Why 4.2 and 4.5 ?
Discussion
Was in the local a few weeks ago (only just remembered, should've posted back then) and Cerbs came in to the conversation. 'Yeah' says me, '4.0 six and 4.2 and 4.5 V8, TVR's own engines..' I'm then asked (being the resident TVR know it all because I own a Chim) What's the difference between a 4.2 and a 4.5 then ? Hmm, about 300cc I reply in a somewhat smart arse fashion, realising, that apart from that small nugget I have absolutely no idea.... Or is the capacity difference really the only difference ? Would appreciate any info on this chaps...
However, it also led me on to wonder why are they 4.2 and 4.5 ? Was there a good reason for these specific engine sizes ? Something to do with bore/stroke restrictions or optimum ratio's ?? And why two capacities that seem so near to each other, only 300 cc ? (bigger the engine the less the capacity differential..) Last question, two cars same condition history price etc etc one is 4.2 the other 4.5 which one would be the one to buy ? and why ?
Thanks chaps... R.
However, it also led me on to wonder why are they 4.2 and 4.5 ? Was there a good reason for these specific engine sizes ? Something to do with bore/stroke restrictions or optimum ratio's ?? And why two capacities that seem so near to each other, only 300 cc ? (bigger the engine the less the capacity differential..) Last question, two cars same condition history price etc etc one is 4.2 the other 4.5 which one would be the one to buy ? and why ?
Thanks chaps... R.
You'll get a few responses I'm sure but the 4.2 was only a 4.2 until about 2000 when it was in fact a 4.5 but with a 4.2 induction/top end.
The 4.5 was meant, afaik, to be a better 'GT' ie less intense but also more powerful. The reality was that whilst the engine was slightly less vicious in its delivery the 4.5 was hardly any more powerful. The debate re magazine road tests and owners experiences can swap this debate a little.
Ultimately the 4.5 is more tuneable and users will see 400 - 440 depending on, for example, how much they spend whereas the 4.5's disguised as 4.2's are a little less tuneable and a little less powerful. The true 4.2's have less room again for tuning, afaik, and will probably be circa 350 - 370 bhp?
IMHO.
The 4.5 was meant, afaik, to be a better 'GT' ie less intense but also more powerful. The reality was that whilst the engine was slightly less vicious in its delivery the 4.5 was hardly any more powerful. The debate re magazine road tests and owners experiences can swap this debate a little.
Ultimately the 4.5 is more tuneable and users will see 400 - 440 depending on, for example, how much they spend whereas the 4.5's disguised as 4.2's are a little less tuneable and a little less powerful. The true 4.2's have less room again for tuning, afaik, and will probably be circa 350 - 370 bhp?
IMHO.
Byker28i said:
Unless Joo worked his magic, then you can squeeze an extra 10 horses
Exactly, not much improvement from tuning. Mikeinsheffield has approx 399.9 from his late 4.2 (ie a 4.5) whereas I believe the earlier 4.2's even with the same work from Joolz will not be quite as powerful as this (assuming it is representative). Gazzab said:
Exactly, not much improvement from tuning. Mikeinsheffield has approx 399.9 from his late 4.2 (ie a 4.5) whereas I believe the earlier 4.2's even with the same work from Joolz will not be quite as powerful as this (assuming it is representative).
Clivef's 4.2 made 404hp IIRC - That work of art belonged in the Tate.
Gazzab said:
You'll get a few responses I'm sure but the 4.2 was only a 4.2 until about 2000 when it was in fact a 4.5 but with a 4.2 induction/top end.
The 4.5 was meant, afaik, to be a better 'GT' ie less intense but also more powerful. The reality was that whilst the engine was slightly less vicious in its delivery the 4.5 was hardly any more powerful. The debate re magazine road tests and owners experiences can swap this debate a little.
Ultimately the 4.5 is more tuneable and users will see 400 - 440 depending on, for example, how much they spend whereas the 4.5's disguised as 4.2's are a little less tuneable and a little less powerful. The true 4.2's have less room again for tuning, afaik, and will probably be circa 350 - 370 bhp?
IMHO.
Cheers gazzab, so if i understand this correctly, the 4.5 has the same top end, presumably induction, heads ?, exhaust ? as the 4.2, with an extra 300cc provided by either bore increase or stroking (different pistons ?). and as athomp04 says, bigger discs front and rear ? So what is meant by easier to tune ? Is it a case of induction mods are more effective because the 4.2 top end strangles the extra capacity of the 4.5 ? Or are/and the heads on the 4.5 different (porting/valves maybe ?)therefore taking better advantage of any induction mods ? Another question, do the 4.2 and 4.5 share the same cam ?The 4.5 was meant, afaik, to be a better 'GT' ie less intense but also more powerful. The reality was that whilst the engine was slightly less vicious in its delivery the 4.5 was hardly any more powerful. The debate re magazine road tests and owners experiences can swap this debate a little.
Ultimately the 4.5 is more tuneable and users will see 400 - 440 depending on, for example, how much they spend whereas the 4.5's disguised as 4.2's are a little less tuneable and a little less powerful. The true 4.2's have less room again for tuning, afaik, and will probably be circa 350 - 370 bhp?
IMHO.
Question still not answered: why those particular capacities ? Sounds to me that perhaps 4.5 is the optimum capacity given the bore/stroke ratios but this wasn't established until after the 4.2 was in production ?? maybe perhaps... Or where both capacities offered right from the outset ? Or am I way off the mark ?
Chilliman said:
Cheers gazzab, so if i understand this correctly, the 4.5 has the same top end, presumably induction, heads ?, exhaust ? as the 4.2, with an extra 300cc provided by either bore increase or stroking (different pistons ?). and as athomp04 says, bigger discs front and rear ? So what is meant by easier to tune ? Is it a case of induction mods are more effective because the 4.2 top end strangles the extra capacity of the 4.5 ? Or are/and the heads on the 4.5 different (porting/valves maybe ?)therefore taking better advantage of any induction mods ? Another question, do the 4.2 and 4.5 share the same cam ?
Question still not answered: why those particular capacities ? Sounds to me that perhaps 4.5 is the optimum capacity given the bore/stroke ratios but this wasn't established until after the 4.2 was in production ?? maybe perhaps... Or where both capacities offered right from the outset ? Or am I way off the mark ?
Ummm....nope. The later 4.2 and 4.5 are the same bottom end but with the 4.5 having different 'top end' (capacity, induction etc)Question still not answered: why those particular capacities ? Sounds to me that perhaps 4.5 is the optimum capacity given the bore/stroke ratios but this wasn't established until after the 4.2 was in production ?? maybe perhaps... Or where both capacities offered right from the outset ? Or am I way off the mark ?
The front brakes were different in 98 - 00 ish time when the 4.5 had separate bells and rotors, I think later on the two models both had 'tuscan S' front brakes.
Im no expert, ive only had a Cerb for 3 years, but as i understand it.
The main differance is the 4.5 has a bigger bore, the stroke is the same except for the odd example of a AJP tuscan race engine.
It was found that the clyinder liners on the 4.2 partly mask the fuel/air inlet valve, and there fore restricted performance, this was over come with the bigger bore of the 4.5 pistons and thinner clyinder liners so the inlet valve is not masked on the 4.5 and hence the big performane gain from only an extra 300 cc.
Even better is the 4.7 conversion which is the same again, more fuel and air getting in due to more clearance.
As for the 4.8,,,, i think thats a myth made up by Gazzab to get us all going
If you remove the induction from a 4.5 and a 4.2 the rest of the engine is the same, possibley a differance in the cranks but thats about it i think
The main differance is the 4.5 has a bigger bore, the stroke is the same except for the odd example of a AJP tuscan race engine.
It was found that the clyinder liners on the 4.2 partly mask the fuel/air inlet valve, and there fore restricted performance, this was over come with the bigger bore of the 4.5 pistons and thinner clyinder liners so the inlet valve is not masked on the 4.5 and hence the big performane gain from only an extra 300 cc.
Even better is the 4.7 conversion which is the same again, more fuel and air getting in due to more clearance.
As for the 4.8,,,, i think thats a myth made up by Gazzab to get us all going
If you remove the induction from a 4.5 and a 4.2 the rest of the engine is the same, possibley a differance in the cranks but thats about it i think
fatjon said:
The late "4.2" post 1999 was in every way identical to a 4.5 except for the inlet manifolds and ECU firmware. Same crank, cams, pistons, rods, heads, valves, everything.
God knows how they got away with being economical with the truth on the CC number on the log books.
Jon
Cheers Jon, er, I might be being a bit thick here, but is this saying that from 2000 on all new cerbs had a capacity of 4.5 litres, however the one's badged as 4.2 (and sighted as 4.2 in the log book) had a different inlet manifold and ECU than the cars badged as 4.5 ?God knows how they got away with being economical with the truth on the CC number on the log books.
Jon
So what was the difference between the pre 2000 4.2 and 4.5 ? Presumably pre 2000 4.2's were the same as 2000 on 4.2's but with a capacity of only 4.2 ? Jeez this is confusing. Thank God I've got an RV8
(which is a 5 litre 3.9 engine 
)
Chilliman said:
And why two capacities that seem so near to each other, only 300 cc ? (bigger the engine the less the capacity differential..)
OK here's an answer to your initial question: PRW just liked to increase the cc on engines. As mentioned above, there are other capacities and TVR are not alone in offeriing large engine sizes close together, eg Jensen with the 7.2 and rarely sold 7.0 Hemi option.Another reason is to differentiate it from the early engines. The early engines had a few problems and the parts had MCD stamped on them. As the parts were developed the TVR designed engine bits lost the MCD stamp. When PRW fell out with AM he was keen to do away with the AM references and changed as many engine bits as possible, inc the name to the TVR V8. The main difference was the larger journal crank and to further differentiate the engines the new ones had the 300cc increase.
JR said:
..... When PRW fell out with AM he was keen to do away with the AM references and changed as many engine bits as possible, inc the name to the TVR V8. The main difference was the larger journal crank .....
Aha ! Always good to hear from someone whio knows. Thanks for that, Jonathan !Have you any idea when this happened ?
e.g. During or post Series 1 models ?
Ta !
Paul
JR said:
Chilliman said:
And why two capacities that seem so near to each other, only 300 cc ? (bigger the engine the less the capacity differential..)
OK here's an answer to your initial question: PRW just liked to increase the cc on engines. As mentioned above, there are other capacities and TVR are not alone in offeriing large engine sizes close together, eg Jensen with the 7.2 and rarely sold 7.0 Hemi option.Another reason is to differentiate it from the early engines. The early engines had a few problems and the parts had MCD stamped on them. As the parts were developed the TVR designed engine bits lost the MCD stamp. When PRW fell out with AM he was keen to do away with the AM references and changed as many engine bits as possible, inc the name to the TVR V8. The main difference was the larger journal crank and to further differentiate the engines the new ones had the 300cc increase.
(like PW's dog biting a chunk out of the front corner of the Chimaera body prototype). I also thought the story about Clarkson falling out with PW and subsequent derogatory remarks about TVR on Top Gear very amusing (and a bit sad at the same time..)Cheers, Richard.
Gassing Station | Cerbera | Top of Page | What's New | My Stuff