For your perusal and entertainment - 164 12v vs 916 GTA 24v 3.0 Busso - Alfa Romeo Forum
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(Post Link) post #1 of 15 Old 18-05-19 Thread Starter
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For your perusal and entertainment - 164 12v vs 916 GTA 24v 3.0 Busso

Another day, another speculative Ebay purchase. I found a cheap 916 gtv Busso block on Ebay, minus it's sump, conrods, crankshaft, liners, etc. The chrome trumpets looked in pretty good condition (except for one small dent) and I thought I could do a quick comparison between the 12v and 24v blocks before I binned the rest, so thought 'why not'?

When I went to pick them up it turns out the block isn't the sad remains of catastrophic bottom end failure, it's actually a near-immaculate low mileage block which has been used for speccing and measuring by an engineering shop who supplied parts for EBSpares

So if anyone needs a very nice 24v 3.0 block or heads, drop me a PM

But without further ado, down to the comparison...

Firstly, the really, really interesting bit. Looking at the casting for the 24v pump vs the 12v pump, you can see there are small differences in the cavity size, but the waterways and bolt holes match perfectly.




And sure enough, a 12v pump fits into the space rather nicely, and spins freely when bolted down.



Following through, I could see no discernible difference between the 12v and 24v heads' or blocks' waterways.




And even more interesting, it looks like it'd be a simple job to remove the core plugs from the front of the 24v heads and block off the waterway at the rear end, to make it suitable for a front-mounted stat.






Rest of block is extremely similar (24v would have an extra bit bolted on to hold the oil filter, though presumably the housing could easily be tapped to accept the older type oil filter if necessary). So, could it be, after all these years of commonly held wisdom, that the more modern 24v can easily be converted to have it's stat and housing at the cambelt side of the engine? However, there is one fly in the ointment - spot the difference:




Damn. Though the bracket at the bottom could easily be modified to take an early 164 24v's pump, the casting the pump shaft would need to run through has been removed.




The common way around this is either to modify a 75 sump to fit around the later 916-style oil pump, or to dry sump it. And I don't have the skill / expertise to do either of those, so sadly, despite it's lovely condition, this block's no use to me. I won't have any use for the 24v heads either, since they're lacking the necessary casting too.
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(Post Link) post #2 of 15 Old 18-05-19 Thread Starter
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However, it looks like all the bolt holes for fitting a hydraulic detensioner are still present, though I've no idea if it'd be possible to drill though to an oil gallery to supply the necessary pressure for it since the casting in that area has changed.




Unless I've missed something or someone's tried similar experiments in the past and come a cropper, that opens up something really interesting for 116 GTV and 75 owners - theoretically you can easily convert a later-type engine so it won't foul the bulkhead. This means you could fit a 3.2 'GTA' type engine with minimal modification to the cooling system and none to the bulkhead at all! You would need to do some engineering around the oil pump issue, though that'd be no problem at all for a race engine since presumably it'd be dry sumped anyway.

One other interesting difference - the 24v block has extra drillings in the main bearings leading to spray jets mounted beneath the pistons, whereas the 12v doesn't. Wish I could reverse engineer that bit...




Ok, on to other comparisons.

Unsurprisingly the inlet and exhaust ports for the 12v and 24v are completely different. 1-0 to the later 24v. Or is it?






12v and 24v plenums are exactly the same size, apart from the mounting and 'bling' the only difference is the later 24v has a different mounting flange for the throttle body.





And now for the interesting bit in this; good for me, not so good for 24v owners. The 24v trumpet size exactly matches the 12v inlet, there is no step whatsoever.




And also the 12v 164 inlet has exactly the same bore as the old 116 2.5 GTV inlet too.



So that means the 3.0 24v which should theoretically be able to suck in much more air through it's extra valves and increased displacement, can only breathe as well as the venerable 2.5 12v! Bet a few horses could be easily released from a later 24v simply by fitting it with a bigger plenum and trumpets which actually fit...
Finally, the common bits. Everything from the front end of a 12v will just bolt on to a later 24v; that came as a surprise too.

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Cheers mate, interesting read. I've never done much with the old 12v, there are barely any left now. I've probably seen more of them in old Hawk Stratos replicas than I have in Alfas.
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Cheers mate, interesting read. I've never done much with the old 12v, there are barely any left now. I've probably seen more of them in old Hawk Stratos replicas than I have in Alfas.

No probs, I'm having trouble finding bits and bobs for the 12v because of their rarity, which is why I thought it'd be a useful comparison to make - common wisdom says they're completely incompatible, but it looks like there's a lot of parts interchangeability apart from the heads / oil pump, and presumably the crank.

E.g people often say the sump from a 75 won't fit on a later 12v, but from what I can gather, excepting the oil pump issue, the main problem is the front panel with the crankshaft seal in it. But if the panel from a 12v will just bolt on, that's not such a problem after all
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Quick update and more proof the internals are very similar - with the correct front cover the 12v crank fits fine:



As does the sump pan:





So the only issue would be the oil pump!
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And the final one in the series - 2.5 24v crankshaft with 3.0 pistons and rods. Should be no issue at all since the conrods are the same length and sure enough, it isn't

3.0 crankshaft



2.5 crankshaft



So using the 2.5 crankshaft would give a low compression engine (roughly 7.0:1) ideal for turbocharging, and would have the advantage of making it a non-interference engine so less chance of catastrophic damage if the cambelt snaps

Don't think this 2.5 crankshaft would be much good as it is however - there is one vital difference between the 12v 3.0 crankshaft and the 2.5 24v - the bearing which the oil seal beds down on is missing from the later one:



The space where it should be is normally filled by the oil pump drive cog. Anyone got one of those going spare which I can grind down by any chance?
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...And another little update, I saw a front crankcase cover brand new on Ebay for 20 for the later 24v, so thought I might as well get it so I could compare the old vs new covers, and this well and truly explains where the idea the 116-style sump won't fit on a 24v without drilling new bolt holes comes from:



You can plainly see the bolt holes are in different places, but the rest of the crankcase bolt holes line up just fine with the sump. So to fit a 116-style sump to a late 24v or vice versa, you just need the front cover (excluding the oil pump issues noted above).

And also interestingly putting the new front cover on the old 12v crankcase clearly illustrates how the more modern solid cambelt tensioner is fitted - it does just bolt in place of where the hydraulic detensioner was fitted, just with a longer extension on the front cover to firmly hold it in place:


And finally, some other goodies arrived today



They won't be used quite yet (need to make sure the engine runs reliably as it is first) but the pistons are dramatically different to the originals, all are within 1g of each other, and they're considerably lighter too. But somewhat bizarrely, the gudgeon pins are also only within 1g of each other, and there's one more 'heavy' gudgeon pin than 'light' piston so might have to get one pin machined a little to make them balance perfectly.

Must... Resist... Using... Them!
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Final note before I get on with bolting the 12v bottom end together and sell the unused 24v bits - there wouldn't be any advantage swapping to the later cam tensioner on 12v / early 24v and in fact it might make it more likely to skip a cambelt tooth since the detensioners allow the engine to run a tighter cambelt on startup. But later cambelt tensioners are cheaper / easier to find so might be a good temporary swap whilst searching through hen's teeth for early tensioner parts.
Right, time to sell off all these 24v bits and get on with doing something useful
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The 3.0 24V injector plates are 42mm ID. The bug QV runners are 45mm OD, same as the GTA runners. The 2.5 24V ones are smaller, maybe the same size as the 12V. That's why even on the Squadra tuning site it specifically mentions that anyone with a 156/166 2.5 24V who wants to install the 45mm QV runners need to get 3.0 injector plates. The runners are also smaller on the engine injector plate side, unless you get the 24V QV or GTA.

Not sure what size the GTV runners are, but the 164 Super 24V has small runners, but the injector plates are the same compared to the QV ones.

Maybe the engine you got had swapped injector plates and runners? Sometimes it's possible used engines get all the goodies swapped.
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Quote:
Originally Posted by mj2k View Post

So that means the 3.0 24v which should theoretically be able to suck in much more air through it's extra valves and increased displacement, can only breathe as well as the venerable 2.5 12v! Bet a few horses could be easily released from a later 24v simply by fitting it with a bigger plenum and trumpets which actually fit...
Finally, the common bits. Everything from the front end of a 12v will just bolt on to a later 24v; that came as a surprise too.
You'd probably get a few more horses but only at the top end. The 24v was tuned for a relatively flat torque curve to assist in low speed tractability. Narrower intake dimensions assist in low speed torque as airflow velocity is increased; of course at some point you restrict top end power. Increasing intake port diameter could actually reduce low speed torque.
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You'd probably get a few more horses but only at the top end. The 24v was tuned for a relatively flat torque curve to assist in low speed tractability. Narrower intake dimensions assist in low speed torque as airflow velocity is increased; of course at some point you restrict top end power. Increasing intake port diameter could actually reduce low speed torque.
Interesting, and makes sense now I think about it, otherwise there'd be no need for twin plenums on some normally aspirated performance cars. It'd follow the same would apply to turbocharged cars too, smaller intake ports would assist low-end torque and at mid-range onwards the forced induction would take care of airflow, which explains why most road-going turbo cars have relatively restrictive inlet manifolds.
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The 3.0 24V injector plates are 42mm ID. The bug QV runners are 45mm OD, same as the GTA runners. The 2.5 24V ones are smaller, maybe the same size as the 12V. That's why even on the Squadra tuning site it specifically mentions that anyone with a 156/166 2.5 24V who wants to install the 45mm QV runners need to get 3.0 injector plates. The runners are also smaller on the engine injector plate side, unless you get the 24V QV or GTA.

Not sure what size the GTV runners are, but the 164 Super 24V has small runners, but the injector plates are the same compared to the QV ones.

Maybe the engine you got had swapped injector plates and runners? Sometimes it's possible used engines get all the goodies swapped.

Sorry, didn't notice your post, yes it's entirely possible it already has all the 'goodies' - it was a part-finished project which was supposed to go in an Alfetta track car, but it looks like the project ground to a halt when the hybrid 75/164 oil pump proved to be an obstacle.
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Very informative, thanks for taking the time to do all that!
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Very informative, thanks for taking the time to do all that!
No probs, it was fun
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I managed to crock myself a month and a bit ago stupidly trying to lift a transaxle out of my car without an engine hoist (did some damage internally somehow, not a bad back!) so I haven't been able to do anything with the engine proper, but I have sold most of the 3.0 24v bits now, except the cam covers.

And, I picked up an original 116 GTV 2.5 v6 crankshaft for a song, so thought I'd share the comparison between the 2.5 v6 24v crankshaft outand the original 'long' 2.5 12v shaft.





Suffice to say never the twain shall meet! Creating an extra shim for the flywheel and creating an extra bearing for the front cover (in place of the 24v's oil pump drive) would be a ridiculous amount of work and would probably result in a heavier, weaker crankshaft with some seepage from the front cover, so as effectively non-interchangeable as the block and heads.

Which also raises the question - since creating a shim to fit the earlier 'long shaft' flywheel to a later engine would put the shim further away from the bearing (this increasing the mechanical force and risk of the shaft being out of balance) than the original crankshaft (which effectively has the shim cast right next to the rear bearing), would this mean using the earlier type flywheel with the later type crankshaft could possibly lessen engine life a little?
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