Rover V8 Looking for help to smooth idle and sub 2000 rpm

[Else]

Hello all.

History:
I have been developing my Rover V8, in a TVR Chimaera, with the help of a well known Rover V8 engine company who supplied and fitted special heads developed along with David Vizard.

Engine size 5,200cc
Compression is 10.3
Valves are 1.83 inlets and 1.55 exhaust
fully ported with raised roofs on inlet and exhaust and welded floors on both.
Bespoke twin plenum, one per bank.
Twin large diameter throttle butterflies
Rod length is 6
Emerald ecu mapped ignition and fuel injection.

I have had problems with lobe wear on 2 conventional hydraulic camshafts after a few thousand miles each time so to extend cam life have had a new roller cam fitted supplied by Woody at the Wedgeshop in the US.

I don't understand the figures quoted, see below, with relation to the behaviour of the engine, can anyone explain?


This is the conversation between me, V8D and Woody when we decided on the cam spec. My basic requirement was a stable idle but wouldn’t mind having to raise idle rpm or retard ignition to smooth the idle out.

Woody said:

Some Fuel injection system do not adapt to a lot of overlap because at idle it may be too rich for the system. So you can correct that by bringing the Lobe Center up say to a 110 instead of a 108. The motor still makes good power up top but maybe not as intense. The actual overlap is the 242-250 @.050.
Lift 544
Dur. 310/318
Dur @ .050 242/250

Lobe Center 110 or 108 for more high end and a little lopey idle
We could go go 234-242 but my Minium choice for your motor would 242-242 LC 110 and still my first choice is my Original on a 110.
I have a TR7 V8 with a Nice custom built 10.1 comp.3.9 running a roller Cam that is 222-228 on a !C of 111. This is my Traveling car, i drive appox 7k mile a summer with this car.
Bad 8 had roller with the Spec's i sent you on a 108, now has a Flat tappet cam 254-250 on a 104 LC LOL of this is my HOT ROD

V8D said:
I would definitely go with the wider lca, I am a little concerned with the duration, that is huge for a road car! Typically yours that is in there runs around 220, it will certainly make some big numbers lol

I have had the engine mapped and have subsequently tried to tame the characteristics in the idle to 2000rpm range with limited success. It shunts quite a lot which makes town driving unpleasant. I have backed off the ignition to 0 degrees in this range which has helped and I have also richened it up to between 12-12.5AFR in the same range but it still lurches and jumps. My old cam was brilliant, pulling cleanly from 1000rpm without any hesitations.

It has been suggested that changing the cam timing might help, can anyone advise which way, how much etc?

I would like to get it back to a smooth running and torquey engine if I possibly can.

Thanks Andy

[stevieturbo]

What V8D say makes sense. That IS a big cam, and probably intended for a high rpm screamer. Not an ideal choice and unlikely to ever fulfil your requirement of a smooth idle.

And what are the details of those plenums and intake ? That could be playing a role too, and not necessarily a good one. And as one of the guys here found out recently via a lot of testing, the RV8 seems to need pretty long runners to make any decent power although that would come down to testing.

[GreenV8S]

Else said:

.
Bespoke twin plenum, one per bank.

I assume you mean the two banks are isolated. Not sure whether that will be making it better or worse than a single plenum, given the firing order. Has anyone else got a similar setup on a similar engine for comparison? Throttle bodies are the best known way to tame a cam. Is that an option?

[Else]

Thanks for the replies.

The twin plenum is 1 plenum per bank with an 80mm butterfly at the front of each. Both draw cool air from in front of the radiator.
Joolz at Kits & Classics did the mapping and he is of the opinion that the runners are too short.
He noted that the new cam lost power all through the rev range except for the top. This is exactly the opposite of what I wanted so you can guess I am a more than a little disappointed. I was led to beleive that a roller cam can open and close the valves more quickly which should enable the valves to be open longer to produce morepower without compromising low revs driveability.
I dont understand the figures quoted, can anyone explain?

Thanks Andy

[Kokkolanpoika]

Your compression ratio is on the low side. Have you got any idea when inlet valve is closing? Cam card? You need at least 12CR on that cam.

I will run Kent M256 camshaft and throttle bodies and it will idle like a stock car. But im running 11.8:1 compression ratio witch is too low still.. i do not have any problem with mot or idle issue etc.

With my new compo wild cat heads and same Kent M256 cam. I will try to reach 12.3:1 compression ratio.
I do not like those plenum inlet manifolds if we are trying to make smoot ride and power. ITB is way to go.

[Else]

Mmm, nobody mentioned minimum CR when discussing the the best cam for my engine?
ITBs may be the only way to go then to make it driveable. According to Joolz i need a long inlet tract, what would be the best type to go for bearing in mind my heads are offset on the block so would meed each bank to be seperate?

[Kokkolanpoika]

Please check cam card if you have got more data for inlet closing point. I think it is near 80deg... Also roller cam has got more agressive open/closing ramps. So it wont make it any better than normal cam.
When choosing cam. It is nessecary to check compression also. Too wild cam and low compression make it run poor.

Ps: my engine is also 5200cc and i can drive it 800-1000rpm in 1st gear without issues. Ignition advance is 8deg at idle to 1500rpm.

[Mignon]

I'm not sure what you expect anyone in here to say. You took out what was obviously a nice tractable road cam and replaced it with a 310/318 degree race one. Surely it should come as no surprise that it's now sh11te at low rpm? Maybe this Woody person didn't understand that your car is a road car or maybe he's just a f**king idiot like most in the tuning world. Selling engine parts is no guarantee that someone knows anything about actual engines or speccing components properly.

Solution is easy. Take it out and put a proper road cam back in.

[stevieturbo]

Else said:

Thanks for the replies.

The twin plenum is 1 plenum per bank with an 80mm butterfly at the front of each. Both draw cool air from in front of the radiator.
Joolz at Kits & Classics did the mapping and he is of the opinion that the runners are too short.
He noted that the new cam lost power all through the rev range except for the top. This is exactly the opposite of what I wanted so you can guess I am a more than a little disappointed. I was led to beleive that a roller cam can open and close the valves more quickly which should enable the valves to be open longer to produce morepower without compromising low revs driveability.
I dont understand the figures quoted, can anyone explain?

Thanks Andy

I really cant imagine why anyone would ever think a Rover V8 would ever need an 80mm throttle blade, nevermind two of them !!!

Sounds like a very poor and badly designed package all round.

And "roller" cam means nothing, other than it's intended to be used with roller lifters.

Your cam has far too much duration, too much overlap, induction sounds very poor choice......time to go back to the drawing board.

Although some could be salvaged with a more sensible cam profile.

[anonymous-user]

You can make an engine with a fixed (ie none VVT) aggressive cam idle well (not OEM well, but well enough) but it takes port throttles to do so. This is to prevent charge exchange on the overlap, ie to maximise the unthrottled to throttled volume. Put the throttles close the valves, and when those throttles are closed at low loads, they are of course choked (supersonic flow)), hence they prevent any significant charge reversal or charge robbing, even with high overlap valve timing under low charge intertia conditions (low speed and load).

[anonymous-user]

Regarding runner lengths, every runner ever made, with the exception of an F1 engine doing 20,000 rpm is "too short" ie it's pretty much impossible to make a practical runner long enough that can tune to the fundamental harmonic!

Consider the speed of sound at 1 bar and 25 degC, which is 346 m/s. Consider a 4 stroke engine going 7000rpm, ie firing at 3500rpm, which is one firing event per 0.017 seconds, in which time the shock wave has travelled 5.93 meters! ie to tune to the fundamental at that speed you're going to need a port that is pretty much 3 meters long!!

[Kokkolanpoika]

http://www.johnealesroverv8.co.uk/7.html

I will go Eales Down Draught manifolds. They are separate, so can be bolted to your heads if bolt pattern is std. And then buy set of Jenvey throttle bodies and air horns.

[GreenV8S]

Isn't the duration of the intake stroke the significant value for resonance? So roughly twice as long as you're calculating, for the intake stroke duration to match the runner resonance duration.

The intake doesn't have to hit resonance to affect the mass flow, though. The inertia is just delaying the mass flow relative to the valve timing, as I see it. So a longer runner means you can keep the intake open longer past btc without getting flow reversal, and so on.

[227bhp]

Else said:

I don't understand the figures quoted, can anyone explain?

Thanks Andy

You can find it on the internet if you look, it's no secret.

What is a bit more hidden is 'DCR' so you need to go looking for an explanation of 'Dynamic compression ratio'. This will outline how when the static CR goes up you match it with more cam duration; big cams and high SCR go together, smaller cams and low CR go together.

LCA (lobe centre angle) is how much overlap you have, basically how far both valves (intake & exhaust) are open together at TDC. The further they are open at this point the more power you will eventually make, but unless you make provision (throttle bodies) you will have poor idle and loss of low down power/torque as the exhaust and the inlet valve are both open at the same time, so the gas travels back through one and up the other.
At high rpm the air speeds are much higher so the reverse happens - the exhaust gas pulls the intake charge into the cylinder before the valve closes.

[Else]

Mignon said:

I'm not sure what you expect anyone in here to say. You took out what was obviously a nice tractable road cam and replaced it with a 310/318 degree race one. Surely it should come as no surprise that it's now sh11te at low rpm? Maybe this Woody person didn't understand that your car is a road car or maybe he's just a f**king idiot like most in the tuning world. Selling engine parts is no guarantee that someone knows anything about actual engines or speccing components properly.

Solution is easy. Take it out and put a proper road cam back in.

Hello Mignon, I congratulate your honesty. I'll give you the history first then maybe we can come up with a plan to sort this shyte mess out.
I have followed advice all the way through this project when I bought and had fitted the special raised port David Vizard heads. Because the standard manifold would no longer fit I was told to make up a double plenum with each chamber about the size of a 2 litre coke bottle with throttle bodies as big as possible to get lots of air in. So I had the twin plenum inlet manifold made up from scratch and I sourced two 80mm throttle bodies, one fitted to each plenum. Mapping was difficult but we got it to behave well and it was nice to pootle around in but would pull well when opened up.
But during the next couple of years, other minor issues apart, I had to replace 2 cams which failed due to one of the lobes wearing out so was advised to go to a roller cam, details shown previously. When speccing the cam I didn't pretend to understand the figures given, I just wanted a cam that gave me an engine that idled nicely and pulled well from low revs. I was told that the roller cam would give that effect and produce more power overall.

So to sum up, I have ended up with the wrong type of inlet system with the wrong cam in an engine with good heads but the wrong compression ratio. Jesus what a feck up!!

Shoot me down in flames if you like but I thought I was being given good advice.

I now need to take a step back to sort this out. Who would be the best person or company to go to help me?[url]

|https://thumbsnap.com/MR7OwoEn[/url]

[anonymous-user]

BTW, when you say "idles badly" what actually do you mean?

Even with a very unstable burn (misfires) an engine can still be made to idle correctly at a sensibly low speed without stalling (assuming it also has a sensible mass flywheel fitted)


First thing i'd do is to look at the EMS calibration again (particularly with regard to accurate Load Determination (is your LD from MAP or TPS, and are you sure that unstable or oscillatory LD is not erroneously triggering the transient fuel strategy?), and the second thing i'd do is to make sure my EMS has some sort of idle speed control, ideally using Electronic throttle bodies, but if necessary with solenoid / stepper air bypass valve(s)

Edited by anonymous-user on Thursday 14th March 19:28

[Else]

Max_Torque said:

BTW, when you say "idles badly" what actually do you mean?

Even with a very unstable burn (misfires) an engine can still be made to idle correctly at a sensibly low speed without stalling (assuming it also has a sensible mass flywheel fitted)


First thing i'd do is to look at the EMS calibration again (particularly with regard to accurate Load Determination (is your LD from MAP or TPS, and are you sure that unstable or oscillatory LD is not erroneously triggering the transient fuel strategy?), and the second thing i'd do is to make sure my EMS has some sort of idle speed control, ideally using Electronic throttle bodies, but if necessary with solenoid / stepper air bypass valve(s)

Edited by Max_Torque on Thursday 14th March 19:28

I’m not sure I said it idles badly, it is stable at around 1000rpm but it chugs a lot and if you try to creep along in traffic in say 2nd or 3rd gear at idle it shunts the transmission very badly. Then if you open the throttle slightly it seems to misfire and jerks about a bit until you get to around 2000 rpm where it all seems to smooth out. Hope that makes sense

[Else]

Max_Torque said:

First thing i'd do is to look at the EMS calibration again (particularly with regard to accurate Load Determination (is your LD from MAP or TPS, and are you sure that unstable or oscillatory LD is not erroneously triggering the transient fuel strategy?), and the second thing i'd do is to make sure my EMS has some sort of idle speed control, ideally using Electronic throttle bodies, but if necessary with solenoid / stepper air bypass valve(s)

Edited by Max_Torque on Thursday 14th March 19:28

I don’t understand what EMS is but I do know that it is mapped using TPS. Joolz did try mapping via MAP but it was much worse ie shunting very badly.
Idle speed control is via an idle control valve initially then ignition advance for fine control. It seems to work well.

[Else]

Kokkolanpoika said:

http://www.johnealesroverv8.co.uk/7.html

I will go Eales Down Draught manifolds. They are separate, so can be bolted to your heads if bolt pattern is std. And then buy set of Jenvey throttle bodies and air horns.

I don’t have that much space above the engine so would need to mount the throttle bodies horizontally, probably above the rocker covers. I’ve seen curved, banana shaped inlet manifolds that are separate I think.

Edited by Else on Thursday 14th March 21:44

[Arnold Cunningham]

I know it's been stated above - but it's important all the system components complement each other. Cam, head design, bore, stroke, exhaust, intake - it's all part of a tuned system, like an orchestra. So one bit being way off the rest of it, IMVHO, isn't just one bit being off, but screws up the whole song.

Mignon & the others on this thread really know their stuff. Listen and learn from 'em.

Else said:

I don’t understand what EMS is but I do know that it is mapped using TPS. Joolz did try mapping via MAP but it was much worse ie shunting very badly.
Idle speed control is via an idle control valve initially then ignition advance for fine control. It seems to work well.