Exhaust Gaskets, Restricted vs. Open?
 

Hey everyone, I have twin 454s in my 84 Scarab. Stock exhaust, with 3 inch spacers raw water cooled. After 2 engine failures to leaky exhaust (took me 2 times in row to learn the hard way) I am now replacing all the exhaust components. I have become a little gunshy of these systems and am going over it all with a fine tooth comb. I am confused about this whole restrictor gasket vs. open gaskets on the risers and manifolds. Can someone tell me whats the best way to go here and why? I saw the recent bulletin from Mercruiser on the issue but it appears to me its referring to gen V motors and I am Gen IV. Any advice on this? Would be very much appreciated.

The restrictor that goes on top of the 3" riser on both sides is there to help equalize the water pressure between the port and stbd manifolds.. People have run without the restrictors and been ok, I have as well. The only negative on not running the restrictors is that you will probably have a higher temp difference between the risers. The one thing you don't want to do is run one side with a restrictor and the other side without. If you want to keep it factory, run the open gasket on the manifold to spacer joint and the restrictor gasket on the spacer to riser joint. Don't use sierra or paper style gaskets. Use the merc/ quicksilver gaskets..

Thank you mr3dman for the quick response. That makes sense to me. Does it matter which direction the restrictor ports are installed? Do the small restrictor holes face the starboard/port sides of the manifold or bow/stern. Or does it not really matter?

I would think the gasket is longer one way then the other and should only go on one way.

f inscreenname, no I think you are referring to the "log style" manifolds and risers. Mine are perfectly square "center rise" exhuast. http://www.ebay.com/itm/400206792773...84.m1423.l2649

f inscreen is correct in saying that you will find that they are just a tad longer on one side. You will find that out when you install them, same part number for all the iron exhaust from your motor till the 496 came.. Anyway, I believe they will line up with the restrictor holes forward and aft if I remember correctly.

Thanks guys, I am gonna go with the restrictior gaskets. Now I just need to decide if I am buying new elbows now. While the manifolds and spacers looked like they just came off the titanic, the elbows look brand new. I just realized they are stainless merc elbows. I was kind of excited thinking I may not have to buy elbows but after some research...people don't have much good to say about stainless elbows. Complaints that heat across the stainless/iron joints expands at different rates creating gasket failure. Anyone have any experience or knowledge about this? New iron elbows the way to go?

The stainless merc risers are the way to go. Cast is only used when there is nothing else you can use.

f inscreenname, so you think I should keep the ones I have? I think they are 10 years old. They look great though, I don't see any corrosion but the age of these things scares me.

The 3 inch spacers are no good. They raise the height of the riser significantly causing you to have to use longer riser studs. It is nearly impossible to keep these from leaking if you run in any sort of rough water. I recommend you look at imco SS tube elbows that fit the center rise manifolds. I lost 2 engines as well before I switched to these risers. Well worth the cost they are....

Hey thanks Blue Thunder, is this what you did? http://www.imcomarine.com/cal_store/...taller-sa.html Those are expensive...these will work with my existing manifolds? Do they really last longer then the stock stuff or do these need to be replaced as often? I have seen some used stuff out there from GIL and IMCO, are leaks as common? Should I avoid used?

Yes those are it. Mine lasted great, fixed the problem of leaks that 3" spacer was causing and in the end I sold them on OSO for 75% of what I paid for them when I went to headers. I would have no problem buying used ones either as there is not that much to them to cause leakes. Not like a tube header. Make sure you buy the shifter/module brackets though, relocating that stuff got to be a cluster. They did not offer those when I did mine about 10 yrs ago or I would have for sure used them.

A thousand dollars a riser?? Hell you can buy a whole set up for 2200 on their site but they want 2 grand just for risers? IMHO Thats just stupid.

f inscreename, I know hah? I am thinking that's alot of money to put ontop of some crappy GLM manifolds..on the other hand they are new manifolds and I already have sticker shock...haha. However it's 1000 for a pair, but I have two motors so I am 2k for both engines vs. 5k for complete setups at 2500 a pair. I have really mixed emotions. Then there is this http://www.ebay.com/itm/160872905195...84.m1423.l2649 do you guys think these will really work? The listing says they can be "retrofit" but I have read other posts that say the 496 stuff in NOT compatible. But I am tempted to give it a shot at this price. Even if its just for one motor, this is dirt cheap!

Its 900 per set.

I know the 496 exhaust will work because I am using them on my 454 Mark IV (496 stroker) now. Now will it be tall enough.... not sure if even the "tall" 496 risers will be tall enough being they are not that tall to begin with. So you will be stuck using spacers again and the spacers for the 496 exhaust must be made of gold cause they are insanely high priced.
I have the same issue with the race boat. The front motor sits so low in the hull that I have to use 2 six inch spacers per side. Thought about using 496 exhaust manifolds and risers and trying to find someone to cut the risers apart and make them taller. The risers are just SS tube and look easy for someone to extend for someone who knows how to weld.

Yeah I have been reading about that all night. I need to measure my setup now and then find measurements for the 496. It looks like they made several different risers for the 496, but yes...price is nuts. I see complete EMI setups on ebay for around 1400/pair, I don't know how tall their risers are. It says to call when you order so they can get it right. If the I can get the height dialed in, used 496 stuff looks like the way to go. Do you agree?

Its a lot better then stock 454 stuff thats for sure and the prices for the most part cant be beat. If it will work thats the way I would go.