stevenb

I bought a cam last week and I was told it wasn't very good for what im lookin for. I think you all know what I mean by the rough choppy idle sound. I've heard it be referred to as a cat purring haha. Well my specs are....


DUR @ .50 244(INT) 244(EXH)
VALVE LIFT .510(INT) .510(EXH)
LOBE SEP 107(INT) 109 (EXH)
LASH HOT HYD.

B=16=07

So is this what I'm lookin for or not? Thanks!

customblackbird

iTrader: (15)

the lob is not great, then again i dont kno much about cams but i kno that the lobe shouldnt be lower than 112...so 112 to 114 is pretty good. i think the lobe is wats making it choppy

Apeiron

It would help to know what kind of engine this is going into.

stevenb

350 carb

Apeiron

Roller or flat tappet? What heads?

stevenb

World Sportsman 2 heads, not sure about being a roller or not but I would assume it isnt?

xpndbl3

iTrader: (5)

rough choppy idle is due to a bigger cam with a closer LSA like a 106. Which means big compression, big gears, big stall and not as streetable as a more mild cam. Choppy idle means spinning the motor to the moon typically as well.

327???

what year block? type of intake? carb size? stall size? rear gear? vehicle weight? intended use?

all those things are important to picking a cam.

stevenb

Well if I have 107 and 109 is that close? My compressions should be around 9-9.5:1 with my flat top pistons I assume.

Air_Adam

A cam with 244* @ .050 is a pretty big cam for any 350. That will definitely give you the rough idle you are looking for, if thats all you are after. The XE274 I have in my 350 definitely has some lope, although not "rough"... its only 230/236 degrees @ .050. I hope you have alot of compression in that engine (11:1+) if you plan on actually driving the car with that engine, because if you are just putting it into a basically stock, low compression 350 (like under 10:1), then its going to be a total pig and probably won't be very fast.

Those Sportsman heads are pretty good heads, 200cc intakes and 64cc chambers if they are like mine. I haven't used my Sportsmans yet, but they should work quite well with my XE274 and 10:1-ish compression. You'll need quite a bit more compression than me to get the most out of that big 'stick though.

A local guy I know, who is also on this board, uses a solid roller cam with similar duration specs (although around .620 lift) and a 108 LSA in a 406" engine, 11:1 compression, and it goes like a raped ape. But all the extra cubic inches and compression in his 406ci tames that cam down ALOT compared to what it would behave like in a 350ci engine, and its still got a pretty 'lumpy' idle.

I'd be sure you know what you are getting into with a cam that big in a little 350ci engine. Its not even going to start making power untill 3500 rpms, so I hope you'd have an intake and exhaust that will support power to at least 6500 rpm, and a bottom end that can handle that kind of rpm. If this is just for a street car, you'd probably be happier with something in the 220-230 degree (at .050") unless this engine is being built to match that cam.

stevenb

Well the pistons I have are true flat tops(.40) with 4 valve release. Is that good enough or is there other things that make up compression?

Stekman

Bore, stroke, head gasket diameter and thickness, cc's of the combustion chamber, piston volume, and deck clearance is what creates a static compression ratio.

Who makes the cam? What kind of cam is it?

Sonix

iTrader: (1)

Yea, i'm thinking it's the edelbrock RPM cam, but the straight pattern version. Ie, nice slow ramps that'll make it a dismal performer. 244/.510" lift seems oddly familiar eh?
Except that has a 108LSA doesn't it? Hmm...

flat tops with 64cc heads will give you pretty close to 10:1 CR, depending on head gasket and if the block is decked, but those don't have a gigantic effect on it. (also the pistons if they're 1.54" Comp height or 1.56", which kinda goes along with the block being decked or not.) I'd say you're in the high 9's, 9.7 range or so. But if I were you i'd want to know what it was EXACTLY, if it was my motor.

stevenb

It is not an edelbrock RPM cam, the brand is engine pro
It is a flat tippet cam btw and it is a 78 357 with an edelbrock alum intake witha holley 750 double pumper carb

Sonix

iTrader: (1)

Yea, same thing though. It just has two of the exhaust lobes from the edelbrock RPM cam. Ugh.

stevenb

So in conclusion...rough choppy idle or no?

Sonix

iTrader: (1)

Oh yea.

But not necessarily in a good way. It may not perform as good as possible, but choppy idle is indeed what you'll have

stevenb

What do you recommend to get it to perform good?

xpndbl3

iTrader: (5)

look at the comp XE lineup or the lunati voodoo lineup

Sonix

iTrader: (1)

'zactly.

BadSS

This is about as big as you'll want to go that will perform decent and give you the chop you want and have decent brakes. It's a 226/226 on a 106 spread (102I and 110E).
http://store.summitracing.com/partde...2&autoview=sku

The XE cam will make more power,,, but I don't think one matched for your combination will give you that old school "hear each cylinder fire" type "chop" your looking for.

The 244/244 -108 (107I and 109E) will give you a more of a rough idle than a "chop" and you'll have little to no brakes with your compression and cubes. As said earlier,, it'll take a while to get up on the cam and be very sluggish until you do.

Actually,,, the 218/218 - 106 (below) would probably be a better choice for overall performance,, and idled down a little lower than "normal" would give you the rat-a-tat sound idling through the parking lots. You just won't be able to stab the throttle off the lower than normal idle or it could stall out,, or go dead on you,, brakes might be a little hairy also idled low. Idled "right",, it would have more chop than most,,, decent brakes,,, and have extremely good response between 2600 and 5000 rpm.
http://store.summitracing.com/partde...2&autoview=sku

F-BIRD'88

Steve: this cam is a fairly big street racer/ bracket racer Saturday night bad boy cam. It will have a rough idle and low(er) manifold vacuum.
I recomend you install this cam slightly more advanced than normal for best results. the "107 and 109" refers to the intake and exhaust lobe position.
It indicates that the cam is ground on a 108LSA and advanced in the motor by 1 deg. i would advance it further by about 4 to 5deg. Now the intake C/L is on 103deg. this will enhance the overall usable power in your street driven motor with plenty of top end. It will be very responsive with this little bit of additional advance dialed in during the install.
I would also modify the distributor advance by locking out the mechanical advance and set your timing at 34-36deg at idle. this big cam requires this much initial timing. Unless you do this mod the throttle responce will be not so good.
I would also replace the power valve (holley) or metering rod power step spring ( Qjet or Edelbrock) to a light 4.5" rated. this will ensure the carb idles correctly with the big cams reduced intake manifold vacuum.
Anythiong you can do to improve cylinder head flow is a bonus. Sportsman heads respond very well to simple port clean up and valve guide boss contouring. Major hogging is not required.
A performer RPM or a Vic Jr intake will both work very well.

This cam likes rpm. it will want a 4.10:1 (or more) rear gear and a 3500rpm stall converter (10") This cam requires a better than stock valve spring. An affordable Lunati 73943 or Comp 981 spring set at mininum. If your sportsmans alrady have the medium sized performance 1.44" diameter valve springs installed you should be good to go.
This cam needs an exhaust system that can breath. 1-5/8" or 1-3/4" long tube headers and 2.5" dual exhaust with dual hi flow mufflers is best.
Really likes open headers and collector extensions at the track.
This is how you set up the motor to work with this cam. Follow these guidelines and it will work very well for you. It will have a rough but steady 900rpm idle speed once warmed up. Power brakes will probabily be marginal but not unmanagable because of the reduced manifold vacuum at idle. A vacuum reseviour canister helps.

stevenb

Thanks a lot for your help.

I have upgraded to stiffer springs already. How do you lower the degree of the LSA? I bought a pair of Hooker Shorty Pro Comp headers also. Are you saying I should swap this carb for an edelbrock or qjet?

rjt76

lsa is ground into the cam i believe.

Sonix

iTrader: (1)

Yes, it's ground into the cam. See my primer if you want some info on cams
https://www.thirdgen.org/sbc-camshafts-primer


F-bird was just saying that with either cam, you'll have to tune it, since it'll have less vacuum at idle than stock, and you don't want it to kick onto the power system too early and flood the engine and make it bog like crazy.

jjlabinski

all your power will be at the top end. you will not have torque off the line with the set up you are contemplating.

SpitotRs305

thats what the big stall and tall gears are for...

F-BIRD'88

The LSA stays the same (108deg)
It's ground into the cam and cannot be changed.
According to your info the cam is advanced 1deg (107in C/L 109ex C/L ) I advise advancing it a little further by about 4 to 5deg { intake on 103 C/L ex on 113C/L } . You can advance a cam in a motor by using a cam gear offset bushing set. This involves drilling out the 3 cam bolt holes oversize. Drilling out the cam dowel pin hole in the cam gear oversize then installing a offset bushing on the cam dowel pin in the cam gear dowel pin hole.
Installin the offset in one direction will retard the cam. The other direction will advance the cam. No offset at all and the cam stays in The position ground in by the manufaturer.
A cam gear bolt locking plate is then used to lock the bolts and retain the offset bushing in the cam gear.
You use a degree wheel on the crank and a dial indicator on the lifter edge to find the cam's opening and closing timing points @.050" lifter rise to determine wether it is "straight up", "advanced" or "retarded" in the motor relative to the crankshaft position. You adjust the position of the cam in the motor using the cam gear offset bushings (availiable in a set) Advancing the cam increases the lower end of the torque curve. (This does not turn a big cam into a small cam. It does adjust or bias the cams nature to the lower end of its power band (3000 to 6000 rpm) to maximize overall torque. It only compromises peak horsepower a little but. Overall usable torque is much more important.

Shorty headers are better than nothing but this motor (with this cam) should have long tube headers.

I'm not telling you to use any particular carb. I'm telling you what you need to modify in any carb to run a big cam like this one.

I'd change the headers, not the carb. What carb do you have?

stevenb

Holley 750 double pumper

F-BIRD'88

that will work great.

stevenb

So if I do not alter my cam and/or LSA, am I going to lose horsepower and torque? If so, how much?

sofakingdom

iTrader: (1)

Probably. How much, would depend on what cam you have now. If you picked it the same way, probably not too much. If it's a good cam, maybe alot.

Maybe a better idea, if it really makes any difference what it runs like, would be to put in a more sensible cam, and get one of these. http://www.vroombox.com/vroombox/

stevenb

Right now I am currently rebuilding the block, and there was no cam in it

F-BIRD'88

What is the problem with following my guideline above and set it up as outlined?
It's not that hard.

stevenb

I am just making sure I know everything thats good/bad and that I fully understand

stevenb

UPDATE UPDATE UPDATE


So...I had a guy do a valve job for me over the weekend because I needed valve guides cut...and the World Sportsman 2 heads are 64cc heads and I will be running 11:1 compression, and I thought before that I would be running 9.5:1 so I was wrong. Any new thoughts?

SpitotRs305

go bigger with the cam

stevenb

Bigger valve lift? How come?

SpitotRs305

not lift duration/lsa bleed off some of the compression 11:1 is a little high for pump gas. but not so bad with Al heads so really it will be a compromise

stevenb

Can i stick with regular or do I have to switch to premium?

SpitotRs305

i would be running premium in that engine to be safe you might get away with a mid grade

but that depends on a lot of factors i mean you might have detonation with premium depending on altitude, engine temps, timing ,quench, piston shape, combustion chaimber condition... it is hard to say for sure

stevenb

So are you saying that I have good enough compression but still need a better LSA for what I'm looking for?

SpitotRs305

the term LSA refers to Lobe seperation angle... basicaly it refers to exh/intake over lap... the amount of time both valves are open at the same time... this is ok because of exhaust scavanging where the flow of exhaust out of the heads will actually be pulling intake air into the cylinder to completely expel all exhaust gases...

a longer duration cam will help drop you Dynamic compression ratio... dynamic is really the important one not just static. dynamic takes into acount the intake valve closeing event which is when the cylinder actually starts to see compression... the longer the intake valve is open the further the piston is in its travel up the bore before the valve is closed effectivly droping the CR of the engine by not allowing the engine to compress its total swept volume

stevenb

can you give me an example of a good duration I'm looking for?

SpitotRs305

but as for an actual cam i would look at the XE282... depending on what you are planing on doing with the car... but that cam might be to big but i think the xe274 will be a little to small for pump gas
http://store.summitracing.com/partde...8&autoview=sku

stevenb

I dont have high hopes and dreams for this car just trying to make a decently beefy street car which I may take to the track a few times

SpitotRs305

do you plan to run it on the street often?

stevenb

Yes everyday until winter then I switch to my truck and when it gets nice Ill bring her out again

Stekman

How are you getting 11:1 cr?

85Firebird350

iTrader: (3)

I dont know too much about engines being that I'm only 18 but that compression ratio seems a little high to me. My 383 stroker with 11cc domed SRP high compression pistons, with a .040" head gasket. is yielding a 11.8:1 CR. with 76cc heads. So 11:1 seems kinda high for that setup to me.