CAM CHOICE.

pres589 said:

.510 lift in a truck application sounds like plenty of lift to me...

But's its not a typical truck application. IT's truck in body arrangement only. More auto-x/musclecar do fun things with tire smoke all the time than anything even remotely truck related. 

For some perspective on lift vs duration, Comp's suggested cam is .510" valve lift on a 236/242 duration at .050", 288/294 total duration.  The cam in my Jeep is .480" valve lift with a .050" duration of 206/212 (258/264 total duration).  And I'm running it with higher ratio rockers, giving .512" total lift at the valves and faster lift.  

In other words, that cam is almost at old-school flat tappet levels of wimpy lift vs duration.  

And likely with much faster ramps making it act on the bottom (end of the power band)  like a smaller cam, and on the top like the duration it actually is, with the benefit of not having crazy lift.

It is still an old school small block. In the 80's my go-to cam was .508" lift 234/244 at .050 hydraulic flat tappet. Bob's recommended cam is very close in numbers but will have much better manners than what I used to run.

BTW, with the higher ratio rockers you're running more duration than you think, though still not a lot.

Streetwiseguy said:

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.

Stop calling me dingleberry??

NickD said:

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.

I normally agree with Nick, but I don't agree with this.  While this is normally a wise decision, Comp will try to sell you the biggest cam with new valve springs (that will be poorly matched to the cam) and then tell you it will run mid-9s in the 1/4 mile.  I have spent 20 years fighting with Comp about their valve spring rates and duration specs.  Many of the cam sellers out there will just sell as big as they can.

20 years ago, Nick would be spot-on with his recommendation.  Cam companies had reputations to keep and time slips to maintain.  The art of engine tuning has kinda fallen into the hands of guys with vape pens and laptops.  It's a new era and it's great, but cam choice has become a lost art.  I will admit that even I have lost much of what I knew.

First:  Which flat tops?  SBC can't really do true flat-tops, especially with 2.02 valves without reliefs in the crown.  With 64cc chambers, we can assume anywhere from 9:1 up to 9.5:1, correct?

Second: What is the head casting number or aftermarket name? When it comes to SBC heads, port size means very little.  There are old-school 200cc ports that flow less than some modern 170cc heads.  It is also important to know which head is being used because 9:1 compression with a "camel hump" head might need 94 octane while 10:1 with a Vortec head might need 87 octane.

I really don't like the air-gap intakes.  IMHO, they are a big gimmick.  The whole idea of keeping the runners cooler to make a cooler intake charge makes less than zero difference after 15 minutes of running the engine.  It is a chunk of aluminum.  It doesn't really matter if there is air under the runners or not, the aluminum will soak up heat just the same and you might have a minute or two of cooler intake charge.  The only real advantage they have is that they are slightly taller with runners that are more angled... but only by 1/4" and you'll never notice any difference at the 350-400 hp level.  I strongly suggest doing neither the RPM nor the air gap.  Just do a Performer.  The AirGap might make sense for a 12-second drag car that wants a tenth of a second because the engine is only running for one minute and the runners don't have time to get hot, not for a 350-hp street truck.  The step up to the RPM really only means speed if your torque curve doesn't peak until about 3500 rpm or higher.  Below that rev mark, you'll give up more torque than you gain in HP and have a slower truck.

Let me know your head casting numbers or aftermarket brand and we'll talk cams.  This used to be my thing.  I'll admit to being rusty, but 20 years of building old-school hot rods kinda sticks with you.

Sorry... missed the post with the head specs.

Let me research a bit, but I think Comp went over the top with their recommendation. 

no hurries. I'm on vacation this week and won't be back until next week.

Curtis said:

NickD said:

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.

I normally agree with Nick, but I don't agree with this.  While this is normally a wise decision, Comp will try to sell you the biggest cam with new valve springs (that will be poorly matched to the cam) and then tell you it will run mid-9s in the 1/4 mile.  I have spent 20 years fighting with Comp about their valve spring rates and duration specs.  Many of the cam sellers out there will just sell as big as they can.

20 years ago, Nick would be spot-on with his recommendation.  Cam companies had reputations to keep and time slips to maintain.  The art of engine tuning has kinda fallen into the hands of guys with vape pens and laptops.  It's a new era and it's great, but cam choice has become a lost art.  I will admit that even I have lost much of what I knew.

First:  Which flat tops?  SBC can't really do true flat-tops, especially with 2.02 valves without reliefs in the crown.  With 64cc chambers, we can assume anywhere from 9:1 up to 9.5:1, correct?

Second: What is the head casting number or aftermarket name? When it comes to SBC heads, port size means very little.  There are old-school 200cc ports that flow less than some modern 170cc heads.  It is also important to know which head is being used because 9:1 compression with a "camel hump" head might need 94 octane while 10:1 with a Vortec head might need 87 octane.

I really don't like the air-gap intakes.  IMHO, they are a big gimmick.  The whole idea of keeping the runners cooler to make a cooler intake charge makes less than zero difference after 15 minutes of running the engine.  It is a chunk of aluminum.  It doesn't really matter if there is air under the runners or not, the aluminum will soak up heat just the same and you might have a minute or two of cooler intake charge.  The only real advantage they have is that they are slightly taller with runners that are more angled... but only by 1/4" and you'll never notice any difference at the 350-400 hp level.  I strongly suggest doing neither the RPM nor the air gap.  Just do a Performer.  The AirGap might make sense for a 12-second drag car that wants a tenth of a second because the engine is only running for one minute and the runners don't have time to get hot, not for a 350-hp street truck.  The step up to the RPM really only means speed if your torque curve doesn't peak until about 3500 rpm or higher.  Below that rev mark, you'll give up more torque than you gain in HP and have a slower truck.

Let me know your head casting numbers or aftermarket brand and we'll talk cams.  This used to be my thing.  I'll admit to being rusty, but 20 years of building old-school hot rods kinda sticks with you.

Curtis, most of what you say about the engine is spot on the money.  The exception is regarding the air gap manifolds.  

The intake charge away from the heat of the water jacket is a power improver.  While there will be some heat gained from the engine, incoming fuel /air charge will be cooler without the water jacket heat gained.

If you’ve ever raced  a sprint car on a cool night you can actually see frost forming on the intake trumpets. 

Now power will be improved but fuel mileage will take a real hit as will pollution be increased. 

I am not a fan of air gap manifolds on street driven cars.  Hot intake manifolds keep the fuel suspended in the air, and therefore better drivability and economy.  You don't need a gigantic accelerator pump shot with a hot manifold.

This is why all of the Kettering designed V8s (practically all GM V8s, as well as some others) have the center cylinders' exhaust ports next to each other, with a hefty exhaust crossover between them under the carburetor.  It hurts peak power and the two exhaust valves next to each other make cooling system issues, but for the 99% of the time you are idling around, you don't need to firehose fuel down the carb every time the throttle moves.

frenchyd said:

Curtis said:

NickD said:

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.

I normally agree with Nick, but I don't agree with this.  While this is normally a wise decision, Comp will try to sell you the biggest cam with new valve springs (that will be poorly matched to the cam) and then tell you it will run mid-9s in the 1/4 mile.  I have spent 20 years fighting with Comp about their valve spring rates and duration specs.  Many of the cam sellers out there will just sell as big as they can.

20 years ago, Nick would be spot-on with his recommendation.  Cam companies had reputations to keep and time slips to maintain.  The art of engine tuning has kinda fallen into the hands of guys with vape pens and laptops.  It's a new era and it's great, but cam choice has become a lost art.  I will admit that even I have lost much of what I knew.

First:  Which flat tops?  SBC can't really do true flat-tops, especially with 2.02 valves without reliefs in the crown.  With 64cc chambers, we can assume anywhere from 9:1 up to 9.5:1, correct?

Second: What is the head casting number or aftermarket name? When it comes to SBC heads, port size means very little.  There are old-school 200cc ports that flow less than some modern 170cc heads.  It is also important to know which head is being used because 9:1 compression with a "camel hump" head might need 94 octane while 10:1 with a Vortec head might need 87 octane.

I really don't like the air-gap intakes.  IMHO, they are a big gimmick.  The whole idea of keeping the runners cooler to make a cooler intake charge makes less than zero difference after 15 minutes of running the engine.  It is a chunk of aluminum.  It doesn't really matter if there is air under the runners or not, the aluminum will soak up heat just the same and you might have a minute or two of cooler intake charge.  The only real advantage they have is that they are slightly taller with runners that are more angled... but only by 1/4" and you'll never notice any difference at the 350-400 hp level.  I strongly suggest doing neither the RPM nor the air gap.  Just do a Performer.  The AirGap might make sense for a 12-second drag car that wants a tenth of a second because the engine is only running for one minute and the runners don't have time to get hot, not for a 350-hp street truck.  The step up to the RPM really only means speed if your torque curve doesn't peak until about 3500 rpm or higher.  Below that rev mark, you'll give up more torque than you gain in HP and have a slower truck.

Let me know your head casting numbers or aftermarket brand and we'll talk cams.  This used to be my thing.  I'll admit to being rusty, but 20 years of building old-school hot rods kinda sticks with you.

Curtis, most of what you say about the engine is spot on the money.  The exception is regarding the air gap manifolds.  

The intake charge away from the heat of the water jacket is a power improver.  While there will be some heat gained from the engine, incoming fuel /air charge will be cooler without the water jacket heat gained.

If you’ve ever raced  a sprint car on a cool night you can actually see frost forming on the intake trumpets. 

Now power will be improved but fuel mileage will take a real hit as will pollution be increased. 

Real-world testing on street vehicles disagrees in every way.  I suppose its possible that the higher volumes of fuel and air help on a race vehicle along with open air engine bays, but that is kind of my point.

Let's say you have two identical C10 pickups one with an air gap and one with a non air gap.  If you point a laser thermometer at and air gap and a non-air gap before starting the engine, they will of course be the same temp.  Start them up and put them through the same drive cycles.  In 15 minutes, the non-air gap intake runners are 150 degrees and the air gap runners are 90 degrees.  Within 20 minutes, they are both 150 degrees.

Air gap intakes were designed for drag racing advantages on street cars.  Their benefit there is that they stay cool longer allowing for a few extra hp in 1/4 mile, but they eventually reach the same exact temps as a non-air gap.  The reason they stay cooler longer is not because you have air flowing around them, its because the aluminum has less surface area attached to the base of the manifold and it just takes longer for the heat to soak into them.  The air under the hood of a street car is 200 degrees anyway.  That air isn't cooling anything about the intake runners, in fact with the evaporation happening in those runners, the air is heating them.  In your sprint car/frosting example, take that same situation and put that engine in a 200-degree engine bay under a hood.  You wouldn't see the same frosting and power would drop.

Think of it this way:  Take the two different manifolds and set them both on a stove burner.  Then measure the carb flange temps over time.  The air gap intake will get just as hot, but it will just take 5 minutes longer for the heat to travel the "long way" around.

Multiple tests have been done by all kinds of race engine shops, Hot Rod, Car Craft, Super Chevy... for a while it was like you couldn't open a magazine without an "air gap vs. performer" comparison test.  They all concur.  The main advantage to an air gap is the short amount of time you have at cooler temps and the slightly higher rise to the runners offering a tiny bit of help from inertia.  HP tests are also pretty inconclusive.  They may make a few extra HP, but the real kicker is that they don't show any different delta-T when cold or hot.  For instance, if an non-air gap makes 400hp cold and 395 hot 15 minutes later, you would expect that a switch to an air gap would show a smaller disparity in those numbers, but it may make 410 cold and 405 hot 25 minutes later... indicating that the air gap part did nothing for the heat, it just gained 10hp from being a taller intake and took a few minutes longer for it to soak up the same heat.

I'm not doubting your sprint car experience. Tunnel Rams used to do the same thing. I fully believe it, but real world testing in a real street car does not share that experience.  Hence why I call it a gimmick.

Also, agreed on the power improvement/MPG/pollution comment

Curtis said:

frenchyd said:

Curtis said:

NickD said:

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.

I normally agree with Nick, but I don't agree with this.  While this is normally a wise decision, Comp will try to sell you the biggest cam with new valve springs (that will be poorly matched to the cam) and then tell you it will run mid-9s in the 1/4 mile.  I have spent 20 years fighting with Comp about their valve spring rates and duration specs.  Many of the cam sellers out there will just sell as big as they can.

20 years ago, Nick would be spot-on with his recommendation.  Cam companies had reputations to keep and time slips to maintain.  The art of engine tuning has kinda fallen into the hands of guys with vape pens and laptops.  It's a new era and it's great, but cam choice has become a lost art.  I will admit that even I have lost much of what I knew.

First:  Which flat tops?  SBC can't really do true flat-tops, especially with 2.02 valves without reliefs in the crown.  With 64cc chambers, we can assume anywhere from 9:1 up to 9.5:1, correct?

Second: What is the head casting number or aftermarket name? When it comes to SBC heads, port size means very little.  There are old-school 200cc ports that flow less than some modern 170cc heads.  It is also important to know which head is being used because 9:1 compression with a "camel hump" head might need 94 octane while 10:1 with a Vortec head might need 87 octane.

I really don't like the air-gap intakes.  IMHO, they are a big gimmick.  The whole idea of keeping the runners cooler to make a cooler intake charge makes less than zero difference after 15 minutes of running the engine.  It is a chunk of aluminum.  It doesn't really matter if there is air under the runners or not, the aluminum will soak up heat just the same and you might have a minute or two of cooler intake charge.  The only real advantage they have is that they are slightly taller with runners that are more angled... but only by 1/4" and you'll never notice any difference at the 350-400 hp level.  I strongly suggest doing neither the RPM nor the air gap.  Just do a Performer.  The AirGap might make sense for a 12-second drag car that wants a tenth of a second because the engine is only running for one minute and the runners don't have time to get hot, not for a 350-hp street truck.  The step up to the RPM really only means speed if your torque curve doesn't peak until about 3500 rpm or higher.  Below that rev mark, you'll give up more torque than you gain in HP and have a slower truck.

Let me know your head casting numbers or aftermarket brand and we'll talk cams.  This used to be my thing.  I'll admit to being rusty, but 20 years of building old-school hot rods kinda sticks with you.

Curtis, most of what you say about the engine is spot on the money.  The exception is regarding the air gap manifolds.  

The intake charge away from the heat of the water jacket is a power improver.  While there will be some heat gained from the engine, incoming fuel /air charge will be cooler without the water jacket heat gained.

If you’ve ever raced  a sprint car on a cool night you can actually see frost forming on the intake trumpets. 

Now power will be improved but fuel mileage will take a real hit as will pollution be increased. 

Real-world testing on street vehicles disagrees in every way.  I suppose its possible that the higher volumes of fuel and air help on a race vehicle along with open air engine bays, but that is kind of my point.

Let's say you have two identical C10 pickups one with an air gap and one with a non air gap.  If you point a laser thermometer at and air gap and a non-air gap before starting the engine, they will of course be the same temp.  Start them up and put them through the same drive cycles.  In 15 minutes, the non-air gap intake runners are 150 degrees and the air gap runners are 90 degrees.  Within 20 minutes, they are both 150 degrees.

Air gap intakes were designed for drag racing advantages on street cars.  Their benefit there is that they stay cool longer allowing for a few extra hp in 1/4 mile, but they eventually reach the same exact temps as a non-air gap.  The reason they stay cooler longer is not because you have air flowing around them, its because the aluminum has less surface area attached to the base of the manifold and it just takes longer for the heat to soak into them.  The air under the hood of a street car is 200 degrees anyway.  That air isn't cooling anything about the intake runners, in fact with the evaporation happening in those runners, the air is heating them.  In your sprint car/frosting example, take that same situation and put that engine in a 200-degree engine bay under a hood.  You wouldn't see the same frosting and power would drop.

Think of it this way:  Take the two different manifolds and set them both on a stove burner.  Then measure the carb flange temps over time.  The air gap intake will get just as hot, but it will just take 5 minutes longer for the heat to travel the "long way" around.

Multiple tests have been done by all kinds of race engine shops, Hot Rod, Car Craft, Super Chevy... for a while it was like you couldn't open a magazine without an "air gap vs. performer" comparison test.  They all concur.  The main advantage to an air gap is the short amount of time you have at cooler temps and the slightly higher rise to the runners offering a tiny bit of help from inertia.  HP tests are also pretty inconclusive.  They may make a few extra HP, but the real kicker is that they don't show any different delta-T when cold or hot.  For instance, if an non-air gap makes 400hp cold and 395 hot 15 minutes later, you would expect that a switch to an air gap would show a smaller disparity in those numbers, but it may make 410 cold and 405 hot 25 minutes later... indicating that the air gap part did nothing for the heat, it just gained 10hp from being a taller intake and took a few minutes longer for it to soak up the same heat.

I'm not doubting your sprint car experience. Tunnel Rams used to do the same thing. I fully believe it, but real world testing in a real street car does not share that experience.  Hence why I call it a gimmick.

Also, agreed on the power improvement/MPG/pollution comment

You may have a valid point.  But it really depends. That longer intake tract can have a real benefit. Depending on the cam specs.  The formula for for exhaust and intake length are both dependent on the camshaft events. 

It’s easier with the tunnel ram and dual carbs to figure out the length from the intake  to the valves because they would be closer to equal.  With a single carb lengths will vary significantly from  end cylinders to middle. I’m not sure they would be complimentary or not but the longer they are the greater chance of that occurring especially at lower RPM. 

I’m remembering the Chrysler cross ram manifold and even Chevy’s 2 four barrel manifold of 1968?  The one in the Camero? 

block is done. Time for the final recommendations. If I don't hear a better option I'll likely go with the one COMP offered. 

In reply to bobzilla :

Go one cam less than the one Comp recommended.  :-)

It's very similar to the roller Howard's recommended for my truck (after I had chosen my own cam and driven it for three years).

I'm curious how well this works. I say go for it, and get back to us with your review.  You know, for Science.

bobzilla said:

block is done. Time for the final recommendations. If I don't hear a better option I'll likely go with the one COMP offered. 

It all comes down to idle Bob. Can you handle the rough idle of mid 230's duration?  That cam should easily meet your 350 - 400 HP requirement but one or two cams less would probably do the trick too. The likely reason they made that recommendation is the heads and that 4.10 gear. Like I said before, 5000 RPM is going to come up real fast with 4.10's so I think you'll want a little more cam than you originally spec'd. If the rough idle is not your thing then you could go one or even two less.

Comp 432 is 230/236 still pretty rough

Comp 423 is 224/230 Mild idle but good daily driver cam

Any of the three will do the job but Comps recommendation is almost spot on what I said on page two - but I like lot's of cam.

EDIT: I just realized that last one is your original choice. If you're concerned wth Comp's recommendation split the difference, go with the 432

I'm not concerned, just wondered of the brain trust had a better option. I don't think this cam will be much issue for me. It's a toy. It does get some dd miles in the 3 seasons, it will see track time. IT will get beat like a red headed step child. 

I wussed out. I ordered the 423. 

That one should be a good pick IMO.  And if you want to wake things up a little more without making the low end manners worse, think about stepping up one in the rocker ratio department.  It'll give you more lift and make the lift rates faster.  

In reply to rslifkin :

I'm going to start with the 1.5's and see how it feels first. 

I've been trying to get some recommendations together for you, but my internet up here is dsl over wifi that is 1000' away.  My access to internet ranges from somewhere between 1mb and 2400 baud.  I wish I were being facetious.

ain't no biggie. I was hoping to put the long block together this weekend but the crank won't be here until Monday. 

bobzilla said:

I wussed out. I ordered the 423. 

Shocked (see my sig)

For the majority of what you're likely going to do with it, it's probably the most comfortable choice.

Suprf1y said:

bobzilla said:

block is done. Time for the final recommendations. If I don't hear a better option I'll likely go with the one COMP offered. 

It all comes down to idle Bob. Can you handle the rough idle of mid 230's duration?  That cam should easily meet your 350 - 400 HP requirement but one or two cams less would probably do the trick too. The likely reason they made that recommendation is the heads and that 4.10 gear. Like I said before, 5000 RPM is going to come up real fast with 4.10's so I think you'll want a little more cam than you originally spec'd. If the rough idle is not your thing then you could go one or even two less.

Comp 432 is 230/236 still pretty rough

Comp 423 is 224/230 Mild idle but good daily driver cam

Any of the three will do the job but Comps recommendation is almost spot on what I said on page two - but I like lot's of cam.

EDIT: I just realized that last one is your original choice. If you're concerned wth Comp's recommendation split the difference, go with the 432

With his manual and (probably) 2.66:1 first gear and 4.10s, I think he made a wise choice.  Choppy idle plus higher first gear final drive ratio it will make it a little tough to modulate driving under 15 mph.  Choppy cam plus manual trans makes for difficult street driving.

One thing you could do is do a digital spark box so you can tune the ignition curve how you want.

One of the tricks I like to do with EFI or a programmable spark box is to back the timing down a few degrees at idle.  That will make the cam "sound" bigger, but not have the downsides of cam surge above idle from having a larger cam.

I'll be doing that with my LS/T56.  My cam is 233/248 duration on 111 LSA.  It will have some chop to it, but it is a slightly larger displacement, 11.3:1 compression, and EFI.  I can (hopefully) smooth it out with tuning in the lower RPM ranges, but when the TPS indicates no throttle I'll have it drop out a few degrees of advance.  That will really chop up the idle, but then jump to smoother operation as soon as you're off idle.  It should also help with easier starting with that 11.3:1 compression.  I'm also doing the maths on final drive ratios and might choose 4.56 rear gears depending on what tires I go with.  That will shrink the range of choppy RPMs when the clutch is engaged but still keep a decent cruise RPM. 4.56 gears would make the RPM range of choppy operation only happen during very slow speeds. My 0.5:1 double OD makes 4.10 gears act like 2.05:1 final.

My long-winded point is that with careful ignition programming you can make a cam sound bigger at idle without the drawbacks of a cam that is too big.

I run full manifold vacuum on my '77 C10 at idle.  Base timing is 18°, and 12° vacuum on top of that.  This gives me 8inHg vacuum in drive with my 231°/231° 108LSA cam and 2500stall converter, and it still works the power brakes. Manifold vacuum makes the idle fluctuate more, because there isn't much vacuum happening. I love the idle, BUT, I kind of wish I had a lot more low end grunt.

I think you chose well.  Probably the cam I should have put in my truck......