cam option

[NixVegaGT]

old cam was 20/60/56/27 but that was with 8.0 compression

Rod,

The DCR at 6.42:1 with this timing is terrible! I can see why you wanted a change. How did it idle? It couldn't have been great. This cam actually isn't bad for your new compession. The DCR is still pretty low at 7.7:1 but better.

so once again..anyone have a cam choice suggestion..
2.78 diff 1100kg car 2100rpm at 60mph

If this cam had more lift maybe. A similar cam would be the Isky 262. It's about the same duration with a larger 0.445" lift. I'm not certain what the actual valve timing is though. If it's close to your current valve timing than it's decent. That's my best guess.

Anybody else?

[roverman]

Hello V8ians, I'm pancakeing on, cams options. Anyone have suggested data for "direct cam on 4 valve" applications? I'm preparing to build ,4 cams-1 motor. I would like them to be optimum. Scenario:Lotus 907 heads with O.S.valves, I.R. runners,E-85 fuel, 3.73" bore/3.3" stroke= 4.6L. Lotsa rpm, 8k? vs Jensen Healy, approx 2,200 lbs. with up-grades. Davd Vizzard-like formulas?  Thanks, roverman.

[roverman]

Hello again, About that hyd.lifter preload. If your using adjustable pushrods or adjustable rockers,(even better),Check  the threads per inch with a pitch gage or lay a known pitch thread along side of the adjuster thread. When they perfect match, thats your pitch. Now lets do the math, 20 pitch thread = 1000 div. by 20= .050" per rev. So you could put an index mark on push rod/rocker and a mark on adjuster. Adjust till free-play is gone, decide how much preload and turn the crude-but effective internal micrometer, based on known pitch to desired preload. In this example, 1 turn = .050" preload. If we're using Buick/Rover heads, the early Volvo 4 cyl. push rod motor has quite durable adj, rockers and shafts,(need to cut in middle and add press-fit spacer) This set-up is what Huffaker used in my GT-1 motor. Worked quite well up to 8,000 rpm with serious roller. Des Hamill's, Rover V8 book mentions OEM., steel, adjustable, replacement rockers. Haven't priced them yet. Power to the People, Art.

[castlesid]

Art,

Thanks for the tip re adjusting the preload, it obviously a bit of a guess now that the engines built and don't particularly want to pull the manifold off to get into the lifter area so will be a bit of trial and error.

I'll try tightening the noisy lifter a couple of flats at a time and see what happems.

The adjustable steel rockers you mentioned are I believe the old Volvo ones originally used in the Group A spec race engines.

Kevin.

[NixVegaGT]

The Volvo rockers come from the 16b engine. They are very close to the stock dimensions but the shaft bushing is a bit bigger ID. It looked like 20 thou or so. Here's a pic for comparison:



This one is missing the adj stud. I'm pretty sure it uses a ball with a cup on the rod if I remember right. The ratio is different too. 1.55:1

[MGBV8]

Just needs a bushing in it.

[NixVegaGT]

I don't suppose you know a part number or something? I'll post it on my website just in case it's useful to someone.

[MGBV8]

I don't know of an off the shelf bushing. A number of our gang (not me) would find that to be a very basic machining exercise.

[BlownMGB-V8]

Just got done degreeing my cam and the specs are a bit different from what I expected to see.I tried to check it as accurately as possible using an 18" wheel and a .050" sweep 1" dial indicator but found I was fighting 5* of backlash in the new double roller chain, compliments of the align bore (About a quarter inch of slack). I used a pair of solid lifters swapped in for checking. Anyway the actual specs are .424/.424 lift, intake open at 5* atdc (all at .050") closed at 52* abdc, exhaust open at 38* bbdc and closed at 7* atdc. Specs were .436/.436, -4btdc, 36*abdc, 40*bbdc and -8*atdc. The biggest discrepancies were closing of the intake (16* later than spec) and closing of exhaust (15* later than spec).

My measurement for lobe centers was 105 for exhaust measured at max lift vs 114 specified and I had a little trouble getting a good read on the intake, first measurement was 115 but it didn't take account of the chain slop. 2nd measurement was 121, vs. spec of 110. Lobe separation was specified at 112. I don't understand how you calculate the lobe separation angle so I wasn't able to come up with that measurement.

This is the first time I've used a degree wheel, could some of you more experienced individuals perhaps throw me a bone here and tell me what this all means? It sounds to me like the grind doesn't match the spec card and everything is lagging by almost 15 degrees except the opening points. As it stands I'm at a real loss as to whether the cam should be installed straight up or perhaps advanced some and if so how much.

This is a high compression (10.6:1) blower engine with low boost. We were shooting for economy and extended rpm range, not maximum power output. I suspect Charles may have extended the duration to enable the higher speed operation, but how much is that going to affect the economy?

Jim

[NixVegaGT]

Did you mean to say -5º ATDC? If it's 5º ATDC that seems strange. the difference between 36º and 52º is insane. WOW.

I was going to say you could advance the cam a bit to balance the numbers.

Now that I look at it I really don't get -8º atdc for the exhaust opening from the adv. specs. And the intake opening at -4º btdc? This would equate to both valves being closed where there is overlap. Maybe it means -4º ATDC for intake opening and 8º ATDC for the exhaust. That would make more sense to me. Then again this is at 0.050" so maybe there is a tiny bit of adv overlap. Is this because it's for a superchager?

[BlownMGB-V8]

No typo Nick, at least not on my end. -4btdc would be 4atdc, off 1* from what I measured (5). The .050" measuring point does mean there is some overlap, but maybe not all that much. Charles *was* grinding it for a blower app. TA says in their catalog that all stock timing chain sets have 4* advance built in, which would (should) shift the numbers a little if I use the silent chain set. Maybe I can use the V6 chain tensioner with that. I'm looking into it. That assumes my double roller set is "straight up" and it may not be.

Jim

[MGBV8]

"TA says in their catalog that all stock timing chain sets have 4* advance built in"

That's so when it stretches breaking in, it will be closer to correct.  

[BlownMGB-V8]

Maybe so. These numbers are at the stock location. Guess I'll run it like that and see, just need to get an oversize timing set, looks like probably .008" over. Anybody know of a good place to get that?

Jim