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gt2betubbed 06-02-2003 06:22 PM

Cam Selection on Blown BBC
I need your guys' advise on this one. I'm building a 62 Pro Street Nova. The motor is going to be a Blown BBC. I have the blower (Dyers 6-71), 4340 eagle crank, H-Beam Rods, speedpro blower pistons (7.5 comp w/ 119cc heads), speedpro rings. I don't have the heads yet, but I'm looking at a few different sets, all have 2.25/1.88 valves, and 119cc chanbers. I'm looking for a cam that would be streetable, but have a VERY NASTY idle. I got a custom cam grind spec of 267I/272E @.050, .683I/636E lift, and a lobe sep of 110* quoted from a place called LAZER CAMS. My problem with this is, I've heard a blower needs a lot of lobe sep., typically 114* or higher. The guy said having a lower lobe sep. would give my idle that nasty rumble I want and give me an rpm range of 2500 to 6000. Is this true?, and would this cause any early damage to my motor that a cam with a bigger lobe sep. wouldn't? This is my first blower motor, and I don't know anyone with one, just don't want to make any stupid "rookie" mistakes. Thanks in advance, and sorry for the long post. Oh yeah, I have a set of 2 850 dbl. pumpers for the carbs.

roys63 06-02-2003 06:29 PM

You can trust The Lazer Guy!!!!

gt2betubbed 06-03-2003 06:22 AM

Thanks Roy. It helps to hear that. But do you (or anyone) know how the lobe sep at 110* is going to react with my blower?

andybird 06-03-2003 06:54 AM

I would ask the question of several cam manufacturers to be sure, looking at the comp cams blower cams list, theirs all have 114 - 116 degrees,

and I don't see why you would want that much more intake lift than exhaust, comp cams ones all have equal or more exhaust not less

just an opinion/observation rather than experience talking

gt2betubbed 06-03-2003 09:07 AM

That's what I'm thinking Andy. When I asked for the cam, I asked for the most radical sounding cam (biggest duration), while still being streetable. The guy at Lazer said that with the lobe sep being smaller, it would drop my rpm range down to a streetable level. My biggest question is does this sound like a good way to go?

TurboS10 06-03-2003 12:01 PM

I would guess that he is looking at forced induction cams in general. With a turbo setup, the shorter exhaust lobe is sometimes used to help with reversion. Same is true of the wide lsa. I believe blower engines are usually more happy with an equal or higher exhaust spec. You do want the wide lsa, though. I would look into competition cams. They have several forced induction and nitrous(same as forced) cams available. Remember that all cams with the same specs are not created equal. Comp. supposedly puts alot of time into lobe design, ramps, etc.


gt2betubbed 06-03-2003 12:27 PM

Thanks for the insight Turbo, nice truck by the way. I checked out your pics and it turned out very nice! :D

deuce_454 06-03-2003 01:07 PM

there are two schools of forced induction cams, one is the old school of very small overlap and more exhaust opening than intake opening, the other one is running a cam that is close to a naturally aspirated cam, the cam closer to the NA cam will have less boost becaust of less restriction, and a bit more blowby, but will make almost the same power as the blower grind does (with the same pulleys) but the engine caracteristics will resemble a NA engine more, but if you run the same boost level, although you have to overdrive the blower more to run the same boost with a NA cam than with a blower specific, you will make more power from the NA style. (I am guessing thats why he specified the 110 degeree lobe seperation, for a BBC with a relatively small blower)

if i were you i would go with the 110 LS cam and be happy with sound and idle you were asking for, i mean the guy specified a cam for what you told him you wanted. why second guess that, if you wanted max power and big lobe seoeration he propably would have said somthing different.

just remember that you are building a pro STREET car, if you wanted max power you should build a totally different engine. starting with a 14-71 or 16-71 high helix cobelco blower, on a 5 inch borespacing DCRE 750 cui block and Dart Big chief heads. Not to mention the Enderle Buzzard catcher and methanol injection Hat.

Stick with what the expert said matched your demands, and dont try and sub-optimize every little choice, that way the final combo will be missmatched

gt2betubbed 06-03-2003 02:05 PM

Thanks a lot Duece! Even though I went to an expert, I'm new and wanted second opinions about what he suggested. The only thing now is that in order to make more power I have to run more boost which causes more heat and that's bad on a street motor. BUT, in order to get what I want, I guess I have to comprimise a little. It's good to know that I still can turn up the boost when I hit the track. Thanks for everyone's advise, I needed it!

TurboS10 06-03-2003 02:23 PM

[quote]Originally posted by gt2betubbed:
<strong>Thanks for the insight Turbo, nice truck by the way. I checked out your pics and it turned out very nice! :D </strong><hr></blockquote>


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