Comp CS268XFI HR13 Reversion in SBC 383
 

I have blown my head gaskets in my engine in the past. So this year am trying to make sure everything is copacetic

I just ran the engine on a stand and I'm getting water in my risers and exhaust manifolds. I ran it for about 3 minutes mostly at idle with a couple of light rev's to maybe 1800 or so rpm.
What's puzzling me is another guy who's active in here has that cam in a 350, so I took it as safe. Maybe it has something to do with my engine being a little more displacement, or maybe the compression has some effect. My compression is 10:1. I run high test fuel by the way.
I have looked through Comp cam's spec sheets and their recommended max cam for stern drive has one less degree of lobe separation, and one more degree of cam centerline. So in those specs the cams are darn close. What is different is that my cam has more valve lift. It has .570/.565 vs the .495/.503 of their max sterndrive cam.

I will happily change out the cam to be done with this issue. But I already have some performance parts and I hate to miss out on optimizing them. I have some EMI stainless extra height long tube risers, and I have some Scorpion 1.6:1 roller rockers.
I'm thinking of getting the Comp XM270 HR to reduce the lift, but using the 1.6 rockers since I have the better exhaust.


Roast me.

268XFI HR13

Advertised Duration at .006": 268 int./276 exh
Duration at 050 inch Lift:218 int./224 exh.
Lobe Separation (degrees):113
46 degree overlap at seat duration of .006"
-5 deg overlap at .050" duration
Lift with 1.5 rockers: .534 int./ .530 exh
Lift with 1.6 rockers: .570 int./.565 exh

COMP Cams Xtreme Marine XM270HR

Advertised Duration at .006": 270 int./276 exh
Duration at 050 inch Lift: 218 int./224 exh.
Lobe Separation (degrees):112
49 degree overlap at seat duration of .006"
-3 deg overlap at .050"
Lift with 1.5 rockers: .495 int./.503 exh.
Lift with 1.6 rockers: .528 int / .537 exh

-------------------------------------------------------------------------------------------

what do you have for exhaust on it now before those EMI w/long risers? I forget ? Or is this what it is reverting with ?

Look at the 270, it's effectively our cam. What can I be missing?

I bought the EMI pipes for the cam. They have always run together. 3 summers, 3 HG's. I have a stock exhaust sitting on my takeout 350 Mag, but using that doesn't make any sense.
I'm afraid I have to get a smaller cam so I can idle without reversion.

BTW I just put on a DUI ignition and it's stellar. The engine fires instantly and with authority.

Also, in the interest of full disclosure. I ran it yesterday afternoon. using city water pressure to the Mercruiser thermostat housing. Pulled the risers, they were wet by the manifolds. Then I looked down the manifold exits and they were wet. Then I removed the exhaust manifolds, and a few teaspoons of water fell out.

Around 2 hours later I decided I would blow out the combustion chambers. No water was seen.
Am I making a mountain out of a molehill? Don't think so.

OK, time for confession. Hopefully someone else can learn from my mistake.
I had my Cloyes 3 way crank sprocket in at 4 degrees retard. I'll be installing it straight up and will report back.
What a friggin dope.

Do you have a degree wheel ? Top of my head cam should be installed so intake centerline is 109 icl and exhaust centerline is 117 ecl.

BTW: Why do you feel this hurt the headgasket ? I would think something else did that. And what part of the headgasket was hurt ?

This is theory til proved. But here's my conjecture.
Retarded cam timing allowed reversion, water in combustion chambers caused compression to be too high. High compression overcame head gaskets seals.
My engine use could have contributed too. I spend 10 or more minutes idling in and out of the marina. Since my brother bought my dad's place I have been racking the boat at West Alton Marina where there's a few hundred yards run out to the lake. Plus there are some times we'd just putt.
I did not know I had this issue and changed my distributor...I was theorizing that the Thunderbolt V knock sensor may have been listening for a different frequency than the one my forged 383 would produce.
If the knock sensor was wrong it would send the timing ahead which would cause preignition and/or detonation. No proof of that though. I never did confirm which sensor is used in the later Mercruiser 383's and 377's.
I'm going to work Wednesday and Thursday, but I'm thinking of taking a personal day Friday to do a run test on my engine, that way I can install it Friday and Sunday.
I don't see a way to get it installed On Friday unless I can get a helper. Setting up my gantry takes time.
Maybe I'll pay a tow truck to install it to save some time. Or maybe the marine repair up the street will drop it in for me.

I was trying to degree the cam by using a piston stop to find TDC and I could not feel the piston hitting my POS piston stop. I was partway through degreeing when I came across the cam timing mistake. My heads are on and they are a pain to remove and reinstall.
To get my quench I use steel shim gaskets. Year 1 I put the shim HG's in dry and ran it, failed. Year 2 I put in cometic mls gaskets and gave up I think about half a point of compression. I did not get the heads surfaced, although I did check them with a (non professional) straightedge. That put my quench outside of ideal, but not horrible. Maybe they were imperfect then. Can't go back now. This year I had my heads surfaced by a machinist we use at my work. They took, I think he said .003" to get flat. I installed them this time with copper coat, and retorqued them after a heat cycle. So I want to leave them on.

So I jumped over the degreeing. Hope I'm not being dumb.
The gaskets looked like the heads got pushed up. The heads had wet marks on them. I'm an administrator and sales guy at a repair and tire company. I'm not a pro, so I can't say where the HG's failed
BTW the heads are Dart Iron Eagle. I did some porting to them this spring since they came with small ports that had a little bit of shrouding So I removed the shrouds and opened the runners a touch while port matching them to my intake.
Fingers are crossed.

I can tell you I have the short length Eddie Marine risers and we do long put put's at times too. In your area We used to eat at Sandy Point all the time...and still Pop's Clam Shack since the day we hunted Dinosaurs. :) LOL.

We go to Braun Bay all the time and have to idle under long island bridge which can be a while......we also fit under the short bridge in Wolfeboro so we do the long idle under that to the Wolfetrap restaurant. :)

I bring it too 800-900rpm in gear....I think ? No wake at all though....anyway, still super slow speed wise...small prop....

I have TBIV. Set to 12* initial and has 34 total.
As you know 5.7, same cam as you. I used a timing wheel. It came in at 110* ICL (1* from where it was supposed to), so I left it.
GGB mufflers slid into the barely out of water tips. They go under water a lot. He made me custom sized since my tips are only 3" diameter. Boat too small for 4" tips....had to cut the 3" tip's flanges as they where. He.He. SO, yes, risers are 4" so I have 4" to 3" reducers before the tips. I thought this and the ugly mufflers would bottle up water but they don't. Maybe the mufflers dampen exhaust pulses enough ? I dunno....tons of people run the XM270 with extended inner risers using stock or glm and have no issues.

It just maybe your TBV having to much timing initial...as far as the reversion......but causing headgaskets ??? I have seen a few engines with bent connecting rods from too much water getting in......but we did not find that until rebuild times on those motors...Doh !

Only time I have had to replace headgaskets on any marine engine for any person on the lake where for engines overheating and burning the part of ringland that runs in between cylinders. On small blocks this is usually in between the center cylinders because of the exhaust ports being siamesed and this part overheating before rest of motor. Or, detonation of course, typically from supercharger or bad injector or etc.....

This is my exact manifold/riser but color. Mine are black.

https://cimg9.ibsrv.net/gimg/www.off...86be9d36a9.jpg

Okay, made a few edits above ^^^.

Yup, I have the black manifolds and the extra height long risers.
I sure hope this is my solution. I want to spend some time and effort on cosmetics. My cover is ancient, and my stern seat isn't torn but it's old and crummy. I'd also like to have some time to redo my electrics, most of them llok like they are from 1987 the year my hull was built. My exterior is good though, The work I put into polish and compound was worthwhile. I get compliments at the docks from guys who realize it's an 80's boat.
I have the GGB inserts too. They really do lower the bark. I was wondering if they were part of the issue. Maybe I can put them back in to lower the decibels a bit.
I grew up across from Braun Bay before it became the hangout it is now. We'd ski right around Gline's Island which is now a no wake zone.

I'm 50. We were the 1st generation of hang out partiers there (ie: lots and lots of boats partying )when I was 17/18. So, later 80's.Are you older ? If not, it was going on ! And better than now since less police involvement and no rafting rules and etc. Pre-internet and smartphones, so not much evidence thank god ! :) we still go there most Sundays, so less rowdy. Your area too....Sundays also. Boat doesn't use much gas.

You'll love this - this aphibian car got pulled over in your area(Alton Bay) several years ago . LOL. My wife must have taken 100 photos. hah ! :lolhit:

https://cimg8.ibsrv.net/gimg/www.off...5006570c30.jpg
https://cimg6.ibsrv.net/gimg/www.off...4f403ea145.jpg

why did they get pulled over?

Our lake patrol does a lot of pulling over for dubious reasons. I suppose it keeps folks from getting hurt.
I saw one in the water outside the marine patrol hqtrs the year before last. I think the skipper was being smart and staying out of the deep chop outside that cove. Bet that thing would sink like a stone.

I just hope my exhaust never gets db tested. It sounds to me as if it might fail.

Yup, I'm older, but I'm still working. Don't drink as much beer as I used to force down. I think I am maturing.

Breaking the speed limit :) ? Kidding.

Who knows really. Probably being checked for reg/ life jackets/etc...was funny though. Cop ran'm, down quick ! Had'm for like 20min before we bailed and they where still pulled over. :)

and the water cops wonder why people hate them.

NHGuy - what headgasket are you using and where is it being damaged ?

Oops, look above in post 8. I am using a .017 shim gasket. With an OE block that puts quench at .042 with my forged flat tops. But this time I copper coated the HG and retorqued after the first run. First time it was installed dry.
BTW I ran the engine today on a stand with the results I was looking for. The exhaust manifolds were a touch damp after the run but not the burbling sound and 3 or 4 ounces water in each manifold I had with the cam retarded. When I unbolted them no water fell out at all.
My neighbor gave me a hand standing up the gantry.
I'm working a short-ish day tomorrow. Tomorrow night I want to put some wire loom on the engine wiring to make it presentable. It looks like a hellish bird's nest right now.
And hopefully the install will happen Sunday.

So, since the cam was -4 installed and now +4,you have removed 8 degrees overlap from ATDC - ie when piston is going down with exhaust valve open. :)

Okay, was wondering what ,aufacturer and #, 'steel shim' still doesn;t tell me much. Some are steel with no sealing layer, some have a rubber outer layer to seal,and etc.

Anyway, so, steel with no sealing layer you always want to spray copper coat or etc for sealing.

What caused the MLS gaskets to go ?

Looked back, I used Felpro steel #1094. They are .015 compressed., they're plain, no layers or coating. Perhaps the poor install on the first HG's caused the marks on the heads. Cuz you don't hear about MLS gaskets failing.
And I put the cam at zero from the crank. So if it's like yours it 110 degrees or if it's as designed it's 109 degrees.

Yup, plain steel always needs a coating of something. Way back, it was aluminum paint, until they came out with the copper spray, hi tack, and Holomer (sp?)

Some of the steel shim gaskets need a finer RA deck like MLS believe it or not.

Sure it's not cooling or high compression/detonation issues failing these ?

Could be cooling and/or detonation but there's little proof.

When I first ran the engine I ran it kind of easy with a lot of rpm change, trying to seat the rings properly. I don't think it passed 3300.

The first time I really let it rev I was coming north between Long Island and Moultonboro Neck, my absolutely home territory, toward the Long Island Bridge you mentioned..
So I cracked the throttle to 90% for a couple of seconds. Speed built immediately, I was stoked, wind, awesome sound. Check gauges, and its 210. Pulled back and shut down, I had blown a hose off the feed line. And there was 8" of water in the bilge.
It hadn't got to the starter or any electrics, I pumped it out, reconnected the hose and went along cautiously. But in hindsight, that, along with dry stainless head gaskets and single torque, could have all been involved.
Also, remember the original Thunderbolt V has knock sensing to control and manage timing advance. The TB V came with a cast piston 350 and I was running it in my stroked, forged piston 383. So there's the possibility the knock sensor would not identify knock in my 383. So if that was involved it could have been detonating, Who can hear detonation in an open pipe boat? Not me.

I have addressed those things with a plain ol' all- in-at-3000-rpm ignition, heads were skimmed, gaskets were copper coated, heads retorqued after first heat cycle.
Fingers are crossed now,. As I said, after setting the cam from minus 4 to straight up, it ran on the stand with no measurable water in the exhaust manifolds.

Revisiting this thread to let folks know that the engine has run right this season.
It has always had 93 octane fuel. Now it has the plain HEI ignition from Davis Unified (DUI) at 30 degrees all in. I may go to 32 degrees, but meh?
I ran it to 4500 yesterday on the way down the lake and it was happily accelerating til I backed off the stick.
And I have to say I really enjoyed how the boat acts at upper speeds. It feels solid and controlled even when it gets a little lift off some of the lumps in the water. It wasn't enough to break prop grip, more like unweighting feels when you are in the middle of a turn or a bump snow skiing.
Then it idled down the canal into the marina for 10 minutes without issue, where the last 2 years it has fouled plugs through there.
So I feel a little better.
I don't have a weekday off for about ten days, weekends middays have too much chop for me to run max speed.
I will probably will do the full pull when there's a weekday off, or if I am on the water early on another day.

did that fix the reversion ? I am battling something similar. I sold my 383 to a buddy I swapped out cam to basic stock size cam out of his 300hp vortec marine motor. I used cloyes timing set and it has crossed my mind that might be my issue but then I get guys telling me the extra stroke will cause reversion. I'm in the middle of making dry to tip tails for his stock manifolds .just wondering if I need to pull motor and check gear. Thanks

Oops long time between answers. Yes no more water in chambers. Buuut, remember I also took off that Thunderbolt V ignition. And I also needed my heads resurfaced. It was a very small cut according to my machinist. And I have sent him heads from the shop where I am assistant mgr for years.

thanks . I ended up useing a cam comp said "should" work but still was getting reversion . ended up making dry to almost tip tails.are you still running stock manifolds?

STart new thread and tell us everything and anything.

"I get guys telling me the extra stroke will cause reversion." I wonder if Mercruiser knows this? They have built the 377-383 for years with no reversion problems.:lolhit:

I ran out of solutions other than making a dry to almost tip tails. I took a perfectly good running fresh 383 I used last summer .i put about 50 hours on it. Block was zero decked.cheap pro comp heads and a decent cam ,cmi headers.made 420 hp on dyno .sold motor to a friend that cracked his block last winter .i swapped cam out from my buddys 300 hp vortec motor and had bad reversion with stock manifolds.and risers . Had him replace them because they were looking a little old .still had it. Added 3" riser extensions still didn't fix it. The dry tails fixed it . maybe mercury has a custom ground cam to except the longer stroke Idk ? I doubt mercury calls comp cams and orders their over the counter marine cam designed for a 350 ,maybe I'm wrong but I do know what I just went through to fix it.

Many thing can contribute to water reversion.

Topic of cid came up. More cid's pulls more air, no ? Since the anwser is yes, it can also pull more water in the exhaust too.
During ATDC of overlap, both valves are open and the piston is going down Air/fuel from intake and exhaust/water/air are all trying to fill the increasing void left by the piston going down. Larger this void is, the more the atmosphere tried to fill it. Remember, again, during overlap the atmosphere can enter from the exhaust too.

So, as we know, cam overlap, internal exhaust design, it's rate of fall, where water is introduced to the exhaust stream, intake manifold design, cyl head design, engine rpm, and etc,etc all contribute to how much exhaust reversion happens.

thanks SB ! You hit on my point exactly and then some, it just took trial and error for me to come to that conclusion.

You shouldn't of need dry tails though. Not with a cam that made 300hp in a 350, unless it was some dumb cam like the GM 290hp/350 cam.

Something else was probably fubared.

The cracked motor was a Michigan motorz 300hp vortec motor. After I kept getting reversion I called comp It ended up with a cam that comp cam said "should" work but didn't .i left it in.
grind # CS xm270hr-12. It also had the intake off his vortec motor on it also. Only things different from when I ran motor last summer was cam,carb and intake.and of course the exhaust both the cams I tried were both smaller than what I was running in it. The cam I was running went in to my new build

I can't follow your typing and I live in the dirt, so I'm used to bad english. LOL.

I thought you said 300hp cam ?

The XM270hr-12 has been used in a bazzillion marine 350's and 383's. Cam of choice actually for really good, but nothing wild, performance. Yes, exhaust needs to have inner pipe extended a bit. Tons of threads on this.

sorry for not being clear .i couldn't find a clear answer ,probably using wrong key words.I got it figured out tho ,thanks