Hi,
I'm entered in a long distance rally event where the quality of fuel is an unknown. In similar past events, people have been advised that for places it can be as low as 80 Octane. To me, this dictates building a pretty low compression motor - maybe 8:1 - but I still want some oomph for the competitive sections.
Any ideas on how to do this, within the constraints of a 2 litre B20 motor? I don't think we will be allowed to bore/stroke the motor, which makes it a bit challenging.
Regards
JohnH
--
JohnH, Sydney, Australia

I do not think that a cooling system will help you if the problem is low octane fuel.

The problem would be early ignition, nor pre-ignition - the actual ignition would be determined by timing, but too early for the fuel.

Can you obtain some of this poor fuel for testing?

If I remember correctly, my '68 VW had a timing notch about 15 or 20 degrees away from the normal notch that was to be used for countries with bad fuel.

If you are going to use bad fuel you will need to change the timing.
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks

More information on the route suggests that we'll avoid the really low octane/low quality fuels that plague Africa and far eastern Europe/Asia. The only places in Asia that we go are Thailand and Burma. Both those places seem to get reliable high octane fuel. Burma sources fuel out of Singapore.

Inland Australia might be a bit of a problem of octane rather than quality. A lot of the more remote places will only stock our 91 RON Octane (US equivalent about 85 (R+M)/2 measurement).

From Burma/Thailand we fly the cars to Abu Dhabi - if they can't get decent fuel, who can - and then overland to Paris and onto London. So most of the route should be ok.

My current plan - and it is a work in progress - is to build the engine to cope with about 95RON and carry enough additives to see me through the occasional lower octane places.

Regards

JohnH
--
JohnH, Sydney, Australia

Someone else mentioned it as well, but it just occurs to me that both preignition and knocking show up under too-hot conditions. Did you consider some sort of water injection setup, like a mega-squirt or a custom connection for a cold-start injector? I wouldn't expect any change in mileage, but it might cool your initial combustion temperatures enough to eliminate the issues.

Just my "keep it stupid simple" 2 cents.

Happy bricking and enjoy your rally!
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Our '35 Maxim fire truck has a choke and timing lever right on the steering wheel.

Wouldn't it be relatively easy to fabricate something to change the timing from the driver's position no matter how you build the engine.

I would suggest a control similar to a fire truck throttle - It is a knob you turn to make minute adjustments.

Perhaps you could fit a knock sensor that gives you a read out to allow you to time knocks away.

I have seen an electronic knock indicating device fitted to a super charged muscle car - I think a Buick Grand Sport.
--
'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks

I would run your normal or High output engine and either enrich the fuel mixture and reduce the timing, or use a simple water or alcohol injection system when it is necessary to avoid detonation.

Hi all,
I've just been told by the organisers that we'll be avoiding all the worst low octane areas and the worst we will see is 90RON - so a much more conventional higher power but reliable engine is called for. Maybe I should see if Phil S still has the MPPE for sale....
Regards and thanks
JohnH
--
JohnH, Sydney, Australia

I've been off the board for a while so by now you have probably already won the race ;-). But can add that in South Africa my dad used 100 octane (same rating used in AU) at the coast and when we went inland we would drop to 95.

I'm now in New Zealand with my dad's 144. Here I would consider (if I was driving lots and since it is readily available) to convert it to LPG which is about 110 octane. Burning characteristics are slightly different, so for comparison it is more like 100 octane which the car was designed for.

I would not run 91 unless I had a knock sensing electronic ignition and let the performance suffer. Or water injection as someone suggested. Of a friend of mine has used a hydrogen generating cell fed through a vacuum hose which doubled his fuel economy, that might help as well. But then you need a closed loop electronic fuel injection (not open loop D-jet or mechanical K-jet).

No, haven't won it yet: it's not until 2014! I had a contract in South Africa in the mid 1970s and was based at J'burg - altitude 5700 ft, a bit higher than Denver. We certainly noticed it ourselves and were told when we went down to the coast I would have to rejet the carbs. American members of the board would be more familiar with these altitude changes than us Austalasians.

Equally important is power loss: as a rule of thumb you'll lose 3% for every 1000ft (about 300m to us Australasians!). ANd that's if you rejet all the time.

Food for thought.

Regards

JohnH
--
JohnH, Sydney, Australia

I've had plenty of low compression motors that went much harder than stock.

I don't think we will be allowed to bore/stroke the motor, which makes it a bit challenging.

Find out what you are allowed to do! I think if you are running under some kind of C.A.M.S. rules, then you might be restricted to +10% capacity.

As far as low compression is concerned, it's all the same except your cam which needs to have an exhaust lobe a little smaller than the inlet. (Low compression is slower burning, so you can't open the exhaust valve too soon.)

What intake & exhaust are you running?

--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Supp regs aren't out until Feb, but based on previous similar events e.g.

"B.6.2. Engine capacity is restricted to the manufacturer's specifications for cars produced prior to the "Date" or a homologated option prior to the "Date". Engine overbores are not permitted beyond 60 thousandths of an inch over the manufacturer's original specification. Such overbores will not affect class eligibility"


That pretty much says I can overbore to 60thou and the capacity limitation presumably means no stroking allowed. Regs have been FIA based rather than CAMS.

I'm not sure I understood your last question. If you mean what sort of fuel supply to the motor, manifolds and carbs have been free and FI was allowed if available at the time. I'm currently thinking SUs for simplicity and ease of changing mixture (needles) if we are doing high altitude - which is likely.

Regards
JohnH
--
JohnH, Sydney, Australia

If +.060" is it, I'd just go to the +.040" stock style Mahle pistons. The head gasket is oval shaped, so you can notch the bores on the intake side & open the head up around 44mm inlets.

SU's are pretty limiting, can you use 2x 45 DCOE's?

--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.

I'm expecting carbs to be free, so DCOEs shouldbe ok. I have them in 45s on a reasonably worked B20 in a 142 and find them good, but very thirsty. Have you had any experience with Mikunis? John Parker - who obviously sells them - swears by them, but web comments are mixed at best.
Regards
JohnH

Thirsty means they need a tuneup & be jetted prperly, all things being equal, DCOE's are nearly as good on fuel as SU's

I have them in 45s on a reasonably worked B20 in a 142

What's wrong with trying that engine out on some of the fuel you will be using? I'd lock up a distrubutor & try it at °10.

One thing to remember about 2x DCOE's is that they will give a very big boost to the torque curve. Have a look in the R-Sport at the power & torque figures, the mild R-Sport B20s have the same torque as a B30E.

Have you had any experience with Mikunis? John Parker - who obviously sells them - swears by them, but web comments are mixed at best.

Nil personal experience with the Mikunis, but they would be at least the equal of DCOE's, BUT, I am talking about using them one throat per cylinder. Put them on the SU manifold, you still have a bad manifold limiting the flow & doing badly in the wave tuning departments. John Parker has great success with them because he always puts a baby cam with them. I imagine they would be very economical & fun to drive around town when sorted out.


--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Still on the mikunis: any thoughts on putting 2 on one of the Lynx (I think) manifolds designed for a single DCOE? I know they have pretty severe bends in them but at least each port flows to the best 2 cylinders.
I have one with a 45DCOE on a B20 in an Amazon and while it doesn't set the world on fire, it seems at least as good as the original Strombergs.
Regards
JohnH
--
JohnH, Sydney, Australia

The Lynx manifold restricts above 6000rpm & gives a little bit more grunt around 3000rpm. I could not work out how to jet one econimically & but I never had a problem with jetting proper dual DCOE's. The bendy parts in the manifold are very big, so they likely do flow OK, just not in an efficent way.

If you are putting Mikunis on the Lynx manifold, you would want small ones. The size DCOE you pick would be smaller than what you would pick for duals. (because it is a 360° manifold)

I'd nearly always use 2x HIF6 or 2x 45/48mm DCOE's

I had a car running well for ages with K-Jet, but I would not take that away from running locally because the bits are all one of. I have a couple of complete K-Jet system from a B21E, but the parts are all similar but different....

--
Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Seriously, a majority of folks on this list are from the USA, and here "octane" is defined as the average of RON and MON, or =(RON+MON)/2 as it's shown on our gas pumps. In fact, a new term (defined exactly the same way) has started appearing, called AKI ("anti knock index").

To say that you need to use 80 octane fuel is significant. That's really way less than anything in this country, the lowest here being about 87 (I think that's a federally mandated minimum for unleaded fuel, but that might be wrong).

Nevertheless, in other countries its possible that octane is defined differently, so I think that in order to have a better idea of the challenge you face, we ought to know whether octane in Australia is the same as in the USA, or different. And if it's different, how that relates to our (RON+MON)/2.

We have 85 everywhere here in Colorado.

Octane requirements drop with altitude. 85 octane regular is common in mountain states.

I think generally, where it's different, the advertised number is higher, like the old number that used to be advertised here. It's the RON only number, a little more optimistic. Usually 5 - 7 points higher than the RON+MON/2 number.

As for making a peppy motor that can run on low octane gas, as already mentioned, don't just go for lower compression via thicker a head gasket. The B18/20 has a 'vintage' style bath tub combustion chamber. It's intentionally designed with flat protruding shelves on two sides, with the other two sides reaching out nearly to the cylinder walls. This is to accomplish a neat trick. At TDC, the piston approaches the head at a pretty high speed, and the top edge of it gets really close to those protruding shelves. The closer the piston gets, the less room there is left in between the piston and the head shelves, the more violently the air gets *snapped* out of that space and violently hurled into the center chamber. This turbulence and swirl is a very beneficial thing, in terms of combustion and in terms of knock resistance.

Rods stretch when they get warm, and also under the G-loads resulting from hauling that piston down to a stop at 7000 rpm, so the general gap to aim for I've heard from people who would know a lot better than I is .032", or slightly more. The knock resistance effect lessens as the gap increases, by .050 or so it's mostly gone, and the motor will be more prone to pinging, until you drop the compression way down. But really low compression makes for a less peppy motor.

So personally, I'd aim for a reasonably medium compression ratio, but to make the engine ping resistance through a tightly gapped piston clearance. Study the available head gasket thicknesses (Cometic makes steel gaskets that don't compress for a very precise installed height). Then build the bottom end to suit, by having the block decked to appropriately locate the pistons at TDC to be that .032" from the head when it's installed.

B20F heads have larger chambers, making 8.7:1 CR stock. Might be lower than you need for a nice tight squish build. Another option might be to use some dished pistons for a few more chamber CC's, they still have full height edges for that squish effect.

And last, but not least, there;s the difference between static compression, the theoretical compression ratio of the cylinder/stroke volume / chamber volume, and the dynamic compression ratio, which is what the motor actually does in motion. Cam timing, specifically. The intake valves tend to remain open well past BDC. Snortier, racier cams will generally lower the dynamic compression ratio more than more sedate tractor cams.
--
'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)

There are indications I've seen that you can shoot for much less than 0.032" squish and continue the benefits of the compression snap at TDC with shelved combustion chambers. There are people running B21's and B23's here in Portland with 0.020" without contact issues. I am currently running a 0.027" B21. At those lower squish numbers, you can run 87 octane without ping and with super advanced timing. I bet giving the distributor a twist to retard the timing on the 80 octane portions would be enough to avoid ping with squish that low.

Lower octane fuel has a higher energy density and faster burn rate, so if you can swing it without ping, you should see increased performance.

Many of the things you could do to lower the CR also thickens the squish zone, which eliminates the value of lower CR. I'd say a wild cam would help. Can you carry some premium grade with you to mix with the lowest octane stuff? Also don't advance the ignition timing TOO far.
--
George Downs Bartlesville, Oklahoma

The idea of the wild cam being to effectively let me keep the squish zone at .032 or thereabouts while running a higher CR?
I don't know how long the low octane stages will be, so carrying octane booster may be sufficient.
Re the above question, in Australia we do use RON which is effectivly about 4-5 points higher than the (RON+MON)/2 that I understand is used in the US. ie what we call 98, you'd call about 93 or 94.
Regards
JohnH
--
JohnH, Sydney, Australia

I always run the cheapest gas here in the US and they call it "87 octane", which may not
be too far different from your 80 octane gas. I NEVER use octane additives and occasionally
get some pinking at heavy loads at low speeds but all in all it is not a problem.
The advantage of the wilder cam is that it keeps cylinder pressures lower at the speeds
where pinking will be the worst problem while enhancing breathing at higher speeds.
Note what the other guys said - I think we generally agree.
Thick head gaskets are probably more of a problem-maker than a cure!
--
George Downs Bartlesville, Oklahoma

George, According to what this fellow has said about octane rating "down under" his concern over the 80 octane gas is real. Think about it--when we started driving (pre R+M/2) we could buy 98-102 rated premium--now the best we can do is 93 (by R+M/2). So his 80 would translate to mid-low 70's here. -- Dave

Maybe so. If the Japanese cars will run on it I'll bet the Volvos will run on it also.
He said he was carrying some octane additive - maybe it will help.
--
George Downs Bartlesville, Oklahoma