Anyway to calculate vacuum from camshaft overlap? - LS1TECH



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Anyway to calculate vacuum from camshaft overlap?

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Old 03-15-2017, 10:07 AM   #1
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Default Anyway to calculate vacuum from camshaft overlap?

As the title says... is there any rule of thumb way to do this?

I know rings, compression, engine size, and intake manifold design all play a role in vacuum... but the cam is still the biggest variable in how much vacuum you'll pull.

Is there a way to calculate this?
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Old 03-15-2017, 06:30 PM   #2
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Lance Nist (Pantera EFI) will do it for you if you give him the rundown on the combo.
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Old 03-15-2017, 09:00 PM   #3
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I'd like to know how that's done.
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Old 03-15-2017, 09:15 PM   #4
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Way too many variables. Even the efficiency of the exhaust system affects the vacuum since overlap is present
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Old 03-15-2017, 09:30 PM   #5
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I know there are a lot of variables. But there has to be a method to ballpark this stuff.

It's just math.
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Old 03-15-2017, 10:18 PM   #6
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It is just math, but some of the factors you need to know to make it easier to calculate can only be gotten from an engine that's already running, at which point you won't need to do the math in the first place.

Cam specs will be biggest factor, idle speed being 2nd, idle airflow being 3rd.
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Old 03-15-2017, 10:50 PM   #7
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I'm curious as to what a 244/256 114 cam would do on a 12:1 CR 408 with TFS 245 heads.

With the 373s I'm installing, I'm setting it so lockup won't happen until after 50mph. So, I'll never cruise below 1800RPM. So I can run almost any reasonable hydraulic cam and with that much engine speed, it should drive fine. The only issue is what will it pull at idle? 10" of vacuum?

Still weighing the Procharger on the current setup vs a big motor. Price is better on the 408...

I don't have to lockup at 50... but with the Kooks drone at 1600-1700rpm, I actually clear it by locking up later. Can't do that right now with the 323s unless I want lockup at 65.

So it does present some differences in what I can do for streetability.

Of course, the easiest issue is to cut off the bullets and put some Magnaflows in there. With the Procharger, I'd probably do that and lockup at 40 with the current setup. That's still 1400rpm. I figure the 244/256 114 would drive fine there too. My 234/242 111 drove fine above 1400 and it had 16 degrees of overlap in a 346 and had 9.5" of vacuum with 11.2:1 CR. I figure the 244/256 114 would drive better than that with the added cubes and compression. But I'm just wondering how much better?

Last edited by JakeFusion; 03-15-2017 at 10:57 PM.
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Old 03-16-2017, 11:45 AM   #8
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Default Eap @ 23 cfm 15 hp

HI Jake, your report was provided in your Advanced Engineering thread.

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Old 03-16-2017, 02:11 PM   #9
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Thanks Lance!

I need to get EAP. That's a cool program. The overlap there is pretty horrific @ 7.5" hg with that cam.

So D1SC it is!
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Old 03-16-2017, 05:28 PM   #10
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Also that blower will help get some extra air into the motor even at idle or cruise so I think overlap is a little more palitable.
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Old 03-17-2017, 11:21 AM   #11
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Default SC Camshaft Design

Hi Jake, yes your SC choice may be WELL educated.

I have had good luck with turbocompressor pumps.
I have NRAC design software.

I have installed them the Pantera, over the transaxle, belt drive from a pulley on the flywheel.
I have also used them on boats and sold many ECU-882C's to LS/SBC/BBC Centrifugal users.
I have made Charge Coolers the use the AC system present on the car.
I have installed a SC on a Ford 5.4 supercharged Raptor Truck for Chet H. with that same Freon Intercooler with Charge Air COLDER than Ambient AIR.

I have had Crower Cams grind cams to my specifications.

My suggestion 224/256 .627/.550 @ 124 C/L.

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Old 03-19-2017, 09:47 AM   #12
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This how to calculate: for every $1K you spend on your motor you lose .69 in. of vacuum.

I have 23* of overlap and about 11- 12in at warm idle
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Old 03-19-2017, 10:07 AM   #13
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Well that cam was 22 degrees in a 408-418. I can't imagine it'd be at 6-7" when so many people run cams that size.
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Old 03-19-2017, 10:36 AM   #14
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Jake,
What about a Nitrous exhaust port and
+6-8* split VS 12* or are you running
200+ N2O?
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Old 03-19-2017, 10:53 AM   #15
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Just re-read other post with flow #s.
My .02, 4-6* Split will hit your goal by
7000 RPM! in a hydraulic with your exhaust
port and system.
You have Way to much overlap for you're
E/I Ratio even with LLSR & 8000 RPM!
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Old 03-19-2017, 10:58 AM   #16
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Quote:
Originally Posted by 64post View Post
This how to calculate: for every $1K you spend on your motor you lose .69 in. of vacuum.

I have 23* of overlap and about 11- 12in at warm idle
Lol.

Man. That actually looks pretty good. My 383 with only 5* of overlap makes around 12-14in at idle. 750-800rpm. I wonder if it's the manifold you have on the car. Maybe smaller overall area inside? What rpm is it idling?
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Old 03-19-2017, 11:05 AM   #17
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244*/250* 114*+3* with good ring seal and 11.5:1+ Comp
should have ~ 11-11.5" @ 950 RPM.
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Old 03-19-2017, 12:37 PM   #18
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NAVYBLUE210 - it's a proven camshaft that makes 600rwhp in an F-body with a 416 with those heads. So that's why I'm considering it.

If I could hit 575 through a locked automatic, it'd be a lot of fun. And then throw 300 shot on top of it.

But of course the current setup with the D1 would do 650-670 on low boost and probably close to 800 with Meth and max boost.

The difference is I'm idling around 14" of vacuum now and the car drives pretty awesome. Going to a larger cam/motor combo - if I'm idling at 8" or so of vacuum - is not something I want to do since it's a street car. Though, the 416+nitrous would outrun the D1SC at the track. By a pretty wide margin.
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Old 03-19-2017, 01:46 PM   #19
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It may have made 600 RWHP NA but I still stand by my statement,
80% E/I ratio does not need more than +4-6* exhaust split NA,
HR, up to 7000 RPM through 1 7/8" LTs with 3" true duals.
More exhaust split then needed
= Lost/Wasted Torque & Vacuum!

64 Post with 243/251 with Dart 225s, maybe 75% E/I, 517/383".
Jeremy's 416", MAMOFIED AFR 230s, ~ 75% E/I, 243/247,
663 FWHP, 580 RWHP M6 Firebird.
SpeedTigger's 403" LLSR with 12* split designed for
300 shot N2O going bottom 10s NA with +400 lbs!

I would go MMS LS3s. LLSR 245/253, 114+3 .670"/.640",
FAST 102, standard runners on street, shift ~6600-6800,
Mid-Length @ Track shift ~7600-7800 RPM.
9 seconds at the track, mellow 12" vacuum on street.

With the 245s mentioned, LLSR, 247/251, & MAMMOFIED MSD.

Last edited by NAVYBLUE210; 03-19-2017 at 01:57 PM.
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Old 03-19-2017, 06:02 PM   #20
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If I was go do a hydraulic roller motor with a Fast 102 I see no need for a square port cylinder head for a 402-418ci setup.

Me personally I would do a set of Tooley 245 heads rubbed over with the intake ported to match then a badass setup from nitrous outlet if I was go spray. Maybe even a direct port nitrous setup.

Plenty of cars running 9s and 10s on motor with a Fast intake and hydraulic roller with cathedral heads 205cc-245cc intake runner.
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