5600 rpm stutter
Hi, I have a problem that is driving me crazy i'm hoping you guys can help.
I have a new 383 stroke sb chevy, and this is what it has,
I'll try to fill in some blanks for ya to help.
it has a 373 rear end gear, tb 350 trans with a 3000 B&M stall, it's a 383 stroker 10.5 compression, rhs aluminum heads with 205/160 valves ,three angle valve job,magnum pro rockers,68 compression chambers,everything is balanced to within half a gram,200 cc runners, victor jr intake,holley 750 vacume seondaires with block added to rear instead of plate ,i think the jets right now are 73 front and 84 rear, i have played with it lower and higher on jets that it was really rich because it seemed like at first the plugs were kinda white but i never read them the correct way i guess by running hard and pulling over right away and looking at them.
spark plugs are gapped now at 50 but i started at 35 and worked up.
I have a summit digital ignition and HEI with davis unified coil and cap and rotor but i have bypassed it with a stock HEI for testing and it didn't matter.
spring pressure is 110 lbs. cam is Voodoo Camshafts
Camshaft & Lifter Kit
RPM Range: 2500-6600
it has this tuter at 5600 rpm that i can't figure out why, I have a sumitt digital ignition system , i thought it was bad so i bypassed ther whole thing with a stock HEI and new cap rotor coil , no change.
I had a carter strip mechanical pump so i thought maybe it wasn't good enough so i talked to jegs tech line and he said the pump was not good enough and he recomended the edlebrock victor series race pump and regulator , did that no change, then i put in a holley electric blue pump and blocked off the mech pump and still no change, i have replaced the fuel filter, played with timing and it made no difference,played with jets changes no change untill i went too high and it was hard to idle because it was so rich.
I am talking to a friend and he thinks I need anti pump up lifters, what do you think?
The rev limit is dictated with a iron fist by the valve train so I would say that is where your issue is. The lifters pumping up usually occurs around the 6000 RPM mark so you could say 5600 is close enough.
If it were mine, I would re-gap the plugs to 0.035" and see what happens. If it still stuttered, I would be thinking valve springs. What do the plugs look like currently? If they are black and sooty, you may also have too much fuel pressure. With a Holley, I personally would not run more than 6 psi at the fuel bowl inlet.
Have you checked your set-up height?<<springs
I would like to research the camshaft, lifters, and valve springs if you have the information on all of it. What rockers do you have?
X2 what everybody's saying about the valve train. VooDoo cams are Lunati and have an aggressive ramp, more so than their other shelf grinds. My custom solid roller grind was based on the VooDoo profile and required a rev kit along with the heavy springs. Did your camshaft and lifter kit include correct (new) springs?
You're not hitting a limiter are you?
I have gaped the plugs from 30 to 50 and never got a change good or bad.
I have steel magnum pro rockers.
I bought the voodoo kit that comes with cam and lifters but not springs, these springs were set at the machine shop at 110 lbs but i don't know what the open pressure is.
I read that lunati springs are 108 lbs but i don't know what difference their springs are otherwise than what i have now, not sure what they are ,the machine shop put them on.
the machine shop says i need anti pump up lifters.
what do you all think?
what should the springs be ?
what is the rev kit ?
i am not hitting the rev limiter because I bypassed by whole ignition system and limiter once and it still stuttered at 5600.
When it comes to aggressive cams like yours I fully recommend using the springs Lunati makes for that cam. Sure, on the older old faithful grinds we could throw whatever had enough to cover the lift on there and be fine, on these newer cams it changes the ball game with the springs somewhat so springs maybe something you should look into. Call Lunati, get there opinion on it. If your springs are giving up early you`ll never get the bug worked out until there right.
Will it go past the stutter at 5600 rpm, or at that point it won't rpm any more??
My vote is also for the valvesprings, you can set the spring seat load of a spring to match what is needed but that don't mean the springs rate is enough. 110 lbs seems too low to me anyway, I'd want 120-125lbs on the seat but you need to know if the open pressure is correct too.
Anti pump lifters will not be a fix, IMO, springs are the problem. with the right springs, stock hydraulic lifters will turn 7200 rpm.
Thats what i was wondering if he was hitting the rev limiter.
I'm with EricNova72 and Double vision so far.
I'm thinking spring rate and set-up height. I assume the steel rockers are 1.5/1?.
If the springs are rated 110lbs seat pressure it is at a specified set up height. If the shop installed +.100" not uncommon, and didn't bother to adjust set up height to spec that would hurt the seat pressure a lot. Or your heads could have deeper valve pockets, maybe. Aggressive cams need close attention paid to every aspect of the springs, and valves.
I like rev kits when I'm going much over 6000. Use the search term "Rev kit"on Ebay and check 'um out.
I bypassed the rev limiter so i know i'm not hitting that.
The shop might be too old school and not up on what springs to install with this cam and i'm not sure he even set it up for open pressure.
the cam kit only came with lifters not the springs, lunati does offer separate springs and they are 108 lbs but i don't know if they are stiffer or what the difference would be with what springs i have now set at 110 lbs.
rockers are 1.5
It trys to pull thru the stutter but it is steady so i don't let it stutter too long.
thanks for the help, i appriciate it, i'll call lunati tomorrow.
Is it very smooth at 5400rpm and it happens all at once when passing 5500? Have you tried running it with with the tach disconnected??? :)
Don't even know what vehicle this engine is in, but if it's an aftermarket tach It can act like a rev limiter because of some electronic quirk. Seen it a few times over the years.. Was common in the Sixties and Seventies with the old style instruments.
I would measure my set up height though if the valve covers come off for any reason.
Really sounds like valve float to me, now that you described it further. springs would be the first thing i would look at. You could try Duntov's tach disconnect idea, I've seen that happen once also.
Lunati's lifters are good lifters, I would not suspect them at all.
I have seen a lot of machine shop installed "good enough" springs be not very good at all.
EDIT: I just looked up that recommended spring, it has a pretty stout 462lbs/inch rate, I'm betting your shop sourced springs are lucky to be 350 lbs/inch rate.
clicked wrong button, will post concerning this later.
I have found discrepancies in the information offered by Lunati and this is no exception. Eric has found the recommended spring to be a 73943 single spring with damper. This is the spring recommended if you go to the main page and enter 60105 into the search and come up with the spec card.
However, if you go to the application chart and look up the supporting components, you see a 73100 dual spring with damper or a beehive spring 74818.
The 73943 is 1.266" O.D., 108 lbs on the seat installed at 1.750" and 339 over the nose @1.250". The rate is 462 lbs/in.
The 73100 is 1.450" O.D., 125 lbs on the seat installed at
1.850" and 325 over the nose @1.250". The rate is 333 lbs/in.
The 74818 is 1.290" O.D., 130 lbs on the seat installed at 1.800" and 318 over the nose @1.200" The rate is 313 lbs/in.
With all the conflicting information, it's a wonder to me that ANYBODY gets the correct springs on their Lunati camshaft.
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