Whn do I have to worry about reversion (cam duration) [Archive]

speedymopars

11-22-2007, 11:00 PM

OK, so when is reversion (and sucking in water back into they cylinder) a problem? Wet headers and a bigger cam (over what duration, 240?250?etc) only? Does sit apply to logs / water injectors / snails ? TT exhaust? I am specing out a cam right now for my build, but I don't want to run into issues... I am running tt exhaust and straight through Nicson water injectors fed by edelbrock water logs. They are 3.5 inch ID, so I am hoping they aren't as restrictive as the Hardins I had on the olds...I would think that I can get away with (and I need!) a lot more exhaust duration as the water injectors are far away from the exhaust valve, but I don't want to assume anything at this point.

jetboatperformance

11-23-2007, 08:39 AM

jetboatperformance

11-23-2007, 08:49 AM

Speedy here some info from Rewarder that might help Tom
Reversion, what is it? It is simply the exhaust pulse flowing backwards momentarily during the overlap phase of the camshaft at low cycling rates. During the overlap phase the piston is pushing out the last of the exhaust gases and prior to reaching top dead center (T.D.C) the intake valve and the exhaust valve is still closing. At this point in the engine cycle both valves are in the open position. At high cycling rates the inertia of the incoming intake charge and the outgoing exhaust pulses keep the exhaust flowing in the proper direction. But at low cycling rates, as the piston is pushing out the last of the exhaust gases the intake valve opens and some of the spent exhaust charge is pushed into the intake manifold. As the piston reaches T.D.C. and begins the intake stroke the exhaust valve is still not completely closed. As a result, the piston pulls from the intake and exhaust valves simultaneously causing the exhaust gases to flow in a reverse direction. This is normally not a problem until you add water into the exhaust stream. Reversion can be severe enough to stall the engine, add water to the oil, rust the exhaust seats, etc. This effect only happens at idle speeds, but remember that during shut down the engine encounters the greatest reversion.
For these reasons Rewarder Custom Headers has guidelines for camshaft selection. Our guidelines are based on 454 c.i. with a 285 degree camshaft (242 at .050), on a 114 degree lobe center. Larger cams may cause reversion. These figures are just guidelines. Cubic inches, valve size, exhaust valve timing, etc., all will have an effect on reversion. The only true test is to run the engine with the headers attached, shut it down, remove the headers and check for water residue in the header ports to check for an occurrence of water reversion.

H20MOFO

11-23-2007, 10:27 AM

Tom I like your idea about putting a gate valve up by the drivers seat, also wouldn't say a 496 be more prone to reversion than say a 427,with all else being equal.(LONGER STROKE)

396_WAYS_TO_SPIT

11-23-2007, 10:43 AM

Remarine makes a killer billet valve for shutting water down by the seat......

Sleeper CP

11-23-2007, 12:09 PM

The reversion isn't just from the water injected at the headers. I was going to back off the valve train on the engine yesterday for the winter and I decided to fire it up in the drive way. No water running to the Basset valve just into the engine and then it dumps out into the collectors on both sides of the engine.
Well, at idel the reversion was sucking the water out of the collector and back thru the pipes (Bassett TT headers) and the water was getting spit out of the weep holes at the flange:eek: I might even be getting some contamination in the clyniders and oil. It didn't do it on the four days on the water this year:confused: :idea:
The engine was idling at 1,100 rpms when I shut off the water the idle would go to 1,400 - 1,500 rpms so the water was having a big effect on the engine. I guess I'll have to chase it next year.:mad:
Oh, the cam is 278-285 duration @ .050 net lift of .750+ lobe sep 113 with a 4.25" stroke and 4.600" bore.
Sleeper CP
Big Inch Ford Lover

jetboatperformance

11-23-2007, 07:14 PM

Tom I like your idea about putting a gate valve up by the drivers seat, also wouldn't say a 496 be more prone to reversion than say a 427,with all else being equal.(LONGER STROKE)
Honestly Kreg I dont belive theres a "hard and Fast" rule to this It might make sense that the stroke could affect things however Its just like Jims (rewarder) notes say experiment and check to be sure . Mikey that billet water valve is cool I use/sell them but a Hdwr store lever ball valve works well too! Tom
control,control,control (everything has a valve or adjustment)
(note to your left of the Distributor)
http://i147.photobucket.com/albums/r319/jetboatperformance/josh/408install.jpg

speedymopars

11-23-2007, 11:23 PM

Speedy we stay @/below 235 to maybe 245 @ 50 (with logs and stock center rizer) ,Not usually an issue with W/I headers ,my cam in my flat is huge (duration) with no problems(we always create a positive shut off for header idle water)Also you didn't say what lobe center? Tom
The cam I was looking at is 246/250 duration, .606/.614 lift, 108 lsa hyd flat tappet.
If I need to keep the duration down, the new V series Rhodes lifters give you the ability to adjust out up to 20 degrees of cam timing at idle and have it all back at 4K. Could this be the hot ticket for keeping reversion at bay while having mid and top end?
If I did that, I would have 230ish duration at idle, but still have a top end charge.

H20MOFO

11-24-2007, 09:57 AM

I've always wondered if rhoades lifters would do what they claim:idea:

speedymopars

11-24-2007, 02:23 PM

I've always wondered if rhoades lifters would do what they claim:idea:
They do. I used the same trick to get my van in the 12's. Heavy vehicle, no gear, no stall, needs little to no cam duration (read : low end torque) to move it off the line, but once it is moving, that same help off the line kills it by not letting it breathe. By using the variable duration lifters, the "cam" came on at 3200 RPM, and gave it power up on top.
In this case, I really wouldn't need to to do more than make it a mellow cam at idle to kill of the reversion. May help pulling up a skiier too, but that wouldn't be the primary reason for it.

speedymopars

11-24-2007, 02:36 PM

Oh, the cam is 278-285 duration @ .050 net lift of .750+ lobe sep 113 with a 4.25" stroke and 4.600" bore.
Sleeper CP
Big Inch Ford Lover
I love big rollers and big cubes....In the duster I have 296 @ .050...with 312 adv on a 108 - wanna talk steep ramps? I wonder how long my springs will last this time???? :-)
I am half temped to put a roller in my boat engine, but between the reversion issues and the inability to change the duration, I am a little worried about that. Plus a hyd is a little less work and a little more reliable for the family boat. I still may do it though...I have all the parts except the appropriate cam lobe which can be reground pretty easily...
CP - With it idling so high and with a jet (that is a jet, right??) , that thing must be a bear at the ramps. Do you have some way to disconnect the jet (ie neutral?) or what do you do?
JBP - Thanks! I was thinking you could use one of those bypass overpressure valves you guys were talking about in one of the other threads, but use the "dump" to hit the headers / water injectors instead of the normal engine water out. That way, at idle, that bypass wouldn't be active, and therefore no water hits the exhaust. On the gas with the jet moving some water and the valve dumping, suddenly there would be water there...

jetboatperformance

11-24-2007, 07:46 PM

The Rhoades thing might just do the 'deed" certainly worth the try,you could also create a OB dump and limit the H2o to the exaust hoses (be carefull) (keeping enough to keep the cool) We do this on thru hull headers too :idea: Tom
BTW we all seem have a tendancy to want to "overcam" I belive its a "Guy thing" start with the small cams and work the "scenarios" you'll probably be pleasantly suprised at what you come up with ,not sure what Motor your working with but having been a Mopar tech (back in the day) The Muscle car 440's and 383's made Big power with "puny" cam profiles by todays standards . re BBC we still use a "small cam" (L88 profile) in a few Jet boat applications .weve even run Old "duntov" grinds in some of the SBC's weve built

BrendellaJet

11-24-2007, 07:48 PM

Hold on a minute. Do your logs have the snails on them? If so Id say you dont have to worry at all.
Im running a big solid roller( I dont have specs on me but its a 548 Chevy making 800 NA HP, so you know its not small-I'll get specs for comparison)through transom under water at idle-No probs. I was concerned, but I decided to run it rather than moving the exhaust and after several trips there is no sign of reversion. Anchor with the bow out and keep the revs up when coming off plane just to prevent water from rushing in.
If you are running logs without the snails, then you have reason for concern.

396_WAYS_TO_SPIT

11-25-2007, 01:05 AM

The cam I was looking at is 246/250 duration, .606/.614 lift, 108 lsa hyd flat tappet.
If I need to keep the duration down, the new V series Rhodes lifters give you the ability to adjust out up to 20 degrees of cam timing at idle and have it all back at 4K. Could this be the hot ticket for keeping reversion at bay while having mid and top end?
If I did that, I would have 230ish duration at isle, but still have a top end charge.
That cam is pretty stout. I ran a 108 on my last boat and there is no way I would run water. I personally like to keep them at 110 with water.

396_WAYS_TO_SPIT

11-25-2007, 01:05 AM

. Mikey that billet water valve is cool I use/sell them but a Hdwr store lever ball valve works well too! Tom
control,control,control (everything has a valve or adjustment)
(note to your left of the Distributor)
http://i147.photobucket.com/albums/r319/jetboatperformance/josh/408install.jpg
Thats the valve Thomas Jefferson ;)

396_WAYS_TO_SPIT

11-25-2007, 01:07 AM

Why not run a banderlog valve and have the water come in at 3000RPM's? :idea: This way you dont worry about sucking water in. Also they make fittings with reducers in them so you dont get too much water:idea:
Spitter

speedymopars

11-25-2007, 05:50 AM

The Nicson water injectors I'm running look like http://www.glenwoodmarine.net/Catalog/MANIFOLDS.pdf
Page 7, top right. I have a 3.5 inch ID. I guess my question now is should (or do I need) to run snails or a banderlog?
The cams I am looking at take advantage of the Mopar .904 lifter, and have modern cam lobes with steep ramps. I can make power on the Chevy lobes, which most cam companies have, but I am leaving a good 30+ HP on the table if I do.
Stock unported Mopar heads stop flowing around .500 lift, and that is where you have to start cutting guides, the spring step, and basically start reworking the heads. The biggest cam is the .509 where you don't have to cut anything. Hence the reason so many Mopar cams are small. They also have a 1.5 rocker instead of Ford's 1.73 or Chevy's 1.7 ratio, so given the same lobe lift, the mopar one is going to be smaller.
My heads previously had a .670 roller on them, they are ported as big as they can go, and flow well past 700 lift. Probably giving up another 15 HP if I don't lift the valve on these specific heads.
I agree, most overcam. I am *trying* not to, that is why I am not using my .670 (280@.050) complete solid roller setup I have sitting in the garage. I feel won't be able to rpm that cam enough. The reccomended hyd jet cam from crane is a 235/245 duration, and all the rest say keep it between 230-245 - however if I use the rhoades, then it looks like that on the bottom end, but on top I have a longer duration cam for power. Basically have my cake and eat it too.
Generally:
Duration - effective rpm range - longer = higher rpm
Lift and ramps - HP - steeper and higher is better for power
LSA - width of power range - bigger is wider, narrow is peekier but taller.
I was assuming that low end really isn't a need in a jet boat, am I wrong on this? I wanted to set it up for max power in the 2500-6K range, but if I need lower end to spin an A, I would need to go shorter duration...I was assuming the short duration was for the reversion issues...My other issue is this is turing out to be somewhere between 10:.2 and 10.4:1 static compression. I need some duration to make sure I don't ping. Av gas is not something I want to run...
Do you need / care about sub 2500 rpm performance with a jet?
I *really* appriciate everyones help..

BrendellaJet

11-25-2007, 08:05 AM

speedymopars

11-25-2007, 08:38 AM

With those elbows you will potentially have a problem with reversion, assuming the tip is underwater. If its not then Id say run it.
A Banderlog valve will be of no use to you. It is used for systems using water injected tubular headers, not logs.
Snails(page 6 on your catalog) might hurt performance some, but considering you are running logs(probably the worst alternative in terms of performance) the snails might be a good idea just to avoid the reversion issue.
The tips are definately under the surface. I'm running logs because it is in an enclosed compartment, and lets just say finding some EMI thunder type headers for a 440 is impossible. I don't have the 3K it would take to have some made either, I'll just add more cam duration at that point (which of course causes more reversion issues).....
If I have to go buy some snails I will, but prefer not to. The snails I have are 2.x inches, too small..they are older too, I can't cut them to make it bigger either :-(

jetboatperformance

11-25-2007, 08:44 AM

Speedy ,Its probably not what you got your heart se on but check the Page
http://www.compcams.com/catalog/128_129.html
21-306-4 lifts a bit small, RPM range is right, lobe centers Ok.... re the logs you can swap out the snalis and tips for the 3.5 inch (readily available)and worth some power
http://i147.photobucket.com/albums/r319/jetboatperformance/Misc/ResizeofResizeof128_1291.jpg

BrendellaJet

11-25-2007, 11:22 AM

I bet if you keep an eye out in the spam section you will find a set of snails with the bigger ports. They may not be new and pretty, but a little elbow grease and they would look good-if you are worried about that.
My bro might have some-Ill check with him.

H20MOFO

11-25-2007, 12:01 PM

I just threw my motor in this morning in my 21' if a guy is running tt,and was woried about reversion sould I try to "fudge" my tips up as much as possible,(there are no holes drilled yet), or would that make it worse by causing a low spot between the tip and the collector? I'm not overly worried about noise because I'm going to run some type of muffler.

speedymopars

11-25-2007, 01:14 PM

OK, so I may need big port snails then. Don't feel like killing the engine...(anyone have some they are trying to get rid of??) I will have to check out where the exhaust actually sits - the Mopar exhaust ports sit 7 inches higher than the Olds do. I know that could affect it, but unsure on the details...
On my 455 olds, I had a .490 lift, 230 duration herbert hyd flat tappet cam, performer manifold, 850 DP, hardin logs, small snails, and 9:1 compression. When I first got it, it had a 750 vac sec on it, and 4K RPM was a real struggle. I put my 850DP on it, and immediately it was quicker everywhere. I hit 5200 RPM on the first try out.
The next time I took it out with a GPS and a co pilot, it did a dissapointing best of 43 MPH at 4300 RPM (it was a test and tune day for me). I was never able to best that RPM or speed on the other couple of times I had it out before the accident.
I have no idea if the 5200 RPM was due to cavitation, the chop, better conditions, etc. It only happened the one time, and I have no idea if the speed was correspondingly faster.
I would like to do significantly better with this engine, hence my desire for more lift and duration, and the hardware around it...
I was shooting for the 108 LC and 240-250 duration (with whatever max lift / ramp I could get), because it seemed to me that jets operate in a narrow band, 3-6K, and I wanted to maximize the power there. Am I thinking correctly or way off base?
Thanks again for everyone's opinion, theory only gets you so far...

Sleeper CP

11-25-2007, 01:48 PM

CP - With it idling so high and with a jet (that is a jet, right??) , that thing must be a bear at the ramps. Do you have some way to disconnect the jet (ie neutral?) or what do you do?
..
In the water the impeller pulls it down to 900 - 1,000 rpms with a lope. It's not bad at all around the ramp or water skiing just have to pay attention to the forward/reverse handle.
Sleeper CP
Big Inch Ford Lover

Longstr

11-25-2007, 02:01 PM

This is why Tom (impatient1) and his uncle billy run everything DRY... may be loud, and hot, but you dont have to worry about water back in your mota..:D

H20MOFO

11-25-2007, 03:03 PM

Has anyone figured out how to run a set of logs or tt's dry?:confused:

Longstr

11-25-2007, 03:17 PM

Has anyone figured out how to run a set of logs or tt's dry?:confused:
Sure dont put any water in them.... :D run your lines to your block and back out the transom or even the exit of your logs... the logs may WARP (aluminum) really bad though because with out water they will be getting really hot.. Just get some HEADERS...

396_WAYS_TO_SPIT

11-25-2007, 04:12 PM

Sure dont put any water in them.... :D run your lines to your block and back out the transom or even the exit of your logs... the logs may WARP (aluminum) really bad though because with out water they will be getting really hot.. Just get some HEADERS...
What about the big boats? They have thru transom headers that run dry and only dump water ner the transom:idea: I would like to see an exploded view of those type.
Spitter

Sleeper CP

11-25-2007, 04:25 PM

Has anyone figured out how to run a set of logs or tt's dry?:confused:
Way to much heat for either of them. You'll either burn the rubber or silicone or your transom.:o I don't think it would be a good idea :idea:
Sleeper CP
Big Inch Ford Lover

speedymopars

11-25-2007, 04:31 PM

Basically, out of the jet to the overpressure valve.
Over pressure water goes to water injectors.
regulated 15 psi water goes to logs for preheat, then the engine, then overboard.
A jet puts out only a little pressure at idle, right? That means for the most part the exhaust is dry at idle, but has plenty of water when you are on it. The logs being aluminum water cooled from cold water then connected to another aluminum water injector, may pull out enough heat...
It would be really trick if the jet put out around 15lbs at idle, that way it would mist the water to the injectors rather than a large dump.
Just a thought...

ol guy

11-25-2007, 04:42 PM

If you look at the whole story of camming you will understand that ALL cams breathe. Stock,low end and race. The cam will pulse and create reversion No matter who grinds it and how big or small. If you are worried about back water on slow down, tap the peddle on decell. Water will only back into the pipes after off plane. And stay with chets cam, you cant do better. Again all cams will have a suction on the exhaust at a certain cycle of every rotation of the reciprocating mass. Just tap the throttle and blow it out. Cams do produce more out than in on the exhaust side as we all know..... M

speedymopars

11-25-2007, 05:47 PM

My first cam was a chet, I grew up around Doug, but I won't run their roller lifters. I had a chet roller come off the lifter (the trunion was still there) - sure they offered to replace the roller because it was a manufacturing defect, but the $600 KB oil pump, the custom ground cam, the crank, the rods, wrist pins, and the schrapnel from the chunks wiped out about 4K worth of parts.
I don't use Fram anymore either. Apparently if you have enough flow with metal in it, it will go right through the filter and into the engine.

ol guy

11-25-2007, 08:45 PM

600 dollar oil pump?????????????????????????????????????????????? ??????????

speedymopars

11-25-2007, 09:04 PM

Yep. You want to live at 8500+ rpm with a big block, you better be prepared to buy the best of everything.
That includes a billet KB pump, single -16 line, external fed.
http://www.keithblack.com/racing_kboil.html

BrendellaJet

11-25-2007, 09:16 PM

Reversion is not just a problem coming off plane, but when idling too... Tough to just "tap the throttle & blow it out" without attracting attention in the no wake zone... An occasional rev should be okay, I agree.
Sure all cams will suffer from reversion, not all will have a strong enugh signal to pull water back into the combustion chamber. I think its safe to say that the setup in question without snails will have a problem.When, not if, is the question.

speedymopars

12-01-2007, 09:53 PM

On another board I'm on, someone just posted some pics of the Herbert solid roller - Those are actually the same as cranes. These are the same ones I have been running for 15 years, I'd recognize them anywhere. They are NOT the same ones that nuked on me oh so long ago. I officially have changed my mind on the Herberts.
So I've decided to back of the cam a bit, and stick with something under 245 duration the exhaust. There are several cams I can run, but comp seems like they have what I'm looking for. I may call Herbert on Monday just to see what donnie can do for me.
How many of you are running hyd, solids, or rollers?

jetboatperformance

12-02-2007, 10:16 AM

What about the big boats? They have thru transom headers that run dry and only dump water ner the transom:idea: I would like to see an exploded view of those type.
Spitter
Mike RE "big boats" Its all in the tail pipe exit water ,in the pic the water in these tail pipes enters into a jacket in side the riser and doesn't "mix" with eaxaust untill the lower connection .All the big center rise mfg's make standard risers for mild applications and custom long tail pipe styles to work with bigger cams and HP Tom
Kreg if you run the logs or TT's dry its prolly' a fast trip to Davie Jones locker , with no way to cool the rubber connections not to mention lots of other problems Tom
http://i147.photobucket.com/albums/r319/jetboatperformance/Eliminator%20V-drive/DSC08262.jpg
Just to give a perspective of the heat intensity of dry header running heres a pic "T"
http://i147.photobucket.com/albums/r319/jetboatperformance/R%20hondo/normal_first_time_out_0091.jpg

speedymopars

12-04-2007, 12:24 PM

Looks like I may do a Herbert single profile, 242/242 duration on a 110. Any real advantages to doing the split lobe (example 232/242). I realize that the logs are more restrictive, but I really don't know in the real world how much it will buy me.
The other cam is a comp 236/242 that runs in the 2K to 6K range also on a 110...
getting close...

jetboatperformance

12-04-2007, 12:30 PM

Thats pretty reasonable ,right at the edge Curious to see how it works Tom
Herbert(Donny/cam grinder) are good folks ,Bought my first 12/18 Duntov regrind from Chet in 69' :D

BLEWBAYOU1

12-04-2007, 04:47 PM

How about using a Banderlog valve, Mine works great! and ajustable RPM setting.
Brian

jetboatperformance

12-04-2007, 08:07 PM

How about using a Banderlog valve, Mine works great! and ajustable RPM setting.
Brian
The "Bander-valve" is the "shiznit" for 4 tube water injected headers, no doubt about it but you can't limit water supply (significantly) to Logs or center rize thru transoms Tom

ck7684

12-05-2007, 06:46 AM

For comparison sake, I have a solid roller in my BBC, 468ci...specs are 249 duration, 110 LSA, and .631 lift. I am running logs and snails (stock Indmar pieces) which are nothing special. I have so far turned 5300 RPM with an "A" Impeller in a freshly overhauled pump and Ultimate Wear Ring from HTP, before running out of lake. (lake had only about 1/4 mile of usable area)

speedymopars

12-05-2007, 07:26 AM