fooling my small block

-
S

stroker mike

Well-Known Member
Joined
Jan 21, 2007
Messages
336
Reaction score
0
Location
San Jose, CA
Will a tight lobe seperation compensate for the loss of velocity described when you put 340 2.02 heads on a 318?? Large runner/port volume reduces velocity in this combo but a cam on a 108 or a 107 will use the overlap to draw more mixture in, right? but close the intake cycle faster to keep up dynamic compression? Theoretically a tight LSA should balance that loss of velocity within reasonable parameters, right? I have the 318 with 340 J heads, 2.02/1.60 valves and I'm trying to pick a cam for my combo, I have a factory high stall converter, 2.75 first gear, and 3.55's. The cam I was looking at is an Isky 216/445 on a 108. My second choice is a crower #31918, with a 214/224 at 444/467 on a 112. The crower grind will slip in, which is a prerequisite for me at this time, and there is plenty of room for the isky, the only two issues I have are price and LSA. I have run small 50-75 shots of N02 before, but this is only for fun and not criteria. I want a nice lopey 108 sound, too, that's nice. But, people say that with the 108 nitrous is a no no. The true criteria for me is an optimal use of what I have to work with, and the final choice has come down to this, and I could use some more input from the ones who've been here. Thanks again! People tell me not to overthink it but I can't help it, I work too hard on my car, and to earn the parts I get so I hope noone is getting tired of my endless queries!
 
My impression is, you want a sound, and that's a foolish want...lol. The narrower LSA will not help with too-large a port, nor with lack of static compression. Think about two of the same cut keys on one ring. when they are stacked, they overlap identically. As you scissor your fingers and they seperate, less and less overlap. The further apart they are, the less overlap there is. Cam lobes are just keys on the same ring. For a given size lobe, you can only overlap them so far before the exhuast is flowing up into the intake at low rpm. Tighter LSAs tend to make peaky power, and hurt low end response and performance. The amount of hurt depends on a lot. You see a lot of 112 LSAs now because it flattens out the power peaks without sacrificing too much overall, and keeps the low end as best as possible. If it were me, I would go with the Crower split pattern and install it at 112 if you plan to squeeze it. You will want as much cylinder pressure as possible. The 108 has that idle sound because at low end it's not very good...lol. With NOS, that can mean a bad studder and pop at the line when it's hit.
 
I would call comps tech line. If they cant answer call Diamond back racing engines and talk to Damon. He used to be a cam designer.
 
Diamondback is a freaking joke.....

Call comp like what was suggested or call Scott Brown at Straighline Cams:

http://www.straightline-perf.com/

I think there are plenty of people here that can help with the question instead of going to some flyby night outfit like diamondback.
 
well, sound is not my goal. I just happen to LIKE a lumpy sounding cam. what I want is as much cam as I can use within the limits of my combo, the primary criteria being that I can't yank the heads off to have guide work done right now, so my lift is limited severely, I can get away with maybe .465 or so before I start clipping seals, and I know this. My theory was that the tight LSA WILL draw more mixture into the cylinder, having the effect of increasing lost velocity and ADDING torque, which is something good to think about when you put j heads with 2.02's on a 318. And, Hughes engines seems to concur in this belief, look at the muscle car series, they do exactly this, and they state the results. "explosive torque off idle, no vacuum problems' but you loose on the peak, which is no big deal to me, if I drive it every day. You see what I'm sayin? Tell me, how can I get at least 215/216 and 450-460 lift for 200 dollars-cam and lifters- like the isky as opposed to the 350 plus for the crower with it's corresponing kit? You can't, cause every one markets very high lift cams now with lobe profiles that take advantage of the .904 lifter, which is awesome, and works great for alot of enthusiasts, but they forgot about people who can't afford to do head work, but want to do what 80% of the new mopar fans out here are trying for their first build: 340/360 heads on a 318, cause it's cheap, and accessable. Do you get what I mean Moper? but I do like a lumpy sound!! LOL! But please don't brush me off as a don't know, cause you got the wrong guy.
 
Sounds like Hughes has the cam you want or can do what you are looking for so why don't you get one of their cams? They make good quality stuff.
 
I haven brushed anyone off I dont think. Least I didnt try to.. sorry if you took it looked that way I get a lot of "I just want the sound.." type questions. IMO, that's like shopping for a new car by color alone...lol. So if i offended, I apologize for that.
A short story/salespitch: I drove a '74 Cuda for a few years. It was a stick, 3.23 SG, and had a stock ring and bearinged '68 340, stock X heads, stock '71 intake and Thermoquad carb, small tube headers, and 175 shot on it. Well, being young and stupid, I got stuck, ran cheap gas, and blew 1/2 the ringlands off a piston. So I pulled it, replaced the shortblock with a stock '74 318 (guess from where??), stuck the same cam and top end and NOS on it, and ran it. The car went 13.50s off the spray with the 340 on Dunlop radials. 13.60s with the 318. It was so good in fact, that only a few friends who noticed the color change on the block ever knew I had hurt the 340. The cam was the 268H Comp Hi Energy. 218°@.050, 268° advertised, .454 lift. It had a noticable idle in the 318. It was not soft just off idle tho. I drove this car everywhere, and didnt have to slip the clutch to get moving. My point being, that cam is an old school single pattern with 110°.
Huges can do whatever they want. The latest grinds I've heard about make me wonder what they're doing. But that's them. They've forgotten more than I know now...lol. I'll stick to what I know. The best way for any short stroke engine to get air in, is to draw it in until inertia (rpms) helps it out. It cant draw much air in hard at lower rpms if the exh valve is open at the same time. Now, maybe Hughes uses an incredibly fast closing ramp on the exh valve's lobe. To minimize the time they both are open, but still have decent duration under the curve. That might explain thier heavier than what most reccomend for valve springs too. It's hard to control a valve and harmonics when it slams shut that fast. Who knows.
From what you've said, what's holding you back is the valve guide height (not seals). If these are normal X/J/O/915 LA heads, you have more room than you think to go with lift and 1.5 rockers... Guys throw in .484 and .509 lift cams on stock height guides with no issues all the time. You will need matching springs of course, but they will have to be changed anyway. I think it's mid 80s LAs that use a full rubber positive type seal. Install them with the springs. That way you're not squishing the large umbrella seals all the time. It's the Magnum heads, and 360 LA w/exh valve rotators are the ones that can't take a ton of lift in stock form.
If money is the object, give Engle Cams a call. They ground me a custom solid with lifters for $189. They also used to grind Hughe's cams, and have a keen awareness of spring pressures and break in issues. (310)450-0806. They have some very nice looking lobes for mopars, and can also give you a great price. Your going to spend one way or another. Might as well get more of what you want.

"Theoretically a tight LSA should balance that loss of velocity within reasonable parameters, right?"

Right. However, on large port, small stroke, low compression engines, that parameter rpm wise is about 2800-3000 rpm depending on a bunch of other factors.
 
I bought CompCam and lifters XE268 for my 318 for $169 including freight to my house from discountperformanceparts, on ebay. I don't know if this is what you are looking for, but the specs are below. Mike

XTREME ENERGY 268 DESCRIPTION: HYDRAULIC: Great for street machines, largest cam for stock converter, 273-318 works best with 2000 stall.



--------------------------------------------------------------------------------
CAMSHAFT SPECIFICATIONS:

Cam Style: Hydraulic flat tappet
Basic Operating RPM Range: 1,600-5,800 RPM
Intake Duration at 050 inch Lift: 224
Exhaust Duration at 050 inch Lift: 230
Duration at 050 inch Lift: 224 int./230 exh.
Advertised Intake Duration: 268
Advertised Exhaust Duration: 280
Advertised Duration: 268 int./280 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.477 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.480 in.
Valve Lift with Factory Rocker Arm Ratio: 0.477 int./0.480 exh. lift
Lobe Separation (degrees): 110
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Grind Number: CRS XE268H-10
Computer Controlled Compatible: No
Lifters Included: Yes
Lifter Style: Hydraulic flat tappet
Valve Springs Included: No
Retainers Included: No
Locks Included: No
Valve Stem Seals Included: No
Timing Chain and Gears Included: No
Assembly Lubricant Included: Yes
Pushrods Included: No
Rocker Arms Included: No
Gaskets Included: No
Quantity: Sold as a kit.
 
I am a firm believer in new cam technology,every car I build has to be streetable,have a bad *** idle and make maximum power and you can have all this with todays cams.I would go with the comp xe/hughes grind or a lunati voodoo and not think twice,if you really want a good cam sound-(who doesnt?)-good vaccum/driveability and top end.The comp std. xe series has reasonable lift for the duration so it might be best choice.The funny thing is agressive lobe profiling is not new-its been around for ages and Harold from ultradyne has touted them for years-hence lunatis voodoo series came to life when he went to work for them.
 
I had actually looked closely at that cam, but I was told my 2000 stall was too low for it, I had looked at an Isky 270 hl and a crower power beast 268/270 split, as well. I even looked at summit's 218/228, but although the rating is 2000-4500, a tech told me I'd be better with a 2500 stall. soooooo, after many discussions about LSA and etc I was almost ready to make a choice when a friend told me his 480 cam was clipping the seals on his heads and I want a slip in, i.e. no clearance issues, I was gonna run the 219 489 hughes cam, but maybe that won't fit? so, long story short, I'm back where I started looking at comp he268's and wondering if the room is spinning or is it all in my head? So, I spoke to a feller at schneider racing cams today, gonna get a custom grind maybe, and you're right, Moper, I guess I AM gonna spend one way or another. I'm always so de-MAN-ding, according to my wife, it may be true...LOL!!
 
Its not in yet. I'm home porting a set of 302 heads and will install cam with heads. Heads are almost finished. Mike
 
:-D
stroker mike said:
Hey, valiantmike, does that cam rock?
Click to expand...


If you are speaking of the Comp XE268, lemme tell you, it is an awesome cam for a 318. I have lightly machined stock 318 heads and valves, .030 over block, stock compression bottom end. It is perfectly drivable with the stock converter. Not too sluggish out of the hole, even with the soon to be replaced 2.76 gearing. With headers, I have given up nothing in low end torque to the 260H cam, with similar to 340 specs, if anything, gained. I havent taken it over 3,000 RPM yet, but I feel that it has even more reserved for the top end. As for the idle, with the headers, it had a pretty good lope to it and its completely noticible( rumpity, rumpity, rumpity, rump). It sounds down right mean. I am stoked with the combo. It is a good cam in other combos too. One of the best cams made.

As far as idle quality and low end with big chambered heads with low veloscity, it will probably be different than stock heads.
 
well, with my 2000+ stall it should be good even with my heads. I am amazed that they found a way to fit all that duration into such a usable rpm range! I had looked earlier today at the dual energy 275, but I don't want to give up too much bottom, so all hands are pointing to the xe268h and I think I'm done with this, I have checked every known grinder in the lower 48, checked every brand, series and read every spec, and I think I've beat this thing into the ground far enough. Thanks, guys, see you next time.
 
You must log in or register to reply here.
-

Back
Top