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  #21  
Old 02-01-2018, 07:22 AM
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Thanks Randy.

Awesome stuff. I just quickly looked it over, but I'm going to sort through it now.
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Old 02-01-2018, 07:57 AM
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No problem.

I was looking over things this morning. I guessed at the LSA. I didn't take into consideration any rocket arm ratio and the potential total valve lift.
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Old 02-01-2018, 08:47 AM
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Quote:
Originally Posted by Randy H View Post
I guessed at the exhaust port centerline.

Not sure about the degreed Centerline.

5.5mm valve stem? Now I'm thinking it should be 5mm.
5.5mm Valve Stem is correct. The new, non-Hemi's have the 5.0mm stems.

The info for the camshaft I have is..
102 ATDC Intake Centerline
111 Lobe Separation Angle

Since (ICL + ECL) / 2 = LSA
(102 + ECL) / 2= 111
102 + ECL = 222
ECL = 222 - 102
Exhaust Centerline = 120 BTDC

Since 0.050" Duration = 220 degrees,

ICL 102 ATDC
ECL 120 BTDC
111 LSA
0.050 Intake Opening = 8 BTDC
0.050 Intake Closing = 32 ABDC
0.050 Exhaust Opening = 50 BBDC
0.050 Exhaust Closing = 10 BTDC
0.050 Overlap = -2 degrees

Comparing to a CL1 camshaft to see if those number make sense...
ICL = 108.5 ATDC
ECL = 110 BTDC
109.25 LSA
0.050 Intake Opening = 1 BTDC
0.050 Intake Closing = 38 ABDC
0.050 Exhaust Opening = 40 BBDC
0.050 Exhaust Closing = 2 BTDC
0.050 Overlap = -1 degree


So the camshaft event timing I figured seem to be about right.

---------- Post added at 09:00 AM ---------- Previous post was at 08:59 AM ----------

Quote:
Originally Posted by Randy H View Post
No problem.

I was looking over things this morning. I guessed at the LSA. I didn't take into consideration any rocket arm ratio and the potential total valve lift.
I've read stock rockers are 1.05 :1 Ratio. Not sure if that applies to both non-hemi and hemi?

---------- Post added at 09:21 AM ---------- Previous post was at 09:00 AM ----------

Quote:
Originally Posted by Randy H View Post

- Induction System Tuned Lengths - ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 34.182 (usually this Length is never used)
2nd Harmonic= 19.401 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 13.544 (ProStock or Comp SheetMetal Intake • best overall HP )
4th Harmonic= 10.661 (Single-plane Intakes , less Peak Torque • good HP )
5th Harmonic= 8.650 (Torque is reduced, even though Tuned Length)
6th Harmonic= 7.277 (Torque is reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
The intake port in the head is just over 2" long.

If that inverted intake manifold is around 8.5" long (semi-circle with 2.7" radius), I am about right for the 4th Harmonic. Which is still too short and is reducing TQ.

If the total length of the manifold is closer to that of a semi-circle with 3.6" radius, then I could get the 3rd Harmonic, but looking at pics - 8.5" length seems about correct.

---------- Post added at 09:47 AM ---------- Previous post was at 09:21 AM ----------

Quote:
Originally Posted by Randy H View Post
--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
108 FPS at Intake Valve Curtain Area= 0.935 sq.in. at .280 Lift
114 FPS at Intake Valve OD Area and at Convergence Lift = .266
141 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 0.719 sq.in.
--- 5500 RPM Intake Cross-sectional areas in Square Inches ---
350 FPS CSA= 0.288 Port has Sonic-Choke with HP Loss ( too fast FPS )
330 FPS CSA= 0.306 Port may have Sonic-Choke with HP Loss ( too fast FPS )
311 FPS CSA= 0.325 Highest useable Port velocity ( possible HP loss )
300 FPS CSA= 0.337 Smallest Port CSA ( Hi Velocity FPS • good TQ and HP )
285 FPS CSA= 0.354 Smallest Port CSA ( very good TQ and HP combination )
260 FPS CSA= 0.389 Recommended average Intake Port CSA (very good TQ and HP)
250 FPS CSA= 0.404 Largest recommended average Intake Port CSA ( good HP )
240 FPS CSA= 0.421 Largest recommended average Intake Port CSA (less Peak TQ)
235 FPS CSA= 0.430 Largest recommended Intake Port Gasket Entry area CSA
225 FPS CSA= 0.449 Largest Intake Port Gasket Entry CSA ( Slow FPS )
215 FPS CSA= 0.470 Possible Torque Loss with Reversion ( Slow FPS )
210 FPS CSA= 0.481 Torque Loss + Reversion possibility ( too slow FPS )
200 FPS CSA= 0.505 Torque Loss + Reversion possibility ( too slow FPS )
Note : these are calculated average Port cross-sectional areas and FPS

--- Cross-Sectional Areas at various Exhaust Port Velocities (@ 28 in.) ---
99 FPS at Exhaust Valve Curtain Area= 0.866 sq.in. at .280 Lift
113 FPS at Exhaust Valve OD Area and at Convergence Lift = .246
139 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 0.616 sq.in. at 5500 RPM
--- 5500 RPM Exhaust Cross-sectional areas in Square Inches ---
435 FPS CSA= 0.197 Sonic Choke at Throat Area (too fast FPS velocity)
380 FPS CSA= 0.226 Sonic Choke at Throat Area (possibly too fast FPS)
350 FPS CSA= 0.245 Exhaust Port has Sonic-Choke with HP Loss (too fast)
330 FPS CSA= 0.260 Exhaust Port has Sonic-Choke with HP Loss (too fast)
311 FPS CSA= 0.276 smallest Exhaust Port ( very high velocity FPS )
300 FPS CSA= 0.286 smallest recommended Exhaust Port (Hi velocity)
285 FPS CSA= 0.301 smallest recommended Exhaust Port (Hi velocity)
265 FPS CSA= 0.324 Recommended average Exhaust Port CSA
250 FPS CSA= 0.344 Recommended average Exhaust Port gasket area
240 FPS CSA= 0.358 Recommended largest Exhaust Port gasket area
225 FPS CSA= 0.382 Largest Exhaust Port Exit gasket area (Slow FPS)
210 FPS CSA= 0.409 Largest Exhaust Port Exit gasket area (Slow FPS)
190 FPS CSA= 0.452 Torque Loss + Reversion + Scavenging loss (too slow FPS)
180 FPS CSA= 0.477 Torque Loss + Reversion + Scavenging loss (too slow FPS)
Note : these are calculated average Port cross-sectional areas and FPS
I think the throats in the hemi head (around the valve guides) are already bigger than the maximum recommended size. I tried to measure and got about 0.51 sq inches.

Ole4 took a mold and tried to measure and said closer to 0.54 sq inches.
The port opening (near the carb) is 0.75 - 0.80 sq inches.

https://www.oldminibikes.com/forum/h...ad-rework.html
In one of my books it states max airflow per square inch is 146CFM and according to Darin Morgan a good head should have 137CFM per Sq in. I'm sure none of mine come close but I am using that number just to see what the maximum amount of air that would be possible to flow thru the different sections of this port as is. The largest part of the port runner Max CSA (end where carb attaches) is .796 SQ inches. Using the 137CFM number it could flow 109CFM max. The port tapers down to where the bowl is machined to .543 Sq inches which would have a max flow of 74.3 CFM. The Bowl is .974 in diameter and is not tapered is able to flow 102 CFM. The actual port flowed a max of 47.5 CFM. I also took some pictures of the mold so you can see the tilt the runner has going into the bowl which creates a unequal Short side. If you look at how the runner enters the bowl it is offset to the left. I am just guessing here but I bet they designed the hemi without squish to reduce NOX emissions and designed this port for a lot of swirl to compensate.
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  #24  
Old 02-01-2018, 09:24 AM
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I used 50 CFM for the head flow. That's where the 96.26% VE comes from.

I think the DCR number is higher than some of the online calculators. There is a post on that in the Pipemax private forums. I'll have to find that and refresh my memory.

Here is a zip file of pdf's.
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  #25  
Old 02-01-2018, 10:46 AM
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Quote:
Originally Posted by Randy H View Post
I think the DCR number is higher than some of the online calculators. There is a post on that in the Pipemax private forums. I'll have to find that and refresh my memory.
.
That number seems high, which is what I want - but That number also seems big for pump gas. Looking quickly online. Seems like maybe 195 cranking psi for aluminum heads with 93 octane.

---------- Post added at 11:44 AM ---------- Previous post was at 11:41 AM ----------

The other thing I noticed was with the exhaust. Seems like exhaust (valve size) was optimized for higher RPMs than the intake. If the intake was 3-5k RPM, the exhaust was 4.5-6k RPM.

---------- Post added at 11:46 AM ---------- Previous post was at 11:44 AM ----------

I've also been wondering if an 18cc head with 25/24mm valves and smaller ports would be better. +0.020 Rod. 0.045" Gasket. 18cc head. Still about 10.25 static CR.
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Old 02-01-2018, 11:15 PM
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D = K x Square Root(C x n)

where:
D=carb diameter, in millimeters
K= constant between 0.65 and 0.90 (determines the smaller and the biggest diameter to be tested at the specific engine) 0.7seems to work well for our purposes.??? I'll use the low end with K=0.65
C=cylinder displacement, in cubic centimeters
n=RPM at peak power/1,000 (be realist, dreaming only will make you try carbs far bigger than the correct, with results below your needs)

K = 0.65
C = 212
n = 5500/1,000 = 5.5

D= K* SqRt(C*n)=
D = 0.65 * SqRt (212*5.5)
D = 0.65 * SqRt (1,166)
D = 0.65 * 34.15

D = 22mm
22mm carb for 212cc engine at 5,500 RPM

If I use 0.82 for my K-value, then...
D = 28mm


If I use 212cc and 4k RPM with K=0.65, then
D = 19mm
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Old 02-02-2018, 04:48 AM
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Deleted post.
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Last edited by Randy H; 02-02-2018 at 08:53 AM. Reason: CFM vs. Carb size confusion on my part.
  #28  
Old 02-02-2018, 06:25 AM
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But the magic number is always 28.
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Old 02-02-2018, 09:16 AM
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Quote:
Originally Posted by Randy H View Post
Deleted post.
I see the post was deleted, but I'll still post my response anyway. LOL

I agree that the CFM calculated requirements for the engine are much lower than what the carbs' "flowed" cfm numbers are.

If I tried to match a carb with cfm numbers matched to the engine cfm requirement, then a 3600 RPM 212cc with 0.8 V.E only needs 11 CFM or something. A stock carb has 4 times that flow.
Stock carbs have around a 16mm or 17mm venturi

Comparing CFM requirements to carbs' cfm (sizes that are actually used on these engines), there is a discontinuity.

If I tried to match an engine with the "flowed" cfm numbers from a 22mm carb (say the carb flows 88 cfm), my 212cc engine would need to turn 30,000 RPM.

I know people use VM22 carbs. I haven't yet seen a clone turn 30k RPM.

12.9 cubic inches, 30,000 RPM, VE = 0.8
CFM = 88

If I am I picking up what you are putting down, then in order to use a 22mm carby, a 212 engine needs 30k RPM.

This is part of the reason of my confusion. There seems to be a multiplying factor of 3 or 4 when comparing engine cfm requirements to the cfm numbers of the carbs that people actually use.
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Old 02-02-2018, 09:21 AM
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What about ambient air pressure, humidity, temperature? I think you are just scratching the surface, but it doesn't itch.
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Old 02-02-2018, 09:46 AM
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What about ambient air pressure, humidity, temperature? I think you are just scratching the surface, but it doesn't itch.
I think those factors would be more relevant to jetting and tuning and not as much related to actual size. But if you are a mountain person, maybe a bigger carb will help? Maybe it won't. Maybe you just get the same amount of thin air, but now it is moving slower?

I think the one way to size a carb would be to use a vacuum gauge.
Start with a small carb. Open WOT. Check manifold vacuum. Increase carb size until manifold vacuum reaches zero at WOT? If still reading vacuum at WOT, I think it means the carb is choking the engine.
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Old 02-02-2018, 11:19 AM
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Choking is the key. Without it, there is nothing.
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Old 02-02-2018, 11:28 AM
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Choking is the key. Without it, there is nothing.
That's what my lawyer said too. And since there is no evidence, the case should probably get dropped.
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Old 02-02-2018, 11:41 AM
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I think maybe the flow numbers used cause some discrepancy. CFM @28 inches, CFM @1.5 inches, CFM @3 inches.

Beyond calculations I know they're are some rules of thumb on carb size. Percentage of valve size, which is a percentage of bore size. But then this stuff is geared towards full throttle racing.

If I (ever) get healthy again, I've got a pile of engines and carburetors to test (butt dyno). I think building a low RPM very efficient engine isn't so easy.
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  #35  
Old 02-02-2018, 01:51 PM
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Pardon my interruption of this scientific jibber jabber but I have the GPS VM22 intake without the pulse fitting that I am not going to be using and also a set of shorter chromoly pushrods from NR racing that I am not going to be using if you are interested. They are both brand new. Let me know and I will gladly send them to you if you can use them.
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Old 02-02-2018, 02:19 PM
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Pardon my interruption of this scientific jibber jabber but I have the GPS VM22 intake without the pulse fitting that I am not going to be using and also a set of shorter chromoly pushrods from NR racing that I am not going to be using if you are interested. They are both brand new. Let me know and I will gladly send them to you if you can use them.
That is awesome!
Once I figure out what I want to do, I will let you know.
Still trying to make sense of bore, stroke, valve size, carb size,...
I think the mounting holes on that manifold are 48mm, which might work will some of the PZ carbs too.

Are the pushrods 5.440" (-0.100" from stock Hemi length)?
Those would probably work for me, unless I opted for a different head.

---------- Post added at 03:19 PM ---------- Previous post was at 03:15 PM ----------

Back to carb size...

If the throat in the head has a CSA of 0.54 sq inches....
0.54 = pi*r^2
r^2 = 0.54/3.14
r = 0.415
Diameter of Circle with area equal to port throat CSA = 0.83"

21mm
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Old 02-02-2018, 02:45 PM
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Looks like a no go on the pushrods. They are 5.260. Looks like they're for gx200 and 6.5 Chinese ohv. I bought them on accident. Here's a pic of the rods and intake I have.
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Old 02-03-2018, 02:23 AM
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Looks like a no go on the pushrods. They are 5.260. Looks like they're for gx200 and 6.5 Chinese ohv. I bought them on accident. Here's a pic of the rods and intake I have.
I still might use a clone head.
Not sure yet.

I'm trying to determine if I want a 25/24mm head or 27/25mm head.
I don't know if going smaller will be better. ???

I was reading up on some engine math stuff....
I posted this on one of the other builds too.
https://www.cartechbooks.com/techtip...e-performance/

This applies to throat CSA and Valve size.
If using a 1.06" (27mm) intake valve, the flow diameter of the valve is about 1.06" - 0.04" = 1.02" (accounts for width of valve seat).

This article says you want port throat diameter =
85% of valve flow diameter for a street engine.
90% for race engine

1.02" Valve Flow Diameter * 0.85 = 0.867"
Valve Flow Radius = 0.434"
Area = 3.14 * r^2 = 0.59 sq inches

The article is saying that for a street engine using a 27mm intake valve, the intake port throat CSA should equal 0.59 sq in.

The measured throat CSA of 0.54 sq inches means I'm at 81%, not 85 or 90% of the valve flow diameter. I'm fine with that. It wouldn't take much dremel work to go from 0.54 sq in to 0.59 sq in CSA if I wanted to.
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Old 02-03-2018, 08:02 AM
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Don't take this personal, but do you really think 2mm difference in valve size is going to make any noticeable difference??? If you are building this engine for 5500 rpm and low end torque then use the clone head and 22 mm carb. If your building an all out high rpm race motor use the biggest valves and carb along with everything else (stroker crank, largest bore piston, highest lift cam) you can possible get for this engine. I just think your way over thinking your build.
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Old 02-03-2018, 09:24 AM
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Don't take this personal, but do you really think 2mm difference in valve size is going to make any noticeable difference??? If you are building this engine for 5500 rpm and low end torque then use the clone head and 22 mm carb. If your building an all out high rpm race motor use the biggest valves and carb along with everything else (stroker crank, largest bore piston, highest lift cam) you can possible get for this engine. I just think your way over thinking your build.
The whole point is to overthink the build and learn everything I can. Keeps me thinking instead of spending money.

Why not a big bore and stroker crank for low end? Thatís where the biggest torque gain would come from, unless Iím mistaken. Thereís a reason a 420 has double the torque of a 212.

Going from a 25mm to 27mm Valve is a bigger jump than upgrading a 27mm to a 28.5mm Valve. So does this means everybody upgrading
to a 28.5mm valve in a Hemi Head is wasting time?

I really hate when people tell me Iím overthinking things.
Sounds like a response the nuns would give me when I started raising my hand during religion classes at my Catholic grade school.

Increasing 25mm valve to 27mm valve increases Valve Curtain Area by around 8%.
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