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Old 26 Apr 2008, 14:34 (Ref:2187459)   #1
Al Weyman
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SB Chevy valve spring choice with solid roller cam?

I am rebuilding this engine for one of my cars and am changing the cylinderheads to comply with current championship regs. This is the engine I did build up but sprung a leak on the cylinderhead in the spring seat area.

Anyhow the guy that originally built the engine has fitted what appears to me a seriously strong triple valve spring and once the valve lash is taken up you can feel the engine getting far harder to turn over. Now I have read an article by David Vizard who advises not going over the top on valve spring pressures as there is serious horse power gains to be had by having them strong enough to stop float at max rpm and shut the valves quick enough but no more as that is simply wasting horse power.

I also have a set of twin springs here that I was told by another well known specialist in the SBC engine were for a roller cam and they are no where near as stiff as these ones the engine builder who in fact is more renown as a drag engine builder fitted to mine so its got me wondering has he built this thing to pull collosal revs with a seriously stout cam when I have a road race cam cam that pulls from about 3500 rpm and the engine is limited to 7800 rpm. (BTW he also fitted the engine with an unbaffled drag race sump instead of a road race sump which is why the engine let go so I dont have a great deal of faith).

The problem I also have is these triple springs will not fit the legal set of Chevy factory BowTie Phase 2 heads without cutting down the valve guide boss more and enlargening the spring seat more when the Bowtie heads come from the factory already modified in these areas so there should be springs available that will fit. The other set of springs I have fit these perfectly.

The spec on the cam at .050 lobe lift is as follows:

Intake opens 26 deg BTDC
Intake closes 54 deg ABDC
Lobe centre 108 deg
Lift duration 260 deg
Lobe lift .390"
Gross valve lift .585"
Rocker ration 1.5 to 1

Exhaust opens 66deg BBDC
Exhaust closes 24 deg ATDC
Lobe center 110 deg
Lift duration 270 deg
Lobe lift .410
Gross valve lift .615"
Rocker ratio 1.5 to 1

Its as I said a solid roller cam but not as radical as some I have seen although the roller cams do have very rapid ramps and look a lot squarer than a flat tappet cam.

Any help or advice on a suitable spring for a cam of this spec would be appreciated. BTW I doubt I will rev the unit much over 7200rpm.
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Old 27 Apr 2008, 09:58 (Ref:2187918)   #2
Casper
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Casper should be qualifying in the top 10 on the gridCasper should be qualifying in the top 10 on the grid
Ask the question on DV's site, I am sure he or one of the other guys there would give you an answer.
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Old 27 Apr 2008, 10:06 (Ref:2187925)   #3
Al Weyman
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Thanxs casper, I have done a bit more research and it appears for my purposes according to crane cams I need about 220 to 250lbs spring pressure and i recon I should go to the lower side of that as i doubt I need to rev this thing much over 7200/7300rpm and Competiton Cams has a spring at a good price that ticks all the right boxes pressure and size wise so I think I will order a set of those with matching retainers, as DV says in his book moifing Small Block heads at the end of the day its down to dyno testing to really get the best combo and this looks a good starting point.
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Old 27 Apr 2008, 13:17 (Ref:2188095)   #4
AU N EGL
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AU N EGL should be qualifying in the top 10 on the gridAU N EGL should be qualifying in the top 10 on the grid
Al

I run an LS6 with 243 heads (62cc chamber) with Comp 981 springs.

My cam is a 224/224 581/581 112+2 XF-R Comp cam

with a a 6750 red line.

If my memory of cams servers me that is a long dration high lift cam your running.

260/270 585/615 108-2


There is a US web site that has lots and lots of great small block chevy info. LS1tech.com Even though the name is LS 1 Tech lots of other great into on ALL Chevy engines.
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