What factor determines Cam duration? - Third Generation F-Body Message Boards

The link is the first Rabbit hole I went down. I've since gone and dug another one. I'm still flipping and flopping on Cam choice. I'm trying to figure out If I go with a COMP dual pattern or the single pattern ZZ409. The Trick Flow heads I've got flow:

76% @.600,
72% @.500,
72% @.400,
74% @.300,
76% @.200,
87% @.100

I have a ported plenum, Edelbrock runners and lower, and TES headers with a flowmaster exhaust. Based on those flow numbers I believe I'm sitting on the cusp of one way or the other. I welcome advice from those of you that have been down this road before.

 

Dual pattern cams with longer exhaust duration are for high compression and high RPM operation. They hold the exhaust valve open a little longer to allow more time to evcuate the exhaust from the cylinder. This can improve exhaust scavenging at high RPM BUT it bleeds off more cylinder presure which is not good for low RPM power and torque. Some people use a longer exhaust duration to compenate for a poor flowing cylinder head, but everything comes at a cost where cams are concerned. For low and midrange RPM torque on a street-driven car, a single pattern can be more beneficial. Those heads you have don't need the "crutch" of a longer exhaust durtion..

 

You are not locked into a dual pattern Comp cam.
Comp can custom grind you any cam you want including a single pattern cam All you have to do is call them. (or e-mail). Wether you need a single or a dual pattern is a complex subject.

 

Most all combos seem to benefit from more exhaust duration. Rarely see any combos running single pattern, not even turbo cars anymore

 

Single pattern or very small split tends to run best on the street where torque is king. These 8-10 or even 12° split cams are garbage under 5,500 rpm. Comp ground a 10° split for my 383. I stepped back to a 1.5 exhaust rocker from a 1.7 and gained 20+ ft/lbs of torque without losing anything up top. That larger exhaust duration makes your intake lobe act smaller by the same as the split.

 

ever see the truck norris lsx cam dyno numbers? It beats most everything down low and it has big split

 

Is that superior down low torque from the narrow 107LSA & short intake duration?
Amazing cam when tested on Holdener’s channel.

 

It would make even more as a single pattern. Single patterns stay ahead until 5,000+ rpm. Look at what Sledgehammer did with a single pattern 224/224 on a 108. 6,400 rpm is where it made its 450 hp.

Comps XR269HR as well as others make nearly equal power with a much tamer idle.

 

Yes its from the high cylinder pressure on an early IVC.

 

And what RPM is that LSx spinning up to?...

 

Power peak is around 6K with Truck Norris from memory.

I have a theory it is 212/224 @ .050, 107 LSA and 107 ICL based off other BTR cams.

Keep the overlap the same, decrease the exhaust duration, tighten the LSA and it would have the same idle quality and make even more torque.

My 170 Etec headed L30 305 had a 221/221 @ 0.050 single pattern on a 106 LSA. Very nice powerband and it liked being shifted at 6,200 rpm even with a Vortec truck manifold.

 

Thanks all. Great info

 

Fast-
Thats a lot of duration for a little 305!
Who custom ground that cam for you?

 

that’s debatable. If it would dont you think those companies would have come out with that cam as a single pattern? Makes you think

 

mike jones designed engine…loads of torque every where, nice broad curve. Dual pattern and it isnt even tight lsa. Tight lsa doesnt always make torque below the peak rpm…jones even says so above

 

exhaust port and exhaust system can influence the duration required to evacuate cylinder. There is no one size fits all rule. Same head with two different exhaust manifolds could require different exhaust duration. Potentially. So one combo maybe single pattern another may be dual. Most seem to have minor split from everything i ever seen spec’d for sbc and bbc combos

 

2-4° split is normally all that is required. 10-12° is blowing torque out of the tail pipe.

 

Any recommendations I've received from just about any cam designer or cam company suggests a split. LSAs are the typically wide variety with nothing less than 110 when the word street is part of the equation. When I went looking for a spec for a dyno queen 383, Jones tightened up the LSA to 108 but there was still an extended exhaust duration.
Now, getting into the world of Stock and Super Stock drag racers, with the narrow RPM window they run, in some cases under 1000 RPM if the converter is designed that way, LSA tightens right up. At least the 350 SBCs I'm seeing are in the 108-106 range. Often lift limited but heavy on the .050" duration spec. I can't recall what if any split there was.

 

again, application specific. It may but also may not

 

If you think that a dual pattern cam is for you
try this way of looking at it.
Most people look at the intake duration "shoe size"
then add extra to the exhaust side..
Try this instead for a street car that has to make good power and torque and yet drive well overall.
Look at the exhaust side duration (how much time for flow). .. Give it enough time for the intended job..
Then look at the intake side and shorten it up a bit.
EG: that Sledgehammer engine camshaft.
224/224 on 108 LSA..
Keep the 224 exhaust duration and shorten up the intake side a bit.
Say 220 in/224 ex.. I suggest 108 110 ish LSA
I kinda like this one for this job.
220/224 @.050" .495"/.503". 110 lsa 107/113
Its Melling cam #22280 (OEM Roller block)
Melling just aquired a big valve spring company in europe. They have a whole good line of street friendly springs and recomend one specificly for
this. You can look it up on the Melling site.
Something to consider.

 

Engine masters recently did a test of a single pattern cam vs. a dual pattern that was identical except for 6° increased exhaust duration. It picked up power almost everywhere and didn't lose anything down low, and this was with AFR heads and long tube headers so fairly ideal evacuation scenario. I'm sure there exists a combination where a single pattern cam is the right choice, but it seems like the majority of heads you're going to find for a street application are going to benefit from at least 4-6° of split, intake valve durations being equal.

 

Where did they start the pull? 3,000? 3,500? You absolutely will lose low speed torque from an earlier EVO. If you keep the overlap the same it will make close to the same top-end power with a single pattern.

 

Just adding duration doesnt mean its at the opening side. Could have kept same opening by changing centerlines and just closed later. The problem with some of the tests are they dont do enough testing to see the affects of the valve events. Changing exhaust duration alone could do several things.

example the sledgehammer 350 cam that was 224/224 on a 108 intake center and 108 lsa.
events intake open 4 deg intake close 40
exhaust open 40 deg close 4 deg.

if i wanted to try 230 deg duration on exhaust side, how would you do it? Do we hold intake events where they are and just add 3 deg to both exhaust open and close?
224/230 on a 108 in at 108 icl. Intake events same 4 and 40. Exhaust now 43 and 7. If it changed power, was it from earlier opening? Later closing? Both? Duration alone? More overlap?
224/224 has 8 deg overlap. The 224/230 would have 11.

So say we want to keep intake events the same with the same overlap but with 230 exhaust. Cam now becomes 224/230 in on the 108 icl but now 109.5 lsa. Same intake events but exhaust now becomes 46 open 4 close. So this test only changes exhaust open by 6 degs. So what changed the power? Exhaust open only? Duration? We could take the 224/224 and move centerline to open exhaust earlier to see…

lets close the exhaust valve later by 6 deg keeping same exhaust opening as original cam of 40. Cam now becomes 224/230 on a 108 icl and a 106.5 lsa. Exhaust open 40 and close 10. Does power change? Was it due to only later closing? Or is it overlap window again because it just became 14? Both?

as you might expect, those 3 different 224/230 cams will likely behave abit differently. The effect of 6 deg duration lobe has alot of variables you could test for.

and we didnt even mess with intake position yet. What if increased exhaust side or changing of exhaust event creates more pull on intake side? What if its overscavenging with the header system on the car? Can we move intake earlier to take advantage of this? Increase VE?

 

I've noticed Vizard likes single patterns. At the same time he also tends to go a little more aggressive on LSA and overlap. To test you need a lot of cams. So many that it's be impossible to accurately do and more so I'd bet you'd be able to optimize both setups to the extent where they behave about the same. Or not...

 

I would gladly pay Richard Holdener on Tuesday to test out Orr’s entire #23 post today lol!
Fascinating engineering treatise for street rpm single vs double pattern.

 

Somewhere, someplace it was explained that the typical catalogue cam with a split duration has the bulk of the added duration on the exhaust opening. Which would make sense from the volume / time equation with respect to evacuating the cylinder.
One cam designer of note has stated that for the exhaust he first has to determine the intake side and how much time is required to fill the cylinder and what that volume would be. Then it can be calculated how long it takes to empty that said volume. It should be noted too that I've never seen a spec from this designer that's anything other than a split pattern.
If you've read as much Vizard as I have he's all about maximizing torque and working with the exhaust induced induction cycle. And one of his foremost cam characteristics is the overlap. Enough is required to allow that induction cycle to exist, along with a properly designed exhaust system, but keeping duration in check. So exists the tight LSA he's known for. Overlap comes as a result and so does the torque.

It's been shown over and over that this tends to produce less of a broad curve. Output on the other hand, is enhanced. So if you were to build a truly drag orientated car, one where you have the optimum shift points and can keep the rev range tight (think Stock class drag racing), that tight LSA undoubtedly pays dividends. That seems to be reflected in their cam specs if you're fortunate to come across those.

Throw the word "street" in there, and all bets are off I think. At the very least, there's a considerable conflict between Vizard's spec, such as what's produced via his Torque Master program, and what you'll get from Bullet, Jones, or the usual group of suspects.
I'm not sure Vizard's relevance is as strong as it once was. The best I can do is model one cam vs the other in simulation and make a determination from there. (My in car cam swapping days are over...).

 

I believe that if you wanted to replicate that Sledgehammer engine build you want to call Lunati to make the custom hydraulic roller camshaft . I believe it is in fact a single pattern Voodoo HR cam "VHR-14" .227/227 .353"/.353" (.565"/.565") 1.6:1rr. 108 LSA.. I do not know the cams exact installed position.. Straight up would create the most peak horsepower on a dyno (impressive for a magazine artical ) but not nessessarily the best overall engine power curve in a car.. That you'd have to tweek for your self.
The hit in peak horsepower will be small VS the gain in low and midrange torq by advancing that cam.
4-6 degress for effect.
You could also tweek it a bit by using that 227° cam lobe on the exhaust side but then use the next smaller Voodoo cam lobe (219@.050") on the intake side.. Again ground on a 108 LSA and advanced a bit for optimum power curve in the car.
Now you have a tweeked custom dual pattern Voodoo hr cam. SledgeHammer 2.0....
VHR12 in / VHR-14 ex. 108 LSA
A version with a bit (lot) more low end torque and street tractability with only slightly less peak horsepower
A streetified version. Something for you to ponder.

I bet if you bothered to call or e-mail David Vizard personally. He may well help you on this.

 

FBird-
Your above cam creation combo would be one stunning addition to a carb’d head-modded Vortec L31 swapped street third gen.
(Truly IMHO after reading Harold Brookshire, David Vizard, etc & of course the gifted gurus here over the years)

 

thats always been one of my fav specs. I wanted to say lunati sold the 219/227 cam but on wider lsa. I always felt putting it on a 108-109 would be a great cam for most mild 350-355’s, maybe even a 383.

 

In case anyone missed it, here's the original Sledgehammer magazine article.
https://www.motortrend.com/news/0611...c-small-block/

 

Starting to sound very much like a Torque Master spec.
355 would be targeted with a 108 LSA with a Vortec 1.94" intake valve and 10-10.5:1 CR. ICL would be stated as 104.
Either split or single pattern as selected by the end user.

​​​​​

 

There is a guy on the vette forum that had a 396 with the XFI 218/224, so similar. It ran up beyond 6000 and made great midrange power. Had excellent heads and induction. It was a road race car and to my knowledge ran extremely well for what it was. (Note I have weighted in on these things when considering my cam)

So yes, I can see that working well in say a 355.

 

I was just reading that article. As far as heads for a small block. They're using a 180 CC runner with a 62 CC chamber. I'm looking at Trick FLows 195CC with a 64 CC chamber. Now I'm thinking that may be to big. Would I be better served with a 175CC runner and 57 CC chamber? The flow ratio is better on the 175 head then it is on the 195. Upwards of 80% at some lifts

 

Are those TES headers a short version? (Interwebs search indicates yes....).
And if so, what is the y-pipe size at a minimum?
Also, would that be with a single muffler in the stock location? Which muffler? Also Flowmaster?

 

I think the collectors are 2.75" that connect to a 3" out. It's 3" from there all the way to the back and ending at a single flowmaster 80 series muffler. They are the shorty's with air tubes.

 

Tge Trick Flow super 23. 195cc port heads you are looking at are fine... They are a good choice for this.

 

Not unlike mine although I have mid-length headers with a custom 2 x 2.5" y-pipe. Then a single 3" to a single Flowmaster. That Flowmaster, at least mine, is a real cork. Some back to back dragstrip testing demonstrated that.
Problem is, that despite what appears to be a reasonable I/E ratio for your heads, that isn't likely to be realized once the full exhaust is hung on there. And any benefit of the overlap will be diminished as the reflected pulse needed to accomplish that exhaust induced induction is weak.
You may find that you're being on the cusp between a split or single pattern is more towards the split pattern.
Just an observation on my part as our two projects have some similarities in the engine architecture. My biggest weakness from an output point of view is the exhaust system. Future racing will be tuned length open headers. It may be at that point, things might swing to a single pattern but I'm not there yet.

 

This is why I was inquiring about the 175's. They seem to flow better in the other direction. However I assume that's more of a head suited to a 305. I also may be over complicating things. I just don't want to get into all this and end up with the wrong combination with a slug for a motor.

 

The 175 i believe was designed for smaller bores. Good for very mild 350’s imo but no reason why a good 190-195cc head cant be used for almost all 350 applications short of max effort race deals. Its a good overall size that works with most street goals and cam sizes.

i always liked afr out the box, but tfs is good too. Just gotta match the springs to the cam for shelf heads, and i liked afr’s two hyd roller spring choices they had offered in the past and should still have now. Nice light 1.27 and 1.29” diameter duals. Good for most lobes

 

The 195 Trick Flows run a dual 1.460 spring. I had this motor completely overhauled back in 99. It's only had 49'000 miles put on since then and never raced so I'm planning on doing a head swap right in the car. Back then is when it was bored .020 with hypereutectic pistons. Thats the extend of the block mods. This is also a pure street machine. It'll never see a track. I just want something fun with some jam to it. I do like this idea of the ZZ409 if it'll work with that 195 combination.

 

Flow ratio is over emphasized by the cookie cutter cam grinds. The exhaust flow of a running engine cannot be duplicated on a bench.

 

Worked very well on the factory LT4s which were the most powerful factory 23* headed small blocks ever built.

170 can serve a 350 well, but mine ran better with 200s than 170s even with very mild cam timing. I put the 170s on the 305 in my Tahoe.

 

Never been a fan of the flowmaster mufflers.
Flowmaster does have a lot of good exhaust components thou.. Y pipes, 4-2-1 collectors etc.
You can always swap out the muffler to another type.. Or be an *** like me and cut it open and create your own custon muffler(s).. ha ha.

I'll also be working with mid length style headers vs long tube on my next one..(G Body car). I think it just needs a different approach to cam timing events on the exhaust side for its best possible results on the car. The exhaust does scavenge but the arrival time of the returning exhaust scavenge wave pulse is different (time).
One of the troubles with looking at various engine dyno tests is the dyno exhaust does not match the exhaust you are using on your car.
The power/ torque curve is not going to be exactly the same.

 

For a 355 and a 175 cc inlet port, support is into mid 6000's. That's about 250 CFM give or take. There's probably another 500 RPM there too.
I've got one option to take my 175 cc versions and plan for 6500 RPM shift with enough capacity to carry to 7k.
Advertised intake was in it around the 280-284.

 

The cam that looks the best in modeling will then need to be re- thought a bit to then work best it can using the on car headers/ exhaust system.
Its all about the net in car end result you get VS open exhaust dyno testing.

 

Unless of course you're building to run an open exhaust.

 

If I had any plan to rev it up that high I would not use a HR cam.. Not any... I would go to a Solid street roller cam. The Voodoo Solid Street rollers are great for this. Even the off the shelf catalog versions are fine for this.
Lunati #40120731 (#60131) w/ 1.6/ 1.5 rockers would be a blast on the street with mid length headers 2 into 1 big exhaust. Use Good
PSI Ct-1225 dual valve springs 1.80" installed height. Now you can rev it up.
This one will perform with open exhaust and closed exhaust. But ditch the flowmaster muff.

 

I would customize the 2 into 1 3rd gen f body exhaust to both improve perf and allow for 2 high flow cat converters so it is street legal.
Move the 2 into 1 Y pipe back further near the rear axle to allow
A. Longer primary "collector pipes" off the mid length headers and.
B. room for 2 high flow cats under the car.
Then the Y pipe (Flowmaster Y250300)
(its now back just in front of the rear axle passenger side)
Then over the axle to a big single 3" in dual 2.50" out Magna flow muffler. The 2 x 2.50" tail pipes exit the muffler to the rear bumper on the drivers side.
(Gives the car a european look)

If you are willing you could cut open your flowmaster muffler and mod it like this inside.
Weld it back up when modded.
You can build this custom 2 into 1 street legal F-Body exhaust system using Flowmaster and DynoMax (Walker) exhaust pipe components
and the 2 high flow cats.

 

This sounds like a good plan. Thanks for that idea. I never thought of dragging the split back which would technically make the header almost long tube. Good thinking. As for heads. I know I'll get chastised for this but hear me out: I have an option for brand new Flo-tek 180 heads. However, these ones will be stripped by a machine shop, checked, and built back up with whatever I want for springs and other hardware for a very good price. This solves two problems. 1: No one has any heads in stock. 2: It helps cost wise because the U.S dollar is killing us in Canada. This now frees up some capital for that exhaust mod. This is pure street. It'll never see a strip or oval.

 

I see you're in Mississauga.
Who's your machine shop of choice?