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Making an aggressive camshaft drive better at low rpm

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Hi all,

I have a rover v8, with aftermarket higher flow heads, custom headers and a few other modifications. The camshaft that came with the setup has a large amount of overlap. I’ve searched for the specs but have yet to find them. In RV8 circles all I can find is that the cam is one of the most severe

The car is running the stock rover / TVR single plenum with standard trumpets.

The problem I have is that the car is near undriveable under 2k rpm. The car will shunt and buck on part throttle and under deceleration. If I am accelerating or load the car it is fine. But the low speed manners makes city driving speeds (anything under 40mph) a complete chore, lots of clutch slipping, coasting and such.

I believe the main problem is that all cylinders sharing the same low capacity plenum is resulting in charge robbing and contamination. I attempted to space the plenum to increase capacity, but this did nothing to help.

There are no reasonable cost or prove dual plane intake setups that have been proven.

Are there any recommendations anyone has on how to improve low rpm manners and make the car somewhat more drive-able in such a setup?

I am running an aftermarket ecu, so am able to adjust most parameters.

thanks.

Play with injector phasing and soft ignition timing, most things with a lot of overlap can be tamed a bit with measured lambda about 0.85

Make sure you don't have a bad throttle position sensor. I had one that only failed at low-load cruise speeds -- it was just worn out in that area. Another vehicle had a broken wire for the TPS making a "noisy" signal at certain RPMs / vibrations.

Make sure you can have a smooth throttle and map sensor values, so that acceleration enrichment isn't getting involved.

I would expect the engine uses some form of airflow metering device? What I expect is there is a LOT of reversion - the pistons pushing the charge back through the intake ports - because of the overlap. This in turn moves some of the air in the plenum back through the metering device and that part is effectively measured 3 times - in, out, back in with the rest of the charge being measured once.

There can also be, as you surmise, a problem with airflow distribution within the manifold/plenum.

As Michael said, you can sometimes compensate to a point by carefully mapping the engine's fuelling and timing. If it does use an AFM on the intake(s) to the plenum, you may get some improvement by placing them further from the plenum, but at the cost of some response - you may have already noticed that with the plenum spacer. Oh, you could also try retarding the camshaft slightly, if you have the valve to piston clearance, as that will open the intake a little later and can make a big difference to the engine's torque characteristics - 4-6 degrees should be plenty to show a change. Heck, you may not have it correctly timed now?

Ultimately, though, you may have to either put up with it, fit a milder camshaft, maybe with high lift rockers - it may be too much duration for the package, anyway? Perhaps consider a different plenum/manifold setup - on the last, there have been many different designs used over the years on the variations of that engine - is it an original RV8 one? Is it a single or dual plenum intake? Has it been modified?

Thanks for the response, I had considered swapping out the TPS to see if that helps. The car doesn’t run a MAF, it used a MAP and IAT sensor.

I have heard that with aggressive camshafts the map sensor can also get a bad signal at low rpm / part load as mentioned, but wouldn’t be sure how to smooth that out if that was the case.

It is still running the single sd1 intake plenum. I have considered ITB’s or a dual plane in hope that may help, but there do not appear to be many options over here, and I could be into 1000’s with no guarantee it would make the car drive better.

I’ll do some more research to try and discover exact cam specs and to see if perhaps the cam timing can be adjusted as well thanks.

With injector phasing on an aggressive cam, what would you expect to make a difference?

Thanks.

I had a quick check for "Rover V8 Plenum" and came up with a variety of options, most dual inlet - IIRC there was also a factory duel inlet plenum for the SDi's back in the day?