valve springs
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Elder User
Joined: Aug 2004
Posts: 620
Likes: 1
From: NE Wisconsin
valve springs
I know typically not to reuse your valve springs with a new cam, but....
There is only 6000 mi. on the cam and springs. Currently I have an Isky supercam 256 .492 max lift exhast and intake. Not really impressed. Would like to try the comp xe256h with a max lift of .48? int. .493 exh. Would my current valve springs be ok to use?
There is only 6000 mi. on the cam and springs. Currently I have an Isky supercam 256 .492 max lift exhast and intake. Not really impressed. Would like to try the comp xe256h with a max lift of .48? int. .493 exh. Would my current valve springs be ok to use?
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Those valve springs should be OK. It is the lifters that you can't reuse, unless they a roller lifters.
What are the specs on that Isky cam, Intake/exhaust duration @0.050 and seat-to-seat, lift, Lobe Separation, and Intake centerline?
If you can give me the grind #, I can look it up.
What is the problem with that cam that you don't like?
What are the specs on that Isky cam, Intake/exhaust duration @0.050 and seat-to-seat, lift, Lobe Separation, and Intake centerline?
If you can give me the grind #, I can look it up.
What is the problem with that cam that you don't like?
Thread Starter
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Elder User
Joined: Aug 2004
Posts: 620
Likes: 1
From: NE Wisconsin
hydrolic flat tappet
202@50 on both
256 overall on both
112 lobe seperation
cant find intake centerline (here's something; intake open 5atdc close 27abdc)
256 supercam
decent low end but not what I would expect it should be. Reading on here at least.
My build:
'78 truck 400cid .030 over
Badger flat tops
stock block
Isky 256
wieand dual plane
holley 4160 600cfm
long tube headers into 2 1/4 duals with cross over
no egr
recurved dist.
stock ignition (duraspark)
stock heads
202@50 on both
256 overall on both
112 lobe seperation
cant find intake centerline (here's something; intake open 5atdc close 27abdc)
256 supercam
decent low end but not what I would expect it should be. Reading on here at least.
My build:
'78 truck 400cid .030 over
Badger flat tops
stock block
Isky 256
wieand dual plane
holley 4160 600cfm
long tube headers into 2 1/4 duals with cross over
no egr
recurved dist.
stock ignition (duraspark)
stock heads
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Dyno Sim for the Isky is 439 ft-lbs peak tq@2000 RPM and 419 Ft-lbs @3500 RPM.
The 255 DEH is 443@2000 RPM peak torque, and 438 ft-lbs@3500 RPM.
The longer exhaust duration helps at 2000 RPM and more at 3500 RPM. The result is a flatter torque curve.
Here is the Comp XE 256.
Torque = 442@2000 RPM, and 439@3500 RPM.
that is flatter yet.
Of course the most HP will be the one that has the highest torque at high RPM.
The 255 DEH is 443@2000 RPM peak torque, and 438 ft-lbs@3500 RPM.
The longer exhaust duration helps at 2000 RPM and more at 3500 RPM. The result is a flatter torque curve.
Here is the Comp XE 256.
Torque = 442@2000 RPM, and 439@3500 RPM.
that is flatter yet.
Of course the most HP will be the one that has the highest torque at high RPM.
Thread Starter
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Elder User
Joined: Aug 2004
Posts: 620
Likes: 1
From: NE Wisconsin
So really, there should not be a huge difference by going to the comp cam. Maybe my lack luster performance is in the tranny. (c6) Torque is higher than I figured. My guess was shy of 400ft.lbs.
3.54s with 33" tires ain't helpin' either.
3.54s with 33" tires ain't helpin' either.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
These motors make lots of torque. You should have a strong motor with that setup. The gear ratio and tall tires don't help.
What do you mean by lackluster performance?
What are you expecting from it?
What do you mean by lackluster performance?
What are you expecting from it?
Thread Starter
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Elder User
Joined: Aug 2004
Posts: 620
Likes: 1
From: NE Wisconsin
truck won't spin the tires unless going around a corner, even before the lockright. Won't do a brakestand either. It does pull a trailer pretty nicely. Maybe too much torque for the horsepower.lol I wouldn't doubt if the tranny has something to do with it. It shifts pretty soft from gear to gear. Kind of falls in, not a good solid shift.
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Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
Did you install the timing set 'straight up'? The factory timing set is retarded 4 degrees. That will hurt the torque at low RPMs.
You should have used a good aftermarket double roller timing set and set the cam timing at 0 degrees. If you check the Intake Center Line with a Degree Wheel it should be at 106 degrees for the Isky cam that you specified.
You should have used a good aftermarket double roller timing set and set the cam timing at 0 degrees. If you check the Intake Center Line with a Degree Wheel it should be at 106 degrees for the Isky cam that you specified.
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Thread Starter
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Elder User
Joined: Aug 2004
Posts: 620
Likes: 1
From: NE Wisconsin
Yes, I have a double roller timing set and unless I screwed up, It is set at 0 deg. I called Isky and they said it has 2 deg. ground in also. I was thinking of checking the valve timing. Where can I get a degree wheel, and how do I check with the engine in? Never done that before.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
You can get a degree wheel on Ebay, and probably at a good local auto store. You also need a dial indicator.
Here is a link to Crane Cams instructions for degreeing a cam.
http://www.cranecams.com/pdf/803.pdf
You shouldn't need to check every parameter, but just the Intake Valve Center Line, unless you think that you have the wrong cam.
You should ask Isky what the ICL should be.
Here is a link to Crane Cams instructions for degreeing a cam.
http://www.cranecams.com/pdf/803.pdf
You shouldn't need to check every parameter, but just the Intake Valve Center Line, unless you think that you have the wrong cam.
You should ask Isky what the ICL should be.
Postmaster
Joined: Aug 2001
Posts: 4,270
Likes: 5
From: Delaware
An ICL of 109 degrees vs 106 degrees will improve the high RPM performance, but hurt the low RPM power. It is not much however. After you use the degree wheel and find out where the cam is set, then we should be able to tell if it's the cam timing.