Discussion
Morning chaps,
I was just having a ponder and thinking about the Rover V8.. (not in a pervy way, dont worry
)
Anyway, in relation to it's capacity it doesnt seem to produce particularly high HP.
Does anyone have the low-down on what restricts its performance? Be it Valve Size, Head Design etc etc?
I'd be very interested to know.. In comparison the AJP8 seems to be able to churn out very respectable BHP both standard and with mild mods.
Cheers gang,
Nick
I was just having a ponder and thinking about the Rover V8.. (not in a pervy way, dont worry
) Anyway, in relation to it's capacity it doesnt seem to produce particularly high HP.
Does anyone have the low-down on what restricts its performance? Be it Valve Size, Head Design etc etc?
I'd be very interested to know.. In comparison the AJP8 seems to be able to churn out very respectable BHP both standard and with mild mods.
Cheers gang,
Nick
AJP and RV8 are completely different designs. I might have this wrong, but I think the flat plane crank of the AJP means it only fires half as often per revolution compared to the 90deg crank of the RV8. This means it revs higher, develops its torque further up the rpm band and hence develops a lot more bhp. Chalk and cheese though in terms of driveability (note to Cerbie owners - I don't mean the AJP is any less driveable - just that it's characteristics when driving are very different...).
The AJP is a four stroke engine, so each cylinder fires once for every two crank revolutions, just like the rover V8. The difference is that the crank has its throws in only one plane, so the engine is effectively two inline fours connected via a common crank. The single plane crank gives rise to the vibey feel of the AJP, since it's not naturally balanced as the RV8 is.
Steve.
Steve.
Edited by Steve_T on Tuesday 3rd October 11:31
Yeah i've heard the flat-plane crank scenario regarding the AJP..
Ok, perhaps a better comparison, the current ford V8 used in the Mustang is around 300bhp standard in 4.6 guise with all the emmission malarkey.. Obviously the V8's in the BMW's make some pretty big BHP..
I was interested to know if there was one specific aspect of the RV8 which makes it very lazy on BHP.. By the sounds of it Head Design seems quite an issue..
Ok, perhaps a better comparison, the current ford V8 used in the Mustang is around 300bhp standard in 4.6 guise with all the emmission malarkey.. Obviously the V8's in the BMW's make some pretty big BHP..
I was interested to know if there was one specific aspect of the RV8 which makes it very lazy on BHP.. By the sounds of it Head Design seems quite an issue..
It's a 2 valve per cylinder pushrod motor designed eons ago. They always make grunt as opposed to bhp which is what the yanks like
It's held back by the inability to breath at upper rpm's because the valve are is small compared to a 4 valve head arrangement. The heads are also pish poor and have never been revamped by the factory.
Boosted.
It's held back by the inability to breath at upper rpm's because the valve are is small compared to a 4 valve head arrangement. The heads are also pish poor and have never been revamped by the factory. Boosted.
Boosted LS1 said:
It's a 2 valve per cylinder pushrod motor designed eons ago. They always make grunt as opposed to bhp which is what the yanks like It's held back by the inability to breath at upper rpm's because the valve are is small compared to a 4 valve head arrangement. The heads are also pish poor and have never been revamped by the factory.
Boosted.
It's held back by the inability to breath at upper rpm's because the valve are is small compared to a 4 valve head arrangement. The heads are also pish poor and have never been revamped by the factory. Boosted.
Thanks for that... i've been following your conversations regarding Turbo upgrades with great interest for when the finances allow.
Asking the obvious question, is it not possible to have the heads 'done' and fit extra large valves, reasonably cost effectively? or do the sums just not add up, hence the forced induction routes which are cropping up?
BHP is a function of engine revs. If you look at the specs on something like a BMW V8, you'll find it produces it's max bhp well in excess of 5200rpm. By making the engine rev higher (overhead cams and per-cylinder ignition help), you can fit a different camshaft profile and move the torque band higher in the rev range. If the torque band is higher in the rev range, you immediately get a higher bhp figure which is excellent for selling cars. Of course if you look closely, you'll see that the torque figure isn't much different to the Rover V8.
The question is, do you want a car with lots of bhp or a car with the torque band in a more useable position. As Joolz once explained, it's the area under the torque curve which indicates the performance of the engine. Personally, I like to be able to tootle around at 1500rpm and get immediate hyperspace when required rather than having to change down 2 gears first.
Ian A.
The question is, do you want a car with lots of bhp or a car with the torque band in a more useable position. As Joolz once explained, it's the area under the torque curve which indicates the performance of the engine. Personally, I like to be able to tootle around at 1500rpm and get immediate hyperspace when required rather than having to change down 2 gears first.
Ian A.
Fire99 said:
Boosted LS1 said:
It's a 2 valve per cylinder pushrod motor designed eons ago.
Thanks for that... is it not possible to have the heads 'done' and fit extra large valves...IPAddis said:
BHP is a function of engine revs. If you look at the specs on something like a BMW V8, you'll find it produces it's max bhp well in excess of 5200rpm. By making the engine rev higher (overhead cams and per-cylinder ignition help), you can fit a different camshaft profile and move the torque band higher in the rev range. If the torque band is higher in the rev range, you immediately get a higher bhp figure which is excellent for selling cars. Of course if you look closely, you'll see that the torque figure isn't much different to the Rover V8.
The question is, do you want a car with lots of bhp or a car with the torque band in a more useable position. As Joolz once explained, it's the area under the torque curve which indicates the performance of the engine. Personally, I like to be able to tootle around at 1500rpm and get immediate hyperspace when required rather than having to change down 2 gears first.
Ian A.
The question is, do you want a car with lots of bhp or a car with the torque band in a more useable position. As Joolz once explained, it's the area under the torque curve which indicates the performance of the engine. Personally, I like to be able to tootle around at 1500rpm and get immediate hyperspace when required rather than having to change down 2 gears first.
Ian A.
Yep very good point.. Though another 100-150bhp would be nice with the same torque curve.
Lots of low down torque is definitely a fine attribute of the RV8
Steve_T said:
The AJP is a four stroke engine, so each cylinder fires once for every two crank revolutions, just like the rover V8. The difference is that the crank has its throws in only one plane, so the engine is effectively two inline fours connected via a common crank. The single plane crank gives rise to the vibey feel of the AJP, since it's not naturally balanced as the RV8 is.
Steve.
Steve.
Edited by Steve_T on Tuesday 3rd October 11:31
Nicely explained by dodged the question..
The reason is many fold - AJP engine was designed (around 1993) from the offset to be a class leading sprorts car engine, it had very well designed heads and huge valves.
In 4.5 guise and with a dry sump - it achieved a genuine 450 bhp.. but with production cost saving this figure dropped.
As many Chevy fans (Jelly) will tell you - having 'just' 2 valves and not 4 per cylinder does not harm at all at lower revs - 4 valve heads really only come it to their own at higher revs.
To get back to the Rover V8 - this was designed in the 1950's by Oldsmobile (in USA) and was not made to be a sports car engine ..
The heads are very restrictive - do not have a good combustion chamber shape, inlet and exhaust vavles are not central restricting valve size and the ports are very small.
The engine has been around a long time - so man have worked around the basic head limitation - increasing capacity is the mod that has seen the biggest gains..
But compare the heads with a small block chevy and you can see the problem.
A 5.0 l Griff engine will tryically produce 270 bhp out of the box and with modifications can achieve 330 bhp and 350 ft lbs of torque.
A stage 3 head tops out at around 100 CFM of air (inlet) not many bettering this or people even will to say what theirs does.
Hope that helps
Wildfire said:
Another factor to bear in mind is that the RV8 is not really a modern design. It's quite old now.
It's ancient (not as ancient as a ford though) but light and that's it's really big plus.
In reply to other posts,
BHP is also related to torque, not just revs so this is where turbo's score big time. Cram in the boost, increase the torque but keep the revs stock so the mechanicals aren't additionaly stressed. Manage the extra heat and you have a big block rover engine. For the valves, I always think of 80mm in my head. This is like 43 and 37 mm valves. You can move the bias either way you like but 80 is the figure. Go past 80 and you need to move the guides further apart. Porting a rover head will always help with turbo applications but if you're on a budget then fit a turbo for now and port in the future.
Boosted.
Thanks alot guys for taking the time to explain the situation...
I've always known the RV8 is old and a very simple design but you see over the years some huge hp from the LS series Chevy lump (be it rather highly developed) so was interested to see where the RV8 weakness is.
Taa Muchly.
Economically i think Boosted's approach scores in the £'s per BHP stakes.
I'm looking at next years plan at the moment, to keep the Chim and boost the HP a touch or move to a Cerb.. Obviously the Cerb route is easier but there is the big issue of the Roof (or lack of one in a Chim) and the Tuscan Convertible will be out of my price bracket. (anyway i'm drifting off topic here... and i started the thread )
It explains very well why the RV8 was chosen for the Wedges through to Chim...
I've always known the RV8 is old and a very simple design but you see over the years some huge hp from the LS series Chevy lump (be it rather highly developed) so was interested to see where the RV8 weakness is.
Taa Muchly.
Economically i think Boosted's approach scores in the £'s per BHP stakes.
I'm looking at next years plan at the moment, to keep the Chim and boost the HP a touch or move to a Cerb.. Obviously the Cerb route is easier but there is the big issue of the Roof (or lack of one in a Chim) and the Tuscan Convertible will be out of my price bracket. (anyway i'm drifting off topic here... and i started the thread
) It explains very well why the RV8 was chosen for the Wedges through to Chim...
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