I wont use the maxported head on my boosted engine, it would suffer from to bad exhaustflow! When we ported the head that I am using for this engine we have had focus on the exhaust port because that´s a big problem with the A-series head when boosted. We started from a round ported A14 head and found great flowfigures from the exhaustport, flowfigures on the intake suffered a bit from the round port but we managed to get a good flowfigure at excellent gasspeed. This head will work great at low rpm without boost, then at higher boostlevels there will be no problems....


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I can only speak from personal experience, which (as far as high boost, and for 280bhp you'll need at least decent boost/rpm) isn't specifically datto a - series - but without exception I've found more power from the improved ring seal of thicker bore walls on a boosted engine. The 'push' lasts a lot longer, and so it'll be higher pressure when the piston is further down the bore, further away from the deck (which itself helps stop the bore ballooning out a little).

Years ago (actually decades ago) when local holden 6s were still popular, and people were running more and more boost through them, well the std 'big' bore size for a holden 6 was 3.625 (apart from the 202, which had a 3.25 stroke, all holden red motors were 3.0 stroke and capacity varied by bore size - so there were 138, 149, 161, 173 and 179 ci capacities, then the 186 came out with a 3.625 bore, then later the 202 with same bore and 3.25 stroke) anyway - back when they were trying to find even more power from the 186s, people actually tried 179s (it seemed the factory 'might' have used the same casting patterns for the 179 and 186, so the 179 was essentially a very thick bore wall block - and I can attest to boring more than one of them 142.5thou oversize (which made them 0.080 for a 186). Anyhoo, people tried running 179s or getting 186s and sleeving them down to 179, adn believe it or not, even though it led to more valve shrouding (holden motors don't have the valves over the middle of the bore, they are offset, sadly, and the flow has to do a bit of a 180 to get in there) - anyway - despite those factors, they still found more power with thicker bore walls (people ran over 35psi, which was probably the limit of the turbo compressors of the time, and were of course breaking blocks, around the main bearing webbing/saddle area too).

I've seen the same thing happen with mini a series engines - most can take some serious oversizes (going from 70.6mm bore out to and in excess of 73mm (and some people have used datto a12 pistons in there too). Even NA they make more power out to 1380cc than the next overbore which takes them to 1400cc (but is often 'necessary' as the bore is worn on a high output race engine). If they drop power, ostensibly due to blowby/ring seal/cylinder wall flexing when NA, then you can imagine the trouble they have if you apply boost on top.

But to be more specific, if I was in your shoes and wanted a big power boosted A series - I'd definitely start with an a15, and find one that is standard bore, and then go the minimum oversize necessary to clean up the bores. The thicker bore walls will give you more power than the few extra ccs you get. Extra capacity is the big deal without a turbo, because you need to get all the air in there you can manage. With a turbo (or blower) you can always get enough air in there, you instead have to focus on 'handling' and transmitting the power it makes available.

If it is for drag racing, you'll get away with some serious boost/power with cast pistons. If you avoid detonation, that is half the battle, but even if there is none of that, eventually you get to a stage where the total amount of heat energy being transferred to the pistons, gets too much for their ability to conduct it away. It's called 'heat soak' and eventually, even if the peak temperature isn't that much higher than an NA engine, it's like double as much burnign at the same temp, and eventually it will damage pistons. It is far less likely to happen drag racing - there isn't enough time. But on a circuit (or on the road, setting a new top speed record - lets say somewhere in the world where it is legal to do so) with a long/uphill straight, it can happen. And it is almost 100% definitely going to happen in tractor pulling. So not only do you have to avoid detonation or pre-ignition, but heat soak has to be allowed for. Forged pistons are denser and will tolerate more heat energy, so worth it for a high powered setup. You can also look at stuff like oil squirter jets installed in the block, to spray pressurised oil from the oil pump up at the undersides of the piston crowns. This will take some serious heat out of there, and help a lot. Of course then you also have to deal with the oil running hotter, and eventually you'd need to consider an external oil cooler (or run a big capacity sump, so there's much more oil to heat up, and it will reach the end of the straight, and have some time to cool, before it overheats....

Another general tip is to run the exhaust valve seat contact width a fair bit wider than you would for an NA car. It will cost a little bit of flow, but the valve cools on the seat, and on a boosted engine, there's more heat for the exhaust valve to deal with (a lot more) so the wider seat will help it conduct more heat away in between each combustion cycle. And since exhaust valve temperature is one of the big factors which can lead to pre-ignition/detonation, it's worth a small drop in ex flow to have the extra safety margin.

Jmac

Could I trade you my underwhelming 1500 post "Dattomaster" status for your 370 post encylopedic level of knoweldge!

Every time i read one of your essay size posts, it amazes me how much i dont know. I would never in a million worlds thought that you could get bore flex in a boosted application, causing blowby.

And you highlight another misconception that going to the max of everything is not always the best way forward. Less bore, more boost.

very informative and worth the read.
Cheers

To be fair, there are exceptions - some older (pushrod) volvo 4s and I dunno - packard V8s (anyone here actually heard of the second one? :) ) can be bored ridiculous amounts (some packards 1/4" - 6 bloody mm plus!. they made the blocks practically indestructible. Maybe not all that impressive as far as power per litre goes, but you could boost something like that to buggery and it'll never get bore wall flex.

Eventually car manufacturers realised two thinigs (some had known it forever - Henry Ford once said that if he could have a legal monopoly on the spare parts and servicing, he'd manufacturer and give the cars away for free) - the first is that a car that never wears out, never needs to be replaced, so there is reliable, then there is indestructible. The second is that if you are making a few hundred thousand engines per year and you can make the engines with thinner bores (and lighter elsewhere) they can save a truckload in raw material costs. Factor that in over the long run and it makes sense.

Ford actually underwent a couple of lightening re-designs of the last of the windsor V8s. Whilst their heads were better flowing, the later blocks are nowhere near as good as the early ones (for either high rpm or for boost). The trick there is to get the last of the 351 truck blocks, which, due to their usage, kept the earlier heavier design. Somewhere on the net there are pics of the 'light' blocks that have literally split in half when pushed with a little boost. It's the reason why v8 supertaxis (sorry, I mean v8 supercars) in Aus used a 'ford motorsport' block, not a production line windsor (and I forget what specific chevy block the holden guys used) . I dunno what they have run in the past few years, I just haven't paid any attention to it - the cars are silhouettes of one another, no individuality, no real charisma, unlike racing back in the 70s and early 80s which saw all types being campaigned.. not that I was old enough to appreciate just how good it was at the time!!

Similarly - some gemini blocks - very thick bores, and you can safely take them oversize and still have really good bore walls for high boost.

TO give another holden related 'rule of thumb' as far as bore wall thickness and its importance - the holden HQ race series - they run VERY heavily restricted 202s with 1 barrel strombergs, unpoted head, mandated 'control' spec cam and so forth. They don't produce huge power (well not compared to a historic racing spec 202, but they produce insane power for how restricted they are with regard to mods) Anyway - they are free to run any bore size from std to 0.060. As I mentioned, the blocks aren't that bad, they'll all take 0.060 unless there's some very unusual core shift, and there were even 0.080 pistons for them (and 186 blocks) too back in the day. EVen though they could run 0.060 over practically nobody does. 0.040" oversize is the best result for output (and they spend some serious time on the dyno trying everything under the sun to get even 2-3bhp consistently - anmd it's also why they use engine dynos, not chassis dynos, as the losses aren't drivetrain, they are a result of hte chassis dyno process, so ultra consistent predictable readings for accurate comparison of small gains just aren't there). So if 0.040" over on a block that can take double that safely results in more power on such a relatively low spec/revving setup, you can imagine how it starts to work when boost is added to the mix.

the other 'big' issue by the way if you want to start looking at engines for massive boost - is bore size (generally the bigger it gets the harder it is to seal with the same amt of bolts because there is more distance between each bolt) and number of head bolts per cylinder. although they overlap, you can sort of consider most small 4 cylinders as having 4 bolts per cylinder. That's not too bad because they have smallish bore sizes. On big sixes, it starts to be an issue (probably one of the big deals with high boost hemis}. running thicker studs isn't a perfect answer, as there will still be flexing between each bolt. So things like the sb chevy has 5 bolts per cylinder, and you practically never hear of head gasket issues with them. Something like the old studebaker v8s (the smaller capacity ones are better in general too) have six bolts per cylinder, and seal exceptionally well. On that note, some of the guys heavily contributing to the early days of the blowthruturbo mailing list (which was a goldmine in the early years, but now it has run it's course and there's practically zero new posts in the last year or so) - well they ran factory superchargers. Being belt driven etc, the studebaker specialsts used to spin them to 7000 odd rpm, to get blower speed up (the drive belt ratio was about maxxed out, and frankly so were the superchargers, even when they ran two). The motors just didn't like the high rpm, and would fail. A few guys decided to buck the trend, and went with some very affordable used turbos, upped the boost (blowthrough carbed still) and kept the redline down to 6000rpm. Suddenly they started running consistently, a lot quicker too, and stopped breaking blocks (one bloke in particular had chalked up nearly 20 years of regular drag racing - sub 10s by the end of it in a relatively heavy car - all on the same bottom end build, never had to look at it through all that time!).

Point of all this, if bore wall thickness is one of the hidden keys to boosted engine 'success' then running up behind it is rpms. It varies for each engine. Datto engines in general seem to be extremely comfortable with decent rpm on board, but the basic idea is that you wouldn't have to push them to the rpm range of a NA motor to make more pwer, and it'll stress teh engine less to drop 1500rpm or so off the redline of a NA racer buildup target, and up the boost. That gives you the sort of combo that will last as long as an a-b stocker (or nearly as much) and awesome output.

The only exceptions to such things are where the gearboxes or drivetrain just 'can't' be improved enough to handle the much higher torque of higher boost/less rpm (a motor making 200bhp at 9000rpm has half the torque at that rpm than a motor making 200bhp at 4500rpm) Off the top of my head the combo I can think of is mid 80s Saabs. A guy on the jyturbo list worked out how to hold them together at up to and even over 9000rpm (at which time the valvetrain started to fail), but aimed at mid 8000s, which they'd actually handle all day. then used boost to increase the power, or stop it dropping off, as rpms increased. The torque output never actually rose to be much above around 50% more than stock, but it ran out each gear to 8700rpm or so, and became quite formidable. He actually got so intune with the fuel cut rpm, that he could time the gearshift as the limiter engaged, and not have to lift off the throttle. This is of course a rarity, and the drivetrain schematics of the saab (a front wheel drive with the engine over the gearbox and a chain drive) didn't lend themselves to easily adapting anything else.

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Now I remember where I read what I wrote above. Jmac wrote it (words to that effect) on the moparmarket forums. Clever bugger that man!

Jmac, thank you for taking your time to share your experiance with us! Your posts was very helpful. My biggest problem has been finding suitable pistons under 79mm. I know that I could order some custom ones but when I already have a set of 79mm Wiseco forgies I´d rather use theam... and it´s always interestning to try somethin new...... test the limits! My current engine is 150hp/5000rpm at the wheels with only 0,7bar boost! That´s with stock internals, carbs and mechanical ignition. With decent internals, more cc, a good cylinderhead, electronic injection and ignition and a suitable turbo, 280hp isn´t far away!?

Marcus

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blowby is the enemy in both boosted and na engines and at 79mm
Id seriously consider offset sleeving for extra thickness in the
cylinder walls then when its time for more boost you dont have
to start all over again.

I talked to my friend who owns the speedshop yesterday and he had the same experiance as Jmac, cylinderwall thickness is very important! When he competed in dragrace in the beginning of 2000 his team struggled with braking cylinders-walls. They had a Volvo B230 16V engine that was pushed to the limits, the cylinderwalls were 3,5mm but they still broke due to massive detonation. They had over 1000hp and ran a impressive time of 7,96 in 2003, this was the European record for four cylinder cars back then. They also tried sleeves but ended up casting new billet blocks.

Marcus

machining billet blocks is not affordable for us datto fellas :)
If 3.5mm of wall thickness can handle halve of the 1000hp Im sure
that big sleeves wont be an issue.

I can't say 100% for sure, but personally I'd be worried about 79mm and more boost - enough to get you the 280bhp goal. Is there any chance you could sell them to somebody with a NA datsun engine project that is high revving/output. I'd honestly personally prefer going 76.5 or 77mm if absolutely no option. If you can tune it very safe, rich under boost and not too much timing (richer than you would go for another turbo setup with the same boost but stronger bore walls), water injection, then it's probably doable, but not ideal.

NO engine in the world will stand up too long with detonation (or preignition, which is usually actually worse, esp in a boosted setup, due to the sheer amount of air/fuel to be burning too early (as the piston is still rising in the bore, which causes the burn temperature to go through the roof. Generally there's a small gap between the piston top and where the flame actually reaches (it's only a few thou) so it protects the piston crown a little. (it's why tight quench helps prevent detonation - flame can't pass through the small gap - it's why some old kerosene home heaters have a wire mesh over the flame to stop it reaching any higher).. Anyway, if you experience any severe shocks (detonation) or just massive pressure (more related to pre-ignition) then it can compromise that layer, and the heat the piston is exposed to is higher still.

SO obviously - no engine will handle det/pre-ign for long at all (and every little tiny bit of damage just stacks up on top of each other) - but even if you avoid that, it might still be pushing it.

Don't get me wrong, the datto engine is darn strong, esp for when it was made. And it's a smaller engine and 2 valve/pushrod valvetrain. Effectively a turbo would have to work harder to produce 280bhp out of an a15 than it would out of an sr20 (esp since it could do it at less boost, so less heating up of the intake charge. So that means (usually) more heat in the intake charge, but you also lose a little more power to exhaust pumping losses, and the pumping losses scenario leads to more heat trapped/lingering between the exhaust valve and the turbo exhaust housing, so more heat the exhaust valve has to deal with. It sort of goes around in circles, with these issues all affecting each other.

Sometimes you have a 'win' here and there with boosted projects. For example - supercharged setups - if you mounted a blower on a bench, and then spun it with an electric motor (and a restrictor on the blower outlet that is adjustable, you could spin it to any rpm you liked, and then adjust the outlet restrictor size until the supercharger is making X amount of boost (lets say 10psi). Now you could calculate how much power was required by the electric motor to achieve that. So then you could work out how much power the supercharger is stealing in order to produce 10psi at (for example) 6000rpm. And you'd have the answer. Except it wouldn't be the real answer. Here is where things get interesting - essentially that 'force' of pressurised air being shoved into the cylinder - well it actually creates some 'push' on the piston going down in the bore. So 'some' of the superchargers energy cost is actually paid back. The difference isn't like night and day, but it's one of those weird ones that hardly anyone might think about (and for the record, I didn't come up with this myself, it was a result of a discussion on the jyturbo list, where one of the posters there was - no kidding - a rocket scientist)

What is the situation in Koskela with available fuel and octane ratings? Recently in Aus we've been seeing the introduction of ethanol blended into petrol (which increases fuel consumption, and isn't profitable/viable without government subsidies or brazil where wages are lower on average,so there's a cheap workforce) - anyway they do it because of 'climate change' - basically to get votes).. OK so the regulr unleaded is being phased out to be replaced with e10 - 10% ethanol.

That's bad, but on the flip side, there's also (in probably 20-30 places around the country, but growing slowly) e85 - which is 85% ehtanol and the rest regular fuel. It doesn't require as much fuel as methanol does, but it has a _lot_ of the same sort of cooling effect that methanol does. So effectively you have to increase flow by about 40% or so (vs 100% or more for methanol) - which increases fuel consumption even at part throttle. It's still reasonable enough that a car can be street driven with a fuel like E85 (methanol goes beyond that0 but you'll get the chance to run more boost safely (or the same boost but maybe not needing water injection or a bigger intercooler)

People here are using E85 in various racing categories, and the power it makes is higher than when they previously ran on special high octane petroleum/gasoline based race fuel - and it only takes them literally the first few corners of the start of the next race to se just how big the improvements are. If you can get something like that fuel, certainly it'd be a good option

If