David Vizard E7TE Ported Heads for 306 Ford Dyno, Ultrasonic Measurement and Port Textures

David Vizard E7TE Ported Heads for 306 Ford Dyno, Ultrasonic Measurement and Port Textures by Charles Servedio

[@robertwest3093]

I would rather meet David Vizard than any movie star. I have most of his books and have applied a lot of his techniques to my projects and when he says something works....IT WORKS!

[@servediocylinderheads]

He is great! Fun too.

[@pro-seriesfabrication3810]

Schedule a trip to PRI in December. He's usually floating around or giving a seminar

[@gordocarbo]

@@servediocylinderheads Id spend my paper route money on his books at thelocal chevy dealer or bookstore. Counter guys would give me strange looks lol.

[@andrewevans1658]

Nice video. Thanks for talking about sonic testing, nobody talks about it and it is extremely important!!! I would also recommend pressure testing equipment because a sonic tester won't detect pinholes and certain casting flaws.

[@elmerfudpucker3204]

This is the best info I have found for these heads so far. Thank you for sharing this.

[@servediocylinderheads]

I am hoping to post more on these this weekend. Thanks!

[@johnhennery8820]

Another great video thanks again for sharing this with us I learn more and more about the dos and do nots Im really glad you showed the Sonic tester I will get one and check the port and than as I go really great video thanks for your time in helping us and say hi to David for me

[@jimurrata6785]

Glad I've found your channel!

[@allenavery2789]

Nice job. You guys do great work!

[@ronfarrell2889]

Thank you Charlie for showing us all this knowledge that is put into E7 I was surprised @ output on the test Dyno, also back in eighties Daryle Hale from California used to port D6 & E7 heads he would make a shark fin with thermactor bump,his company was called AfFordable performance,A mag article was done on him

[@shawnlibby675]

Great information 🙂

[@ericscrutchins6350]

Larry Lombardo was Jenkins cylinder head guy and I'm sure that they seen David's work in those publication books back in the 70s that's why they ran pretty good back then with the 331 small block in the Monza

[@thomasleclair7418]

,,,,,,,,,,,,,,,,,,,,,,,,,,Larry was his race car driver.................................

[@littlevman2997]

Absolutely love your content!

[@servediocylinderheads]

Glad you do. Thanks

[@davidb7699]

Killer Video with Awesome information…

[@servediocylinderheads]

Thanks!

[@servediocylinderheads]

I will be making another video on these E7's much closer to 100%.

[@86foureyefreak22]

I have a set of e7’s I would like to have ported.

[@servediocylinderheads]

@@86foureyefreak22 Are you sure you want that?

[@86foureyefreak22]

@@servediocylinderheads is the cost outrageous? I’ve been looking at some trickflows.

[@servediocylinderheads]

Well, yeah. They are pricey. I usually only do this type of head for a good friend. If I only charge a minimal for my time they would be $2k without a bare. Insane? You bet! I have to be to work this hard to make sleeper iron heads.

[@servediocylinderheads]

$2k bare.

[@hotrodray6802]

👍😎🇺🇸 One of THE BEST that Ive ever seen!! Wish I could see the 289 peanut chambler C6OE-B (4 bbl) head). Yes they are obsolete 😨

[@servediocylinderheads]

Thanks Ray, everything I work on is really obsolete. They can still get the job done. Bringing up the efficiency is really what is going on.

[@hotrodray6802]

I have a new set of those C60EB peanut chambers, 194/160 fully ported/ relieved in 1999. 56 cc. Never run. That peanut shape is much different. Might update chambers if I knew what. Ancient tech but FREE 😁😁 not building a race car. Thank you Charlie 👍👍

[@mikedeal8659]

Thanks for sharing this

[@jimrutin]

Thank you very much for your video.

[@RonnieMoscaAmericanstangs6033]

I'm doing a set of e7TE heads now

[@servediocylinderheads]

They need a ton of work!

[@jarradbilman982]

Would love to see some info on the promaxx heads and what you’ve done

[@servediocylinderheads]

I was told they were Promaxx but I am not sure if that. Whomever did the original airflow work on the casting did quite a good job.

[@chestrockwell8328]

I'm in for more information on the ProMaxx heads as well.

[@russelljohnstone8355]

Hi Charlie, Great videos, there are still plenty of us practicing the medieval art of cast iron head porting ! I have always wondered how the exhaust cross over port / channel in the windsor heads effects flow numbers on that exhaust port ? Do you have any examples.? Cheers, Russell.

[@servediocylinderheads]

It flows better than a standard port as far as cfm. The Helmholtz tuning of that port will be less due to the exhaust splitting directions. I feel it is a wash. On an all out head I would think about filling it with aluminum or ceramic epoxy.

[@russelljohnstone8355]

@@servediocylinderheads Thanks Charlie.

[@jimurrata6785]

@@servediocylinderheads Anything to say about grinding the thermactor humps out of the exhaust ports? Weld them up or just plug them?

[@servediocylinderheads]

@@jimurrata6785 I grind them out. I am also careful not to make them too thin there.

[@rennypizarro4432]

Sorry I was asking about the GT40p heads.

[@shawnlibby675]

Iv see...202..gm valve's cutt and installed in the E7....head......good combo

[@servediocylinderheads]

Not sure how they do that without changing the valve centerlines. The plug recess just makes 1.94". I guess if you sink the seat quite a bit a 2.02" would work. Hmmm

[@superkillr]

In DV's video, his graph shows that HIS E7's went almost 280 cfm....which is completely insane

[@servediocylinderheads]

Yeah. I hate to say it but that is a mistake. It happens, it was more like 238 cfm.

[@servediocylinderheads]

I should add to that statement that D.V. may have changed a few things after I ported them.

[@dennisrobinson8008]

@@servediocylinderheads Good ported E7's were 220-230cfm. I wasn't sure how one could make 280 without adding extra iron and extensive modification.

[@servediocylinderheads]

@@dennisrobinson8008 I know he changed the valve job but I do not think 280 can be done without welding.

[@dennisrobinson8008]

@@servediocylinderheads Welding is fair game it needs to be simply stated. Most good ported E7's are going to the 220-230cfm and bad ones do 180-190 cfm like a gt40 head, i'm not sure any one of us have seen more.

[@groceboysgarage1958]

Great video. I am doing a set of e7s and was wondering about valve sizing. currently the valves are liberty performance 12 degree intake at 2.020 and 1.5 exhaust, don't remember UHA on the ex. But I bought the valves big so I could cut them down to correct sizing. What would you recommend for valve sizing? Valve job will Probably be NWN cutters with a chamber relief on the intake side and a radius on the exhaust throat up to the 45.

[@servediocylinderheads]

The set I did for D.V. were 1.97"/1.6" my most recent set are 1.85"/1.6" I am hoping to get a better shape on the ssr with smaller valve. It will not be possible to shape the bowl right for 2.02" just not enough iron in a few spots.

[@ghj1502]

Also can you show us more about those caylon valve guides? very interesting stuff

[@servediocylinderheads]

I did a whole video on k line guides. It should be easy to find. I did one on honing them to size as well.

[@ghj1502]

@@servediocylinderheads Thanks

[@shawnlibby4762]

I know some one that worked the me7..heads to put in a 202... Valves...,

[@servediocylinderheads]

In order to use a 2.02" valve the seats need to be sunk a bit because of the recess by the plug. Not really my style. Thanks

[@gordocarbo]

Recommend a good electric die grinder? Bought a foredom pedal speed control My old mutabos had adjustable speeds so pedals would work on them. They finally burned out though Any more info on your (model?) sonic tester? at the point I really need to start using one. Esp for imported alum heads, some areas the metal gets goofy

[@servediocylinderheads]

@@gordocarbo I use a small Dewalt 887? Good for the price. Single speed. I have scr speed controllers. My sonic is no longer made. They do have a new model but I know nothing about it. Thanks

[@tonytate2964]

Loved it do you do anything with the bump hole in exhaust port

[@servediocylinderheads]

Machined out. Nearly flat. I will show it on the next video. Thanks

[@NoFox_Given]

Really enjoying your videos, do you have any previous experience with Canfield Ford heads specifically the 192 or similar?

[@servediocylinderheads]

Nope, never seen one in person. Thanks!

[@95Sn95]

I've wondered for awhile has anyone added the heart dip shape to a combustion chamber with weld and grinding? Just curious one of those huh worker if you could thing. If so would it do anything other than lower chamber volume like induce some swirl?

[@servediocylinderheads]

Iron welding is tricky.

[@grabber289]

I'm from Mexico city, congratulations for your explanation, i had that kind of heads, mi cuestión is, the size of the valves?

[@servediocylinderheads]

Original 1.78/1.46 modified 1.94/1.6

[@grabber289]

@@servediocylinderheads tanks

[@jeffdiehl8394]

great video! I cannot tell you how many nights I spent breathing cast iron dust as a teenager in the late 80's messing up all sorts of early and late iron 289/302/351 heads in the back shed. testing at Englishtown the next weekend! do you think the early 351 port, given it starts about 140 ish cc's can be shaped as well as this? curious. have a set ported by a friend of mine with 1.94 valves - note he did work doing pro stock heads professionally for a while so he has some knowledge. claims 240 cfm which sounds plausable. cannot wait to try them on a good 310" shortblock.

[@servediocylinderheads]

I was going to Westhampton dragway before they closed it. 351 head should easily go 240cfm but I haven't had one on my bench. Thanks, Charlie

[@hotrodray6802]

Wow !! Of course the porting costs as much as alloy heads.🤔🤔

[@servediocylinderheads]

@@hotrodray6802 The part everyone seems to forget is brand new alloy need to be gone through for valve guide clearance, valve seat concentricity, and valve spring load at the minimum. Be sure to add that to the price.

[@hotrodray6802]

understood, no out of the box stuff is trusted.

[@thomasleclair7418]

@@servediocylinderheads ,,,,,,wow ,,you got Long Island history........

[@DS-mo6md]

awesome to see finally! Did you ever switch that one build to roller? I feel a little more confident in my first porting job after seeing this.. I painstakingly did with an 1/8th inch rotary ( which isn't bad for fine shaping and less chance of a big mistake) .. but it takes forever to mic.... I dont have a flow bench but outside of measurements I did find a chinese anemometer and pitot tube on ebay for like $130 and that way I was able to at least see that ports are well enough cloned. I used that with an air mattress blower and plastic bottle ... I wish I had the texture though... I'm worried I hogged out my exhaust ports a little much .. before I really started learning I just used the gasket of the jegs 302 long tube headers to about 85% but later I opened up the port bowl less. The intake I was very careful on and didn't even really open up the ports... but I'm glad to see your valve guide walls on the intake look as thin as mine... ( almost like a knife ) because I was worried I went too far... I wasn't sure of that dog leg ( the right side next to the exhaust) but I saw one porting clip of the guy that worked for Saleen... Valenko? he has an inside caliper to about .560 from the OD to the wall.. so I'm wondering if you have a figure or measurement on that? I haven't dared the Vizard cut on the chamber or anything but I'd kind of like to... Anyway... I'm going to be running 6 psi of centrifugal / water meth, so it doesn't seem as critical as it was when I was truly chasing NA numbers for this build with factory iron. But I really took my time ( did it very part time over the course of years it seems or seasons rather) .. Do you have an email? Would you mind giving me any feedback or honest opinion? Obviously a bench and measurements / dyno is much more telling but it would be cool to have some expertise.

[@servediocylinderheads]

Just copying from pictures or video is tough because they flow best just before they turn into sprinklers. Join Speedtalk.com, I haven't posted in a while but I have some very detailed threads. The Speedtalk search doesn't work very well but google Carnut1 E7TE or 289 and they should come up. My Build a Lightning Bronco? thread is a gt40 351 build, pretty detailed. You can message me through Speedtalk.com. At this moment I am not listing my contact information. It is not like I mind helping but what sometimes happens is it snowballs and I can't even watch a movie with Wiffy. Sorry, 2:00am rambling. Thanks, Charlie

[@DS-mo6md]

@@servediocylinderheads no problem yeah i may check it out .. Yeah one port on thermactor side i managed to grind and open a small hole below the original bump but am 99% sure was just part of the thermactor tunnel. (I want to triple check that but looking at e7 cross cut i dont think its water). I filled in and over with jb weld extreme heat (2400 degrees) and then actually plugged the thermactor holes inside the port and ground them down. Figure might as well make the tunnels as smoothe (not in texture but obstruction). I dont know if I like that but I figure even if it didnt stick itd just be blown into the headers and hopefully not reverted into the chamber. In hindsight leaving an extra little hole into the thermactor chamber would have been fine..

[@servediocylinderheads]

@@DS-mo6md It does get thin by thermactor. Not the end of the world but you are also close to water at that point. I am interested to see if the epoxy will hold up.

[@servediocylinderheads]

Homemade flow techniques can be helpful. I used to pressurize intake manifolds and then with a Dwyer air speed gauge find out where the air was flowing and evening the ports as much as possible. Out of the box thinking...

[@DS-mo6md]

@@servediocylinderheads its rated at 2400 degrees (which is really cool it exists as a product) but originally i had it thin going over part of the roof and the hole but as I ground down it cracked and you could like pick small sections with your fingernail so it got to the point where its just in the little hole..and I got rid of a lot of it.. So i mean I cleaned those tunnels and alcohol and I guess some portions just wouldnt adhere.. My thinking now is like.. Thats probably some potentially "greasy" carbon in the hole so i realized theyre probably not adhered at all or very little.. maybe they just wont come out but it would suck if they got loose while holding themselves in from forming a foot by means of gravity making an obstruction larger than the original thermactor bump.. So thats why i got a supercharger

[@purestress2597]

Are those second wholes in the exhaust port the actual port that the egr system draws from? that's pretty cool, and I wonder if you were to weld them closed and give that material a finish could you gain a little from that?

[@servediocylinderheads]

The TFS high ports I am doing have the egr ports welded closed. On the bench the added holes flow a tiny bit more. On a running engine weldded holes would be worth a few hp.

[@purestress2597]

That's really cool. Probably not much worth the time, but if someone's already hard into porting an e7 I guess every bit could be made to count.

[@servediocylinderheads]

@@purestress2597 Nobody is that stupid...wait.

[@purestress2597]

@@servediocylinderheads You may be looking at nobody. Money is temporary, but time spent welding and grinding is a profession.

[@spotliterrr]

What is the best casting for porting? Torque not high rpm?

[@servediocylinderheads]

Small port volume properly modified.

[@garykarenmcgruther6386]

Charlie, I see the exhaust is not level on both sides of the valve guide? Im having issues wanting to level that area and you will break threw.

[@servediocylinderheads]

It should be angled a bit. Flow is coming from the center of the bore and moving toward the cylinder wall.

[@garykarenmcgruther6386]

@@servediocylinderheads thank you

[@CrkdFngrGngrBndt]

How does one go about either purchasing your heads already ported or getting heads ported as I have a pair of GT40P heads I’d like to put on a new short block with a cam similar to the specs of the 306 that was dyno’d at 371 tq and 361 hp a few years ago

[@servediocylinderheads]

Ask?

[@servediocylinderheads]

[e-mail] Send me your name and phone number I will get back to you. Thanks, Charlie

[@DS-mo6md]

So I forgot to ask... is there any way that you could take like an inside caliper and tell what the measurement is between the OD of the valve stem guide hole is to the dog leg wall you're pointing to at around 8:00+ I think I took mine to around .560ish" but I wasn't sure how close I was. Then just cloned all 8. Kind of going by the look of it. Definitely opened it up some but if there was like a point or limit you could say would help me. all I have are inside calipers and t gauges no sonic stuff. I would have hated to waste my time if they are supposed to be like .600 for any improvement.

[@DS-mo6md]

important to note I am running stock valve sizes so taking in bowl percentage size ( i forget if its like no more than 85-90%) into factor also

[@servediocylinderheads]

Running a stock sized valve changes where and how far away you want that wall. That wall is thin where you need area.

[@DS-mo6md]

@@servediocylinderheads thank you..(didnt see this for some reason) that makes sense actually.. I think I left it at .560" Just kind of voodoo visual and kept in mind the percentage rule of the valve face .. but I did do some of the work in the combustion chamber.. I guess what I can't tell when you say rounded down above the exhaust valve is the edge of the combustion area also rounded down? It's hard to tell I just flattened that area down a bit (inside the edge) and took out a smidge above kind of going on looking at this video . We need 3d video lol

[@servediocylinderheads]

@@DS-mo6md If I understand your question the answer is yes.

[@JohnThomas-vb9se]

Just curious if any of this applies to the 3bar gt40 head or how they would compare? They already have 1.84/1.54 valves and a larger port stock. I’ve seen magazine articles decades ago saying they’d go in the 240’s on the intake and maybe around 200 on the exhaust. Thanks for the video.

[@servediocylinderheads]

I am actually doing a set of gt40p now. The gt40's are very similar to E7's but have better shaped ports. It is almost like they were modeled after ported E7's. I did a thread on the gt40's on Speedtalk.com. Google Build a Lightning Bronco? It should come up. Thanks, Charlie

[@garykarenmcgruther6386]

@@servediocylinderheads have you seen the article in SpeedTech on the 1969-70 351 Windsor cylinder heads? There is a guy named Joel Allen Dubose of Pat Musi racing engines. He did a set long long time ago that seems impossible but it indeed happened. It was definitely north of 260 CFM. I'm chasing the SpeedTech flow numbers, 248 CFM.

[@servediocylinderheads]

@@garykarenmcgruther6386 I haven't but since the 351 ports are a bit larger I don't see why it is not possible. Thanks, Charlie

[@servediocylinderheads]

Chasing a flow number is called "Flow blind". It is contagious...

[@shawnlibby675]

@@servediocylinderheads 3 bar...match..93..cobra heads..from what...iv gathered....

[@ericsmcmahan]

Charles Servedio, is it possible to get the air speeds the same on both sides of the bowl without negatively affecting Swirl?

[@servediocylinderheads]

As a rule I don't port for swirl. I may do chamber mods for swirl. I port for max airflow with min csa.

[@ericsmcmahan]

@@servediocylinderheads does porting intake bowls with more port bias on the cylinder wall side increase swirl. And is that the primary reason for port bias or is the primary reason because u can't take as much metal out of the c.o.c. side?

[@servediocylinderheads]

@@ericsmcmahan It helps in two ways, it increases flow and increases swirl at least in the sbc head. I would think sbf would follow.

[@servediocylinderheads]

Well you can't take as much, exhaust port. Also hot so it needs some metal.

[@brianmeyer5535]

Charles do you work the gt40p heads?

[@servediocylinderheads]

I do, Thanks, Charlie

[@eddiefe428]

Hello,do you work on ford fe 390 heads

[@servediocylinderheads]

@@eddiefe428 I have no 390 experience.

[@rennypizarro4432]

Would you use a similar cam to the E7 engine. 9:1?

[@hotrodray6802]

CC xe264 or xe274 👍

[@hotrodray6802]

carbed id tighten the LSA to 110

[@sorbicsagor5080]

Thanks for posting. I have E7's with 1.94/1.60 valves and a decent amount of porting in the bowls and runners. The biggest difference I saw was they didn't really work the intake valve guides on mine. My exhaust guides have been worked a bit but not nearly as much as these ones. They will go on a 306 w/Trick flow stage one roller cam, w/slightly ported GT40 intake and into an 88 Cougar (about 3500-3650 lbs). My main concern is is mid range power with decent throttle response. Do you think the the 1.94/1.60 valves will kill my lower/mid range or do you think the smallish size of the runners on these E7's will keep it ok. I just keep kicking between just going with mostly stock GT40 heads or the ported E7s I already have.

[@servediocylinderheads]

Spend a few $ and have the E7's flowed. You will have your answer quick. I bet if the guy did a decent job they flow at least what the gt's flow and do it with a smaller port so you will have more midrange.

[@msk3905]

Hell no they will scream mid range I ran a set of E7TEs ported with 1.94 x 1.6 on a 306 with GT40 intake and B303, power increased everywhere! Made 267 rwhp with that combo, forget the rwtq this was in 90s. Even ported E7s are still a small head for 5.0L, I changed the ported E7s with TW 170 aluminum and still picked up power across entire rpm range.

[@sorbicsagor5080]

@@servediocylinderheads Thanks for the feedback! I have a friend who's worked at our local machine shop for ~20yrs look them over and he said he also thought they should work well for my needs.

[@sorbicsagor5080]

@@msk3905 Good to hear. I recently finished a full 306 build w/comp XE274 and Promaxx aluminum heads for my Mustang but the E7's are for my 88 Cougar. What you had is pretty close to what she will run. I got an Explorer GT40 intake, 65mm TB (might go 70) and will be running a TF Stage 1 cam. If I get anywhere near 267 that would be a huge improvement over it's current 155.

[@msk3905]

@@sorbicsagor5080 E7s ported pull nice they were fun but I was blown away at how much I gained everywhere with the better flowing aluminum head, my combo was 9.7:1 cr, GT40 intake, ported E7s w/larger vlvs, 75mm MAF, 65mm TB (believe size of intake opening, 24lb inj, underdrive pullies, 1 5/8 shorties, 2 1/2” hi flow cat, 2 1/2” Mac cat back, 3.73. Looked up dyno 267rwhp @ 5200 & 302 rwtq @ 3800, added TW heads went over 300rwhp then custom cam added another 10 but more importantly had better manners and increases were across entire power curve.

[@ghj1502]

Aren't you losing venturi effect by opening the throat of the bowls like that?

[@servediocylinderheads]

Good question. If it did flow would decrease.

[@ghj1502]

@@servediocylinderheads Can you measure the velocity of the ports with the flowbench? Not to my knowledge. Part throttle operation is probably worse with those heads because of the nonexistant venturi in the heads, correct?

[@servediocylinderheads]

@@ghj1502 I measure velocity on the flowbench using Pitot gauges. this give accurate steady state air speeds. wwat makes you think there is no venturi? The midrange acceleration on heads done this way is explosive, hard to shift fast enough.

[@Blackking1301]

How much do you charge for the work on a pair of those heads?

[@servediocylinderheads]

$2k labor only, no parts, no shipping, 100+ hours.

[@Blackking1301]

@@servediocylinderheads ok thank you

[@68nitrostang]

What is the cost of ported E7 heads

[@servediocylinderheads]

Expensive. 100+ hours of porting and flowbench development.

[@hkpoweralajmi5170]

What is the valve size

[@servediocylinderheads]

2.1 / 1.625

[@servediocylinderheads]

Sorry wrong video 1.97/ 1.6

[@QuikModsOBS]

How do we contact you for work?

[@servediocylinderheads]

[e-mail]. thanks

[@thomascoker3600]

E7 heads aren't designed for the things your trying to do hell a stock set of GT40 heads will dance circles around e7s

[@servediocylinderheads]

No they won't. They are a bit better not alot better

[@terrygrover6440]

I don't have a flow bench and never did and yet my heads will outrun alot of these heads on KZbin, I have yet to see a 10 second all motor car on any other channel on KZbin , all I hear is alot of hype and see nothing all I hear is flow numbers and dyno results that prove nothing to me , so think twice before you tell people to run if you're having heads ported and they don't have a flow bench just saying its very disrespectful

[@servediocylinderheads]

Terry, I built a 306 in the early 90's for a friend worked E7's no n20. Ran 11:00 @128 with a crappy 60ft. The mph shows it is making some power. Thanks

[@servediocylinderheads]

Most guys aren't you Terry.

[@terrygrover6440]

@Charles Servedio cylinder head porting & flowbench I've had 2 people just mention this to me and they were very offended and they both make big power doing head porting with no flow bench, my friend John is a mopar guy and he whipped up on my friends cougar a 10 60 car all he had was a 360 mopar with his own ported heads and my other friend just made way over 500 hp with a pair of his ported heads with no flow bench I'm just saying people get there feelings hurt over these kinds of comments it isn't necessary

[@servediocylinderheads]

@@terrygrover6440 Gotcha Terry, I didn't say it couldn't be done. I said I did it without a flowbench for years. I have had the bench for 7 years now , there is plenty to learn. Thanks

[@trailerparkcryptoking5213]

@@terrygrover6440. Hang out with men that have hair on their sack....or maybe it’s you with hurt feelings! You should respect the fact that this guy is a professional head porter and a flow bench is an important tool in his trade and that he has that important tool. You and your buddies go have a group hug and tell each other how great y’all are with your 10 second cars. FYI there are new 4x4 F150’s with twin turbo setups running 8’s, now that will hurt a feeling....

[@MrBlackbutang]

Exhaust sucks

[@servediocylinderheads]

But in reality does it after it has been ported correctly?

[@MrBlackbutang]

@@servediocylinderheads you other porters focus on intake valve chambers . If get flow up on exhaust side intake side will improve naturally. Starting with more air and fuel entering the the chambers. Now you are cooking with water.

[@servediocylinderheads]

@@MrBlackbutang Scavenging? Yes, that makes a big difference yanking in the fresh charge.

[@servediocylinderheads]

@@MrBlackbutang It is harder to fill a cylinder than to empty it. Think of the pressure differentials.