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Help needed new 468 build having reversion issues

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Old 02-12-2018, 07:15 PM
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My Boat: 1988 Cruisers Rogue 2420
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Default 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
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Old 02-12-2018, 07:16 PM
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Old 02-12-2018, 07:26 PM
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Thanks AD, I cant post url links yet, can you post one back to the iboats build thread?

Last edited by Scott Danforth; 02-12-2018 at 09:33 PM.
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Old 02-12-2018, 07:32 PM
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Sure will, can edit the name out, thanks

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

Help needed new 468 build having reversion issues-image_284883.jpg

Help needed new 468 build having reversion issues-image_284884.jpg
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Old 02-12-2018, 07:50 PM
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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.
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Old 02-12-2018, 08:05 PM
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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.
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Old 02-12-2018, 08:16 PM
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youtube link
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Old 02-12-2018, 08:16 PM
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Originally Posted by phragle View Post

...
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Old 02-12-2018, 08:27 PM
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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
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Old 02-13-2018, 02:03 AM
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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.
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