Nick, Its sounds like your after a fairly flexible engine. I'd say the 2 litre would suit your needs better than the L18 if your set on a Stanza and SU's. Your other option being a 1600 & L18. You mention you'd be using 1.50" port size SU's which are actually internally about 36mm ID from memory. From there your limited as to the amount of air/fuel that will flow through the carby for each cyl. 36mm port area is approx 1018mm^2. 42mm valves using optimum lift of ~11.74mm (.462"/267dur) is approx 1017mm^2 flow area. You then take the carby,manifold,port,valve flow efficiency into account. I'd say as long as your manifold and port could flow what the carby can supply, then your inlet valve efficiency would be the limiting factor. The flow through the inlet valve likely to be less efficient than at the carby. I'd expect this 87mm L20B to produce its max power at ~5655rpm with the valves being the flow limiting factor followed closely by the carby. I agree with you that both the open and closed chamber heads would give poor squish with dished pistons with excessive piston to head clearance. Yet still the closed chamber is likely to create more turbulence at TDC than the open and have less distance for the flame-front to travel. Whether the small amount of turbulence at TDC with the closed head out weighs the benefit of the open chambered swirl/tumble, both using dished pistons is the question. I'd say the answer lies in engine speed, fuel and the amount of compression. In your case running only ~9:1CR and ~6000rpm using 95octane up and dished pistons the open chambered head would probably give a better power range at low to medium engine speeeds. Since I haven't actually computer modelled it yet, that's my best guess. On the topic of the air/fuel ratios for maximum power it varies depending on the specific calorific heat value of the fuel used. As for premium unleaded running it rich to a certain point can gain up to approx 7% additional power. I can only go by what my friend has told me as 10.5:1. I know the head was decked but not how much, I also think the block may have been decked, the pistons are not standard dishes either. I also found out he runs 2deg timing on super and 8 on AVGAS not what I said earlier, sorry. 12-14 would be more desirable. To answer which configuration would be 'more powerful' l18 or L20B. Using the same V91?(8?) head you have on both engines everything else being equal would require running 580rpm more(6235rpm) for the L18 to produce the same power. But everything is not the same. For example, the L18 has a shorter stroke moving the piston less for ~10% less piston friction. But with more rpm comes more friction. Also the L18 internals are lighter(rod/crank) than the L20B's too, etc... So at the L18's maximum power rpm it may produce a little more power than the L20B at it's maximum power rpm or may not. Some food for thought. All else being equal a lower stroke to bore ratio will produce more power per area. Just look at motorcycle engines ratios, most 1000cc performance bikes run around 98mm bore and 66mm stroke for this reason. The bigger the bore the bigger the valves can be. I'd prefer a high compression, big bore, flat top, L18 with closed chamber head with 44mm inlets and 38mm+ ID carbies in a 1600. :) Enough from me. Craig. Visit the following if your after engine simulation software. Costs $ tho :( http://www.performancetrends.com or http://www.motionsoftware.com abrahamk wrote: > > 1. I would prefer to run in the 1600-2000cc class, which is why I think the > Stanza is such a good car to use (If I can find one!) - 2 litres & ~950 Kg. > 2. I would like to keep the bottom end as stock as possible, including > pistons. > 3. The purpose of squish is, as you said, to promote turbulence in the > mixture at / near TDC. A turbulent flame-front burns significantly faster > than a laminar (quiescent) flame-front and so the combustion process is > closer to the ideal constant volume process, yielding more power, less > susceptibility to detonation, etc... > However the squish areas in the closed chamber head (as I see it) won't work > well unless you run flat-top pistons with about 40 thou clearance between > the piston crown and squish areas, that is, you need to run a +0essive' porting - >any tips? Overall, I think the > head should flow very well and the low compression ratio ( 9:1 on L20B, > 9.22:1 on L18) will limit detonation. How did your mate get 10.5:1, with > 40thou removed from the head I'll only get 9:1 (I haven't CC'd it yet > though). > 5. Your program sounds interesting, what power increase would you get > running the mixture rich (faster flame-front speed), and using super extra > long spark plugs (central ignition source, shorter flame travel distance - > less end gas autoigessive' porting - any tips? Overall, I think the > head should flow very well and the low compression ratio ( 9:1 on L20B, > 9.22:1 on L18) will limit detonation. How did your mate get 10.5:1, with > 40thou removed from the head I'll only get 9:1 (I haven't CC'd it yet > though). > 5. Your program sounds interesting, what power increase would you get > running the mixture rich (faster flame-front speed), and using super extra > long spark plugs (central ignition source, shorter flame travel distance - > less end gas autoignition) > 6.Why do #1 & #4 cylinders have a cut-out for the spark plug, but not #2 & > #3. Should the cut-outs be radiused ??? > 7. I am still not clear on the L18 vs. L20 question, which is more powerful > when modified as discussed? > 8. 180B can only run L18 > > Thanks - Nick --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.datascribe.com.au/ozdatonline/index.htm http://www.datascribe.com.au/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
