Hello,

Years ago, I built some 9 to 1 355 small blocks, with 250/252 @ .050 solid roller cams (112 installed on a 108 CL) with .584 / .598 after lash.. The engines went 15 years @ 6000 rpms with 21 props in a 31 scarab (70.4 on GPS) , with no major failures (other than a pile of MSD boxes, and other stupid stuff like that) , A few years back, I thew a belt, over heated, and huffed a head gasket. After a quick clip of one of the head, slapped it back on in the bilge, & ran another 3 years, Finally, the one engine got a little milky (looked to be from reversion, and some head gasket seepage , so I decided after 15 years, time for a freshen up. I stuck with the small blocks, so I could re-use the accessories, and some parts, and because I like the looks on folks faces, when they see all the room under the hatches cause there's only the little engines back there, after hearing the things.

As we all know, one things leads to another, & I now have 10.6 to 1 421 SBCs, canfield heads all resurfaced, etc, custom carbs, single plane intakes, etc. Cams are a little different, actually a little less in duration, but more lift. 243/249 @.050, .616 / .624 lift (114 installed on a 110 CL). With the longer stroke, I plan on keeping the RPMs, a bit lower (maybe 55-5700). I an thinking these should be about 550 HP, but we'll find out on the dyno.

The issue is I have always run stainless marine manifolds..........stock risers, just modified to be 2 or so inches taller (my small blocks went where big blocks lived at one time). I was debating on keeping the manifolds - I will pressure check them again, but last time they were good. Or, do i change over to a set of say lightning fresh water headers ? Either way, I want to dry out the back - and never worry about reversion again. I do not take the boat in any salt water, so I thought the freshwater headers would be fine, but some folks say you have to empty them all the time - no way I want to do this, but I also don't want to spend the money on the full stainless ones with dry tails (at least not right now). I also do not want to spend 2/3 of that & end up with a bunch of issues later. Seems some of the folks see to have issues with headers leaking, cracking, etc ?

I am not sure if I will see much gains changing to headers, or would it better to just have custom risers / pipes made for my stainless marine (high torque) manifolds ??

Any suggestions are appreciated

For your application I'd have Jerry, (Stainless Marine), make some new dry to the tail pipes or maybe you could send your existing pipes to them and have them lengthened and a water dump fitting added.

Thank you for the response. I currently am running stock Mercruiser exhaust through hull but want to go to headers....how do I contact Jerry?

My response was actually for the OP as he already has SM manifolds but you can contact Jerry at Stainless Marine at (305) 681-7893

View looking into exhaust tip at extension.
The Lightning headers are a better design and will make more power vs SM. No question about that. How much more HP? That's the ?? IMO you MIGHT get 10-15hp vs current setup. That's not a good $$ per HP ratio.

I've always heard of draining water from headers after use. Seems to me you would have more corrosion once water was drained and air introduced. Do you currently drain your manifolds? I don't. Same as most others.

If your current SM manifolds pressure test ok then I would reuse them. Hard to beat them for a SBC manifold. I assume your risers are SM that mix water/exhaust in the stock location? If so simply weld stainless extensions to the inner exhaust portion of your risers. Extend to around 1" off your transom exhaust tips. The exhaust mixes with water there. Or, spend the $$ and have SM extend them fully water jacketed to transom.




My 496 risers with 12.5" extensions.

With that engine you want to mix water/exhaust as far back as possible. I would still pull a riser after idling and check manifold ports for water pooling in runners.

Condensation issues maybe ? Sometimes I see a ton of water on that outside of the manifolds.....so maybe some have on the inside ?