally Posted by terence bower

Just one mill o/bore is possibly worth 2-3bhp,is it worth the risk?.Who built the original?

A company called Competition Engine Services, a couple of ex-McLaren engine people.

The company doesn't exist any more but I am still in touch with the engine builder.

This would be done as part of a capacity increase from 1626 to 1700. I am trying to keep the stroke increase to a minimum for obvious reasons.

[terence]

If you,re allowed stroking Dennis ,i,d have though that to be the way forward,far more to be gained than boring.Maybe get more use from the port sizes !

[GORDON STREETER]

Denis there is only a certain amount of power a block will put up with and be reliable. As Zef said its very close to a Ford Kent block bore size, and most of them being 30+ years old wont bore to 85mm without going through. I would think the Toyota block should be OK to 84mm. Its like anything in motor racing if you spend enough money you can get over most problems ! Decent bonded in top hat thick walled liners would ultimately be the way to go as boring always weakens the block . I know that Cosworth in the F1 1500cc turbo days were limited by the BD block at the time as it just fell to pieces on the Dyno, but it was probably giving 4 times the power it was designed for at the time. !

[coln72]

There is a larger version of this engine, the 7A which was around 1800cc, though it was never released as a performance version. Think it featured a larger stroke from factory. A few people have made 4AGE and 7A hybrids but I can not make a comment on their durability when pushed to the limits as I have never played with one.

[Notso Swift]

For those others who don't know the 4AGE is pretty much a copy of the BDA, hence the similarities.
So with an 82 mm bore you are currently at +1.0, that is a reasonable overbore and honestly, an extra 0.5mm or even 1.0 mm will not give a lot in power. And it will not change the limit of power capable from the head. The slightly larger volume may suck a little more air in, but really… negligible
I presume you are not able to get any bigger valves in? With your sort of power I am guessing you are already up around 31 or maybe 31.5 mm, so up to +1.5/2.0mm inlet, if you have to you may consider sacrificing a little exhaust valve size (though not below standard) to push a little more… but really your motor is already at the edge. That sort of power from that motor is pretty good, the best of the best Atlantic Motors were told to have 240 bhp, but the horses may be different sizes to yours, besides, you need torque to lug a saloon body around.

Looking at the efficiency of the Motor you have, 220 hp/9500 rpm that is a BMEP of 12.8 bar, that is very good, indeed I bet that your peak power is at a bit less than the max RPM (say 9200-9300), which would give over 13 bar, that means you are pretty much exceptional for a production based motor. Your head guys are worth what you are paying! Even the hero motorbike motors and F1 struggle to go much more than 14 bar…

So what to do, the best suggestion with the 4AGE I can make is to get the same power, but try and make it lower and wider. This would suggest playing with bore/stoke ratios and rod length. Since you need new ones anyway. Maybe a simulation package would be ok to play with as a start, like Dyno2000, which is cheap and accessible (though a little to V8 centric) A longer stroke will suck on those ports a bit more, more efficiently than a overbore.

Can you re-engine?
Sprinters (AE82) fitted with a 3SGE is common here to run in our under 2 litre class, even if you were to de-stroke to hit a 1800cc class break or something it would be a better and cheaper option. It would give you more torque and about 40 bhp more. We use to have a Starlet with a 4AGE, I am sure that he ran out of development options at about the same time as you, he couldn’t fit a 3SGE in so went to another motor (from the existing Corolla IIRC, then got it out to 1960cc). With the 4AGE, he did bore it, you may want to try and look him up, the name is Dave Loftus. Go to the IPRA forum http://www.techmasters.com.au/forum/index.php and send a PM to “lofty”. I am not sure how much you will learn that you don’t already know, but it can’t hurt to contact a “real” racer who has been through the same thing.

[greenamex2]

Thanks for the comments. After a long discussion with the engine builder we are just going to keep the bore at +1mm (82mm) and stroke it from 77mm to 80mm. The walls are just to thin for this sort of RPM.

As the engine was always designed for a single seater but is in a 825Kg saloon we are hoping that the extra torque will more than offset the loss in RPM capability.

As for the BMEP, peak power is around 9000RPM, what does that make it Notsoswift?

Unfortunately I can't even re-block it let alone re-engine it. The 7A was considered but it has some inherent defficiencies that would have to be designed around. It's only really benefit is being able to go up in stroke, not something I want to do if I can help it.

As for the 240BHP figure, given that a lot of those engines left the UK with 220BHP when they were built, and were running control cams, ECU, bodies etc, it would be very interesting to know where the 20BHP came from!

[Notso Swift]

****************kW x 1200
BMEP = ---------------
****************litres x rpm

So 13.5 bar for you, F1 motors have something like 14.3.... but more rpm means more power. And basically that is where you are, you will only get more power if you pump more revs into it, but revs cost a lot and make failures more common. The stroking option may mean that you only have the same maximum power but your average power should be better.

As for the 240BHP figure, given that a lot of those engines left the UK with 220BHP when they were built, and were running control cams, ECU, bodies etc, it would be very interesting to know where the 20BHP came from!

THAT is why is said Horses come in different sizes!
Trust me, PM lofty as I said above, he will help you and he has done this exact exercise. Since he holds more Under 2 litre track records than anyone else I know he is doing something right. Even if you end up doing the same thing at least you know you have gotten an experienced opinion from a circuit racer.

[RacerRich]

We were getting 225 and 155lb ft on the dyno- unrestricted on the 20v motor.
That set up was 81.5 x 79.0 = 1649cc, legal for class 11 tarmac rallying in Ireland.
We were gettting huge BMEP out of this unit, and finding that with flicking back between 16 & 20v motors, we were able to cross pollenate and really home in on the engine's sweet spots, and not so sweet spots, culminating on a 1599cc at 217 on a 4-2-1 manifold- 140 torque but stupidly high up. Best torque we had on a 16v was 147 recorded installed.
The 20 valves always ran with 4-2-1 manifolds, and no doubt would have given more numbers on a racing set up with unrestricted (ie short) length side exit- or single seater length manifold- maybe another =10? on standard super unleaded at 12.2 CR.
The 4A was designed as a toyoa standard fare unit a lot earlier than the 16 valve conversion, so never really was optimised- and as usual, Toyota tried so hard in the "over engineering" department, but the thing is, the quality is there.
The need to go to a bigger bore is a bit of a red herring, as straight line acceleration is decided by cumulative torque though the rev band available via gearing choice, and change up point. I think the Puma 1700 rally motor is something like 81 x 81, and goes like stink.
The main problem with the Toyota block is the water drilling, I don't know if anyone ever came up with a way of doong away with it? I imagine one would need to liner the block, and then use a seriosuly trick head gasket with wire ring fixing to get it to stop blowing itself apart with such a spall space between cylinders.