Help needed new 468 build having reversion issues
 

Thought I would post here looking for guidance.

have a 468 that i built that is going into a 1988 Cruisers Rogue 2420. The motor build is on iboats.

Long story short, Gen VI production block, Merlin 269cc oval port heads, RPM Air-Gap intake, GM performance forged crank, Scat Rods, Wiseco forged slugs
Heads have been ported, chambers polished and they cc'd
compression is 9.6:1
block was decked 0.005", line-honed
slugs are +.010 on compression height with a 0.041" gasket for a quench distance of 0.046

The cam was originally ordered thru AZ Speed. I picked up the cam, valve-train and exhaust from a friend in WI for his EFI 509’s. He purchased the cam, lifters, springs, etc. in 2010 or so . He dyno tested one of the motors and decided to build 540 blowers instead

The cam is supposed to be an HP500 clone grind from Arizona Speed Marine. it is a custom Comp Cams grind

Here are the old crane specs for the HP500 EFI.

292*/298* @ .004"
230*/236* @ .050"
.352"/.359" lobe
.598"/.610" valve
114* LSA
109* ICL
119* ECL

Here are the HP500 carb’d cam specs

284*/292* @ .004"
222*/230* @ .050"
.576"/.598" valve
110* LSA
105* ICL
115* ECL

The comp-Cams custom grind version thru AZSM

277*/287* @ .004”
228*/232* @ .050”
.588”/.596” valve lift
114* LSA
110* ICL
VOI 4
VOE 54
VCI 44
VCE -2

I verified the cam when I installed it using a degree wheel, dial indicator and a tubing wrench as a piston stop. I checked cylinder 1 and 3. The actual valve lift I was measuring was .586”(.344”) and 0.594” (0.349”) using checking springs ($3 from ace hardware). cam valve events match the cam card

I measured 3 times prior to buttoning up the timing cover, bolting the heads on for the last time and

Per recommendations of AZSM and Comp, the cam is installed straight up.

the exhaust is Stainless Marine, manifolds. originally standard height, long-tube

Carb is a holley 715cfm sitting on top of a phenolic spacer.

youtube video of first run after bolting cab back on - SgT1yWtRm6k (cant post url links until I get 10 posts under my belt)

I did idle down to 650 for a bit, and the reversion was worse. I have tried idling at 650, 700, 750, 800, 850, 900, and 950. Letting the exhaust completely dry between each run, then firing it up, idling it for about 3 minutes, then killing the ignition.

At 650, the entire pipe is wet inside, water dripping from the top of the pipe, etc, and you can see the reversion pulse pulling in the water spray in the video.
At 950, about 50% of the pipe is wet inside, however water still gets in

The motor is sitting on the skid on the engine hoist, tilted forward about 5 degrees. I have run it with the motor tilted forward, level and tilted backwards about 10 degrees.. The water is being pulled in from the end of the elbows as the water exists about 2” upstream from the inner tube. I don’t have the rest of the exhaust system mocked up yet as I was originally looking to go with selectable exhaust as I picked up a complete Corsa kit thru a buddy (old stock from an 8.1 install at Chris Craft). I may end up only using the side exits and mufflers, however would prefer to use the diverters for when the admiral is on board. Either way, I need to get the water vapor to quit getting sucked back in before I install the motor in the boat.

Doing some reading on OSO and other sites, the SM exhaust seems to have reversion issues if the v-band flange gasket has any leaks. I did not have the v-bands overly tight initially. then I lubed up the gaskets with permatex #3 which did nothing. I also read that the HP500 is prone to reversion.

Last weekend, I picked up some +6" elbows to tackle the reversion.

engine idling at 950 RPM, you can still see the water vapor being pulled into the exhaust and there is still water pooling in the manifold, even with the +6 elbows. nowhere as bad as before, however enough that I wont install the motor until I get this problem solved.

my current thought is to make an H-pipe cross-over just behind the block, then continue dry tubes for about a foot until I mix exhaust/water into the corsa diverters.

So right now I have 4 +6" elbows, two standard height / long tube elbows, 4 45 degree bends, 2 corsa diverters, two corsa mufflers and two corsa tips..... all which are a pile of shiney parts that cant get used until I get the exhaust system to stop pulling in water vapor

any guidance would be appreciated

Subscribed

Thanks AD, I cant post url links yet, can you post one back to the iboats build thread?

Sure will, can edit the name out, thanks

https://forums.iboats.com/forum/engi...admiral/page14

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Sounds like a great build you have going. You should not have any problems with that cam and that exhaust. How are you taking a video to see water reversion? Pay the money and become a member. It's cheap and you can post as soon as you pay up. Lots of good advise on the site.

I was using a go-pro hero 3 as well as looking up the exhaust with a flash light and using a bore scope in between runs. pulling the exhaust manifold confirmed what I was seeing.

youtube link

...

to quote the lightning headers tech page on reversion

" THE ONLY TRUE TEST FOR REVERSION IS TO IDLE THE ENGINE WITH THE HEADERS ATTACHED AND WATER GOING THROUGH THEM. SHUT THE ENGINE DOWN. REMOVE THE HEADERS AND IF YOU HAVE WATER RESIDUE LAYING IN THE EXHAUST PORTS OF THE HEADER, YOU HAVE REVERSION "

based on that sentence alone, I have reversion with either elbow installed on the manifolds

does anyone have experience building a marine H-pipe or X-pipe. on my hot-rods, it was easy as there is 10+ feet between the cylinder heads and tail pips on a boat, its a pain in the butt as there isnt much room between the motor and the transom So i would like to hear if the H-pipe will even out the pulses enough to reduce the reversion I am seeing

The video looks like the engine isn't sitting level and is angled forward. Not sure if it just looks that way or it really is.

the engine in that video is sitting a bit forward on the skid I made up. as stated in the original post, I have run the motor as far as tipped backwards 10 degrees, and it doesnt change the reversion.

every part comes into play dealing with this, cam, cam timing, intake(yes intake) heads, timing, and of course exhaust. seeing how your cam is getting close to the HP500 cams and they carb one was known to revert(mine did somewhat) I am not so sure what you are seeing is not normal...there is always scavanging in the exhaust, introduce water and there you go. Running thru the prop will make worse, I would put in boat run and check then, hard to tell without running complete

What is the ignition timing set to at idle?

ignition is currently at 14 BTDC with base timing at 800 RPM and a 22 degree advance kit. Dizzy is all in at 3200 RPM at 36 BTDC

quick post to get count up to 10

yet another

.....

........

OK, so I may have access to a bit of tools.... going to take the pile of exhaust parts and build this

the short H-pipe should help scavenge at low RPM, it will also equalize the pulses prior to where I am mixing water and exhaust (about 50" down stream.) and should eliminate any chance of reversion above about 3000 RPM, the cross over will become ineffectual however I only need it at low RPM's. an X-pipe would yield better high RPM scavenging, however I don't have room and reversion is at low RPM anyway.

the cross-over will be jacketed. just not sure I am going with a half-marmon flange or a hose

https://forums.iboats.com/filedata/f...otoid=10537350

https://forums.iboats.com/filedata/f...otoid=10537351

I did super-impose a 8.1/bravo for reference even though I have a carb'd VP 290 DP

Nice grafics....how are you going to cool the section of exhaust pipes exiting from the exhaust manifolds?

To me the motor doesn't sound right. I would go back to basics and make sure you are firing on all eight and do a leak down to make sure your not holding a valve open. In my opinion your cam should not be reverting with that exhaust setup.

Bingo, just listened to the video, it doesn't sound right, sounds flat and lazy, firing order off, valve lash

An exhaust leak at the head or elbow can mess up your world too.....

I have done a leak down as well as compression test. all cylinders within a 7 psi window. all plugs look the same, burning a bit rich at idle.

its all jacketed up to the end. the last elbow is my current standard height elbow simply turned 90 degrees. the main elbow with curved extension is two of my +6" elbows cut apart and welded back together

I did not draw the nipples yet, as most will be left in their current position on the elbows / pipes. as I have to cut the existing welds and do some sectioning prior to welding together


https://forums.iboats.com/filedata/f...8&d=1516492126
https://forums.iboats.com/filedata/f...otoid=10534891

Absolutely. When I put O2 bungs on my headers I ran them without a cap and water was squirting everywhere. I put the cap back on and pulled it off after running and it was dry as a bone and sooty. An exhaust leak can wreak havoc.

I agree with Kvogt and F2, I'd be going back and looking at the valvetrain after hearing you rev it at :35 seconds here...and if you have water pizzing out of that flange as the video shows, I wouldnt rule out a leaking manifold or tailpipe weld.

I have already pressure tested the manifold and tail pipe. they held 15 psi for over an hour prior to me looking into reversion

the water coming out the joint is what was being pulled back into the cylinder and pooling in the maifold. also note in the video above, I idled the motor down to 650 RPM and the motor is sitting at 5 degrees tilted forward. I am back up to 950 currently and it doesnt mater where the motor sits as it still pulls water vapor back up.

it does it with brand new (never run before) +6" elbows too

sealing the flange gaskets with permatex #3 took care of the water leaking from the joint, however still did nothing for the inside of the pipe getting wet as the water was pulled back in. still have water with the +6" manifolds. not a lot, however still have it being drawn into the exhaust

If i put a rubber sheet over the end of the elbow so the water is deflected away from the inner pipe, i can run it for 20 minutes without water in the pipe.

Yeah, when the engine is in the boat at idle and it will be 3 to 5 degrees leaning to the back, pointing the pipes furthur down.

I had a similar problem when I ran mine on stands. Be VERY careful with the hose/water pressure. Its getting way more water then when its at rest pulling it up through the pickup.

Moisture is different than reversion. Do you have standing water or moisture? Most of these cams still revert a little moisture. For example, O2 sensors dont last long and calcify from moisture. There is an article on here somewhere on OSO that discusses Moisture vs Reversion. For that reason, you have to get the engine good and hot up to temperature to truly validate.

Agreed on the angle, however doesnt seem to matter if the motor is 10 degrees backwards, flat, or straight up.

it is pooling water in the bottom of the manifold with the motor at temperature. you can see each exhaust pulse at idle and each reversion wave between the pulses. Will fire up the go-pro again, will post a slowed down video this weekend. you can see each cylinder fire, then draw back.

it could be the 114 degree LSA with the carb as most cams for carbs are closer to 110 or 112

I hear something tapping pretty hard on the rev up, sounds like a rocker

What Go-Pro attachment are you using for this that stands up to 800+ degree EGT?

What do the OSO experts think about a lifter problem or cam timing? The motor does not sound right to me.

Im not an engine expert nor well versed on cams, but that looks like a smaller cam than a 500 efi and with a 114 lsa should not in my feeble brain not revert with decent exhaust,

Like I said, my name is not Bob Straub, I am not a cam guru, but I think you have a problem other than the problem you think you have.

Need to fix that loose rocker or collapsed lifter before going any further

I am no expert but the odd bank looks like it has a miss to it. if you watch the mist it is erratic unlike the even side that stays pretty steady. also yes you can hear a lifter or rocker rattle in it for sure. another problem, it was pointed out that any leak in the system will cause it to revert, there is water coming out from the joint between the manifold and riser so there is a leak. you then said that you tested everything and there is no leak but point out that the water is coming out the leak at the joint. what they are trying to tell you is that leak in the joint to the outside air causes it to revert more, not that there is a leak in the manifold. before you worry about some really complicated H pipe that will probably cause more problems than it helps you need to fix the lifter noise, flat running and the leaks in the exhaust stream. also you dont need to worry about the mist being drawn into the ends of the pipes as they will always do that no matter the length. as was pointed out, if it does not pool in the bottom of the manifold it is not a problem.

As already mentioned the leak at the riser/manifold joint can and will cause reversion. Don't think it's leaking because of reverting. That leak will cause it.

Thanks for all the responses

I will be re-taking videos this weekend

since this video was taken almost a month ago: the following has been done

the leak at the flange has been taken care of. - this helped a bit, however did not resolve the issue
the angle has been addressed - changed from 5 degrees forward to 10 degrees back - helped a bit, however did not resolve the issue
the types of elbows used has changed - standard height in the video to the +6 in the pictures - helped the most, however did not resolve the issue
compression test taken - range is 7 psi between low and high value, nominal 153psi with the throttle plates closed
leak down test of each cylinder - no leaks to intake or exhaust except when tapping the valves with the deadblow. I used my compression testing whip so I do not have a percentage, however I know pressure took about 20 seconds per cylinder to decay thru the gap in the rings.
spark plug review - all plugs show burning slightly rich, however motor only run at idle, and only rough adjustment of carb has been done.
and what you guys are saying is a rattle is actually the exhaust noise echoing in the garage off the tin garage door directly above the motor and not being picked up properly by my crappy phone.

I will post the go-pro videos this weekend along with the pictures of the pools of water at the bottom of the manifolds

that is not true, nor is it the issue. Plenty of carbed marine engines came with 114lsa or wider cams. The only issue i see with the camshaft, is if you installed it incorrectly, and your cam timing is jacked.

your valvetrain is rattling, i would solve that first.

any reason you chose to use a vacuum secondary carburetor?

Had the vac secondary carb on the shelf

I have a question.
You mentioned that you installed the cam "straight up", which on a 114 LSA cam, means a 114 ICL..
But your cam specs are based on a +4 installation (114 LSA, 110 ICL).
Not trying to stir up trouble, but WHICH is it?

114/114 will keep the exhaust valve open longer as the piston is moving down creating vacuum that encourages reversion.
If you look at your figures, the exhaust valve does not fully close until your crank has pulled the piston down for 30 degrees of rotation.

At 114/110, you are 4 degrees BETTER in that respect.
While this number doesnt seem to mean much, let's look at it in a way that's easier to visualize.

With a 4" stroke and a 6.135" rod length, at 26 degrees past TDC, the piston has moved down 0.227".
At 30 degrees past TDC, the piston has moved down 0.351".

That's a difference of 0.124", which is 54.6% FARTHER than the initial baseline of .227.
Putting it another way - at .227. the piston has opened up a volume equivalent to 3.31 cubic inches, pulling inwards.
at .351 the piston has opened up a volume equivalent to 5.11 cubic inches, pulling inwards.

Now, you also have the intake valve open at the same time, which you might want to say reduces the amount of "stuff" the downward-moving piston pulls in from the exhaust. This would be true, if the exhaust port and the intake port were both at atmospheric pressure. BUT they are not. The exhaust is operating at a slightly POSITIVE pressure, although at idle it is admittedly not "much" positive pressure. The intake, however, is operating at a significant VACUUM. For this reason, at low rpm (idle or slightly above), when the intake valve opens, any positive pressure remaining in the cylinder tries to rush INTO the intake port, which then turns the cylinder into a negative pressure area as well, sucking exhaust back up towards the cylinder until the exhaust valve closes.

This phenomenon is exaggerated in a multi cylinder motor that uses a shared intake plenum AND/OR a shared exhaust plenum. Your motor shares both.

The actual POSITION of the cam (straight up, +4 advanced) doesn't make as much difference as the seat-to-seat overlap, but it DOES still matter a bit.

Things you can do to make it better.
1) Longer exhaust tailpipes - the farther from the port you can get before you introduce water into the exhaust, the better off you are.
2) Additional cooling water "dump". Put restrictors in to reduce the amount of water that DOES get injected into the tailpipes. Depending on the number and location of water bungs in your tailpipes, you can sometimes still run LOTS of water into the manifolds, into the risers and tailpipes, yet tee off at the rear of the tailpipe to a separate thru hull dump fitting. This reduces the amount of water introduced into the tailpipes. You can even use a spring-ball type arrangement to limit the amount injected at idle, yet at speed, the springs are pushed out of the way and additional volume is injected.
3) Lower your engine's vacuum at idle. While this sounds weird, engine vacuum is a driving force in water reversion. You can pull timing out under 1500 rpm, and your idle vacuum will drop accordingly (mainly because you will be opening up your throttle plates a little more to achieve the same idle rpm - and if you have to open them very much, you should open up the hole in the throttle plates instead).. Can't recall what ignition you are running, but any sort of low-rpm retard module will do the trick OR if you run a mechanical advance, the old staggered spring thing will also work. Use a spring that locks timing at baseline until 1500 rpm, yet allows full advance wherever you currently desire it. You would have to modify the travel stops on your centrifugal weights to end up with your current total advance though.
MC