carbs to efi: which manifold?

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but after all, what is the difference between these two? more torque at low
rpm with thor? why so?

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The Thor has a MUCH longer intake length from valve to throttle butterfly and this increases the inertia of the air at lower revs but restricts air flow at higher revs.
In addition BMW introduced a taper into the inlet which used the Hemholz Resonance effect to increase air volume/velocity at lower revs.

You trade off -10% at higher revs for up to +50% at lower revs say 1500 tapering to 15% at 3000, if you also manage the timing curve by adding advance at lower revs.
Regards Philip A

i see. probably increased airflow at lower rpm would besides higher torque and power also mean increased fuel consumption? :eek:

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No. As long as you control the cruise Air fuel ratio ( usually with o2 sensors) , and add lots of advance the cruising fuel economy is improved quite a bit.

I ended up at around 15L per 100 pulling a 750Kg camper trailer at a true 100Kmh in my 92 RRC 3.9, which is better than the factory claim for no trailer.
Generally the lower the revs the more economical, and that is why most modern 8 speed etc transmissions have about 3 overdrive ratios.

I have found the economy secret with a 3.9 is lots of advance at cruise throttle openings, along with o2 sensors , on a 14CUX. You don't need the o2 sensors if you have a dyno to tune cruise and full throttle mixtures but o2 sensors maintain 14.8:1 AF automatically, or if you have a wide band sensor and the provision in your ECU you can run even leaner.
Regards Philip A

that's great news. after all thor doesn't seem a bad option at all :)
the thing is with earlier advance you face the dangeors of detonations. but i hope the firmware will have provision to control it (with hip9011 i guess) and then i'd need to install two knock sensors. by the way, i heard some bad sounds from the engine at low rpm on fifth gear climbing uphill - could easily be deton (i created a simulated sound- will try posting it tomorrow).
besides that, with early advance you should monitor exgaust temperature?
and yep, i got wbo spartan sensor from 14point7. still have to find proper place for it on my exhaust shiny pipe.

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Just be clear that the limits of advance at high loads and low revs is well known with RV8s and you would not be wise to exceed them.

The advance I am talkng about is cruise or light throttle advance , the modern equivalent of what used to be "vacuum" advance.

Regards Philip A

i thought those limits were related to the camshaft configuration... anyway, i'd first thoroughly examine all available ignition tables (ms and such).
pinging at high load low rews could mean overly sensitive vacuum advance? it should be retarded and i'll gain some torque?
there were couple of intakes available here just a month ago, and now there are none.. :-(
it might be i should start just with ignition for starters (pun nonintended)
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pinging at high load low rews could mean overly sensitive vacuum advance?

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No.
RV8s have a VERY conservative centrifugal advance curve and vacuum advance has nothing to do with high load.
I suggest
1 Your engine has a lot of carbon in it. OR
2 you have too much static advance OR
3 you are using petrol of insufficient octane
4 or you are asking too much of the engine and need to change your driving style.
OR all of the above.
I fthe timing is less than say 9 degrees BTDC then it will be one of the other things.
I don't know whether you have Low compression or high compression. This is stamped next to the engine number either 8.13:1 or 9.35:1.
High compression 9.35:1 needs 98 RON.
Regards Philip A

1. carbon - you mean it's just dirty? or carb is pouring too much fuel?
2. hope to build a stroboscope (or how is it called in english?)
3. definitely. using 92 - but we used to it on many cars, plus the higher-octane fuel here is believed to achieved through some additions, but not from the refined process (sort of artificial?) 98 is available at only few of the petrol stations.
4. could easily be the problem. too lazy to change gears, got used to low revs.

and yep, it's 9.35:1 (d26 block)
here's the sound (i calculated the frequency out of bore size)
(if you add the engine noise - it could easily be what I am talking about)
hope, next time I start the car, if I hear that noise - i'd try to make live recording of it...

Philip, did you also install trigger wheel on your vehicle? Was it a serpentine belt, or an older engine with multiple belts?
I wonder what is the proper sequence of operations to remove the pulley from the crank and how to put it back with lots of belts (alternator, ac, steering pump, what else?)… oh, my car is lhd.

my manifold from 3.5 engine is on its way to my rover. will post pictures soon. meanwhile trying to figure out the cranking revs for the engine... ms guys, any ideas?

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