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Cam timing +2

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1K views 16 replies 7 participants last post by  Glhs60 
#1 ·
With all the experience out there i was wanting to ask what the best degree is for a roller cam with a two piece intake. I had a roller cam in my 85 with a single piece intake. I didnt have a adjustable gear for a square tooth so i ran 4 degrees advanced and it seemed to stop pulling around 5 grand. Now i have a two piece intake with a adjustable square tooth gear. I learned from the past and set it at two degrees advanced after adjusting for the square tooth from round. So the gear says 6 degrees advanced. Anyways does any one have dyno numbers to support the best degree of timing? This setup pulls damn hard till i surprise myself with the rev limiter. I need to do better watching the tach. and maybe go more advanced on the cam.
 
#4 ·
----Rule of thumb----

Advancing the cam enhances the lower RPM

Retarding the cam enhances the upper RPM


Since you seem to have more unexpected power in your upper RPM band you would advance the cam a little to move the power band down a little and enhance the power at the start, like 'off-the-line' starting power.

What are your goals for the car??

Good Luck
 
#7 ·
Its a luggy off the line with the 3.05 diff but it destroys most anything starting from 55-60mph. Those new 5.0 mustangs are something else. :mad: I was thinking about playing around with the cam timing to find out for my self but some experienced info might be good before changing something that runs so well. In theory, if its still pulling at red line then i can get more power out of that rpm with a increase in cam timing. I think the only way to know is doing dyno pulls.
 
#9 ·
It must be the TBI cam because i am at six degrees advanced on the gear and have 25 inches of vacuum at idle. I need educated on this more. I was given a turbo head by a guy that sold his car. All i know is that this head was a roller and had "T" embossed on the exhaust valve. "TBI" stands for what? I still have the head because i thought it was the same as the head on my 86.
 
#10 ·
25" HG @ idle is almost an impossibility, most vehicles do not even reach that on decel.
Want to verify the accuracy of your vacuum gauge, check Map Sensor output voltage @ idle.
TBI is Throttle Body Injection.
Not sure what the "T" stands for, sure someone does but the exhaust valves are hardened on turbo cars and are not on TBI cars.
 
#12 ·
Read the thread by The Pope that I posted in post #8.

I personally do not know what benefits the added duration of the TBI roller cam will give you.
Being 4 degrees retarded from the turbo roller cam the TBI cam will give you more high rpm power.
 
#13 ·
IMO all the roller cams are 4 degrees retarded using a square tooth. I base this on the two cars that i have owned with a square tooth. I tracked my current cam down and it is from a turbo car not a TBI and i am at 6 degrees advanced on the gear and it runs absolutely awesome. My last car the cam was unknown but i also ran with it advanced.

Kinda getting off topic. Forums do that :thumb: Still looking for hard evidence on advancing. I knew it would be hard to answer my question. Hard core power guys using dynos are not stock like i am. I will have to just go with seat of pants feel and adjust the settings till my butt says "yes that is the best" or find a dyno
 
#17 ·
My buddy Brian had a long dyno session with his 2.5 Holset Turbo Omni.

He found measurable gains retarding the cam timing at higher RPM.

Advancing feels stronger at low RPM but our SOHC Engines need help over 5252 RPM.

As NAJ says, the 1320 does not lie!!

Thanks
Randy
 
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