Anyway to calculate vacuum from camshaft overlap? - LS1TECH - Camaro and Firebird Forum Discussion

 Generation III Internal Engine 1997-2006 LS1 | LS6 Sponsored by:

# Anyway to calculate vacuum from camshaft overlap?

 03-15-2017, 10:07 AM #1 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 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?
 03-15-2017, 06:30 PM #2 Restricted User   Join Date: Mar 2014 Location: Ohio Posts: 4,874 Lance Nist (Pantera EFI) will do it for you if you give him the rundown on the combo.
 03-15-2017, 09:00 PM #3 That's MISTER MODERATOR iTrader: (9)     Join Date: Nov 2005 Location: NYC Posts: 7,441 I'd like to know how that's done.
 03-15-2017, 09:15 PM #4 11 Second Club iTrader: (2)     Join Date: Feb 2011 Location: Fredonia,WI Posts: 3,110 Way too many variables. Even the efficiency of the exhaust system affects the vacuum since overlap is present
 03-15-2017, 09:30 PM #5 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 I know there are a lot of variables. But there has to be a method to ballpark this stuff. It's just math.
 03-15-2017, 10:18 PM #6 Restricted User   Join Date: Mar 2014 Location: Ohio Posts: 4,874 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.
 03-15-2017, 10:50 PM #7 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 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.
 03-16-2017, 11:45 AM #8 LS1Tech Sponsor   Join Date: Jan 2009 Location: Santa Ana, CA. USA Posts: 1,256 Eap @ 23 cfm 15 hp HI Jake, your report was provided in your Advanced Engineering thread. Lance
 03-16-2017, 02:11 PM #9 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 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!
 03-16-2017, 05:28 PM #10 10 Second Club iTrader: (24)     Join Date: Aug 2004 Location: FL Posts: 5,997 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.
 03-17-2017, 11:21 AM #11 LS1Tech Sponsor   Join Date: Jan 2009 Location: Santa Ana, CA. USA Posts: 1,256 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. Lance
 03-19-2017, 09:47 AM #12 TECH Resident iTrader: (3)     Join Date: Nov 2011 Location: Sonoma Co. Ca. Posts: 863 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
 03-19-2017, 10:07 AM #13 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 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.
 03-19-2017, 10:36 AM #14 TECH Fanatic   Join Date: Aug 2009 Location: Coast of San Mateo County Between Pacifica & HMB Posts: 1,172 Jake, What about a Nitrous exhaust port and +6-8* split VS 12* or are you running 200+ N2O?
 03-19-2017, 10:53 AM #15 TECH Fanatic   Join Date: Aug 2009 Location: Coast of San Mateo County Between Pacifica & HMB Posts: 1,172 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!
03-19-2017, 10:58 AM   #16
TECH Fanatic

Join Date: Mar 2012
Location: South Florida
Posts: 1,187

Quote:
 Originally Posted by 64post 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?

 03-19-2017, 11:05 AM #17 TECH Fanatic   Join Date: Aug 2009 Location: Coast of San Mateo County Between Pacifica & HMB Posts: 1,172 244*/250* 114*+3* with good ring seal and 11.5:1+ Comp should have ~ 11-11.5" @ 950 RPM.
 03-19-2017, 12:37 PM #18 Super Hulk Smash Thread Starter iTrader: (7)     Join Date: Aug 2004 Location: Pace, FL Posts: 10,032 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.
 03-19-2017, 01:46 PM #19 TECH Fanatic   Join Date: Aug 2009 Location: Coast of San Mateo County Between Pacifica & HMB Posts: 1,172 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.
 03-19-2017, 06:02 PM #20 TECH Addict     Join Date: Sep 2014 Posts: 2,461 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.

 Related Topics Thread Thread Starter Forum Replies Last Post JakeFusion Advanced Engineering Tech 8 03-16-2017 04:36 PM REDL1NE Conversions & Hybrids 7 01-06-2017 10:22 AM jchevy Conversions & Hybrids 4 09-05-2016 08:43 PM AB6DO Conversions & Hybrids 1 03-11-2016 10:52 AM AB6DO Conversions & Hybrids 2 03-11-2016 09:58 AM

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

All times are GMT -5. The time now is 04:39 AM.