Compression ratio's and pump fuel.

gav look at it this way most modern motorcycles are 11:1 stock and run on pump gas. I also believe the new ford Barra 190 engine has 10.?:1

So I think 10:1 - 11:1 would be tops for pump gas. so the 3.1 will have 11:1 ish = big HP. I have heard that LD28 cranks don't last too long if they see 8500rpm so make sure you have a good rev limiter (if your engine can spin this far)

The old 'rule of thumb' was a max CR of 10:1 running 'super' leaded or premium unleaded.....about 95 octane in each case. You could go a little higher than that using 98 octane, but you need to keep a reasonable safety margin. A car with a CR of 11-12:1 will be a pig to drive around town, as you are talking race car tuning here.

Keep in mind that CR is not the only consideraton - head/intake design also plays a big factor, and the design of L-series engines is _old_ by modern standards - especially the head. Modern cars have very highly developed heads, not to mention advanced digital engine management systems. This means that manufacturers can push CR higher and increase engine efficiency. Also a lot of these engines - even NA - have knock sensors which gives increased protection for the engine from detonation problems with low grade fuels.

As for achieving 8500rpm - don't even think about for a street car. Even race car cranks won't last long at that level. Even if you could achieve it reliably, an L6 that developed power at that rpm level will certainly have sacrificed much at lower rpm, and torque will suffer enormously. For a race car with a close ratio gearbox that's probably fine, but for a road car - esp a daily driver - you want to go the other way. That is boost the spread of torque, while increasing top-end power, but without increasing peak power rpm too far.

One thing I have seen time and again with L6 stroker engines - they don't like to rev, BUT they do produce good torque down low and that is what makes them so 'streetable'.

I found this on ebay.....

Roughly the equivalent of a 76 Wade cam (have to check the specs on the lift tho), which is a race cam. I know people that have used these in road cars, but not daily drivers. 74 is about the max I'd go for a daily driver.

To give you some idea I checked with the 2 common cam suppliers in Melbourne:

Wade: 76 regrind on your cam is $140+GST. To regrind the rockers (mandatory AFAIC with a new cam is $11+GST each).

Clive cams: 76 regrind on your cam is $120+GST, but he can't do rockers.

Interestingly Clive said he can do a billet for about $230, which is a lot less than it used to be (last time i had one done it was $350).

Valve springs: I've used Crow springs without problems for years and they were around $100 for an L6 set.

Lash pads: since Datrally bit the dust I haven't sourced any pads, but these used to be about $15 each (that said, Datrally were never cheap...... ). I've got a couple of other people I can try for these, and even know someone that can make them from scratch, if necessary.

Gav,

Do NOT buy that cam. 256 0.05 dur for a street car are you friggin kidding me? When that guy says working range is from 4500 he really means the inverse is true: it does NOT work below that.

FWIW according to tighe cams the 76 works cam is only 230 0.05 dur ( http://tighecams.com.au/profiles3/nissanlseries.htm )

And I'm not too sure how we got onto cam shafts from compression ratio. The only link I am (mildly) aware of is that the effective compression ratio is lower than static when the cam is not ``working''.

For me the answer to your question depends almost 100% on you choice of fuel delivery. If you are going a proper after market engine management system, I'd say suck it and see. If you want webbers/mikunis/SUs/whatevers forget it. It'll be a total dog.

Dave

And I'm not too sure how we got onto cam shafts from compression ratio.

They go together, no point putting a race cam in a low comp motor, etc, etc.

I'm sceptical about the tighe figures.....the 0.050" lift figure is low for a race camshaft particularly realtive to the advertised duration. AFAIA Wade has the rights to the 'works' profiles and has had for many, many years.....that was the reason DatRally got into trouble with some of their advertising in the early days and were forced to change their descriptions (in fact all datrally cams were Wade grinds).

They go together' date=' no point putting a race cam in a low comp motor, etc, etc.[/quote']

 

Why? I thought you chose the CR based on the fuel, and the cam based on the revs you wanted to work with. Unless you are talking about dynamic compression ratio and then I can see that there is a link though I don't know what it is.

 

I'm sceptical about the tighe figures.....the 0.050" lift figure is low for a race camshaft particularly realtive to the advertised duration.

 

Did you mean 0.050" duration figure? Maybe they are advertising it as a 76 works cam in that is has the same advertised and lift but not 0.05? Who knows.

 

Dave

My advice?....forget the 300HP engine, it will be a pig to drive on anything but a race track. If you want HP, build a turbo engine, then you can dial it up as and when required.

If you want to still go NA, then build a strong 250-260HP engine and keep a good torque curve.....a 3.1L will do that easily. Some judicial porting (DON'T open up the ports within an inch of their lives) and the thing will breath better with triples. Go EFI if you can. The car will have bags of torque and be a helluva lot more fun to drive. Money saved can be spent on handling improvements.

Just my 2c worth.

Gav,

Duration is the period in engine degrees that the valves are open for yes. Advertised duration is from and to the cam lobe (the valve touching the seat), while 0.05 duration is the same thing but for 0.050 of an inch of lift (I'm not sure whether this is measured at the cam or valve).

The reason need both is it gives you an indication of the ramp angle. A very high advertised duration relative to the 0.05 duration means a slow ramp angle. 0.05 is also more indicative of the performance you will get as the flow before there is 0.05 of a gap will be next to nothing.

N/A 300hp is leaning on the L pretty hard. I think you'll be pushing it and loosing a LOT of drivability if you get there.

Dave

Why? I thought you chose the CR based on the fuel' date=' and the cam based on the revs you wanted to work with. Unless you are talking about dynamic compression ratio and then I can see that there is a link though I don't know what it is.[/quote']

 

They aren't mutually exclusive, as it were. Increasing CR gives increasing efficiency, and benefit is maximised with appropriate cam (improved breathing) as does porting.

 

Did you mean 0.050" duration figure? Maybe they are advertising it as a 76 works cam in that is has the same advertised and lift but not 0.05? Who knows.

 

Bad use of words on my part....should have said 'duration at 0.050" lift'.

Good point, everything has to be matched to make the most of things.

Dave