Which cam and other questions

[eventhorizon66]

There is nothing wrong with Crane lifters.

But actually of ALL the cams you have mentioned I like this one the best by far:

http://www.summitracing.com/parts/SUM-K00172/

It is on the proper 106 LCA and with 1.6:1 rockers it would have decent lift for those vortecs at .480".  And it certainly ain't too big for a street 383.  My guess is you'd be very happy with this cam, just lose the exhaust manifolds and pick up some long-tubes ASAP.  Oh, I should also mention this cam is right out of the pages of a Crane Cams catalog.

Look at engine build #4 in Vizard's book.  He used a slightly larger cam with Comp 270 Magnum lobes on a 106 LCA.

[TexasRed]

The only problem I have is the overlap is around 62. That'd be a little hard on a daily driver. I'm not an old man, but this engine'll be carb'ed so no injector noise, it's also balanced, so it should be even smoother than a new engine, plus it's bigger so it can handle some more cam, but I just don't want to throw it all away. Plus I need to check the RPO code in the truck to find the rearend ratio.

[eventhorizon66]

That cam, since it is a Crane Cam, was measured at 0.004" (which means it appears a bit larger than a cam measured at 0.006").  It is safe to assume that David Vizard's overlap measurements are based on 0.006", since that is what Comp Cams uses and he mostly uses Comp Cams.  My best guess is that cam's lobes are very similar to Comp's 268 High Energy lobes, so I would guesstimate more like 56-58° overlap @ 0.006".  On top of that, since it is a 383 it will feel more like 50-52° of overlap would feel in a 350.

You should also know that Isky measures their seat duration at 0.007", so their cams are actually a bit larger at 0.006".

I feel very comfortable sticking with my recommendation (especially since I won't be the one to suffer the consequences ).  If your compression ends up where you said it will and your rear gear is 3.42 or greater (preferably 3.73 - 4.10), you're good to go.  The fact that you are running very efficient 170cc heads on a 383 will also give you some leaway in terms of cam decision as port velocity will be excellent.

[eventhorizon66]

Oh, and I never touched on your pushrod question.  Since you had the heads milled, you ought to grab an adjustable pushrod to find the perfect length that gets the rocker sweep right across the center of the valve tip.  Then order that specific length.  Are you using 1.6:1 rockers?  Roller tip rockers?

[TexasRed]

http://www.youtube.com/watch?v=sDEthCakytU

That's the summit cam idling. Sounds fairly lopey to me. Plus he says narrow power band .

Stock rockers, I may make my own pushrod length checker with a wooden dowel or something.

Would the RPO code be under the hood?

[eventhorizon66]

You really can't tell much from a video like that.  What was his initial timing, vacuum advance hooked to full vacuum, idle mixture screw settings, etc?  My guess is with more initial timing and the vacuum advance canister hooked to full vacuum, that idle would clean right up.  I can make my stock 929 cam sound close to that if I screw with the timing and mixture screws enough, and drop the exhaust.

As far as the narrow power band, it probably just feels that way because narrow LCA's tend to have less flat power curves, but notheless I'd rather have higher average power with a "peakier" curve rather than lower average power with a flat curve.  And we have no idea what compression that engine has.  That would affect the power curve as well.  On top of all this it's a 350, not a 383, so that 106 LCA is not optimal for that engine and needlessly increases overlap.

In conclusion, I wouldn't put any stock in that video.

UPDATE: I just watched the other vids on this engine.  It's a Goodwrench 350 (8.5:1 rated compression) that quote: "Needs a tune-up as the plugs are not so hot anymore"

RPO code would be in the glove box.

[TexasRed]

Well, I don't remember seeing any codes in the glove box. Just a .357. But under the hood it says GQ1 standard ratio. I have a feeling that's like a 3.08.

[eventhorizon66]

Pull the diff cover off and look for the ratio stamped in the ring gear or count teeth (it'll give you an excuse to change the fluid).

[malibu795]

personally i dont liek single pattern cams for DDing..
i have ran this cam on a couple SBC power form 1500-6000rpm
http://www.summitracing.com/parts/SUM-K1103/
Intake Duration at 050 inch Lift  214
Exhaust Duration at 050 inch Lift  224
Duration at 050 inch Lift  214 int./224 exh.
Valve Lift with Factory Rocker Arm Ratio  0.442 int./0.465 exh. lift
Lobe Separation (degrees)  112
i ran this cam wiht 1.6" rockers make for .471/.495 at the valve.

[TexasRed]

Well I ordered the isky a couple days ago. . . . . I had the carrier rebuilt a couple years ago and the truck's been sitting for about 6 months less than that. . . . so. . . .I don't think the fluid needs to be changed yet. I have a feeling it's a 2.73 rear end which may not be enough gear for that cam in 4th. I'll keep it in 3rd or less. How hard is it to change the ring and pinion in one of these? I'm thinking either a 3.42 or 3.23.

[eventhorizon66]

If you do a gear swap don't go for anything less than 3.42 (3.73 - 4.10 would be better).  2.73 gears behind a 700R4 is too long for even a stock engine IMO.  But you should be able to use fourth at highway speeds with the 2.73's and that 264 Megacam in a 383.  It just won't be useful for anything other than high speed cruising.

[SUX2BU99]

I agree with that. I had 2.76 gears and they sucked. A change to 3.40 ratio was much livelier with my new cam and heads.

Event, why is it that Vizard likes the 106 LCA so much? I thought the lower the number, the more narrow the powerband and the more rumpity the cam  ie. less street friendly. I guess if all-out power is the goal, that doesn't matter but 110 is usually what I see recommended for something streetable and livable.

[malibu795]

I agree with that. I had 2.76 gears and they sucked. A change to 3.40 ratio was much livelier with my new cam and heads.

Event, why is it that Vizard likes the 106 LCA so much? I thought the lower the number, the more narrow the powerband and the more rumpity the cam  ie. less street friendly. I guess if all-out power is the goal, that doesn't matter but 110 is usually what I see recommended for something streetable and livable.

LCA/LSA then smaller then number then closer then cam profile are together..

take 2 examples a 106* and a 114*. run then same duration/lift and you get somethign similar in results
this controls how long then exhaust remain open at then end of then exhaust stroke and then begining of then intake and when then intake vlv opens.. esentially have both intake and exhaust vlvs open at then same time.. with a tube head exhaust.. once it hit then exhuat pipe it rapidly cools off..

example we took 10ci of air and heated it to 100ci then rapidly shoved it out then exhaust... were it rapidly cools and shrinks back down ot 10ci... this is calls scavanging effect of then intake air.. it allow you to get more fresh air/fuel in were you would generally not thuse increasing power.


the 114* will generat ~20inhg at low rpms and increase as then rpm get toward the top end of then power band.. efrfectively sufficatein then air flow.

a 106*  will behave the oposite.

[eventhorizon66]

Event, why is it that Vizard likes the 106 LCA so much? I thought the lower the number, the more narrow the powerband and the more rumpity the cam  ie. less street friendly. I guess if all-out power is the goal, that doesn't matter but 110 is usually what I see recommended for something streetable and livable.

You are looking at it the wrong way.  Vizard says the way to spec a cam is to first find the optimal LCA.  This is the most important aspect of the cam and there is only one LCA that will make the most power.  Then select duration figures that will give the desired amount of overlap.  Then go for as much lift as the valvetrain will allow.  For most 383's with 2.02-2.08 valves the optimal LCA will be 106.

If you select the duration first and then a tight LCA second, then, yes, the idle will get much rougher and the cam will become racier, because the overlap has gone up considerably.  But this is the wrong way to spec a cam.

[SUX2BU99]

For lower-lift and duration cams though, you don't often see (or at least I haven't) a 106 LCA. Perhaps I'll keep an eye open for that some more. Curiously, what would the optimal LCA be for the motor I have? Specs are in sig below.