Okay, so here's the deal...I have searched about a billion different threads on the subject of solid cams for small displacement SBC's...my baseline search has been around the 30/30 Duntov and the old LT1 cam...and the basic consensus is that the 30/30 has significantly less bottom end than the LT1, which I understand. My problem is that I can't find a definitive answer, relative to real world use, in MY particular combination. My combination is a 327, 9:1 compression, ported 461 heads (2.02/1.60 valves), my manifold and headers (pic below). I set my manifold up to run the two end carbs as primaries, and the headers are 1 5/8". My requirements are it's gotta be a solid flat tappet (non roller) cam, dual pattern, and as wide a lobe seperation angle as possible (114 to 116). I doubt this motor will ever see the other side of 6500rpm...it might, but I am after a broad torque curve and tons of vaccum...and, of course, the requisite lumpy idle. Anyone have a recommendation? Thanks!
If you want the best cam possible, I'd log on to Compcams.com and have their tech guys suggest one... ask the experts... its safer!
Thirdy... Good advice, and I'll take it. On the other hand, I love the input from the "in the day" and "here's what I did" users on this forum. Thanks
Plowboy...I said it before, and I'll say it again...I appreciate your encouragement Update pics are about a week out...I am changing a couple crossmembers in the frame (I used the frame as a training aid when I was teaching vocational school, and I realized I must suck as a teacher, since on crossmember isn't square), and as soon as thats done, I will start a sequence of build updates. Thanks for keeping tabs
Not related to to your camshaft concerns but that intake manifold and headers are the most unusual and radical I've seen on a SBC. I'm guessing you made them yourself; you are quite the fabricator if that's the case. BUTCH.
Butch... Thanks. Yeah, I made 'em. The support tubes that the carbs are actually go into the plenum, so thay are about 1 1/2" off the plenum floor...my premise is it will create a valid "signal"... The headers are 1 5/8"...bigger than what is "optimal", but they suit my purose. Thanks for the props
With that big log manifold and the 202 valves and wanting a solid rump-rump overlap high lift cam you realize you are doing everything possible to eliminate the possibility of a broad torque curve with vacume and stoplight city driving. Do you want a 70's pro stock style high rpm screamer or a street driver? 2500 rpm on up, you'll have a ball, but you'll bog and feather it to keep it running every time you leave a stop sign or crawl in a traffic jam. Sorry, someone had to say it. You're going for the same basic setup as all of us used to try to get streetable in the 70's with Dual Hi-Rise log setups and big overlap solid cams and valves. Only real difference is you aren't going for the high compression we used to run. Put a clutch in it, you'll need to play with it at low rpms on the street and slip it to get it going.
Thats ok, Joe Yeah, I realize that it's not an optimal configuration...but in an effort to minimize the negative effects of the large plenum, I incorporated "signal" tubes that are relatively close the the plenum floor. The carbs are set up as 2x1...the end carbs are primaries...so the idle and transition events will happen with carb signal directly over the ports. The 461 heads I have were too good to pass up... My premise is that with a decent LSA (old LT1 is 116 degrees, Comps new version of the old 30 30 is 112 degrees) I can maximize vacuum, and make the carbs work. Finally, I am not willing to compromise optimum efficiency for a better manifold/header configuration. I made the parts, and I will make em work. For me, different is better, and I dont think that the configuration is all that of a compromise...or, better said, I have made an effort to minimize the compromises. We'll see. Thanks for the input
I agree, unless you have the plenum filled to at least the top of the runners the plenum is going to puddle fuel which will lead to plug fouling at best and a huge flaming backfire at worst. Running the outboard carbs as primary carbs is bass ackwards to what a 3x2 is all about. Besides choosing the right cam/head/cid/bore and stoke/compression ratio combination to get a broad torque curve you have to have an intake manifold that will have good air speed velocity to promote cylinder filling at low RPMs without being restrictive at high RPMs. From what I see of your manifold the craftsmanship is beautiful and unless you have done something inside the plenum to reduce its volume it is going to like high RPMs only. Then again, what do I know all of the legal documents and doctors say I am nuts.
For what its worth Ive got a 9.7/1 compression 327 w/461 heads running a comp 294 solid and in all honesty its a bit too much even with a 4 speed and 373 gears its a bit touchy driving in town but it pulls like a sumbitch from 3000 to 6500 the 9.0 comp will hurt you even more I would suggest somthing about 280* adv duration I cant remember what the Lobe seperation was but I put it in at intake center @106 and to my suprise it does carry enough vacum to operate power brakes but it likes alot of timing about 42 total all in by 2800.
Intake looks pretty cool, but I hope the lowest thing in it is the floor of the intake ports. Looks to me that fuel would puddle in the center section there that is hanging low. Could be an issue. Have a cam custom-ground for it, you seem to know generally what kind of specs you're looking for. Or run a cheap dirt-track cam, the big name cam companies will have profiles that are pretty close to what you're looking for. What you are wanting to run is very similar to the claimer engines being flogged on dirt every weekend. Myself - I'd have to run the 30/30 cam, just because it has a little nostalgia to it. I hope you've read up on the rash of wiped-out lobes when breaking in flat-tappet cams with modern engine oils. Cliffs Notes: run a high zinc content oil in your car, such as Rotella or Delo, and avoid the more common automotive oils as they have reduced their additive content for environmental reasons.
I have a 1970 Corvette LT-1 and it has plenty of bottom end, but if you're looking for a lumpy idle, this might not be it. In my car, (it's all stock, 350, 11:1, Holley 780, etc..) it is not all that lumpy. It does have excellent throttle response and chirps the tires going into 4th. The idle just barely has a noticeable rumpity sound to it.
I agree with most of the comments about the mainfold; looks cool but concerned about the plenum volume and low rpm function. My main purpose for adding to this discussion is to point out that "lumpy" idle comes from overlap and is inversely but directly related to available vacuum at idle. Want vauum and lumpy? It will be a compromise. Also note that overlap isn't the end-all, it's usually the result of long duration (high rpm) cams timed to get the intake closed and exhaust opened at reasonable points. The result is the exhaust closing and intake opening get moved further past each other, increasing overlap. Unless of course you're marketing "Thumpr" cams or some other stupid thing and lose power intentionally just to make the engine "sound cool" at idle. The techs at any good cam company should be able to make some recomendations. You might want to send them a picture of that nice manifold. BUT, you'll need to decide if you want to be lumpy or smooth. I'd go for smooth and try to keep a strong signal pulling on that plenum.
Just wanted to make sure you understood what you're getting into as a street driver. Me, I'm just ornery enough to put a dual hi-rise setup with an old style rumpy cam in the coupe. I don't like having to tap the horn to get people to notice and move out of the way when I'm parking at an event. I can live with that as it won't be a daily driver only car setup. And I won't have power brakes and stuff that cares about vacume.
Thanks for the input, fellas... The intake runners are at the base of the plenum...I took great pains to radius the runner openings at the plenum floor, and the plenum floor has a slight crown to it, as well. One of the reasons I ran the "signal tubes" down into the plenum was so, if necessary, I could fill the roof of the plenum with epoxy, or some other area-consuming material. My objective is to see if my original design works, first. I can tune it as necessary. I should have been more specific about the rump rump requirement. I understand what causes it, and I am definitely willing to do without it for maximum LSA...vacuum signal being everything, in my opinion. Comp Cams says their remake of the old 30/30, PN 12-673-4, is probably what I am looking for (thanks for the advice, thirdy). Thanks again, guys
Racyredhd...I hear what you are saying about how I have phased my carbs, but I took the advice of one of the resident tri poswer experts (vintakes) and went 2x1 (as he describes the set up). Think about it...typical 1x2 (single primary, two secondaries) is a proven arrangement where economy/performance, in the myriad driving conditions that a street car would see, is applicable. But that doesnt necessaily mean its optimized for performance. Personally, I have NO experience with the 2x1 arrangement, but when I consider the carb placement, and the requirement to get maximum signal under the carbs, and I dont care about economy, it makes perfect sense. So, I went to the source (or the one that I trust the most, since he gives away his knowledge for free). I think it make sense, so I am going to try it. Don't forget...Bruce Crower started his empire sellng U-Fab manifolds. He is a genius, and his products are unsurpassed, but the point is that his business started with the sale of a ton of log style manifolds that the customer was responsible for fabricating. And by modern standards, they were barbaric. And now they are so popular there are aftermarket companies reproducing them! My reason for building a manifold is simple: I never have. I wanted to, because guys like Crower are my heroes, and I wanna be able to say I made one, and it worked. Which I am confident it will, without cataclysmic fireballs. Gotgas...I am a huge fan of Rotella, have empty gallon jugs around the shop, and use it exclusively. Thanks for the tip, though.
Their was another post a few months back on solid cams for SBC. I had a DZ302 with an Engle EP-25 Grind. It was a 10:1 motor with ported 2:02 heads, Holley Z28 syle intake and 650 DP Holley. It had really a wicked idle and worked really well with the 302's high RPM range (7500 RPM easy). Check out the link http://englecams.com/catalog/search_results.php The EP-22 may work better for your application with lower RPM and lower compression. Plus you get to run the cool decal!
Not really technical help, but a buddy runs solids in his 32. He had some oil pressure problems this summer. The solids are so loud that it makes listening for bearning noises impossible. Sure turns alot of heads with the the sound of the solids in an old style rod though!
Your compression sure sucks for the cam that's gonna give you the "lumpy" sound you want. BTW, neither the LT-1 or the 30-30 will give much of a lumpy sound. You need to pull the heads and angle mill them as much as possible and run the "off road" Z-28 "140" cam. It's not a torque monster, but NOTHING is in a 327. But, it works OK in a 302, so it'd be OK in your 327. Plenty of "lump" on the idle, and it works decent. I've used that cam in lots of anemic 302 Camaros over the years. Lots of fun shifting a pipey little small block. It is a stick isn't it?
Not to Jack your thread but while on the subject of Cams, What gives that lumpy idle we love so much. Is it the compression, the duration, the lift, or the lobe center. My cam for example is .488 lift, 234 duration and 114 degree lobe center. It has a nice mild lumpy idle but nothing extreme. I have no clue what my compression ratio is but I am sure the sound of the idle would improve with a nice set of heads. Right now I have a .040 over 350 with a set of stock 305 heads (it is what I had at the time). 3x2 set up with a 25-2700 stall convertor. The car runs great but I would like to increase the "Lump".
Here's how I understand it (and anyone can denounce my understanding...if I was an expert, I wouldn't have asked ) The narrower the lobe seperation angle, the greater the overlap (dependent on duration and, to an extent, on clearance ramp profile). Overlap is that period of time when both valves are off the seat, or more specifically, overlap is when both valve events (opening and closing) are engaged. Excess overlap causes poor cylinder filling and/or evacuation, resulting in low vacuum and an inefficient combustion process, and that is what causes the rumpity sound. A larger LSA allows for an improved cylinder evacuation, filling, and subsequent combustion process, and therefore improves low rpm vacuum. So...here's the specs on Comp Cams 30/30 replica: Lift: Int: .504 Ex: .498 Duration @ .050: .247 .254 Valve Clearnace .012 .012 LSA: 112 degrees Any opinions on those specs for my application? Thanks!
29Sedanman: That cam sounds like something I would be interested in...as I said earlier, I will gladly sacrifice lump for vacuum. I like that 114 degree LSA. Is it a solid? And do you know the manufacturer? Thanks
I'm not trying to hijack, but I've been thinking about solid flat tappets myself. I've a 350 with ported 462 heads, planning on running eventually an Offy 6x2 set up in a model a roadster with a 4 speed and 3.55 rear. I picked up a solid cam with lifters at a garage sale cheap. the cam was new and was custom ground about 10 years ago. Here's what the cam card says: 108.2 lobe center sep. 27.9 crank degrees valve overlap 238.3 intake duration @ .050 .503 in intake valve lift 249 exhaust duration @ .050 .51 in exhaust valve lift valve lash: .022 intake .024 exhaust. whatcha guys think?
Groucho...thanks for the tip. Here are the specs for the -140 cam (PN 3927140): Lift: Int: .493 Ex: .512 Duration @ .050 257 269 LSA 112 degrees Here are the specs for the old LT-1 cam (PN 3972182): Lift: Int: .459 Ex: .485 Duration @ .050 242 254 LSA 116 degrees I am thinking maybe the LT-1 cam might be preferable? Thanks
Ok, I went back and reread your original post just to make sure I dont head off on some tangent as i am prone to do. First of all I commend you on your intake, the workman ship is beautiful. My concern was that a 327 with ported heads and plenum that big the engine would be lazy at low RPMs. Reading your subsequent posts I see that you have allowed for filling the plenum to cut down its volume. I guess that I assumed that with the 3x2 setup you were looking for a degree of economy in less than spirited driving, shame on me. Also I see that you pointed out that the bottom of the plenum is above the bottom of the runners which will minimize the possibility of fuel pooling. I have taken any number of street driven cars WAY past the realm of being street drivable and brought a few back, The things I learned along the way are, for a broad power band the best things are long stroke, unported heads, small overlap cams and smaller carbs than you think that you need. All of which limit high RPM usage. That being said, a couple of areas that have not been touched on are vehicle weight and gearing. If your car is going to weigh less than 2500# and you dont mind getting aggressive with the gearing you can get away with murder. Once again I commend you on your fabrication skills on both the intake and the headers. they are works of art.
Racyredhd... Thanks for the compliments. Yeah, my plan represents making the best compromise. And I was premature in specifying the rumpy thing...it would be great, but I actually know better . Like I mentioned earlier, and you pointed out, the apparent gross plenum volume isn't optimal, nor are the heads (good news there, they are port matched, but not ported...the big valves came with the package, and they were cheap, and 461's, I couldn't pass em up...stainless valves, guide plates, screw in studs, fresh, $200). The plenum volume, as we discussed, can be reduced. Bore and stroke, well...I wanted a 327. Later I will post pics of my PCV arrangement, which includes the use of the road draft tube...point is, I needed an early block to accomplish that. I think the LT1 cam is looking good... Rear tires are 8.25x 16...nearly 33" tall, so I have a 4.10 gear set...for all I know, it might not be steep enough, but we'll see. These are old update pics, (more on the way, Plowboy! )but you can get an idea of what this thing is...add stupid-tall bias ply white walls, glossy black steelies w/o hubcaps, and abbreviated bed, and shiny black paint with lots more of my friend Jeff's pinstriping to the equation, and you get the picture. Thanks again for the compliments
Dollabill, Ever consider the old #3736097 "Duntov" cam?As I remember it was a little rumpy.Was std. item for h/p solid lifter vettes 57/61.The 2x4 and f.i. ones.Really ran good in a stock 283 as well. glider.
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