Extremely Good Thread on Camshaft Design and Valve Events

[zok15]

This is from LS1Tech.com:

https://ls1tech.com/forums/generation-i ... atter.html

There is a lot of reading, but you can just read what user Sales@Tick posts. If anyone else says anything useful, he usually quotes them so you will see it anyways. There are some excellent graphs too that are from actual testing with transducers. I still have more to read myself, but a few pages in and I knew it was worth sharing.

In somewhat of a summary, it is better to think of the cam in terms of when valve events occur, ie exhaust valve opens, intake valve opens, exhaust valve closes, intake valve closes, and how the relationship between them and what is going on with cylinder pressures, intake runner pressures, and exhaust runner pressures allows you to tune the engine to be happy. The tuning of your cam is very much dependent on your intake and exhaust design which greatly influences what the pressures inside them are doing, and how waves in the runners have a frequency affected by intake and exhaust geometry.

Here is a great image from the LS1Tech thread of pressure data from a well tuned engine, ie a cam tuned for how well the exhaust and intake flows. Called out are TDC, BDC, EVO, IVO, EVC, IVC.



But basically at the start of the graph, due to good exhaust design for where the exhaust valve opens and having adequate flow/scavenging at this RPM, cylinder pressures are lower than intake runner pressure when the intake valve opens. When the exhaust valve first opens, there is a massive amount of pressure built, but as it moves through the primary and scavenging starts to take effect, this causes exhaust runner pressure to go negative which causes cylinder pressures to go negative as well. The intake valve opens and pressure in the runner is higher than in the cylinder which helps fill the cylinder and exhaust the last bit of exhaust that the piston cannot push out (~combustion chamber volume). Then as the piston passes TDC, intake air gains momentum on the down-stroke, and it can be seen that the cylinder continues to fill due to this momentum after bottom dead center, when the piston is on the way up. There is a sudden drop off during compression stroke and the intake valve is tuned to close shortly afterwards.

I thought this was really cool, there are graphs of engines outside their tuned area and how they behave, and people ask them what he would recommend for their own setups and he gives detailed answers based on valve events.

[neophile_17]

I haven't gotten to read the thread but I thought that graph looks really familiar. This is where I saw it...

http://www.epi-eng.com/piston_engine_te ... nology.htm

[zok15]

Wow that is the ultimate exhaust article.

[SappySE107]

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[zok15]

Ben, I have your strip cam that is in my LZ9, I was curious if you would be willing to share why the exhaust duration is lower than intake duration? I am mostly just curious. I also noticed the cam has no overlap at 0.050"and was curious about that too, especially seeing as this cam is for higher RPM power. I have been doing a lot of research into determining how my header primaries should be spec'd so I have been looking into this all and plugging all the values from the cam spec sheet into cam calculators.

[zok15]

I've seen that a reverse cam vs standard at the same VEs will make a little less peak but more overall area under the curve. And fwiw my cam from WOTtech came with all the Compcam packaging and the spec sheet.

But I was just curious. Especially with the overlap. I assume it is because these cams are designed for stock compression?

I would love to spec my own cam one day, but I imagine it's hard without an engine dyno.

[ericjon262]

I was actually thinking about starting a thread on the subject of valve events and camshaft design. I've been seriously considering spec'ing out a custom cam for the Banshee's new engine. I've been giving a ton of thought to tightening up the LSA a little bit, maybe going to a 108 or 109, From some of the dyno tests I've seen, that can make a pretty massive difference in midrange performance. but they were also performed on a gen 1 SBC, which might not have had as good of a cylinder head on it as my 3500.

I'll have to read that thread in more detail when I'm not at work.

[zok15]

I can't comment on your experience with Ben, but mine was good, we talked back and forth over email, he answered all my questions, everything was transparent, and everything was shipped nicely and arrived when it was supposed to. My teflon coated SBC cam bearings were pre-installed into the cam bearing spacers with the oiling holes lined up properly, the custom length pushrods came in at the correct lengths, and I was able to get the genuine GM timing components cheaper than anywhere else I could find. I did get them cryo treated myself however as I could get it done cheaper and had other parts I wanted to cryo treat as well. My only minor complaints were that the lifters were just Melling lifters I could have gotten from Rockauto significantly cheaper, and I think the ARP rod bolts selected are a tad short, I am sure they will work fine but they are shorter than the stock rod bolts and therefore have a little less thread engagement. But overall I have no big complaints.

I will definitely get my setup dyno'd and we can see how the cam performs, but I think with the stock intake it will be good. Consensus seems to be with factory intake, mild port work, bigger TB, and a very free flowing exhaust is to go with reverse split.

I did want to pick your brain about your ITB setup on your 3500, I would love to go ITBs on this when I build V2 at some point, I would definitely go with a traditional split on the cam if I had ITBs.

And Eric, it seems like your chosen durations and desired overlap will drive your LSA value, I assume with the turbo setup you are going to target no overlap? But an LSA that tight seems like it will need some overlap unless you are going to go with a pretty low exhaust duration.

[ericjon262]

I went back an forth alot on what I wanted. a part of my idea to run a tighter LSA, and therefore more overlap, was based on an episode of Engine masters, where more overlap made massive gains in the midrange, my theory was that increasing midrange power would mean an increase in midrange intake/exhaust flow, which therefore would cause a more rapid spooling of the turbo, I would be very interested in seeing how exactly this would work out in a car. but swapping swapping cams in a car is a PITA, and finding two otherwise identical setups is also not exactly a cake walk. one way this could be tested easier would be with a DOHC VVT engine.

[ericjon262]

I'd like to add this to the discussion. interviews with Kenny Duttweiler in this particular article suggest that overlap isn't the issue it used to be with turbos, and that adding overlap tends to improve performance with a modern turbo. While I won't go as far as say my turbo setup is optimized, I will say it's far from worse than anything from the early days of turbo street cars.

https://www.motortrend.com/how-to/ctrp- ... aft-guide/

[ericjon262]

well, I did it... I finally ordered a cam, after countless hours of modeling cams, both in CAD, and on desktop dyno, and comparing real world dyno results, I decided upon this:

Comp XFI lobe number 3006 intake, 3036 exhaust, 108 LSA, 110 ICL

Duration at .006"--------------266/282
Duration at .050"--------------216/230
Duration at .200"--------------141/152
Lobe lift ----------------------.354"/.355"
valve lift with 1.6 rocker --.566"/.568"

will it work? we'll find out!

[Shaun41178(2)]

It will work just fine. What were your current cam specs

[ericjon262]

the published numbers when I bought it were 216/224 .506/.506 114 LSA, 113 ICL, without knowing the exact lobe numbers, I have to guess a bit, but looking in the lobe catalog, it suggests the lobes on the cam I ordered go from/to the seat, to .050" slower, and then move faster from .050" to .200", which makes sense because they also have more lift. either way, I'm pretty excited about it, I hope it sounds as good as it looks in simulation.

[ericjon262]

today I learned that there's a machine shop near me that grinds camshafts... I might reach out about the idea of having a 3900 cam reground.

[Shaun41178(2)]

today I learned that there's a machine shop near me that grinds camshafts... I might reach out about the idea of having a 3900 cam reground.

Excellent. Keep us posted

[ericjon262]

it would be great to see back to back testing of camshafts in a 60V6. it would be quite interesting to see where diminishing returns starts to come into play with the stock style intakes, and the gains between a 3400 and LX9 plenum.

As far as I can see, neither of you have provided dyno data to prove your ideas work better than the other's in a 60V6, so further argument is irrelevant until reasonably accurate 60v6 testing data is available.

[ericjon262]

it would be great to see back to back testing of camshafts in a 60V6. it would be quite interesting to see where diminishing returns starts to come into play with the stock style intakes, and the gains between a 3400 and LX9 plenum.

As far as I can see, neither of you have provided dyno data to prove your ideas work better than the other's in a 60V6, so further argument is irrelevant until reasonably accurate 60v6 testing data is available.

We have chassis dyno comparisons between multiple cams, as well as track results. There is no argument for me. Shaun says im stupid, and I don't care what shaun has to say about me. We are just going to learn more about these motors now that the engine dyno is running. I have engines to finish up so we have dedicated test motors for consistency.

My point was not that your cam specifications are better or worse, or that you have or have not performed testing. My point was that as far as I have seen no A to B test of split/reverse split cams have been performed in a 60V6.

[ericjon262]

Can Will or Series move all of shaun and bens lover's quarrel to it's own thread so this one isn't completely ruined? most of the overall "discussion" is irrelevant, their points could be summed up in two posts...

Shaun-"I think bens cams don't work"

Ben-"I perform simulations, and then use them to develop and test cams"

Lets try and keep tech threads tech, and not a pile of trash talking without any substance.

[zok15]

Neat graphs, the dyno for the street strip cam in the LZ9 looks like it agrees with the sim results. Torque peaks a little lower in RPMS but it is also not a stock 3400. From the sim graphs it also looks to be about a 15% increase in peak hp, which it looks like the LZ9 actually peaked a little higher but does have supporting mods. Torque seems to hold out longer in the LZ9 setup than compared to stock 3400.

Edit to also say that Josh said that in this dyno he was picking up a bunch of false knock and it was pulling timing the way he had his exhaust, seems it was vibrating and hitting the motor. Not sure if he ever got a follow up dyno.





Would you be willing to share the sim results for the Strip cam that I have? Curious how it compares to the street strip cam. If you have any chassis dyno results for the strip cam that would be sweet too.

Also exciting to hear you got an engine dyno setup going, do you have any threads about what you are working on over at 60*V6?

[ericjon262]

After a 12 year hiatus from this site, and the few months I have been back, its a safe bet this is my last post.

Good. Bye scammer. Scammers aren't welcome here.

Don't forget to edit your last post too like you did with all your others.

shaun, have you even tried posting a single ounce of useful information in the past few weeks? I'm fairly certain you're the only one here who has an issue with Ben. and you've taken that issue to an extreme.

I'd be willing to bet that you, by yourself, account for 50% of the reason nobody respects the fiero community. you're a bag of hot air, almost no substance to anything you say. you'll call out anyone and everyone about not posting a dyno sheet, than turn around and claim to make 700 HP without one.

Now, a forum that had 7 semi active members, now has 6. You've probably deterred the few who want to get away from the lou dias style retardation of Old Europe from joining too. The worst part is that I'm going to call you out on being a giant piece of shit, and all you're going to do is gloat about it, you're going to sit there and have a little party all by yourself once you've run every member away from here with your fucked up nonsense that you continuously spew.

I can't speak for anyone else here, but every time I've ordered parts from Ben, I promptly got the parts I paid for. that doesn't sound like a scam. his cams? did they improve the performance of the engine? well, judging by the dyno you posted, it gained power almost everywhere, so I'd say that doesn't seem like a scam. could a different cam make more power? who knows, but if you think something else will perform different, then order it and move on.

you absolutely destroyed this thread for no damn reason, thanks asshole.