Mine is loud as HELL in this big heavy truck. lol
Street Demon vs AVS2
- Thread starter qkcuda
- Start date
-
Mine is loud as HELL in this big heavy truck. lol
The idea was a 2.94 gear as a low budget alternative to a lower gear with an overdrive. Again the cars I am looking at turn out to be stretching my budget, so I am trying to work out cheaper ways of meeting my goals. For a cam, the lunati voodoo 10230701 looks good to me 213/220 duration 454/475 lift 112 lsa. Claims 19 inches of idle vacuum and a 1000-5500 range.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,870
- Reaction score
- 13,175
Here's another situation.
Yur tooling along at 32mph being cool. Still 3.23s and now say the A500 with ratios of 2.45-1.45-1.00-.69od. and it has a loc-up. And let's put 88s on there to really fill the wheel wells, cuz anything less than 88s just look sick on that car. (88s are 28' tall)mmm. Ok then; in drive,not locked up, you will be at 1240 rpm.... with a 220 cam and maybe 16* timing plus Vcan but at that throttle opening, on the spark-port, you may have too much advance.. No I don't think that's gonna work. So sticking her in second, the Rs jump up to 1800 at zero-slip, and the mechanical timing might be 28* plus Vcan timing should be active but maybe only 50% so that's 11 more and total is 39* so that should work. Ok so yur tooling along in second at 1800@32mph, with 39* timing, And so you get the urge to go!
You floor it, the Vcan 11* drops out, the trans kicks into first, and the secondaries begin to open; you better not have a double pumper. The Rs pop up to 3200, the timing is 32*, and the fresh cold air, and rich mains have cooled the plugs. The tires light up, and the engine no longer cares about how much timing she's getting, nor about how much too big the carb is.
Yur tooling along at 32mph being cool. Still 3.23s and now say the A500 with ratios of 2.45-1.45-1.00-.69od. and it has a loc-up. And let's put 88s on there to really fill the wheel wells, cuz anything less than 88s just look sick on that car. (88s are 28' tall)mmm. Ok then; in drive,not locked up, you will be at 1240 rpm.... with a 220 cam and maybe 16* timing plus Vcan but at that throttle opening, on the spark-port, you may have too much advance.. No I don't think that's gonna work. So sticking her in second, the Rs jump up to 1800 at zero-slip, and the mechanical timing might be 28* plus Vcan timing should be active but maybe only 50% so that's 11 more and total is 39* so that should work. Ok so yur tooling along in second at 1800@32mph, with 39* timing, And so you get the urge to go!
You floor it, the Vcan 11* drops out, the trans kicks into first, and the secondaries begin to open; you better not have a double pumper. The Rs pop up to 3200, the timing is 32*, and the fresh cold air, and rich mains have cooled the plugs. The tires light up, and the engine no longer cares about how much timing she's getting, nor about how much too big the carb is.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,870
- Reaction score
- 13,175
I don't like wide LSA cams. But if you have too much compression, sometimes they are the lessor of two evils
I'll show you what I mean.
First; lets pretend that 213/220/114 Voodoo is 252/260/114 advertised, and lets pretend your Scr comes in at 9.6. And that you are at 200 ft above sealevel.
Sooooo,
Static compression ratio of 9.6:1.
Ica of 56* (114LSA installed 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 165.42 PSI................ 165
V/P (Volume to Pressure Index) is 162........................... 162
Notice your cylinder pressure here is 165psi, for your application, this is too much pressure, for pumpgas. You will have to reduce the pressure or open the intake a lil later.
Ok so, since the VP is up to a crazy 162,lets just retard the cam-timing to straight up, and I get
Static compression ratio of 9.6:1.
Ica of 60*
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.88:1 .
Your dynamic cranking pressure is 159.28 PSI.............. 159
V/P (Volume to Pressure Index) is 151 ........................ 151
So there you go, pressure is down, probably in 89 gas territory, and the VP is still a generous 151.. I made it work.
But with less compression, say 9.0
Static compression ratio of 9.0:1.
Ica still 60*
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.40:1 .
Your dynamic cranking pressure is 146.58 PSI. ................... 147
V/P (Volume to Pressure Index) is 139 ................................ 139
Look what happened to the pressure!, and the reduced VP. This ain't gonna work.... Well it will; 139 is the beginning of fun at low rpm, and the 147psi will run on any old gas. But it sure ain't optimum, and won't make the power you were expecting.
so lets put the cam back in at 4* advanced
Static compression ratio of 9:1.
Ica of 56* (114LSA@ 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ............... 152
V/P (Volume to Pressure Index) is 147 ............................ 147
Ok so, now we have a tire fryer with the 147VP, but the pressure is down at 152, and yur not gonna get the best mpgs at that pressure.But it will still run on crap-gas.
Remember, this is all the same cam, just messing with the compression ratios and the install.
So by now you should be able to predict what will happen at 10/1 Scr. The pressure is gonna skyrocket and the VP as well, but the pressure even with a retarded cam may be too much.
Lets run it and see
Static compression ratio of 10.0:1.
Ica of 60*,(4* retarded)
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 8.20:1 .
Your dynamic cranking pressure is 167.83 PSI. .................... 168
V/P (Volume to Pressure Index) is 159 ................................ 159
So there you can see the pressure is outta sight! and the VP is ridiculously high.And the cam is already retarded. I can't see this working for you with iron heads
Now, I set this up for the final work-ups.
As you can see, with 168psi, the above combo is ready to self-destruct on pump-gas; but lets change the LSA on that same cam from 114 to 108, and reduce the compression ratio, and see what happens
Static compression ratio of 9:1.
Ica of 54*( straight up)
Effective stroke is 2.83 inches.
Your dynamic compression ratio is 7.71:1 .
Your dynamic cranking pressure is 154.76 PSI..................... 155
V/P (Volume to Pressure Index) is 153 ............................... 153
There you have it; 155psi will cruise on 87E10/15, and the 153Vp is crazy strong bottom end; you can run any rear end you want to; altho you may need 89 or more gas to stay out of detonation, under heavy acceleration.
Lets advance the cam just 2*
Static compression ratio of 9:1.
Ica of 52*, (108* LSA/ 2* advanced)
Effective stroke is 2.87 inches.
Your dynamic compression ratio is 7.80:1 .
Your dynamic cranking pressure is 157.15 PSI. ............... 157
V/P (Volume to Pressure Index) is 158 ........................... 158
Heck yah! Compare the above, to the below; both at 9.0 Scr
Static compression ratio of 9:1.
Ica of 56* (114LSA@ 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ............... 152
V/P (Volume to Pressure Index) is 147 ............................ 147
The only difference in these two is the LSA, and the 4* advance
Check out the HUGE VP increase from 147 to 158, this is soooo big, that you could actually run the next bigger cam,
Lets try a 260/268/110
Static compression ratio of 9.0:1.
Ica of 56* (110LSA cam at 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ................... 152
V/P (Volume to Pressure Index) is 147................................ 147
Look familiar? It is the same 56* Ica, so the numbers come out the same.... but the power is gonna be up maybe 15 hp..... with no loss of performance below 3000 compared to the 252/260/114cam. And now you know why I don't like wide LSA cams. When properly compared, they will cost you power every time. But worse is that they will also cost you hiway-mpgs every time
So why do people run wide LSA cams?
Because they reduce overlap and make the engine run smoother at low rpm, and if an engine is to run for many miles at very low rpm, like a city car would, then this has the bonus effect of increasing city-mpgs by virtue of mixture control. This is why your old LA318 had like 16* of overlap and 2.76 gears.... and idled around town at 35mph=1250rpm in Drive.
But the 340 had 44* overlap and ran 3.23s with a loose TC and 35mph was maybe 1500 in drive, but most guys were in second, cuz, you know, it's a 340, and we got a point to prove; so in second the Rs were around 2200.
At 2200 the overlap was NO LONGER AN ISSUE.
So knowing that now, lets look at your imaginary 252/260/114 cam, with it's 28* of overlap, and compare it to the 260/268/110 with its 44* of overlap.
As you can see the small cam will idle pretty much like a stock 360, cuz that's about what they had (maybe 24* I forget), and the bigger cam will idle like a 340, cuz it has the same 44*. And like the 340, on the hiway, it will like to be up around 2000/2200 for best mpgs. which is why I picked 2100 for you.
Yes there really is a method to my madness, lol.
OK just one more FYI
here we have the next bigger cam again, a 268/276/108customLSA cam
Static compression ratio of 9.6:1.
Ica of 56*(108LSA at straight up)
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.88:1 .
Your dynamic cranking pressure is 159.28 PSI. .................. 159
V/P (Volume to Pressure Index) is 148 .............................. 148
Notice I jumped the compression back up to 9.6
Notice the gas requirement at WOT is back up to probably 91
But notice the VP is up to about the same as the best of the other combos. So this combo will have another 15 or so hp , so now we are up at least 30hp over the 213* cam, but without any loss of low-rpm power. The penalty for this is that overlap is now 56*, and your hiway rpm or speed, may have to be increased to above 2100 to clean up the intake; say 2300, and so at 65mph (still with 28s) you will need a minimum 2.94s. This is the minimum; bigger is Ok. With 2.94s 75mph would be 2650 at zero-slip, which is 350 over 2300 so just a lil buzzy is all........ but a lot easier to engineer the ignition timing curve.
The whole point is this;
the cam and the pressure are like an old married couple, they hold hands in public, but sleep apart because they can't stand each others farts.
You'll get the best results when they are holding hands. If you just slam them together, chances are very good that the result will stink.
I'll show you what I mean.
First; lets pretend that 213/220/114 Voodoo is 252/260/114 advertised, and lets pretend your Scr comes in at 9.6. And that you are at 200 ft above sealevel.
Sooooo,
Static compression ratio of 9.6:1.
Ica of 56* (114LSA installed 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.11:1 .
Your dynamic cranking pressure is 165.42 PSI................ 165
V/P (Volume to Pressure Index) is 162........................... 162
Notice your cylinder pressure here is 165psi, for your application, this is too much pressure, for pumpgas. You will have to reduce the pressure or open the intake a lil later.
Ok so, since the VP is up to a crazy 162,lets just retard the cam-timing to straight up, and I get
Static compression ratio of 9.6:1.
Ica of 60*
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.88:1 .
Your dynamic cranking pressure is 159.28 PSI.............. 159
V/P (Volume to Pressure Index) is 151 ........................ 151
So there you go, pressure is down, probably in 89 gas territory, and the VP is still a generous 151.. I made it work.
But with less compression, say 9.0
Static compression ratio of 9.0:1.
Ica still 60*
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.40:1 .
Your dynamic cranking pressure is 146.58 PSI. ................... 147
V/P (Volume to Pressure Index) is 139 ................................ 139
Look what happened to the pressure!, and the reduced VP. This ain't gonna work.... Well it will; 139 is the beginning of fun at low rpm, and the 147psi will run on any old gas. But it sure ain't optimum, and won't make the power you were expecting.
so lets put the cam back in at 4* advanced
Static compression ratio of 9:1.
Ica of 56* (114LSA@ 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ............... 152
V/P (Volume to Pressure Index) is 147 ............................ 147
Ok so, now we have a tire fryer with the 147VP, but the pressure is down at 152, and yur not gonna get the best mpgs at that pressure.But it will still run on crap-gas.
Remember, this is all the same cam, just messing with the compression ratios and the install.
So by now you should be able to predict what will happen at 10/1 Scr. The pressure is gonna skyrocket and the VP as well, but the pressure even with a retarded cam may be too much.
Lets run it and see
Static compression ratio of 10.0:1.
Ica of 60*,(4* retarded)
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 8.20:1 .
Your dynamic cranking pressure is 167.83 PSI. .................... 168
V/P (Volume to Pressure Index) is 159 ................................ 159
So there you can see the pressure is outta sight! and the VP is ridiculously high.And the cam is already retarded. I can't see this working for you with iron heads
Now, I set this up for the final work-ups.
As you can see, with 168psi, the above combo is ready to self-destruct on pump-gas; but lets change the LSA on that same cam from 114 to 108, and reduce the compression ratio, and see what happens
Static compression ratio of 9:1.
Ica of 54*( straight up)
Effective stroke is 2.83 inches.
Your dynamic compression ratio is 7.71:1 .
Your dynamic cranking pressure is 154.76 PSI..................... 155
V/P (Volume to Pressure Index) is 153 ............................... 153
There you have it; 155psi will cruise on 87E10/15, and the 153Vp is crazy strong bottom end; you can run any rear end you want to; altho you may need 89 or more gas to stay out of detonation, under heavy acceleration.
Lets advance the cam just 2*
Static compression ratio of 9:1.
Ica of 52*, (108* LSA/ 2* advanced)
Effective stroke is 2.87 inches.
Your dynamic compression ratio is 7.80:1 .
Your dynamic cranking pressure is 157.15 PSI. ............... 157
V/P (Volume to Pressure Index) is 158 ........................... 158
Heck yah! Compare the above, to the below; both at 9.0 Scr
Static compression ratio of 9:1.
Ica of 56* (114LSA@ 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ............... 152
V/P (Volume to Pressure Index) is 147 ............................ 147
The only difference in these two is the LSA, and the 4* advance
Check out the HUGE VP increase from 147 to 158, this is soooo big, that you could actually run the next bigger cam,
Lets try a 260/268/110
Static compression ratio of 9.0:1.
Ica of 56* (110LSA cam at 4* advanced)
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.61:1 .
Your dynamic cranking pressure is 152.11 PSI. ................... 152
V/P (Volume to Pressure Index) is 147................................ 147
Look familiar? It is the same 56* Ica, so the numbers come out the same.... but the power is gonna be up maybe 15 hp..... with no loss of performance below 3000 compared to the 252/260/114cam. And now you know why I don't like wide LSA cams. When properly compared, they will cost you power every time. But worse is that they will also cost you hiway-mpgs every time
So why do people run wide LSA cams?
Because they reduce overlap and make the engine run smoother at low rpm, and if an engine is to run for many miles at very low rpm, like a city car would, then this has the bonus effect of increasing city-mpgs by virtue of mixture control. This is why your old LA318 had like 16* of overlap and 2.76 gears.... and idled around town at 35mph=1250rpm in Drive.
But the 340 had 44* overlap and ran 3.23s with a loose TC and 35mph was maybe 1500 in drive, but most guys were in second, cuz, you know, it's a 340, and we got a point to prove; so in second the Rs were around 2200.
At 2200 the overlap was NO LONGER AN ISSUE.
So knowing that now, lets look at your imaginary 252/260/114 cam, with it's 28* of overlap, and compare it to the 260/268/110 with its 44* of overlap.
As you can see the small cam will idle pretty much like a stock 360, cuz that's about what they had (maybe 24* I forget), and the bigger cam will idle like a 340, cuz it has the same 44*. And like the 340, on the hiway, it will like to be up around 2000/2200 for best mpgs. which is why I picked 2100 for you.
Yes there really is a method to my madness, lol.
OK just one more FYI
here we have the next bigger cam again, a 268/276/108customLSA cam
Static compression ratio of 9.6:1.
Ica of 56*(108LSA at straight up)
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 7.88:1 .
Your dynamic cranking pressure is 159.28 PSI. .................. 159
V/P (Volume to Pressure Index) is 148 .............................. 148
Notice I jumped the compression back up to 9.6
Notice the gas requirement at WOT is back up to probably 91
But notice the VP is up to about the same as the best of the other combos. So this combo will have another 15 or so hp , so now we are up at least 30hp over the 213* cam, but without any loss of low-rpm power. The penalty for this is that overlap is now 56*, and your hiway rpm or speed, may have to be increased to above 2100 to clean up the intake; say 2300, and so at 65mph (still with 28s) you will need a minimum 2.94s. This is the minimum; bigger is Ok. With 2.94s 75mph would be 2650 at zero-slip, which is 350 over 2300 so just a lil buzzy is all........ but a lot easier to engineer the ignition timing curve.
The whole point is this;
the cam and the pressure are like an old married couple, they hold hands in public, but sleep apart because they can't stand each others farts.
You'll get the best results when they are holding hands. If you just slam them together, chances are very good that the result will stink.
Last edited:
This is a carburetor thread, so I'll just say this about the cam thing.....maybe we can discuss it in another thread, but if you "hate" wide LSA over narrow, then you've learned incorrectly. They each have their place and every LSA in between. It's totally dependent on "WHAT" you're doing.
I will save any further cam discussion for a later time, because without having nailed down a car, I don't know if I'll be using an existing short block or building one from scratch. I think the carb selection will stay the same no matter what I find.
I am thinking of pulling the trigger on the carb with the black Friday sale at Summit. Can anybody tell me which mopar throttle adapter I need, same as for an Edelbrock or for a Holley?
Demon makes the correct one.
124007DEM
124007DEM
Just ordered the Street Demon 625 and the throttle adapter from Summit, 10% off plus another $25.00 discount and free shipping. Seemed like a good deal.
I got mine cut off today. And I mean SLAM cut off. I disassembled the primary throttle shaft and cut the WHOLE thing out from around the throttle shaft. It was more in depth than I wanted, but that fixed it. lol
Well that sounds like the right way to do it. My fix was a hack, and it looks like one, but it solved the hangup.
I received the Street Demon carb yesterday. It is a very nice piece, but I have to say that the throttle plates look smaller in person than in the pictures. The primaries are really tiny, and the secondary is really not any wider than a conventional square bore carb. Now I can see why they say that it will fit on a square bore manifold.
Could you possibly take a picture of this haircut you gave your carb? (Please)
I think I know what you did but, not sure.
Maybe those reading are interested too
Thanks for your input !
Could you possibly take a picture of this haircut you gave your carb? (Please)
I think I know what you did but, not sure.
Maybe those reading are interested too
Thanks for your input !
Sure, but it's hard to see. It was the phord transmission kickdown lever right behind the regular throttle lever on the carburetor. I'll get you a picture when we get back from town.
Gottcha! thank you !! those phords.....
I know, right? lol
Yep, great deal !
I wish I could have seen your thread a little sooner... Please forgive me for being so tarty.
I feel there's one more aspect that has not quite been covered..
The Holley design has always held it's superiority for HP return per CFM, but the AFB, and especially the AVS for it's metering capabilities. Which, when you boil it all down, is what you're looking for. Too bad the all aluminum body lends itself to heat soak, boiling, etc..
Trade-offs run a muck.
The biggest problem with this whole scenario is, when someone is trying to get their beloved muscle car to have the drive-ability of mom's Toyota with 40 yr old technology.
Kudo's to brother, AJ for taking the time to make this point. There's a lot gong on there, and it's most often overlooked.
My last engine was a 500 stroker, built with torque in mind, using a 750 Holley DP. My previous engine was a stock stroke 400 using an AFB. It was a very flexible street combination that made 450 ft/lbs of torque and 415 HP. The AFB ran well, but I hated the constant smell of gasoline in the garage as the fuel boiled out of the carburetor. The Holley solved that problem. I am now looking at building a slightly detuned version of the 400 I built, which will be easier for long distance cruising with a tall gear. I know there are trade offs, and I am not expecting Toyota mileage, but I think I can find a happy medium. Time will tell.
..and time well spent. glad to see you're ahead of the curve..
Go Mango
Never enough beer...
With the 1/2" thick carb gasket recommended by edelbrock, the heat soak on my '70 340 is non-existent. The original AVS had a problem with it with the standard gasket, but the AVS-2 with the thicker one has cured the problem. I was drawn to the AVS-2 because of the annular discharge secondaries, and haven't been disappointed.
Years ago I was a big fan of the Holley double pumpers, but now I'm not sure I'll ever buy anything but an AVS-2 unless I'm building an engine just for racing.
Years ago I was a big fan of the Holley double pumpers, but now I'm not sure I'll ever buy anything but an AVS-2 unless I'm building an engine just for racing.
Are you skeptical of its performance? I wouldn't be. Get it dialed in it may surprise you, especially its responsiveness. And as compared to other similar sized carbs it can hold its own, and may be better than many.....on the street, and impress at the strip. I've run the SD 750 on the street and strip, as well as an AED 750 DP. The Street Demon is a good performer
'76 Feather Duster
Member
I have the 703 cam in my 340 and it pulls 15 inches, its a larger cam so you should get your vacuum. And it has good bottom end, but I am running 3.23 gears with 28" tires.
Yes I was probably a bit skeptical after seeing it in person, I guess I was comparing it to my old 750 DP. The numbers work, so it should be what I need. I have to keep reminding myself I am not building a drag racer this time.
Yes, I was planning on doing that before I install it. Likely bounced around a lot during delivery.
-
