Cam overlap vs idle quality. 006" lift is the same as a solid .

Cam overlap vs idle quality If closing the exhaust valve earlier improves idle, then it suggests that this is the valve event mainly determining idle quality. Scotty J. Lobe separation affects valve overlap which in turn affects the power curve of the engine, idle quality and vacuum. Combustion characteristics play an essential role on the Mar 8, 2013 · You are barking up the wrong tree. As for a cam for low speed torque vs high speed output, you influence that with overlap. To decide what cam you need the main factors are idle quality, type of driving, and vehicle weight. Apr 5, 2016 · Idle Vacuum is Reduced Idle Quality Suffers Open Valve-Overlap Increases Closed Valve-Overlap Increases Natural EGR Effect Increases Decreases Piston-to-Valve Clearance Widen (larger LSA number) Raise Torque to Higher RPM Reduces Maximum Torque Broadens Power Band Reduce Maximum Cylinder Pressure Decrease Chance of Engine Knock May 13, 2003 · Im still looking at different cams for my 396. 006" lift is the same as a solid Dec 17, 2009 · If the LCA is too tight the motor needs to turn higher rpms before it comes on-the-cam and the idle is rougher. This affects both the power band and driveability. 5, 1000 RPM, but it doesn't seem to like it. 050" vs Idle Quality. When you keep the cam duration and overlap mild for idle quality the top end power is going to be limited. Dec 4, 2020 · Walter R. I've got a LS2 with a cam that has 15* of overlap. Dec 29, 2015 · For example, an oval-track small-block that needs to motivate the car off the turns quickly might have a narrow LSA of around 106 degrees, resulting in more overlap. inefficient combustion since part of the intake charge can go directly out the exhaust valve Jul 29, 2016 · Reducing the valve overlap thru speading the LSA and reducing the intake and exhaust duration while keeping the same intake closing and exhaust opening, will as a general TRENd reduce peak torque, improve idle quality and idle vacuum, and usually also reduce horsepower a bit too. Will Camshaft 2 have a Lumpier idle than Camshaft 1, due to the 5. 8 to 15. 7's advanced 2*. 211/230/112 stock HO cam, -3. Overlap is the most important parameter effecting idle and off idle quality. A cam cannot be a big cam and a small cam at the same time. Vac table, is this the correct one? Thanks for the help! Feb 1, 2007 · Short duration cams can maintain decent idle quality and vacuum with tighter LSA's while boosting low and mid-range torque because they still have relatively short overlap. Open up the LSA to 112°-114° and it will idle smoothly with only a hint of a cam. Yes a cam can be installed way ahead to crutch idle but guess what? 80° overlap hyd roller cam vs 80° solid roller idle quality. 7) to 16. 250" lift backwards. Make a smooth ramp as the RPM increases. 28 g/cyl inclusive (HPT > Engine > Spark Control > Spark Advance > Idle Spark Advance (in Park). 050-inch lift. Pontiac stroker, which uses a 4. Overlap triangle seemed like a As overlap increases, this tends to make the engine idle quality more erratic or lumpy, while improving mid-range and top-end power. Feb 3, 2018 · The larger the cam duration number in degrees, the longer the valve is held open. 181" bore, 4. Is this too rough for the street. the late IVC isn't worth worrying about as the effects would seem to be far less significant at idle than other things. Greater overlap ATDC will show lower vacuum. Im looking for advice in layman's terms on the below: Dec 6, 2023 · A typical 350-based street engine can usually handle a cam grind with up to 60 to 70 degrees of valve overlap and still have enough manifold vacuum to operate power brakes. 5* overlap, pulled 18" vac 231/239/110, 60212, 15* overlap, pulled 13-14" vac Mar 22, 2012 · I think 60 degrees is starting to get a little nasty for traffic. Apr 5, 2016 · Idle Vacuum is Reduced Idle Quality Suffers Open Valve-Overlap Increases Closed Valve-Overlap Increases Natural EGR Effect Increases Decreases Piston-to-Valve Clearance Widen (larger LSA number) Raise Torque to Higher RPM Reduces Maximum Torque Broadens Power Band Reduce Maximum Cylinder Pressure Decrease Chance of Engine Knock 80° overlap hyd roller cam vs 80° solid roller idle quality. 8 in-Hg (inches of mercury). 050 cam A has a fairly rough idle,idles at 900 RPM cam B has a lope at idle,idles at 700 RPM Question is can 8 degrees difference in 050" overlap cause much difference in idle quality? Jan 17, 2006 · The LSA has more effect on idle quality than the advertised overlap does. 31 posts 1; 2; 3; Next; Procharged 434 Pro 80° overlap hyd roller cam vs 80° solid roller idle quality. Car was tuned few weeks ago. 80° overlap hyd roller cam vs 80° solid roller idle quality. The more overlap the more pronounced the effect. Although the overlap period is the same, how much ill effect will the later closing intake on the wider cam have over the tighter one? Jun 11, 2023 · I had a cheap customer buy my cam but not the expensive shim under bucket package . There is a formula for determining your overlap and resultant idle Apr 28, 2010 · Re: 80° overlap hyd roller cam vs 80° solid roller idle quality Post by thisispeace » Wed Apr 28, 2010 10:11 pm If I recall, solids open at the seat a little sooner since they have a bit of slow acceleration at the beginning of the lift curve to reduce contact stresses. Nov 13, 2012 · Cam companies assume everyone has a 350 chitbox engine. 31 posts Previous; 1; 2; 3; Next; pastry_chef Pro Posts: 240 80° overlap hyd roller cam vs 80° solid roller idle quality. Jul 29, 2016 · Comp Cams make a series of cams that are all noise and no go, the Thumper series that are marketed to be noisy at idle. 05” that better predicts idle quality? Second, is the answer to the idle quality question very different with EFI May 28, 2007 · C6 Tech/Performance - CAM idle quality factors - Does advancing a cam affect idle? IE: does a 224/228 on a 114 idle better than a 224/228 on a 114+2? From another thread: The LSA is only one factor that will affect your idle, the other is the duration. It fools your wideband. 1 just scoped out isky and they have a 290/290 250/250 @. But even then, matching engine components to the camshaft is critical for it to perform efficiently. Is this leaner idle parts from the cam overlap? Jul 3, 2021 · That's a significant difference. Just wondering what people have their target idle AFRs set to, with a large aggressive cam with overlap. 050 vs 254 for the GM, likely showed up in idle quality, and still let the Boss pull away up top. Regardless of how you install the cam either advanced or retarded, the duration remains unaffected. Nov 21, 2006 · If you want it to be a touch lopey sounding, use a roller with a really fast exhaust opening ramp and then use good quality headers. 006" lift is the same as a solid . "AKA" The "Mad Porter" "EMC 2006" 3rd place finisher Nov 25, 2006 · As long as you are using advertised duration, that formula is correct. Moderator: Team. A long (depending upon your displacement) duration cam with 104° to 106° LSA will be extremely radical. i have an LT4 stroker running an OBD-I ecm, and 70 degrees of overlap. 3 afr. More duration increases overlap and a tighter lobe separation also increases overlap. The fast ramps will put a more forceful exhaust pulse in the exhaust giving it a slight tick-it sound. For the street, you want a cam that offers a compromise–decent idle quality, respectable vacuum for operating power brakes and such, and good overall power production. The E cam has less durration, no overlap, but more lift. Sep 19, 2021 · ptuomov wrote: ↑ Mon Sep 20, 2021 12:40 am I don’t know the answer to any of these questions, but I do have two thoughts or really further questions: First, for idle rpm (and throttle cracked cruise rpm) engine operating conditions, is it the seat overlap or the overlap at 0. Feb 21, 2017 · Idle quality was rough and the vacuum gauge showed only 9. For example, almost all Comp street cams use a 110-degree lobe separation angle. And that sounds about right for the amount of overlap on a cam with 292 advertised duration on the intake. Do sweeps of intake cam with the exhaust cam fixed, then do the same with the exhaust cam. General engine tech -- Drag Racing to Circle Track. 050" lift. 006" lift is the same Jan 2, 2012 · A cam with a narrow LSA (104-108 degrees) offers greater low and midrange torque production, but a narrower operating range, a choppy idle, and less engine vacuum. I get how overlap is calculated. Smaller LSA results in a broader power-bands and improves low-end torque and idle quality. 5° more of Overlap at . 31 posts Previous; 1; 2; 3; Next; pastry_chef Jul 7, 2004 · A bigger engine needs a more aggressive cam to have the same powerband and idle quality as a smaller engine. 006" lift is the same as a solid May 31, 2004 · The piston is down the cylinders some amount before the exhaust valve closes. May 1, 2015 · All camshafts feature something called overlap. I have found that I get the best vacuum (about 50 kpa) with an idle of about 1200 rpm, lower than that and the idle kpa moves up into the low to mid 70's at about 900 rpm, and below 900 rpm the idle kpa is in the 80's. i rescaled the timing vs map tables, knowing the manifold vacuum for a given engine load would Dec 3, 2011 · Cams over 15º overlap, idle 950-1100 all cells across the board, add 3-4 g/sec to idle airflow across the board both in P/N and in gear (HPT > Engine > Idle > Idle Airflow > Base Running Airflow), add 6º of idle timing 1200 rpm and under and 0. Battery Voltage vs. But then you have the question of LSA. 560 lift on a 108 LSA. Now your observations make sense. Jun 10, 2024 · This affects engine idle quality, engine vacuum levels, throttle response, and overall performance. Nov 29, 2021 · Camshaft Overlap@. That shouldn't matter. If you combine the lobe separation angle with half of the overlap, then multiply that by 2, you get duration. this was a tip from edcmat-l1 i also feel that tuning for 14. Jun 18, 2024 · A tighter/narrower lobe separation angle will result in a greater overlap area, and presumably a more rumbly idle. Without a multi gas analyzer you will be tuning by idle quality errrrr feel. I'll start from the last and go in logical order. values are determined by separate factors: max. It decreases idle quality with no benefit. Tightening LSA increases overlap, the prime reason for rough[er] idle & loss of idle vacuum. Malik wrote: ↑ Sat Dec 05, 2020 4:23 pm Valve OVERLAP and the size of the engine are what will change idle quality and off idle response the most. Sep 10, 2021 · Hi all. I have the B cam on 1. no cam will ever drive like stock because it is not stock. As we show in the graphs below, as the centerline of the two traces get closer together, the overlap area grows. 050" which means not very much overlap. 050", even though they are similar comparing them at . 050 would idle pretty rough in a Aug 11, 2009 · Wouldn't it mostly depend on how much the overlap is reduced? Assuming the same duration on intake and exhaust, reducing duration by 5 deg on both would cut overlap by 5 deg. Nov 22, 2010 · I flow my heads in reverse all the time and almost every time they flow more up to about . Test 1 was easy. Brul spun the engine over with the dyno's starters and recorded 185 psi of cranking compression. Shouldn't I be able to get near stock idle quality and fuel economy from that? It does have a decent amount of lift and duration, just no overlap. 006" lift is the same as a solid Oct 9, 2022 · Hi All. Long duration cam (and specialty cams like the Comp Cams Thumpr) increase this amount of overlap. I'm dealing with the cam that is already in the engine using the other parts I Already Have. But the end result is a loss of performance (the all noise and no go thing. Low vaccume, much rougher idle. There is a page at my site that has some overlap info. Big cams with a bunch of overlap wont achieve full combustion at idle so they end up giving misleading O2 readings. 006" lift, but the two are very different when calculated at . Don't care where the cam is installed the overlap period is the same regardless. 31 posts 1; 2; 3; Next; Procharged 434 Pro Posts: 222 Jan 21, 2023 · Widebands "can" read leaner than actual with a really lumpy cam, so yes, feed the engine what it wants, not numbers that you think it wants. Lobe Centerline – The highest lift point of a cam lobe, expressed in crankshaft degrees. Fueling is on point for cruising and wot. I'm kind of a vag with street cams though. Aug 9, 2024 · Too little overlap may limit performance, while excessive overlap can lead to: Reduced Low-End Torque: Excessive overlap can create significant pumping losses at lower engine speeds, resulting in reduced torque. Pontiacs are not big revers. Is this a car you will drive every day? Is it a race car? Will it need to idle in traffic with AC on? Jul 26, 2020 · If I advance the cam or retard the cam what will that do to the idle quality? In my original post I used a TFS2 cam as an example for easy reference. That means no vacuum during this time. Sep 19, 2021 · As you can see, both camshafts have similar Overlap when calculated at . 006 and . 31 posts Previous; 1; 2; 3; Next; pastry_chef Pro Posts: 240 Mar 27, 2017 · However you can advance or retard the cam in relation to the crank when it’s degreed-in which alters the lobe centerline. 006" lift is the same as a solid Sep 22, 2021 · Camshaft Overlap@. Some comparison of overlap vs idle quality for cams that we ran, either Vince or my motor over the past 5 years. Jan 31, 2016 · I just installed a larger camshaft with more valve overlap, and have run into several differences in engine operation. A narrow, more specific power band is also a product of a narrow LSA, as is a lumpy idle quality–often referred to as the 106 sound. cam A- 60 degrees overlap seat to seat, 12 degrees overlap @. 006" lift is the same as a solid 80° overlap hyd roller cam vs 80° solid roller idle quality. 006" lift is the same as a solid May 5, 2016 · I once used basically a 240* cam with 125 ICL and it idled like a 210* cam on 110ICL because it had almost identical overlap triangle and the lift at tdc as stan says is a quick indicator. I learned this from a Lunati grinder who is retired. Feb 1, 2011 · Idle would be a little racy with the 227/241 on 107LSA, but nothing that I would consider too radical. His car made 1 More HP than my car did . The exhaust scaveging action of tuned tubular exhaust will be Oct 8, 2012 · This is the required intake adv duration based on the LSA and overlap you choose. 800" rod. When this occurs, there is usually Dec 11, 2002 · Yes duration does effect overlap but the LSA is the main factor for overlap. duration, LSA (overlap), and ramp speed. The advertised cam overlap range and what you want out of it. Nov 4, 2010 · Id bet a lot FEWER than you might think! Ive asked questions that they HAD to know to degree in a cam and gotten THAT "deer in the headlight stare" several times, from the guy who claimed to have taken the time and charged for degreeing in the camId bet many of them think degreeing in a cam means, installing the timing set DOT-TO-DOT Hello all. 006" lift is the same as a solid May 29, 2015 · A few rules of thumb based on what we've seen: Don't go too crazy with intake cam advance at idle. As soon as I rev or give any throttle it goes to where it needs to be commanded. Not the lopey idle you want, but a nice sound anyway. A solid cam will behave like a hydraulic with approximately 10 degrees less duration at . May 31, 2023 · The lobe separation angle (LSA) influences an engine’s performance by determining the exhaust and intake valve overlap. Decreased Overlap: Improves low-end torque and idle stability but reduces high-end power. Nov 11, 2016 · Bu too much overlap can really hurt the off-idle performance so the cam companies typically advance the intake lobe and retard the exhaust lobe to maintain a decent lobe separation angle. I have in front of me a cam test done with three Isky cams, identical except for LSA, which were 106, 108, 110. And yes that cam will lope fairly hard. Jan 13, 2018 · LSA's do indeed affect idle vacuum, when no other cam parameters are changed, as in the case the OP mentioned. Idle vacuum was 4, 5 & 6 Mar 5, 2004 · Using those numbers that cam has 3 deg of overlap @0. Ford had a fair chunk more lift via the rockers, but 228@. I know how to help idle quality-most don't. It takes a big cam to get peak HP to 6000 rpm in a Pontiac. The solid lifters idle better and the total off the seat time is about 11- 12 degrees shorter vs the hydro package. The more overlap you have "typically"; the rougher the idle will be; the less manifold vacuum you'll have; the chances are GREATER that you will NOT pass emmissions; just to name a few. Jun 1, 2023 · Many sources say that advancing the cam - earlier intake valve opening, and earlier exhaust valve closing - improves idle. 006"? Oct 9, 2011 · You can see the trend in factory spec'd cams which shows as the cam gets more aggressive leaning towards high end power, overlap moves from negative towards positive duration of overlapping valve events to take advantage of the exhaust pulling the intake charge into the cylinder. LSA determines the cam’s timing, and it has an effect on torque, tone, and rpm range. 5) because apparently with a large cam with overlap, what the WBO2 sensor is seeing May 26, 2004 · The B cam has more durration, alot more overlap, but less lift. Sep 16, 2003 · In particular, the increasing daily use of vehicles in urban traffic bestows more and more importance on the engine idle quality. Can the experts confirm? Mar 18, 2024 · A smaller angle may result in less valve overlap and less overlap can mean more low-end torque. Increasing the duration or decreasing the lobe separation cause an increase in overlap. i. 050), idle quality and especially idle vacuum are effected by where the overlap occurs. If you were to temporarily run that SFT cam at near 0 lash the idle quality would change in a hurry. LSA directly influences valve overlap, which affects the nature of the power curve, idle quality, idle vacuum, etc. I understand on basic level how cams work , intake exhaust open close and lift rates / durations. 05 with . A large overlap causes a rough or lopey idle. explain this: Not my position to be a teacher. A narrower LSA may produce a rougher idle and a wider one a smoother engine operation. Widening LSA 2 deg would cut overlap by 4 deg. I ordered an MPVI2 so I can play with it, but everything I've read about cleaning up idle and cruise relates to dealing with overlap. Oct 11, 2024 · The amount of camshaft overlap significantly affects engine characteristics: Increased Overlap: Enhances high-end power but may compromise low-end torque and idle quality. The higher the overlap the higher the rpm where peaks occur. Jul 28, 2006 · Overlap determines idle quality. So those type of "rough" "choppy" "loopy" comments apply to those guys. Overlap determines where the powerband will fall in the rpm range. 00 (14. The idle is pretty jumpy from 1. Does this mean that a hydraulic roller cam with 80° overlap at 0. In other words, a cam with 230 degrees of duration at . Thinking of changing the Target AFR to something very lean (14. A narrow LSA is one that is considered 110 degrees or less result in more overlap between the intake and exhaust valve opening and closing events, promoting higher engine performance but potentially compromising idle quality and low-speed Sep 19, 2021 · ptuomov wrote: ↑ Mon Sep 20, 2021 12:40 am I don’t know the answer to any of these questions, but I do have two thoughts or really further questions: First, for idle rpm (and throttle cracked cruise rpm) engine operating conditions, is it the seat overlap or the overlap at 0. It has an overlap of 74. Jul 19, 2006 · Idle Vacuum is Reduced Idle Quality Suffers Open Valve-Overlap Increases Closed Valve-Overlap Increases Natural EGR Effect Increases Decreases Piston-to-Valve Clearance Widen : Raise Torque to Higher RPM Reduces Maximum Torque Broadens Power Band Reduce Maximum Cylinder Pressure Decrease Chance of Engine Knock Decrease Cranking Compression Feb 26, 2016 · This is the reason that Lobe Separation Angle alters valve overlap as it also changes the four valve timing events of a camshaft. 7 is wrong, we should be allowing the vehicle to find stoich with its own o2's. Camshaft overlap is the angle in crankshaft degrees at which both the intake and exhaust valves are open at the same time. 55 degrees of overlap on a 112 cam is a different horse than a 108. You need to stick to the specifics of your motor to fix the problem. As duration increases the difference in overlap between otherwise identical cams increases with the tight LSA cam having more degreees of overlap which has a more pronounced affect on idle quality and vacuum and the RPM at Camshaft Overlap@. May 9, 2006 · If you want to measure overlap at whatever degree and attempt to compare cam "A" to cam "B" for a given engine, I suppose one could do that. For a symmetric lobe, the centerline is the Camshaft Overlap@. Dec 1, 1998 · Cam companies often grind their street cams advanced (4 degrees is typical), which allows the end-user to receive the benefits of increased cylinder pressure, yet still install the cam using the Apr 28, 2010 · 80° overlap hyd roller cam vs 80° solid roller idle quality. This cam is between a TFS2 and TFS3. May 4, 2016 · I suspect that there's so little flow when the valve is close to the seat that the slow ramp rate cams with larger seat-seat overlap numbers don't experience much more reversion than a faster ramp cam, so a slow ramp cam with 60 degrees of overlap can sometimes idle smoother than a fast ramp cam with 50 degrees. What are the exact cam specs? Feb 10, 2009 · That's a ton of overlap, it's gonna look lean from all of that fresh air making it's way out through the open exhaust valve. We haven't discussed the cam's limit speed, major intensity, or RPM bounce. 050 cam B-60 degrees overlap seat to seat, 4 degrees overlap @. 08 – 0. I am guessing that either move would have the same affect on idle quality. That big cam needs overlap and duration. 006" lift is the same as a solid Sep 3, 2023 · Problem people run into when tuning big cams with lots of overlap on EFI is they keep trying to maintain 14. In short narrowbands are not for tuners IMHO 80° overlap hyd roller cam vs 80° solid roller idle quality. lift, max. This is where both the intake and exhaust valves are open at the same time. The hydro package makes more power on the same cam for me. Because the idle quality goes as overlap is increased it is better to err slightly on the wide side if we are talking street usage. The engine idle quality is perceived by the user as the constancy of noise tone, low vibrations level and absence of sudden speed drop, noticeable on the steering wheel, gear shift lever, and seat [ 1 ]. Camshaft Overlap@. Dec 21, 2008 · Further,,,, the cam in your buddy's blower car does have valve overlap and a Roots blower acts much like a big check valve greatly taming the bad effects of a big cams overlap at idle. Deciding between 110 or 114 LSA depends on the vehicle’s intended application. Increased Fuel Consumption: Excessive overlap can lead to increased fuel consumption due to inefficient combustion and pumping losses. with the same peripherals and my tune . Apr 12, 2003 · Do higher displacement cams have more lift just to equalize the slope of the cam lobe with the extra duration, or is there another reason? I know that while a high lift cam may have the same advertised duration as a stock cam, it will have a little more duration after . 3rd, which actually should be figured first, but not a formula, but a general guide is the overlap at adv spec, which selects the application of the cam. Longer duration cams improves top end power and moves the HP & torque higher up the RPM range of the engine with a corresponding reduction in low-end horsepower & torque, vacuum, and idle quality. For a race engine then it is best to err on the tight side rather than the wide side. Jul 12, 2012 · Little more to it than just the amount of valve overlap (as measured both at . The 294S has about the same amount or overlap, could The cam I went with has -1* of overlap. 31 posts 1; 2; 3; Next; Procharged 434 Pro Posts: 222 Camshaft Overlap@. Jun 17, 2011 · i also found that using fuel trims seems to lead to better driveability idle quality and overall part throttle torque vs using a wideband. But what about blown or supercharged engines? In a blown engine , the larger the overlap area, the more the boosted charge is being blown straight out the exhaust tailpipe without being compressed in the cylinder. The massive difference in port volume, was more extreme than the cam difference, and of course both had to be reasonably consumer friendly. Jul 30, 2007 · C4 Tech/Performance - Dealing With Cam Overlap - i'm interested in hearing strategies any of you have applied to help drivability with high overlap cams. That will have a good (not smooth, but not choppy either) idle. How would I at idle and just off idle adjust the injector timing to try to keep most of the gas from escaping out the exhaust valve? I've found the injector Offset vs. I also get that the less overlap the smoother idle quality and less loss in compression. 13 Camaro btr red hot cam , centri blower e85. 006" lift is the same as a solid Apr 25, 2021 · And those seem to work very well at any rpm with any cam, I have a 427 I just tuned 13:1 compression 750HP N/A and it rattle and shakes the car with 24X* Of duration cam, and sits comfortably in closed loop wideband control 800rpm idle steady 14. Will this much overlap idle about 800-1000 RPM. However, I don't know how much overlap will give how much vacuum. ) Getting a cam to idle, be driveable and be noisy/lumpy sounding is an oxymoron. I have mine set to 13. 7:1 AFR, which is NOT right when you are running a big cam. But even some of the biggest cams can be tuned to idle very well, it just takes some time. All cams, even stockers, have overlap. Remember the cam's effect on the powerband width, location, and max. Sep 19, 2021 · Ok guys, just for conversation purposes here, what effect does the . Mar 27, 2017 · This is the reason that Lobe Separation Angle alters valve overlap as it also changes the four valve timing events of a camshaft. 050" overlap have on Idle quality and manners for a street engine, in any particular combination? For the example we will use a 467 c. 05” that better predicts idle quality? Second, is the answer to the idle quality question very different with EFI Mar 24, 2011 · Comparing 2 cams to each other. More overlap may generate more top-end horsepower. The overlap is gonna make it stink, but if you have been adding fuel trying to get the AFR down, then it could be too fat. 55 years of grinding the bumps has made both irrelevant, I'd suspect. 2:1 air fuel ratio with no issues. Sometimes you can get the idle down with timing retard at idle, which was a Detroit trick in the first-generation smog controls era to make hot cams in homologation special engines like the Boss 302 able to run smoothly enough at low speed. 250" Stroke, and 6. Kind of sluggish below 3800 but once you hit 3800 it really kicks in hard. Valve Overlap- the time when both valves are open as the piston travels in the bore. 050" of lift because of the increased slope on the cam lobe. All things being equal, advancing the cam will show higher idle vacuum. This occurs when the exhaust valve is just closing and the intake valve is just opening. siwxo neqq wdjc kykq hnqjg bkkhv kods xrodio jstm tawj