How much reversion is too much??
 

Its been awhile since I posted anything, but I stumbled across an issue this past season that I didn't think I had.

My combo is a pair of Gen6 509cid, GM aluminum bowtie heads with Manley severe duty intake/iconel exhaust valves, Merc HP525 cams, Gil HP500 exhaust, Procharger M1 blowers. I have approx. 250hrs in 10years with this combo.

My problem is I'm apparently getting a lot of reversion after extended idle times. The reason it never seemed to broadcast itself was, under my normal boating routine I don't idle a whole bunch. But after an extended time idling at the end of last season, right before I put the boat away and another extended time idling in Mentor at the SBI races this year I noticed some pretty milky looking oil.

Both motors are doing it. After 15 to 20 mins of run time at full temps, the oil looks like new again. In the past I did have a Procharger intercooler start to fail, which milked up the oil. Luckily I found it before a major issue, and replaced it. Both intercoolers have been replaced and I verified neither is leaking (plus if they were the oil wouldn't clean up).

I know Merc supposedly had reversion issues with the HP500's, and went to a different riser shortly before putting the kabash on the Gils altogether. I'm also still running the Gil turbulators.

With all that being said, here's my questions:

1) Does water fatigue Iconel valves faster than normal wear and tear would?

I mean, the reason Iconel is used in the first place is for water ingestion. I did some research on Iconel valves during my last rebuild session in 2013, and got mixed answers. Some people like to replace them during a rebuild as maintenance, but in general they don't go bad. Mine are from 1998, been in two sets of engines and have around 550hrs on them(250hrs with boost). They were all inspected and mic'ed in 2013 and deemed good. And apparently been reverted on for the past 10 years.

2) Will the taller Gil risers(Hardin Marine sells them) eliminate all reversion?

I plan on pulling the exhaust this winter and pressure checking it. The risers do have O2 bungs welded in, and could possibly started to crack around the welds.

3) Has anyone ever had a lower Gil manifold go bad?

Mine have always been used in fresh water.


LE

Water is hard on the valve seats as well as rings. Things u can do that will help fight reversion... Turn up the idle, advance the cam a few degrees, less initial ignition timing (if it's locked unlock).

I did turn up the idle a bit. My timing is locked in at 28*. Leaning toward buying new risers, just want to make sure they will help.

Just an FYI Stainless Marine sells an adapter to go from Gil to there tails. You could go dry all the way out the transom...

28 deg of timing on and engine that is on the edge of reversion is too much timing at idle. I run mine at 10 for that very reason.

Hey Scott,
I have seen instances in the past it's been placement of the exhaust outlets in reference to the water. I know you haul a lot. I suggest you drop all the sausage and Bud Light you haul...... ;) just kidding bro. Hope all is well and u get this figured out.

Jr.

More timing the less cylinder pressure you will have at idle and it will run smother will act like a smaller camshaft.

You might be able to put a Daytona sensors cdi with a boost retard.

24* head hunter 598 at 10to1 I would run 45* at idle and engine would smooth out. And you can close the trotted plates down a bunch lowering cylinder pressure..

imo the 525 cam&gills will be a problem and all the mentioned bandaids won,t do a lot of good if you have long idle times.had a similar issue with a hp500efi cam on long idle times.

i do believe that will work.

to the question '' how much reversion is too much'', I will simply answer : any reversion is too much!

and to the long idling zone, I never had any problem at all and I did like 240 miles distance at idle in vacation this year, stock cam, and no water reversion whatsoever!

Are you gaining oil/water? Is the milky oil all up the dipstick or are you seeing condensation on the head and top end components after a long idle? There is a difference. I get condensation with my aluminum heads and low water temps. I use to think it was reversion and I had Stainless Marine TRS dry to the tip tails.

Scott, you could weld extensions on to your current tails, and make them fully dry to the tip.

I've got 540's with 500EFI intakes and cams. I bought some like-new Gil HP500 risers not realizing they had reversion issues. They're so low and therefore the drop is so minimal it's a wonder to me that they could work with any set-up. After wasting a lot of money trying to fix them I finally had the inner tubes extended through the transom to make them dry. Problem solved. They're a little loud, but with slip-in mufflers it's not too obnoxious. Based on my experience, I wouldn't waste my time trying other alterations or band-aids like timing changes etc. If your Gil manifolds have been fresh-water only I doubt they're the problem but they aren't hard to pressure test.

Good to know.

Do the SM tails for the Gill's have their 'Dam' in them like in their tails for their own manifolds ?

no silent choice on right ? if no, exhaust will need to be changed

Would sound sweet too lol

I run 27/28* locked initial timing with a 900rpm idle in neutral(6M MSD). It has a super strong idle in gear. Not sure if the higher initial timing causes more reversion or not, seems to be a little controversy about it. Not here to argue. I know there are better ways to control my timing, but this works and runs real well.


LE

The problem that arose this year was that the oil actually got milky after the extended idle times. The oil surprisingly cleaned up very well after running at operating temps for 20mins or so. I do however get some condensation on the bottom of my breathers also, which I attribute to the low water temps this combo runs, but those too clean up after running at temps for awhile.

I'm sure with the HP525 cams and the OE 500HP Gils that there has to be some reversion, and I figured there was. It just never seemed to present itself over the past, and I guess I didn't worry about it. I'll be looking into new risers and or modifying the ones I have.

LE

Nope, just OE HP500 risers from 98'.

LE

I plan on pulling the exhaust, inspecting and pressure checking both systems. I also had O2 bungs welded into all 4 risers awhile back, and I want to make sure no cracks or failed weld happened as well.

If all looks good with the risers, I think I will have some extensions welded into them.


LE

Thanks everyone for the info. So, while I have everyone's attention, I have another question.

This combo also makes some pretty high EGT's(1500+)@WOT, which I posted about in the past. Apparently its not causing an issue with the engine's reliability and the conclusion was there wasn't much that can be done to lower them w/o changing the combo. I was however wondering if the extended time with the high heat was taking its toll on the exhaust, and exhaust valves. Throw in reversion, and hence my worries on dropping an exhaust valve.

However, this year I did pull the egt sensors out of the riser's a little with some o2 extenders(my O2 bungs are welded in right above the riser flange). Egt's dropped by over 200/300* across the board, and maybe its because the sensor is shielded a little bit more, or just closer to the outer circumference of the riser, Idk.

With that being said. Are there any heat formula's out there to give me an idea of what the actual egt is coming out of the port? Does the heat multiply as the cylinders combine in the riser? Does the turbulator create more heat? Is it hotter in the middle of the riser then toward the outer edge?

Any thoughts?


LE

If you went with daytona sensors ignitions, you could have all the timing you want at idle, custom map it, pull some timing in the midrange, and add some timing up top . 28 deg total at wot is pretty low, unless you are running a ton of boost, or a vortec style chambered head. I running 34-35 total timing on my supercharged engines from 5500-6000rpm. Between 5000-5500, about 32-33.

I melted some pistons in 2008, and then again in 2013, because I didn't learn my lesson in 2008. It seems my combo is really fast at 30* of timing, and really expensive at 31* of timing.. 9.3 to 1 CR, and 8lbs of boost at 5900rpm. Maybe the cams, heads, higher egt's, Idk. I do know its a crap shoot at 31*s.

LE

Usually melting pistons is from being lean. What kind of air fuel ratio were you running ?

Wasn't monitoring AF in 2008, and I did have a carb issue when I put this combo together in 2007, which I believe helped along my piston issue in 2008. But I do keep a pretty good log of where and what, an I had 31/32* of timing when it melted in 08'(new carbs after that).

In 2013, I was monitoring AF, and its always been on the rich side, between high 10's and mid 11's at WOT. Played with timing on Sat(actually chasing high EGT's) and melted 2 pistons on Sunday with 31*s timing.

I must admit, I've been in the maintain and have fun mode for awhile. Not interested in going full speed all the time, and keeping things a little conservative. I've had good docking, driving and speed with the blow thru carbs, but my next combo is going to be fuel injected with some kind of data logging.


LE

methanol injection / check afr like running now / air gap tunnel ram w blocked exhaust heater / we have lil chev marine makin frost ice on a hot day