ValveSpring Upgrade
Thread Starter
6th Gear
Joined: Oct 2018
Posts: 6
Likes: 0
From: miami fl
ValveSpring Upgrade
hello, i have a 1975 corvette l48 auto, it has RPM performance intake, longtube headers with 2 1/2 exhust and x pipe, edelbrock 600 CFM carb, the car has a cam, i do not know the specs on it , it use to work fine and everything, i had to change the lifters because a couple failed so i change them all and istalled comp cams pushrods and 1.6 roller rockers, it has dual springs, the problem is when i floor it the tras shift around 6k to 6500 and at that rpm the engien is flooding the valves, i need a valvespring upgrade but dont know the specs of the cam, any idea whats prings i can use?
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Le Mans Master
Joined: Mar 2006
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From: Texas
Hydraulic or solid lifters? RPM at idle? What's the idle quality - OEM-like, a little cammy, or really choppy like a race car?
Use these to degree the cam and get its lift:
edit: cam checker tool
Degree wheel
Use these to degree the cam and get its lift:
edit: cam checker tool
Degree wheel
Last edited by sstonebreaker; Jan 23, 2019 at 12:33 AM.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
Ever think that running dual springs was the cause of the lifter failure to begin with? Dual springs puts tons of pressure on the lifters and cam lobes. Are you using oil w/ Zinc? Why do you need to turn more than 6500 RPMs?
If you feel that your engine is slacking at the upper RPM range, perhaps its the small 600CFM carb issue. Or an IGN system that can't keep up.
Leave the springs alone. For street use, dual spring is plenty.
If you want a lower shifting point change out the transmission vacuum modulator to an adjustable unit. Then you can tweak it where you really want it.
If you feel that your engine is slacking at the upper RPM range, perhaps its the small 600CFM carb issue. Or an IGN system that can't keep up.
Leave the springs alone. For street use, dual spring is plenty.
If you want a lower shifting point change out the transmission vacuum modulator to an adjustable unit. Then you can tweak it where you really want it.
Last edited by HeadsU.P.; Jan 23, 2019 at 09:08 AM.
Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Usually I don't even post to questions like this because of so many errors.
first of all it takes planning to exceed 6000 rpm safely. The word is valve FLOAT and it is very distructive. What exactly happened to your past lifters? Do you know if the cam lobes are still good? Higher seat pressure might keep you out of valve float, but do you know if your ignition is sparkling correctly over 6000 rpm.
l 48 were not built with good internal parts and maybe it would be smarter to invest in a good digital sequential rev limiter and set it to a 6000 or less red line
h flat setups are not made to exceed 6000 rpm not even most h roller cams.
first of all it takes planning to exceed 6000 rpm safely. The word is valve FLOAT and it is very distructive. What exactly happened to your past lifters? Do you know if the cam lobes are still good? Higher seat pressure might keep you out of valve float, but do you know if your ignition is sparkling correctly over 6000 rpm.
l 48 were not built with good internal parts and maybe it would be smarter to invest in a good digital sequential rev limiter and set it to a 6000 or less red line
h flat setups are not made to exceed 6000 rpm not even most h roller cams.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
You do not need to rev past 6k if you have stock heads....period.
That said.....you need to take a photo of your valvetrain setup.....I cant give you any more insight than that until I know what you have now.
Jebby
That said.....you need to take a photo of your valvetrain setup.....I cant give you any more insight than that until I know what you have now.
Jebby
Race Director
Joined: May 2003
Posts: 10,956
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From: California
you did not say you replaced the heads... stock heads will not work with 1.6 RR without binding... Compcams make a 1.52 RR for this purpose..
And if you have stock heads, they dont do 6000rpm... lol:-) they will chock out..
And if you have stock heads, they dont do 6000rpm... lol:-) they will chock out..
Last edited by pauldana; Jan 23, 2019 at 11:53 AM.
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Thread Starter
6th Gear
Joined: Oct 2018
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From: miami fl
i have stock 882 heads, i have 1.6 roller tip scorpion rocket arms, i have Lucas High Zinc oil, engine use to run fine and shift great now i cant go WOT cause i have to let go cause the engine starts to run like crap amd exhust sounds changes like if engine wasn’t working properly
Le Mans Master
Joined: Aug 2017
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From: Cool Northern Michigan
Valve Float as some call it, is a warning sign. Take heed. The valvetrain is trying to tell you, you have crap boat anchor heads, small valves, large chambers, poor flow, miss-matched 1.6 rockers and the valvesprings will self destruct soon because the retainers might be striking the valveguides. Pushrods could be rubbing the heads slots. I am surprised you can get 6500 out of it.
I think you have other issues too that only show up at higher revs. Fuel or IGN.
I think you have other issues too that only show up at higher revs. Fuel or IGN.
Last edited by HeadsU.P.; Jan 31, 2019 at 06:56 PM.
Race Director
Joined: May 2003
Posts: 10,956
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From: California
Valve Float as some call it, is a warning sign. Take heed. The valvetrain is trying to tell you, you have crap boat anchor heads, small valves, large chambers, poor flow, miss-matched 1.6 rockers and the valvesprings will self destruct soon because the retainers might be striking the valveguides. Pushrods could be rubbing the heads slots. I am surprised you can get 6500 out of it.
I think you have other issues too that only show up at higher revs. Fuel or IGN.
I think you have other issues too that only show up at higher revs. Fuel or IGN.
Burning Brakes
Joined: Nov 2012
Posts: 788
Likes: 100
From: Indianapolis IN
If,and when, you pull the heads you need to inspect the cam and lifters very closely. You may have introduced more wear when you installed the 1.6 rockers because of pushrod bind. If you find lifters that are no longer convex on their bottoms then the cam lobes have the same wear. Look closer at the lobes that had already worn their lifters, or better yet - plan on a new cam, lifters, and heads instead.