Comparing Busso internals - 75 12v vs 916 GTA 24v
Posted: Sat May 18, 2019 11:14 am
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.
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?
As are the inlets. But the injectors look the same, so I'm keeping those.
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.
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.
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?
As are the inlets. But the injectors look the same, so I'm keeping those.
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.