ykf7b0

I had no idea Straub had his own cam grinding/parts business.

ykf7b0

What are the advertised duration numbers on this cam please?
I would love to know the overlap.

63mako

If you want power and can't swing a roller look at a small tight lash solid flat tappet with EDM lifters. This will be a nice match in a conservative vortec headed 383. Modern tight lash solid flat tappets are a different animal than the old school grinds. As long as you use the right springs and are willing to do an occasional lash check it is bang for the buck.
https://www.summitracing.com/parts/c...make/chevrolet

ykf7b0

Thanks 63mako for the recommendation. The Vette the stroker will be going in is my wife's car. She really couldn't care any less about the engine's high powered performance. The stroker idea was all mine being it's not much more coin to do the 383 kit. The cam has to allow her a good brake pedal and it has to idle well. This is the reason I can't go all out from a performance standpoint. I have just about decided on Howards (110951) 221/231 @ .050 and 275/285 advertised duration. The lift's are .470 on both sides and the LCA is 110. This cam has an overlap of 60. I know its conservative but I feel it will not be a bad performer and it will also pull good vacuum.

63mako

htown81vette

This is the perfect cam for a 383 stroker, imho...

http://www.compcams.com/Company/CC/c...csid=1596&sb=2

StraubTech

282/294. Makes minimum of 11" of vacuum.

NewbVetteGuy

I have to admit, I was getting insanely frustrated watching you get good advice again and again on this thread while it looked like you were going to largely ignore it. Almost all the advice you were getting early in the thread was roughly the same and constantly rebuffed there for a while. (63Mako has pretty epic patience). I'm glad to see that you ended up not TOO far from Chris Schraub's recommendations.

I say all this as probably one of the most annoying CAM seekers on here in probably a while; I went back and forth flipping and flopping and trying to aquire "Internet wisdom" on my cam selection across multiple internet sites for probably almost a year in thread very much like this one, so I definitely understand where you're coming from. When you realize how important the cam is to not just getting power out of the car but making it "streetable" and driving fuel economy, sound, and over-alll character of the way the car drives and sounds you want to understand the overwhelming complexity that's involved in the CAM selection so that you have confidence that you've made a good decision.


I wanted to share that a lot of people were telling you to go bigger, not because "Bigger is better" and they were projecting their engine goals and previous cam choices on you, but because there literally IS such a thing as too small of a cam, and you were there on a couple of your proposed choices early on. -You might already understand this, but I certainly didn't and I've seen other "conservative" cam seekers (I was right there with you 12 months ago) end up at the same place now so I wanted to put something in this thread on the subject. -When you go with too small of a CAM, you're not just "being conservative" and giving yourself more low-end torque and extra vacuum for your brakes while just "leaving HP on the table"; you're actually creating a detonation-prone engine. This is worse with a build like yours that's got the extra cubes and an iron headed vortec engine and probably marginal cooling of the stock radiator. (All these factors and then add the typical "hot" spark plugs and you've got a summer detonation monster if you've got a remotely appropraite starting static CR.)



Here's a great table for a starting point:



This diagram is a rough, rough way to get a duration @ 50 estimate, but a good guideline. You're at almost 48 CID per cylinder with your 383, so you want a duration in the upper end of that middle range; hence at LEAST 220 intake duration as the starting point (a few more points for safety and that close to the safety margin I'd recommend calculating your dynamic compression ratio with a given cam).


To really get laser focused on determining the minimum cam duration @ 50 for your build, you would need to use a Dynamic Compression Ratio calculator which is a decent (for our purposes; the nerds will complain about the 5-10 variables the calculations are missing) estimate of actual cylinder pressures / temperatures and therefore detonation risk- you can then simply add in different cam intake durations to get to an appropriately safe dynamic compression ratio for your build. (It's doing the same thing though- getting you to a safe minimum cam intake duration @ 0.050" to avoid detonation.

A much easier way to get "close enough" is the static compression ratio to intake duration chart here:




All that is just to figure out your minimum (not ideal for your goals) intake duration, but given your conservative goals, sticking closeish to the min seems about right.

Then to figure out your exhaust duration in the easy method (not using exact valve timing events like the pros) you just estimate the quality of your exhaust ports and your actual exhaust setup (true dual C3 vette exhaust with mufflers and high flow cats or no cats and vortec exhaust ports are pretty well known) -hence most people on here ending up with recommendations in the 8-12 degrees of extra exhaust duration. (This is the rougher and far less important stat.)

Your max lift target really shouldn't be based upon your duration #'s at all but the head's flowbench #s and as in the case of the vortec heads max safe lift values; when extra lift stops bringing decent returns in flow you stop because beyond that you're harder on the valve train and I believe you're slowing down velocity with no extra air flow.

Beyond that, you're just fine tuning. Once you understand your min safe duration, the amount of extra exhaust duration for your heads+exhaust system, and the max lift that your heads want, you're then just doing the typical "move the curve" work- you've determined where your max safe cylinder pressure / low end torque staring point is and you're just moving the torque / hp curve up from there to where you want it to be and to match your TC stall if you've got an auto trans.

This is where I'd say something about overlap and vacuum if I understood it more, but I'm a bit fuzzier about that aspect of cam choice. I just glance at the inches of vacuum rating and call it good right now.


Edit: I added way more complexity than necessary above, so here's the quick-and-dirty summary on cam selection:
1. Determine appropriate intake duration/timing of intake valve close event (most important)
a. Especially if you're looking for a very torque-focused / "conservative" cam, determine your minimum safe intake duration (using guideline charts or even better by calculating your actual dynamic compression ratio and upping the intake duration until you get to a dynamic CR that's appropriate for your head type (aluminum vs. iron)
2. Determine how much extra duration is required to make up for limitations in your head's exhaust ports and your exhaust system components
a. Look at your head flow #'s, evaluating the intake vs. exhaust CFM #'s and particulary the Intake to Exhaust CFM ratio (If you've got amazing heads, like modern AFRs you can safely start without any extra duration on the exhaust)
b. Start adding extra duration as you add extra exhaust restriction; rely upon the experienced folks here
3. Make sure your lift is appropriately matched to your head's air flow characteristics (Go to your heads' CFM chart- when airflow increases drop off there's little HP benefit in going higher and probably a torque loss from doing so; definitely a valve train longevity downside to going larger so stop there. If you've got heads that keep flowing but a medium ramp speed flat tappet cam for longevity reasons then consider using higher ratio rockers to get into that CFM/air velocity "sweet spot" range of your heads.)

Real-life example for #3: Here's the airflow chart for my Profiler 195cc intake port heads:
ift Intake CFM Exh CFM % Exh/Int
0.200 145 110 76%
0.300 209 145 69%
0.400 254 180 71%
0.500 273 206 75%
0.600 274 213 78%
0.700 276 216 78%
0.800 276 218 79%
The air flow gains really drop off between 0.500" and 0.600" of lift, so that's the sweet spot. The heads have a 78% exhaust CFM to intake CFM ratio at the expected valve lift(80% or more and you don't need extra exhaust duration and may make more power without the extra exhaust duration bleeding off cylinder pressure) so maybe I need 2 degrees of extra exhaust duration as the starting point. (appropriate sized full length open headers) -I've got full length headers, no cats, full length exhaust and high flow mufflers that are non-restrictive so 2-4 degrees of extra duration on the exhaust side seems about right.

Some other versions of these heads have standard height exhaust ports and will see more like a 74% intake to exhaust ratio so in that case you should up the exhaust duration another couple points. (The professional guys will analyze the exact intake and exhaust timing events, but these back of the envelope estimates are "good enough".)

You'll also see some of the well-known head porters' CFM #'s on these Profiler heads and where the airflow will change (for the good porters) is at higher lift -the CFM will just keep increasing until maybe 0.700" -obviously the intake port size is greater after they're done and then you want more lift to take full advantage of the heads but you generally have to go with a bigger duration cam to get there (lobes can only ramp so fast) or higher ratio RRs. -You'll quickly see where if you bought the wrong sized intake ports on your head for your engine you're not getting to take advantage of the higher lift and as a result you end up with less air velocity (aka torque) because the CSA of the port is usually larger to get the increased airflow at high lifts; it provides perspective on WHY too large of a port head makes for a lazy engine with no low end torque.

4. Move your duration up to move up your HP / torque curve RPM to meet your goals and stall speed (if automatic) -trade low end torque for high rpm HP where desired; here is also where you start thinking about the impact on vacuum and how much you need




Adam

NewbVetteGuy

For perspective: The stock C3 L82 motors had a 222 duration @ 0.050" in our 350 Cubic Inch motors with a lazy, slow-ramp old-school cams. You're looking at a 383 with, I certainly hope a much more modern, faster ramp cam with similar, and even in some cases less duration @ 0.050" and you're concerned about vacuum.

Our brake systems aren't running off of the vacuum directly; that huge tank on the driver's side firewall ("brake booster") is storing up its own extra quantity of vacuum for exactly this reason. Our C3's have a 2nd vacuum reservoir from the factory, too. (Again, our cars come from the factory with two vacuum reservoirs- one dedicated just for the brakes.)

Just like a roller cam will let you go with a bigger cam and still have plenty of vacuum because the ramp is faster, a modern flat tappet should have the same properties but to a lesser degree as they will have slower ramps compared to roller cams. 383s also can deal with bigger cams and behave the same as a 350, so again, a 222 duration @ 0.050" came from the FACTORY over 40 years ago (I think that cam design came out in the late 60s) in with a turtle-slow ramp speed lobe design cam in 350 CU IN; a modern cam in a 383 can certainly go bigger and still maintain from-the-factory L82 levels of vacuum.




Adam

NewbVetteGuy

Final rant: I've now seen loads of people throw down lots of money on things like extra thin ring packages when redoing their bottom-ends for extra power (7 hp on a good LS motor per Engine Masters tests), but they then leave 5x-10x that much torque and HP behind by buying crappy cams that get recommended by the internets or a "one-size-fits-all" website recommendation.

If good enough is good enough and you've got a tight budget, then getting the main things roughly right really is good enough, but a CAM is a very important choice and I really think a lot more people should just go with a professional recommendation (especially the people who are so concerned with eeking out that extra bit of performance where the cost of things like ultra thin ring packages are on the table). -Save the money you were going to spend on that serpentine belt conversion or underdrive pulleys or electric water pump or thin rings and ultra light rotating assembly and just call Chris Straub and have him custom make a cam for your combo.

-I put my money where my mouth is on this one and went with a cam recommended by a professional for my build; the cost was more than I wanted, but I feel like the return on investment was still there vs. my semi-educated guesses and "internet wisdom".


Adam

ykf7b0

I don't know how to respond to your post so I will simply say "Thank you" for the longest post that's ever been posted on my behalf. I haven't completely decided on and I have not bought a kit but "just about". You have provided some great information to consider so "Thanks again"!
I have computed my static and dynamic ratio's and they have always been a consideration at 9.703 static and 7.612 dynamic. This site is not the only place I've sought advice but the sad fact of it all is that I have asked at least ten people and I've gotten another five recommendations. Overall, I think the advice here is really sound advice and I have been taking it all in. A little more duration @ .050 is beginning to look better along this path. I have never built a Chevy engine and my history is with Mopar's. I have a non stroked, 10 second, totally street, pump gas 69 roadrunner that I built on my carport and I know I can't build a Chevy like a 440 Mopar. It is my opinion that a Chevy is much more complicated by the way but that is for another story. Thanks to all for taking the time to help me out with this!!!

ykf7b0

Thanks Straub!

NewbVetteGuy

Hopefully someone on here can chime in on a 7.6:1 dynamic CR with iron heads. I can't find where I wrote down the recommended range for aluminum vs. iron, my guess is that 7.6:1 sounds about right.

You can always pull a bit of engine timing, retard your cam a couple degrees, or upgrade your cooling (best option, IMHO), or upgrade your gas in hot weather if you start to get a bit of detonation. (I REALLY want as much low-end torque as possible so I errored on the side of a higher DCR and figured a cold air intake would help and if I get into trouble I can have an octane booster on hand and then either let the EFI pull some timing, or more likely use that as an excuse to get an engine oil cooler or other cooling enhancements. (Cold air is magical as it means more torque, more HP, AND increased detonation resistance- There's a David Vizard quote on the CR / Octane equivalent improvement gained from each 10 degrees of intake air temp dropp floating around the internets somewhere, but cold air makes a significant difference.)

Edit: Found it! David Vizard's quote is that every 7 F decrease in intake air temperature is a 1 octane equivalent improvement in detonation resistance!

#CAIorDIE!

Adam

ykf7b0

I wanted to post my final choice for those who are following this thread. I went with a Howards 225/235 @.050 and advertised duration of 279 and 289. Lifts are .465 and .470. LSA is 110 and I also chose this ground on a small base circle. I also gave PTC a call and a 10 inch torque converter with a flash stall of 3200 rpm was recommended and is on the way.

ykf7b0

Update for those interested; I'm very satisfied with the engine. It has plenty of vacuum for the power brakes, runs fine with no pinging on 87 octane gas, it's not too lopey for the a/c compressor, idles great, and runs really, really well! The only other change I made was install a new set of Comp Cams roller tip rockers. Thanks to all who help guide me along on this build!!!!