What characteristics would the following cam lend to an engine
110 LSA
488/490 lift increased to 520/522 with rockers
226/228 dur at .05
Would it be possible to smooth the idle? It seems not. I have it installed in a 355cid in a C3. It likes lots of advance. It starts easily, has enough vac to operate the headlights and has good low end power. I can tell that from some experience with it (800 mi so far) but I would be interested to hears some ananysis of the specs.
Re: What character would this cam give an engine? (Marc80)
It sounds like you're happy with it other than it's idle. You didn't say how much initial you're running or your vacuum advance set up but there may be room for more. One of the best ways to increase idle vacuum (which, as you said, does help smooth the idle) is to run the vacuum advance from manifold vacuum and use a canister that fully deploys at idle vacuum. Doing this way allows much more advance at idle than you could otherwise run without screwing up your timing beyond idle or having more initial than your starter can handle. Also make sure that your idle fuel mixture is set properly.
Re: What character would this cam give an engine? (Marc80)
The 110 LSA with those duration and lift numbers means it has a lot of effective overlap, which yields lots of exhaust gas dilution at idle and low revs. Exhaust gas dilution slows flame propagation speed and leads to combustion instability, which is why it needs a lot of idle advance. Your vacuum can should provide full advance at 2" less than idle vacuum and total idle advance (initial plus full vacuum plus any centrifugal if you have a quick curve that begins below idle speed) should be in the range of 25-30 degrees to make the idle as smooth and stable as possible.
IMO the cam has too much overlap unless you have headers. With manifolds speading the LCA to 114 would provide better idle quality and low end torque, without sacraficing top end power.
Re: What character would this cam give an engine? (Marc80)
I am not sure of exact degree of advance. I played around with my MSD distributor with springs and bushings and then set the advance to 36 degrees. It ran like crap. I advanced it to the point of optimum power without detonation and it ran pretty good, even at idle. I think it was probably around 45 degrees or more. I haven't tracked it down yet but as I understand there are three possibilities.
I suspect it is not #2 since I haven't driven it too hard and it is still in breakin.
I am not using vacuum advance. Many people have said to just disconnect it including Lars. Also I am running with headers (Dynomax ceramic coated.)
I appreciate the comments. I am a little unsure what to expect out of this setup. (I am a woodworker). I like the power it has but it does idle like a racecar (I guess it sort of is, but wanted to tune it optimally. The idle is less of a problem after swapping out the stock stall converter for a TCI breakaway model.
Re: What character would this cam give an engine? (Marc80)
i use vacuum advance with a similar cam.
ported was too low and manifold was too high so i mixed the 2 with a Y and a .060" bleed.
No one else does this, but in any case i can't imagine no vacuum advance, but i'm sure Lars and others have found a way to make it work(maybe drilling a larger hole in the butterfly?)
Re: What character would this cam give an engine? (Marc80)
Quote:
I am not sure of exact degree of advance. I played around with my MSD distributor with springs and bushings and then set the advance to 36 degrees. It ran like crap. I advanced it to the point of optimum power without detonation and it ran pretty good, even at idle. I think it was probably around 45 degrees or more. I haven't tracked it down yet but as I understand there are three possibilities.
I suspect it is not #2 since I haven't driven it too hard and it is still in breakin.
I am not using vacuum advance. Many people have said to just disconnect it including Lars. Also I am running with headers (Dynomax ceramic coated.)
I appreciate the comments. I am a little unsure what to expect out of this setup. (I am a woodworker). I like the power it has but it does idle like a racecar (I guess it sort of is, but wanted to tune it optimally. The idle is less of a problem after swapping out the stock stall converter for a TCI breakaway model.
Any more suggestions and coments are appreciated.
Marc
45º total is way too much and will cost you power at higher rpm. What you're feeling isn't the 45º but the effect of more timing before it reaches total. As you noted, it's a good thing. That's the benefit of curving the distributor. You can adjust it to provide lots of advance at low and mid rpm without having too much once it reaches total. I don't know if you're running the same MSD as I am but I use the silver bushing for 25º mechanical and 12º initial. With the lightest springs, my total arrives at about 2,500 rpm and all is well. This curve may be too quick for some cars and a slower curve may be needed to avoid pinging.
If idle quality is a concern (and it sounds like it is), you definitely want to run vacuum advance and run it fully deployed at idle by using manifold vacuum. My MSD came with a B26 canister which only partially deployed at idle vacuum so I replaced it with a B28 can (Napa VC1810) and the idle smoothed out a bunch. This also allowed me to set the fast idle speed a couple hundred rpm lower than before.
Advancing a cam, unless it was way too much, would result in a smoother idle and it would have no effect on ignition timing as long as the timing was set after advancing it. There are also a lot of other things than can cause a rough idle: plugs, dwell, carb adjustment, etc..
Re: What character would this cam give an engine? (Vetterodder)
On a street engine you need the vacuum advance setup that I described in order to obtain reasonable idle quality, fuel economy, and cruise performance. It will also keep the engine from overheating in traffic if your cooling system heat transfer capacity is marginal.
I'm surprised lars told you you don't need a vacuum advance. He is one of the very few other people on this board who understands the ignition advance requirement over an engine's entire operation range to include idle, part throttle, and WOT.
Vetterodder has a good setup!!! The VC1810 provide 16 degrees crankshaft advance at 8". You are ten bucks away from a solution. Be sure to disconnect the vacuum can when you check initial and centrifugal advance, and be sure the signal line is routed to a source that has full manifold vacuum at all times, including idle.
Re: What character would this cam give an engine? (SWCDuke)
Quote:
The 110 LSA with those duration and lift numbers means it has a lot of effective overlap, which yields lots of exhaust gas dilution at idle and low revs. Exhaust gas dilution slows flame propagation speed and leads to combustion instability, which is why it needs a lot of idle advance. Your vacuum can should provide full advance at 2" less than idle vacuum and total idle advance (initial plus full vacuum plus any centrifugal if you have a quick curve that begins below idle speed) should be in the range of 25-30 degrees to make the idle as smooth and stable as possible.
IMO the cam has too much overlap unless you have headers. With manifolds speading the LCA to 114 would provide better idle quality and low end torque, without sacraficing top end power.
Re: What character would this cam give an engine? (Marc80)
Come to think of it, all the advice I got about removing the vacuum advance was for the stock engine, including Lars' article that I found by referencing other posts in the archives.
I did install the light spring set in the MSD and used a bushing that made the steepest curve. Should I stay with that ?
The biggest pain is that the car is in the body shop and I can't play with this situation yet. I guess I am just trying to get a vet-info-fix to ease the pain.
One more item. Mark at AR racing from whom I purchased my engine recommended a 36 degree full advance. (as Lars and others). I could not be really running optimally at 43 degrees total advance with any cam, could I. I suspect instead the culprits listed above.
I advanced initial allot with the bushing on the distributo. Will the vacuum advance just bring the advance on earlier? I could make it advance earlier by swapping the busing. Is that what I should be adjusting towards, earlier advance.
Thanks for the replies!
I see that some of these questions were answered clearly by Vettrodder. I will have to study that post and narrow down my questions. Thanks again. Any more input is certainly enjoyed.
Re: What character would this cam give an engine? (Marc80)
Marc, it's the weight of the springs that determine the rate of the advance. Lighter springs casue the advance to come in sooner but, unless they're incorrect or way too heavy, they don't affect the amount of advance. The bushing determines how much centrifugal advance you get. If you want a certain amount of total, subtract the amount of initial you want from the total and use the bushing that corresponds to the difference. Some engines can take 43º total without any obvious problems but it's likely that some power is being lost at higher rpm.
Vacuum advance works independently of mechanical and is intended to function alongside of it under conditions that can allow more advance than could be run under all conditions.
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What character would this cam give an engine?
