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Cam Timing affect on powerband
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TinCanFab
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PostPosted: Mon Oct 13, 2014 10:11 am    Post subject: Cam Timing affect on powerband Reply with quote

I've been doing a lot of homework regarding cam specs lately. I've learned a lot but I have one question I hope someone maybe with dyno experience can answer: Specific to ACVW engines, when a cam is advanced or retarded and all other things remain equal, how much of a powerband shift is changed for the cam's ideal range?

So, if a cam has a powerband designed for 2000-6500 rpm, and I change it's setting by 1 degree either direction. Has the powerband now become 1900-6400 or 2100-6600? What does 1 degree change? 100 rpm? 500 rpm? I understand the theory behind advancing and retarding, but haven't seen any info other than changing it cause such and such characteristics....
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PostPosted: Mon Oct 13, 2014 10:42 am    Post subject: Reply with quote

Although I have no experience with this I would think your going to want to advance the cam to run higher RPM's ! Probably not more than 5' degrees though! It would be nice to be able to dial in your cam on a dyno after rebuilding the engine. I would be temped to set mine for best torque at lowest RPM but that may be too retarded for overall performance.
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PostPosted: Mon Oct 13, 2014 11:05 am    Post subject: Reply with quote

Danwvw wrote:
Although I have no experience with this I would think your going to want to advance the cam to run higher RPM's ! Probably not more than 5' degrees though! It would be nice to be able to dial in your cam on a dyno after rebuilding the engine. I would be temped to set mine for best torque at lowest RPM but that may be too retarded for overall performance.


Other way around...Advancing the cam brings peak power on sooner and retarting the cam brings power on higher, just like variable cam timing engines.

When the intake valve closes sooner, it feels like a smaller cam and visa-versa.

For the original poster, you will not tell a difference in a single cam degree. 3-4 degrees you still might not "feel" but would show on a dyno.
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And I know you don't know because if you did you would know the reason for my knowing you didn't.


youngnstudly wrote:
I just wasn't sure if I should recommend the 1/3 race cam, the 1/2 race cam, or the 5/8 race cam instead...guess it depends on how much of the race he wants to lead???
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PostPosted: Mon Oct 13, 2014 11:24 am    Post subject: Reply with quote

I am swapping from a turbo grind cam to a 110 cam I found in my parts stash. The engine is a 2017 that was in my bug, now going into my very stock single cab with a big nut trans and tall tires. The gearing is very low and I will not be shifting with boost at 6000 rpm anymore. My powerband needs to be shifted down to match. I won't be doing any dyno runs, but will use a wideband to tune a nice driver. I know that the bigger crankshaft will help with torque. I want to set my timing gear advance to a nice compromise and leave it there. I'm just curious how much 4-6 degrees will affect the engine before I commit to it. Also, I'd like to decide ASAP so I can come up with a dynamic compression ratio. I want to drive my truck without a soggy bottom end because I will actually be using it to haul stuff sometimes. I am tuning for a happy torque bus engine that runs cool.
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PostPosted: Mon Oct 13, 2014 11:33 am    Post subject: Reply with quote

If you do a search for cam timing on here most of the posts are actually talking about ignition timing which is completely different.

As I understand, advancing the cam will move the power down in the rpm's as the valves are opening sooner in relation to the crank. Retarding the cam will move the power up. But the changes are so little per degree that most guys run the gear "straight up"

Quote:
So, if a cam has a powerband designed for 2000-6500 rpm, and I change it's setting by 1 degree either direction. Has the powerband now become 1900-6400 or 2100-6600?


Retard it and the power might move to 2100-6600, Advance it and the power may drop to 1900-6400. That's the idea anyway But different engine combos will respond differently.

More important is to match the opening and closing numbers with the cam card which is another advantage to adjustable gears. Hope this helps
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PostPosted: Mon Oct 13, 2014 11:42 am    Post subject: Reply with quote

roachdub58 wrote:
I am swapping from a turbo grind cam to a 110 cam I found in my parts stash. The engine is a 2017 that was in my bug, now going into my very stock single cab with a big nut trans and tall tires. The gearing is very low and I will not be shifting with boost at 6000 rpm anymore. My powerband needs to be shifted down to match. I won't be doing any dyno runs, but will use a wideband to tune a nice driver. I know that the bigger crankshaft will help with torque. I want to set my timing gear advance to a nice compromise and leave it there. I'm just curious how much 4-6 degrees will affect the engine before I commit to it. Also, I'd like to decide ASAP so I can come up with a dynamic compression ratio. I want to drive my truck without a soggy bottom end because I will actually be using it to haul stuff sometimes. I am tuning for a happy torque bus engine that runs cool.


Since you are changing the cam anyway, its hard to know what it will like. I would run it straight up and see how you like it. Also I've read that Engle grinds a couple degrees advance in their cams anyway.
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PostPosted: Mon Oct 13, 2014 12:07 pm    Post subject: Reply with quote

I talked with a tech at Engle a few days ago and he said older cams are ground with 1 degree advance and newer ones at 4. The cam I have appears to be someone's regrind so that leaves me to do all the work and get it right. I know some people might think I'm splitting hairs here, but if you've ever driven a split bus with gear reduction boxes, you know what I'm up against. Here I'm using an engine that is waaaaay overbuilt for what I'm using it for, so I should go out of my way to make it work well in a stock rpm range. The last thing I want is something that hauls ass in a bug, but is worthless in a bus that only sees 4500-5000 rpm. If I find my cam is ground with extra advance, then I go and advance it another 4-6 degrees, that's a pretty drastic change from what an average 110 cam card shows. If that causes power to build from idle to 4500 rpm or so, I will be very happy. The numbers on the cam are GB110 and 108. I measured the lobes and base circle on this cam and the lift number is very close. I called Gene Berg and they don't come up with this as their part number.
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PostPosted: Mon Oct 13, 2014 12:31 pm    Post subject: Reply with quote

What is the rest of the engine combo? Just the fact that the engine is over 2000cc's will help with low end grunt. As long as the heads and carbs are not too big it should pull nice at lower rpm. Wont the reduction boxes help with low end? I think the 110 is a good cam for the powerband your after no matter how you run it. But we need to know heads, carbs, exhaust, compression, ect...
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PostPosted: Mon Oct 13, 2014 1:00 pm    Post subject: Reply with quote

40 idfs with 32 venturis, added velocity stacks from 44's
1 1/2" standard header
044 Cnc ported heads with 57 cc chambers, smaller round intake ports, 42x37 valves (I know a little on the big side for this, but I think the small ports will keep good velocity)
Switched back to 1.1 rockers
Deck height around .045"
Removed copper head gaskets (should get me around 9:1 static cr)
Still running 12 lb flywheel because of the wedgemate
Plus a ton of standard big engine upgrades
Also since I need a new set of lifters I'm going to go with the CB lightweights based on good reviews here

It seems the engine I built for street turbo use in a bug happens to be really compatible for a nice bus engine with a few easy changes. Cr, header, carbs, cam. I think I got pretty lucky.
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PostPosted: Mon Oct 13, 2014 2:28 pm    Post subject: Reply with quote

#1 , get biger tires.
#2 get rid of the rgb's.
#3 1 degree would be hard to find on a dyno
#4 you can also varry rocker ratio to tune.
#5 get the right cam for your app and build the engine that is needed for the app.
#6 disreguard #5 and build a big motor,taller tires and no rgb's.
#7 do it right ,do it one time,forget about it.
# 8 GO HAVE FUN!!!

#9 diferent cams and diferent cc engines,and diferent inductions,and diferent exhaust,and diferent compression ratios can react vastly diferently in the amount of cam addvance or retard.thats a lot of variables. now refer to #6
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PostPosted: Mon Oct 13, 2014 2:57 pm    Post subject: Reply with quote

Quote:
#1 , get biger tires.

Why would he go with taller tires, it sounds to me like he wants to have low end grunt.
roachdub58 wrote:
now going into my very stock single cab with a big nut trans and tall tires.


I like the engine combo, I still think the 110 straight up would be the right choice if you want to rev it to 5k on occasion. If you are concerned about the cam timing and response of that cam then I would just get a smaller cam like a 100 or similar.

I built a 1745cc engine for my friends 71 westy, Engle 100 cam with 1.25 rockers. He was real happy with the grunt it had pulling hills even when towing.
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PostPosted: Mon Oct 13, 2014 6:03 pm    Post subject: Reply with quote

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Dang Mark, you really think I should change a bunch on this sweet rig? I freakin love it this way! Very Happy
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PostPosted: Mon Oct 13, 2014 9:52 pm    Post subject: ~9.5 cr should put you at around 150_160 hp Reply with quote

I built a maotr for one just like that(execpt it was painted to match his 912 porch) as I recall it was a 2017,duel 44's(dels I think,but may of been idf's) he has all the power he could ever use,he put biger tires on it to lower the rpm,but will probably end up removing the rgb's.I love those SC'c and the DC's. as far as DCR.... Laughing Laughing Laughing Laughing Laughing Laughing Shocked too many things,tomany diferent engines.tomany variables. I gess I should one day put my engine combo/cam in that calculator and see just what it says.Ive got a fealing my cr isant what " THEY" want.....the ever knowing "they" exsperts on everything.
I have done that dcr befor but it dosent use real valve timing....so....IMHO CRAP.
with the rgb's you realy dont need to addvance the cam(unless you have realy lo cr) hell I had 19.5x33 mickeys street pros on my bug.the 1st gear is already low enough for most anything and you have rgb's to lower it farther. I would however go with a low lift cam and ratio rockers to get the lift back.it also has other addvantages.
as for changing your rig...I never said to change the look of it.looks sweet,so make it run sweet too. those heads with a mild cam & 9_9.5cr should put it around 140-160 hp,smooth hp. remember it's your foot that unleashes the power. but no matter what cam you use it will not change the crusing rpm . but if you choose a cam that runs out of power at 60 mph you will kill the motor when you try to run down the innerstate at 70. so....a little biger cam would be better,not much.but rememeber those rgb's. it's better to have power left over than under powered or not able to rpm when you need it to. good luck and have fun!!!
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PostPosted: Mon Oct 13, 2014 11:31 pm    Post subject: Reply with quote

Any time I've advanced a cam 5 or 6 degrees from straight up, the engine just felt bigger.
With the sort of stroke length you're using, you could expect the torque to come on about 600 rpm earlier. It will have less effect on a longer stroke engine.
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PostPosted: Tue Oct 14, 2014 10:37 am    Post subject: Reply with quote

addvancing the cam gives more cylinder pressure at cranking&low speed,thus more grunt.but can also kill starters, and cause detonation.know what your doing and howmto tune it before jumping off the deep end. if just advancing the cam 6 degrees made it feal like a bigger engine dont you think the cam grinders would all do that?? it's a trade off.and a tuneing tool. but what it does and can do varry from setup to setup.witch is best for your's??? you have 1 good thing going for you(well more than 1 ) but you can remove the oil pump to redegree the cam,and that may be the best thing for you if you dont mind messing with it after building it. but what if you assemble it with the cam 4 retarded??? and you drive it and it's great!!!! do you still need that little extra bottom end??? on v8 stuff with timing chain I usualy addvance the cam 3~4 degrees so it will be 1~2 addvanced when the chain streaches and has a real load on it. vw not so much. I hears some that want to chug along in 4th gear at 20 mph. will thats fine...... Shocked how much oil is that oil pump pumping at that rpm/speed in 4th with the engine loaded&chuging along.......not enough and those guys have issues but they also expect about 5000 miles out of thier disposeable engines. know all the affects of everything when you do 1 thing it affects many things.keep thinking.
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PostPosted: Tue Oct 14, 2014 10:57 am    Post subject: Reply with quote

roachdub58 wrote:
I am swapping from a turbo grind cam to a 110 cam I found in my parts stash. The engine is a 2017 that was in my bug, now going into my very stock single cab with a big nut trans and tall tires. The gearing is very low and I will not be shifting with boost at 6000 rpm anymore. My powerband needs to be shifted down to match. I won't be doing any dyno runs, but will use a wideband to tune a nice driver. I know that the bigger crankshaft will help with torque. I want to set my timing gear advance to a nice compromise and leave it there. I'm just curious how much 4-6 degrees will affect the engine before I commit to it. Also, I'd like to decide ASAP so I can come up with a dynamic compression ratio. I want to drive my truck without a soggy bottom end because I will actually be using it to haul stuff sometimes. I am tuning for a happy torque bus engine that runs cool.


Assuming that your "110 cam" is an Engle, it is already advanced 3- 4 degrees dependant on how accurate the grind is. Advancing it further will do little good because the exhaust side will come too far retarded.
Many years ago I accidently advanced a W130 instead of retarding it in a 2275. I did not really notice it until I had it on the dyno apart from I thought it was a tad lazy, but expected to find the missing power on the dyno. It only pulled 156 hp and 210 ish Nm torque. It - was - quite nippy off idle, but lost the grunt way too fast. I took it apart and discovered my woopsie, retarded the cam instead to 107 ILC, which was 3 degrees retarded in this case. Back on the dyno I now saw the numbers I expected, 169 hp and 225 Nm torque.

That was after all also 5 degrees difference, but the performance difference was rather huge.

T
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PostPosted: Tue Oct 14, 2014 10:57 am    Post subject: Reply with quote

there are computer engine simulations you could use to get a good idea of just what each cam will do and retarding or addvancing it. you may want to invest in one to do some what if's befor you buy a cam. I have an old one very old one, there pretty close at thier predictions.
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PostPosted: Tue Oct 14, 2014 11:56 am    Post subject: Reply with quote

Thanks for the input guys. I have my adjustable gear swapped to this cam and tonight I'll mock the engine back up with degree wheel and dial indicator. I've got a cam card from another 110, we'll see how this one looks. I found my 2 degree washers for the gear, so maybe I will keep the adjustment moderate to eliminate bigger problems if the cam is ground advanced.
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PostPosted: Wed Oct 15, 2014 12:53 pm    Post subject: Reply with quote

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So I installed the cam and checked #1 cylinder intake lift at 0.050" with the gear installed counter-clockwise and offset washers installed (this was the proper direction for advance, correct?).

My measurement was 15 degrees intake open. Since this is a mystery cam stamped "110", I'm looking to see how close it is to a real Engle cam card. I called CB and they said my silver colored offset washers are 4 deg., gold is 0 deg., and plain with no plating is 2 deg. If I'm correct, the cam was ground "straight up" with no advance, and my adjustment to the gear makes it equal in spec to the way Engle grinds their 110 nowadays....

Also, with the cam advanced 4 degrees, is 44 deg my "new" intake closing measurement if the cam is correctly reground as a 110?

I'm about to button this thing up soon, and I'm probably going to leave it this way. What do you guys think?
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PostPosted: Wed Oct 15, 2014 3:10 pm    Post subject: Reply with quote

you need to learn how to degree a cam. you are not addvanced your retarded. 19 comes before 14 execpt before y and z.
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