CAM CHOICE.

So, since I'm still waiting for the results and I need to get my mind off it... I need to pick a cam. Considering there are 13.6 million options for a sbc cam, I figured I'd turn to the experts. But Since I don't know any, I came here instead. 

So, looks like it's going to be stock bore/stroke Gen 1 SBC with roller cam. Flat tops, 64cc chambers, 200cc intake, 2.02/1.60 valves. intake is a 650 holley that will be sitting on an RPM airgap and breathing through 1-5/8 headers for the C10 and dual 2.5". Rear end is a 4.10 being fed by a TKO-600. Truck will weigh right around 3500lbs empty. 

So.... what cam to make 350-400hp reliably and why? I don't know if this is a good or bad idea... but Comp XR276hr? 

Go to Comp Cams' website, enter all your data and get a recommendation from them. They're the experts, let them do the work for you (FOR FREE!) and get it right the first time.

In reply to NickD :

yeah, but that doesn't waste time while I try and distract myself from waiting on results that have taken too damn long. 

I have an old flat tappet 272H in my 350.  It is too much cam for a daily driver with cast pistons, because it really starts to pull about 4500 and is still working hard when the valve springs give up around 6200. Those piston speeds concern me, with my Badger flat tops...  268H would have been the better choice for me. 

I presume modern part numbers are at least similar in rpm range.

Edit: Your horsepower will come from the heads, I think.  The cam just helps the cylinder head work, and establishes an rpm range.  Remember the wisdom of Dirty Mary, Crazy Larry.

bobzilla said:

In reply to NickD :

yeah, but that doesn't waste time while I try and distract myself from waiting on results that have taken too damn long. 

 

Or call the Summit Tech Line

XR270HR?

Ran a 268H in my '79 Z-28 w/ flat tops, Torker intake, 1-5/8 headers, 2.5" duals, AT w/ mild stall. Great street cam, pulled good from 2200 up, I really wouldn't want any more cam in a DD/ streeter. Flat tappet tho that won't do ya any good but good baseline starting point. 

270HR looks closest to the 268 specs. But VS the 276HR? I'd still wanna talk to CC or Summit Tech, or hit the SBC forums. 

Call Comp cams.  When my son put together a 351 for his Fox body, they will ask you all the particulars of the vehicle, and make the right grind for you.

Don't select it like I did.  Had a 260 H in the 305 on my Camaro, really nice manners, pulled to 6000, so when I put the 350 in, I thought, one step up would be perfect...so I went two steps.  Too much cam gets boring.

bobzilla said:

So.... what cam to make 350-400hp reliably and why? I don't know if this is a good or bad idea... but Comp XR276hr? 

Nice mild cam. Good choice. 

You could run a little more duration if you don't mind the idle. 5000 RPM will come fast in a 2400 lb truck with a 4.10 gear

In reply to Suprf1y :

I wish it was 2400. Sadly its 3500.

I already sent in the info to Comp. I was just curious what everyone here thought. 

I forget the specs of the cam I had in an old Impala, but it was labeled a "towing cam".  The range was about 1500 RPMs up to about 3500.  Just where I needed it in a daily driver.  Especially with the two barrel carb I had on it.  

I don't know why I haven't put a similar cam in my 1995 C1500 in the past 23 years I've owned it...

More important than a HP number is what the intended use of the truck is.  DD, Drag, Tow, Multipurpose, I have to agree with Streetwiseguy the cam dictates the rpm range of useful power.  You have to be true to what you are able to live with, put the power where you will use it.

Autox, track days, weekend driving. It's a truck in outward appearance only at this point. There will never be a hitch attached.  It might haul the motorcycle occasionally. I'm wanting 6k red line for those longer straights at autox. Right now its floating valves around 5200 or so and honestly it's done by 4500.

a 3/4 cam, duh..

https://grassrootsmotorsports.com/forum/grm/what-is-a-34-racing-cam/56401/page1/

Fueled by Caffeine said:

a 3/4 cam, duh..

 

https://grassrootsmotorsports.com/forum/grm/what-is-a-34-racing-cam/56401/page1/

I have been waiting since yesterday for this answer. Congrats sir, you have won the internets this morning. 

bobzilla said:

So, since I'm still waiting for the results and I need to get my mind off it... I need to pick a cam. Considering there are 13.6 million options for a sbc cam, I figured I'd turn to the experts. But Since I don't know any, I came here instead. 

So, looks like it's going to be stock bore/stroke Gen 1 SBC with roller cam. Flat tops, 64cc chambers, 200cc intake, 2.02/1.60 valves. intake is a 650 holley that will be sitting on an RPM airgap and breathing through 1-5/8 headers for the C10 and dual 2.5". Rear end is a 4.10 being fed by a TKO-600. Truck will weigh right around 3500lbs empty. 

So.... what cam to make 350-400hp reliably and why? I don't know if this is a good or bad idea... but Comp XR276hr? 

This will sound snarky but I’m trying very hard to be helpful.  The critical bits of information are lacking.  

First why do you want more power?  Do you intend to race it ? Or just want bragging rights?  Maybe you’ll be pulling a heavy load?   

All three of those will give you a different answer, but there could be plenty of other reasons. 

Second. What is the flow data of the heads?  For example at .100 lift, .200, .300, .400, .500 

both intake and exhaust.   In addition the length of the primary tube ( are they all the same length?) and collector size 

Lacking that data is like throwing darts blindfolded.  The good news?  It won’t matter. You’ll be content with whatever because it’s not really important.  

I apologize but a camshaft is a trade off. You give up some power at this RPM to gain power here.  With only a 650 cfm carb it doesn’t sound like peak power is critical.  So maybe you’re building a torque monster?  

Are those procomp heads?

JMO here but those are too big for something that needs torque for such ancient architecture. The carb and intake are good choices. The chamber size is a good choice too because of the flat tops, should put you about 9-9.5:1, maybe 10:1 depending on the valve reliefs and if the piston ends up above deck.

I’d expect more of a 180 intake port with the same size exhaust port as the 200cc head.

As for a cam answer to the original question, probably something about 27x intake, 280 exhaust total duration, .550-.560 lift with a 220-230@50 duration on a 110-112 lsa. Just my left field recommendation.

In reply to frenchyd :

Look up a few posts where I describe it's use. I've got a 40 year old engine that doesn't make enough power to keep the rear tires lit on an ass light truck with 4.10s and a manual trans. The 88 C4 made 250-ish hp and 350+ tq everywhere. It was a hoot, but I want something that will rev better. 

These are the heads I went with.Price was right, came in looking better than I expected a set of new $700 heads should look. I wanted more head than I needed so I have room to grow when I get bored. 

In reply to bobzilla :

Well the rev limit is due to either the springs or the hydraulic roller lifters. Stock springs start to float about 5800 rpm . Roller rockers raise that about 200 rpm  ( rockers not lifters) 

My C4 would go to 6500 rpm with the roller lifters although the roller lifters in my boat only go to 5600 rpm before they float. 

The difference may have to do with cam profile, the lifters, or the springs. 

In general  a stiffer spring will give you more RPM but cost you horsepower. 

As to turning tires into smoke. NASCAR with 850+ horsepower and 9000 plus RPM will only  smoke their tires a little bit in spite of the throttle being mashed as they leave the pits.  

And they are lighter than you with nothing in the back except sheet metal and a gas tank.  

The current engine is NOT a roller cam engine. It's just a late 70's worn out pile. 

I'm also currently running 400+tw all seasons pumped to 50psi and not wide and fat race slicks. so the nascar comparison is a bit moot. 

I built a spreadsheet that calculates dynamic compression ratio given cam profile and the other parameters of your engine.  Basically, for a street engine, you want to aim for something like 7.5:1 to 8:1 dynamic compression ratio for pump gas.  I realize this can be a little overly simplistic (it doesn't take valve size into account, for example, nor let you know at what RPM the power comes on) but it will at least tell you if the engine will run pretty well or not.  

Your HP numbers were determined long before you put the cam in the engine.  It's all in the squeeze the bottom end makes and how the heads handle it.  Then you pick the cam that makes those two parts play together nicely.  Simply plugging in a hot cam will not give you more power.  it might move the power to a higher RPM, and it might make the car idle roughly, and it might mean you have no power brakes, and it might mean you use more fuel...

"Flat tops" doesn't tell me much.  Is the top of the piston even with the deck height?  Above it?  Below it?  How thick is the head gasket when compressed? (yes, it matters).  You also want to make sure the engine's running a nice quench distance of around 0.035 to 0.040".  Too much more than that and you'll get detonation, which means you'll have to pull timing, which is never good for power.  

Whether the cam goes in "even up", advanced, or retarded can play into the dynamic CR too.  A cam that might be a little too "hot" when even up might work better a degree or two advanced.  

Only trying to point out the trade offs in a cam. At 9000+ rpm the NASCAR engine is making 850+ horsepower. But coming out of the pits @ 3000 rpm maybe 250 horsepower?  ( remember tires go on cold in NASCAR)  

A few points, a 6 speed is just a 4 speed with 2 overdrive ratios added.  1st gear can be one of two  ratios ( off the top of my head) and a 4.10 final drive sounds promising but I didn’t see the diameter of the tire.  If you’re talking about a 28 inch or taller tire that’s one thing if on the other hand you’ve a 25 - 24 inch tire  that’s another issue entirely.   

You said the cam wasn’t a roller cam, I’m sorry I read that like that’s what you had.   Am I correct in thinking you are going to a roller hydraulic cam? Or will it be a solid lifter roller cam?  

So your current cam is a hydraulic flat tappit? 

Have you checked the lift?  Since catalytic converters came into use oils have been formulated with less and less zinc because it clogs up the lifters. In fact since about 1985 Zddp has gone to zero on oil formulations and as a result cams are dying quickly unless supplemental ZDDP is added. 

You used to be able to buy oils rated for diesels with ZDDP in it but because catalytic converters are in diesels now too that source has dried up.

I digress,  it sounds like you want bottom end torque to smoke your tires,  then be careful not to over cam it for a horsepower number.  

You’ll want a flat ( but big) torque curve  rather than a peaky hp curve to get your number

DAmnit man... seriously. I'm not dealing with the engine in thetruck because it's old as hell and worn out. It leaks everywhere, it has blow-by, there's valve lisp (mostly on the driver's bank), it burns enough oil that changing it is pointless. I know a little about oil, considering it's what I do for a living and have been using diesel engine oil in it since I bought it. That engine is done. 

The engine I'm building is laid out in the opening post. Hyd roller in a early 90's roller cam block. I have no cam for it at all. It was a stock TBI engine and that cam went to the scrap yard along with the TBI heads. 

EDIT: even running 15-40 DEO I'm dropping to single digit oil pressure at idle when hot. Single. Digits. On sunday I would hold the engine at 1500rpm at the start line to build up 25psi of pressure before flogging it for hte next 60 seconds. 

bobzilla said:

DAmnit man... seriously. I'm not dealing with the engine in thetruck because it's old as hell and worn out. It leaks everywhere, it has blow-by, there's valve lisp (mostly on the driver's bank), it burns enough oil that changing it is pointless. I know a little about oil, considering it's what I do for a living and have been using diesel engine oil in it since I bought it. That engine is done. 

The engine I'm building is laid out in the opening post. Hyd roller in a early 90's roller cam block. I have no cam for it at all. It was a stock TBI engine and that cam went to the scrap yard along with the TBI heads. 

Thanks for the clarification. In effect it’s a retro TBI   I made 330 hp with an engine like that  but you want 100 more. Gotta go fire up my engine analyzer program. 

Off the top of my head you may be reaching. But I’ll try. 

No, it's not a retro TBI. IT's more of a poor mans ZZ4