just one more cam selection thread

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rumblefish360 said:
Poor flowing small valves stock heads get the big split. That’s it.
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Well, I had my heads done by IQ52 as well as the intake and custom roller. That cam has a split duration and I wasn't going to argue with him.

Now there may have been a reason for it, such as a proportionally small exhaust valve or he thought it needed a bigger header than I run. Point being, I'm sure there was a good reason and it surely isn't going to hurt anything.
 
roccodart440 said:
Well, I had my heads done by IQ52 as well as the intake and custom roller. That cam has a split duration and I wasn't going to argue with him.

Now there may have been a reason for it, such as a proportionally small exhaust valve or he thought it needed a bigger header than I run. Point being, I'm sure there was a good reason and it surely isn't going to hurt anything.
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What heads? Usually they split the duration and open the LSA to make RPM after peak last longer but they give up a ton in the gear change.

I very rarely ever want to see a split unless it's on alcohol.
 
Just another reason I do not like "one size fits all" cams
you notice how late motors with better exhaust may even use exhaust shorter duration than intakes
best to use head flows to pick durations along with all the rest of needed inputs
rule of thumb is early stock exhaust ports with stock manifolds and restrictive exhaust needs more duration- but even then not as much as some popular catalog grinds
late heads and headers do not need much duration difference but still need a different lobe
Best to calculate each lobe individually
the intake lobe has to match piston demand - which is none at TDC that's header pull-the intake is contoured to the demand- which is also stroke/ rod length related
whereas the exhaust is opening under pressure and wants to open quickly to bled down pressure - but not too early to lose expansion/ power/ mileage
Intake closes as piston is coming up and closing tries to keep intake gas flowing as long as possible without reversion
obviously full power rpm intake close curve is different than driving down the street mostly hardly any throttle opening
 
Just to expand on that a lil;
In my experience; there is a night and day difference between a Hughes HE2330AL and a Hughes HE3037AL.
For the smaller cam, the numbers are;
270/276/110+4/53 overlap/119 compression/108 extraction.
With this cam I was able to gear the engine down to 65mph =1600,( with double overdrive; A833od plus GVod)and the car returned phenomenal fuel mileage. Some would say impossible numbers.
The larger one is;
276/286/110+4/61 overlap/116 compression/103 extraction.
This cam would not pull the numbers. I figured the problem was the headers pulling raw fuel past the open valves during overlap, at the 1600 rpm. So I bumped the stick back one gear and 65=2240, and voila I'm on the right track. Cruise vacuum is up, and so is the fuel mileage.
To cover the loss of 119less 116 degrees of compression, I milled the decks to equalize the cylinder pressure, no problem there.
But the 108 less 103=5 degrees less extraction cannot be overcome so easily. And because of this, and I guess the 61 versus 54 degrees overlap, fuel mileage has dropped to 50%. Well, I changed to 295 tires from 275s at about the same time, so that mightof also contributed to the problem.. All in all I was very sad when that smaller cam dropped lobes.
But the point is this; IMO, there exists, in my combo at least, a switch point between these two cams, and I'm gonna go out on a limb and say it's probably in the split pattern, and my engine liked it. Heckya it makes waaay more power, with the larger cam. But I really miss the fuel-mileage.
I already have ideas for my next cam,lol.It will be a solid FT.
 
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yellow rose said:
What heads? Usually they split the duration and open the LSA to make RPM after peak last longer but they give up a ton in the gear change.

I very rarely ever want to see a split unless it's on alcohol.
Click to expand...


Fully ported (345cfm ip) 2.20 valved eddy rpms with custom solid roller from comp. I forget the exact specs but 250 something duration at .050, .650ish lift and 112LSA.
 
Haven’t even gotten to it yet
I have chosen a Lunati 701 cam
For when I get to it. Seemed to be a good consensus for that cam in about a 9 to 1 engine
Plus or more likely minus a couple of points
The
 
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