cam overlap and lope/rough idle

kingc · Feb 21, 2007

i just calculated what the overlap should be on cams I am having installed i come up with 64* overlap using [(int + ext duration/4) - LSA x 2] for cams with 531* int/ext, total duration 292, lobe separation is 114. I think this might be off? Are these cam specs going to cause a rough idle.?

Thanks

jivepepper · Feb 22, 2007

kingc said:
i just calculated what the overlap should be on cams I am having installed i come up with 64* overlap using [(int + ext duration/4) - LSA x 2] for cams with 531* int/ext, total duration 292, lobe separation is 114. I think this might be off? Are these cam specs going to cause a rough idle.?

Thanks

Are these hp 292s cams?

kingc · Feb 22, 2007

LaserRed01GT · Feb 22, 2007

As long as you are using advertised duration, that formula is correct. And that sounds about right for the amount of overlap on a cam with 292 advertised duration on the intake.

And yes that cam will lope fairly hard. But even some of the biggest cams can be tuned to idle very well, it just takes some time.

What are the exact cam specs?

ROUSH1 · Feb 22, 2007

i am getting my cams tuned next weekend ill try and post up some pics and vids on how it went. i have the comp stage 3 242/246-550/550 says to be a rough idle

Stan Weiss · Feb 22, 2007

ROUSH1 said:
i am getting my cams tuned next weekend ill try and post up some pics and vids on how it went. i have the comp stage 3 242/246-550/550 says to be a rough idle

How much CR are you running with these cams?

kingc · Feb 22, 2007

as far as the "exact" specs on the duration, i'm being the told that the total duration is 292.

LaserRed01GT · Feb 22, 2007

kingc said:
as far as the "exact" specs on the duration, i'm being the told that the total duration is 292.

Yeah, that's the advertised duration, or the duration measured at .006" off the valve seat. That's a pretty healthy cam.

What is being done to your heads? That cam is going to want a lot of compression and a lot of gear.

kingc · Feb 22, 2007

7 angle valve job, with oversized (1mm over stock) stainless valves, and the heads are being ported stg 3 type port job. They replacing all the parts that wear out over time adding bronze guides, and new springs (comp), chains, etc. and anything else that looks as if it needs replacing.

LaserRed01GT · Feb 22, 2007

kingc said:
7 angle valve job, with oversized (1mm over stock) stainless valves, and the heads are being ported stg 3 type port job. They replacing all the parts that wear out over time adding bronze guides, and new springs (comp), chains, etc. and anything else that looks as if it needs replacing.

Please don't take this personally, but I really think you are wasting your time doing a 7 angle valve job. Anything more than a 4 angle cut on a street/strip motor will only provide minimal, and I mean minimal flow gains. And unless you are making some serious power, anything over 4 cuts on the intake valve will allow them to backflow too much and will dilute the intake charge.

You could also tell your machine shop to hand blend the bottom cut(port side) and the top cut into the combustion chamber. But I don't know how serious you are into drag racing as some classes don't allow you to do this type of blending. Just brain storming

4 cuts on the intake and a radius cut on the exhaust valve are all you need. Then you will have some money left over to put towards something else.

kingc · Feb 22, 2007

I dont take that as offensive in any way man, i appreciate your thoughts and input! I can call in the morning, and see where they are on the heads, they may not have gotten to mine yet.

To be honest i have never run my car in the 1/4 mile, and honestly i dont want to. I have just loved fast mustang since i was very young. my plans for the car in the future are for road race applications.

kingc · Feb 22, 2007

Damn i really love that hood Laser.

LaserRed01GT · Feb 22, 2007

kingc said:
Damn i really love that hood Laser.

Thanks, BTW half my family lives in the Houston area. I'm there every year, and I was at HRP every year for the NHRA nationals for the last 10+ years. I don't know if I'll make it this year since I am in Florida for a while.

kingc · Feb 22, 2007

Are you visiting anytime soon?

LaserRed01GT · Feb 22, 2007

kingc said:
Are you visiting anytime soon?

I have a mad busy month coming in March. I have to be in Bradenton, FL for the NMRA Ford Nationals, then I will be in Gainesville the following weekend, then the weekend after that I will be up in Augusta, GA doing some testing with my friends Top Alcohol hydro boat and his other Top Fuel Nitro boat. Then the weekend after that is HRP (Gainesville). If I have enough energy, and money, I would really like to go to HRP. The fuel guys always run well there.

jivepepper · Feb 24, 2007

Mine are still sitting on my living room floor I plan on installing them in the next week are two.

kingc · Feb 24, 2007

After calculation the overlap on lots of different cams I;m wondering now if my stang is gonna even idle at all, guess that's where the tune will come in~ 64* seems a bit too high.

jive am I looking at the right specs for the 292's...

Stan Weiss · Feb 24, 2007

Here are 3 comp cams the top one has only 54 degrees overlay

Comp Cams Xtreme Energy XE262AH Camshaft is designed for the 1999-2004 4.6L 2V engine (Performance Improvement Head vehicles) and provides excellent torque - better low and mid range torque with more power. Will work with stock computer. Valve springs recommended (Part #26113-16)
Duration @ .050 - 226 (intake) / 230 (exhaust)
Advertised Duration - 262 (intake) / 266 (exhaust)
Valve Lift @ 1.825:1 ratio - .550 (in/ex)
Lobe seperation angle - 113 degrees (in/ex)
Overlap 38 Degrees

Comp Cams Xtreme Energy XE270AH Camshaft is designed for the 1999-2004 4.6L 2V engine (Performance Improvement Head vehicles). Hot Street cam - needs 3.55+ gears, 2000+ stall. Intake, exhaust, computer and valve springs recommended (Part #26113-16). Noticeable idle.
Duration @ .050 - 234 (intake) / 238 (exhaust)
Advertised Duration - 270 (intake) / 274 (exhaust)
Valve Lift @ 1.825:1 ratio - .550 (in/ex)
Lobe seperation angle - 113 degrees (in/ex)
Overlap 46 Degrees

Comp Cams Xtreme Energy XE278AH Camshaft is designed for the 1999-2004 4.6L 2V engine (Performance Improvement Head vehicles). Street/Strip, needs 3.73+ gears, 2400+ stall. Intake, exhaust, computer and valve springs recommended (Part #26113-16). Rough idle.
Duration @ .050 - 242 (intake) / 246 (exhaust)
Advertised Duration - 278 (intake) / 282 (exhaust)
Valve Lift @ 1.825:1 ratio - .550 (in/ex)
Lobe seperation angle - 113 degrees (in/ex)
Overlap 54 Degrees

LaserRed01GT · Feb 24, 2007

Stan is correct. The cam in question has 54° of overlap. And yes that will require some attention by your tuner, but if he/she knows what they are doing, it's should be a snap.

fast97gt · Feb 25, 2007

ive been in your shoes and not knowing anything about cams that i thought i did, i had a crash course in them and the thing not to forget, if you dont have enough compression for the advertised duration it will have worse idle and youll actually lose hp. but like mentioned previously you can have the engine tuned and not have to bad of idle. but i say the rougher sounding the meaner it is. although the lobe seperation has alot to do with valve over lap, and with that cam selection itll be hard to really get the full benefit of huffer (s/c or turbo) they like the lobe seperation to be higher like a 116.5 degree. im having a custom grind done with a duration @.050 214in/223exh w/498lift in and exh w a 114 lobe sep. i was also stressed to about the real important numbers is in/exh duration @.050, so your numbers should be around .223/..235ish.

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