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Old 06-21-2012, 07:46 PM
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Sbc High Rpm Retard.

OK I HAVE A SBC 350 60 OVER DOME TOP PISTONS WITH DART PRO 1 230CC HEADS AND A 302/310 DURATION WITH A 645/645 LIFT MY QUESTION IS MY TOTAL TIMING IS SET AT 32DEG AT 3000 AND IT PULLS GOOD BUT AT 6400 IT STARTS TO NOT PULL AS HARD. I BOUGHT A 3 STAGE TIMING RETARDER SO I WAS WONDERING HOW MUCH SHOULD I TRY TO PULL OFF MY TIMING TO RUN BETTER UP HIGH.


A LITTLE MORE INFO. 350 60 OVER VICTOR INTAKE HOLLEY 850 FULLY WORKED FLOWS 1050 FULL MSD DIGITAL6 WITH PRO BILLET DIST. 1 7/8 HEADERS. ITS IN A 1985 CUTLASS WITH A POWERGLIDE WITH A 8" 5000 STALL AND A 8 3/4 CHRYSLER REAREND WITH 4.56 GEARS RUNNING 31-15.50-15S

Last edited by GUTTLASSCUTTLASS; 06-21-2012 at 07:55 PM. Reason: MORE INFO
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Old 06-21-2012, 09:17 PM
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How do you know it needs less timing at high RPMs?




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Old 06-21-2012, 09:25 PM
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Quote:
Originally Posted by GUTTLASSCUTTLASS
OK I HAVE A SBC 350 60 OVER DOME TOP PISTONS WITH DART PRO 1 230CC HEADS AND A 302/310 DURATION WITH A 645/645 LIFT MY QUESTION IS MY TOTAL TIMING IS SET AT 32DEG AT 3000 AND IT PULLS GOOD BUT AT 6400 IT STARTS TO NOT PULL AS HARD. I BOUGHT A 3 STAGE TIMING RETARDER SO I WAS WONDERING HOW MUCH SHOULD I TRY TO PULL OFF MY TIMING TO RUN BETTER UP HIGH.


A LITTLE MORE INFO. 350 60 OVER VICTOR INTAKE HOLLEY 850 FULLY WORKED FLOWS 1050 FULL MSD DIGITAL6 WITH PRO BILLET DIST. 1 7/8 HEADERS. ITS IN A 1985 CUTLASS WITH A POWERGLIDE WITH A 8" 5000 STALL AND A 8 3/4 CHRYSLER REAREND WITH 4.56 GEARS RUNNING 31-15.50-15S
just pull a few degree's at a time untill u find what it likes or doesnt like...


you could also use stronger springs in the dizzy to delay the total advance..

your valve springs and or valvetrain might be a limiting factor... way to much to just say well hey drop 3* and it will PULL lmao
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Old 06-21-2012, 10:15 PM
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setting timing

as far as i know you only need to retard timing when hitting motor with NOS. I rev motor until it hits full advance then set timing to 38 degrees.
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Old 06-22-2012, 07:51 AM
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Well I know more advanced is better low end and the more retarded it is you get better top end. I was told by a engine builder that if you look at a good HEI dist on a motor that you can watch it pull back timing at high RPMs for more top end with out detonation. so I figured I would try it out was just wondering if some body else has done th
is.
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Old 06-22-2012, 08:33 AM
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If this is an NA motor, I don't know why you would pull timing on the top end unless it was detonating, then you would pull timing until it was happy. Are your valve springs up to the task for that cam? As stated above, you could be maxed out. Dome pistons in a SBC with .645 lift and big duration, with a carb flowing 1050??....hmm.

Is this a comp motor running SG??
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Old 06-22-2012, 09:33 AM
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Well its power band for the cam is 5000 to 8000 I normally shift it at 7500 at the track and on the street I just putt around never get it over5500. The springs were good to a 700 lift it was a cam kit cam with the camshaft. Its a solid roller.
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Old 06-22-2012, 10:07 AM
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Quote:
Originally Posted by GUTTLASSCUTTLASS
Well I know more advanced is better low end and the more retarded it is you get better top end. I was told by a engine builder that if you look at a good HEI dist on a motor that you can watch it pull back timing at high RPMs for more top end with out detonation. so I figured I would try it out was just wondering if some body else has done th
is.
The higher the RPM the more advance you need ,at 9000 rpm on my small block I run 44 degrees total! If not my spark would be after top dead center because the piston speed at high rpm is faster then the spark at the plug and the initial burn; The combustion also needs time to expand in the cylinder to push the piston down if you don't advance enough the piston would be already going down the cylinder before the combustion hits the piston dome and you lose power! Thats a simplified explanation I hope it was enough for you to understand> if not there are other members that will explain it better! My lunch is over

Jester
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Old 06-22-2012, 10:43 AM
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retard timing

32 degrees total timing is not a lot to start with.Check absolute total timing and see if your engine will tolerate 34Degrees. Make a few passes with out retarding timing.Then try 3 degrees.
You said your car is street driven? Check valve spring pressures.I run a similar cam on the street and even though I have less than 2,000 miles on the engine,I have already changed the springs once.My engine peaks at 6500 rpm.
You did not mention the lobe separation or intake centre line.I doubt you have the wrong cam,just the springs are not perfect anymore.
nice combo,I use the 950 cfm hp on my engine.
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Old 06-22-2012, 10:45 AM
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On our Stock Eliminator motor we take out 2-3 degrees of timing in high gear. We use the shifter as the trigger.
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Old 06-22-2012, 10:46 AM
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almost sounds like not enough timing, thats why it will not pull as good past 6500 rpm.. are you running alky? or 110 race gas
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Old 06-22-2012, 12:21 PM
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Quote:
Originally Posted by GUTTLASSCUTTLASS
Well I know more advanced is better low end and the more retarded it is you get better top end. I was told by a engine builder that if you look at a good HEI dist on a motor that you can watch it pull back timing at high RPMs for more top end with out detonation. so I figured I would try it out was just wondering if some body else has done th
is.

It started thunder storming so I came back
I see you have cam timeing and ignition timeing confused, an advanced cam gives you better bottom end and when retarded gives you better top end!!! The distributor advance is the opposite the spark advance must increase as rpm increases until you reach the point of pre ignition then you back it off ! Usually in nitrous instalations timeing is retarded because of the extra oxygen causing pre ignition ! Your total advance is too low!

Jester
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Old 06-22-2012, 01:59 PM
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I think what's somewhat misunderstood is why someone would want to retard the timing. When an engine is in a higher gear the advantage gained at low speeds through gearing is lost. The load and rate of the engine accelerating changes. At launch the engine can use a lot of timing. Once the vehicle has shifted out of the lower gears the load on the engine goes up and the rate at which the RPM's climb goes down. Also in turn the cylinder temps go up. At this point too much timing leads to detonation. Taking out some timing prevents some of this.
The amount depends on many factors. We take out 2-3 some guys as much as 8 degrees. If it's really humid we might not take any out if, it's a cool day with a low density altitude we might take out 4-5.
This is something that racers have been doing for years. Jenkins did it years ago. In his case he flipped a switch to swap over to a second set of points. Nowadays there's several options from MSD and others.
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Old 06-23-2012, 06:06 AM
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I would suspect something in the valvetrain not being up to snuff. He shows the gross cam numbers at 302/310. I'd like to see the .050" numbers. They could be anywhere from 242ish/248ish to 264ish/270ish. Then he says the springs are good to .700" lift. That means nothing. That just means at a proper install height, they can handle valve lift up to .700" and still have adequate clearance before going into bind. My cam has similar gross numbers and my springs have 228lbs on the nose and 550lbs open. I also lightened the valvetrain where I could with lightweight retainers and shaft rockers. Everything in there has to be in sync with each other to get the rpm out of it.
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Old 06-23-2012, 09:48 PM
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Quote:
Originally Posted by GUTTLASSCUTTLASS
Well its power band for the cam is 5000 to 8000 I normally shift it at 7500 at the track and on the street I just putt around never get it over5500. The springs were good to a 700 lift it was a cam kit cam with the camshaft. Its a solid roller.
The compression ratio plays a part in this, but given the above, IMO pulling timing out will not add a thing unless you're over advanced already.
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