Camshaft Guru needed

[trotterlg]

OK, here is the cam specs, custom grind, flat tappet:


Engine: Aluminum heads, iron head pistons for about a 12 to 1 CR. Custom intake with a Quadrajet and a distrubutator with points in it. Zero electronics.

Engine starts up and runs great, smoothe no bad noises, good oil pressure.

The issue is trying to get an idle, gets down to about 1,000 or so and just loads up and wants to die, slight bump on the throttle and it springs right back to life, just starts lopeing and wants to quit when it is slow. It idles down with about 13 inches of MP, so what I am curious is wheter or not this cam should be capable of slower idle than this. Pulled a plug and it is a nice light grey, so it looks good. The cam does have a very small LSA and I have no experience with one like this. Larry

[SappySE107]

carb and custom manifold aside, that cam is 31.4% volumetric efficiency @ 1000 RPM in an otherwise stock 3400 with 12:1 compression. To compare, the wot-tech little thumper cam in the same configuration is 42.8%. Id say you are going to be lucky to go under 1100 with that cam.

[trotterlg]

Well, 1,100 is OK, it is in front of a 4 speed, so it is probably good, Just wanted to know if I could expect to do better, don't want to spend time on an un-solvable problem. What would the volumetric efficiency @ 1000 RPM in an otherwise stock 3400 with 12:1 compression of a stock cam be? Just curious about those things. Larry

[trotterlg]

So this means that at 1,000 RPM that about 68% of the intake air gets blown back out either the intake or exhaust? If this is how it works no wonder it has a hard time idleing. Larry

[pocket-rocket]

It means at 1k rpm the engine only able to draw in 31.4% of its displacement.

Sent from my HTC One X using Tapatalk 2

[Superdave]

What is your base timing set to?


Also, you know those triangle air filters flow like crap and are well known to start on fire right?

[trotterlg]

I have the timing set to 10 degrees BTDC and it is a nechanical only advance only distributator. I found several articles that indicate that a quadrajet on an engine with a large cam needs to have the idle jets flow increased, this seems to be a well known issue with these, so I will have at that today. Over all I am really surprised how well this thing works, it will be fun to get it in the car. Larry

http://www.73-87.com/7387garage/drivetrain/myqjet.htm

[Purple pit]

Yeah you need a good drop base with a K&N. Those so called "filters" only keep out rocks. I looked at one years ago, there was so much open area that sand could pass. That was not something I wanted on my "new" engine that I spent so much on.

[SappySE107]

It really isn't a good cam at all from the idle quality to the power curve and total power. If you want it to idle rough as hell and make worse than stock 3400 hp, you got it.

[trotterlg]

When I pulled it (the filter) off this morning to drill out the idle ports it was already melted inside, guess I will take out the foam and just use the screen to keep out nuts and bolts until I can find a better one. Larry

[Purple pit]

Guess you had a backfire through the carb. Man I bet finding a drop base for a Quad would be tough. It's too easy to find one for a Holley. Could you use/mod a stock air cleaner housing?

[trotterlg]

Well guys, life is good now, drilled the idle jets and it runs perfect down to about 800-900 I would say, lower than that and it loads up and dies, but it will idle all day at 800 or so. I will try to find a way to shoot a little video with sound, but it is very nice. Time will tell about how it performs, but the Delta Cam guys are fairly well respected and I just asked them for a cam to wake up the motor up to about 7,000 or so, put LS1 springs in it and so far nothing sounds bad. Video later. Larry

[trotterlg]

Now it seems to idle at about 800 with 10 inches of MP, it lopes a little, but doesn't die, when the video camera gets charged up I will shoot a little and post it up, it definately grabs RPM's fast when you bump the throttle. I think this is going to do OK now. How long should I leave the startup oil with the cam lube in? I used the Quaker state with Zinc and a can of ZZP or whatever it is called. Larry

[trotterlg]

http://youtu.be/ES4mJdirHP0

[Superdave]

It really isn't a good cam at all from the idle quality to the power curve and total power. If you want it to idle rough as hell and make worse than stock 3400 hp, you got it.

Agreed. I just realized how low the lift was...

Trotterlg, Is there a reason you went with such a low lift cam? (and flat tappet???) It's pretty unlikely that the Delta guys know much about gen 3 port flow specs. They probably figured it was an iron head 3.1. lol

The duration is ok but .454 lift doesn't even get you into the sweet spot on the gen 3 heads. There is a good reason most of us run between .500 and .550 lift. That is definitely not going to do what you asked them for.



10 degrees sounds about right, are you limiting the mechanical advance at all?