quick questions

[Tahiti350]

I made a couple of changes to my combination last week, but haven't had a chance to take it out and run it yet, so I thought I would ask the "experts" how much of a difference it should make.
The combo is 350 Chevy, standard bore and crank, stock 882 Chevy heads 1.94 intake and 1.60 exhaust valves, nominal 72 cc chambers (if I remember correctly), dished pistons with 4 valve reliefs, Edelbrock preformer RPM, with 750 Edelbrock carb (stock jetting), Osco cast iron riser style manifolds with thru drive exhaust. Boat is Tahiti 18ST, with OMC 800 out drive running 14 1/2 X 21+ SS tri blade prop.
Previous best run was near zero fuel, no wind, almost glass water, and just me in the boat. Turned up to just over 5000 rpm with considerable nose up trim to get there then minor trim down to stay stable. Had to run thru some moderate Chine walk, then it settled in flat.
Here are the changes
1. replaced Felpro .035 crush comp gaskets with the thin steel shim gaskets.
2. replaced thru drive exhaust with 3" exhaust off of the Osco's risers. At least now it sounds like a performance boat instead of a bayliner.....
3. replaced the incorrect Autolite 685 plugs (360 Chrysler plugs) with the correct Autolite 26 Chevy plugs. Yes I put the wrong plugs in, broke a plug and just grabbed a set from the parts bin. Never realized Chrylser and Chevy used the same thread and depth. Much colder plugs though.
If I remember right the shim gaskets should give me about a quarter to half point of compression over the comp gaskets.
Thoughts??

[SmokinLowriderSS]

I don't think you'll see much. You may gain ... oh, I'll stab a guess of 5 hp from the tad more compression, maybe what, 25RPM?
Plugs won't do ya anything if they were working correctly. Too cold just means they'll foul faster. The spark is the same spark, same ignition energy across a gap in a flamable fuel mixture.
You should see some realistic gains by freeing up the exhaust tho. :idea: I don't know how your current outlets compare to mine but I'll bet mine are worse, and 2 7/16" outlets (for a BBC) Maybe Oh, stab again .. 30 to 40 HP there.
Grand total, maybe couple hundred PRM? Best guess by me but I run a jet. Not much on how HP mods affect RPM in a I/O.

[76BARRON]

Don't know what you have in the way of spark arrester but most small blocks come with a short 1'' or so. If you have room for a less restrictive one(off a big block?) you may see some improvement from that as well.

[Tahiti350]

I know that when I put the Chrysler plugs in it killed the top end, and just didn't seem to run right across the board. They were non-extended tips, the 26's have a long reach, so I'm hoping this is part of the fix. I'm thinking the plugs weren't getting the fire going under load.
The exhaust out of the risers is just over 2 1/2", and was the same size where the down tubes went into the bellhousing. I know the Basset's hanging in the garage would do more, but I need the Stahl pattern adapters for them still, not to mention figuring out the water lines to use a Banderlog valve on an I/O.
As for the spark arrestor, I have a K&N filtered velocity stack, take a close look at the avatar (I will try to add a close shot of the motor tomorrow, not working from my own computer).

[SmokinLowriderSS]

I didn't account for using way to SHORT of plugs in it. Yes, the plugs were likely shrouded and didn't light it well. The right length and style design should help some things there.
Heck your exhaust can't be too bad. I'm blowing a 454 out of 2 2 7/16 holes (till I replace my logs with 4" outletted Lightning headers). Yea BABY!!!!

[EXTREMEBOATS]

:idea: My best advice is replace the 882s with a set of Vortec's. I've made the swap several times and picked up rpm's and bottom end. You can use the intake you have with a minor mod to the four center bolts, or get the vortec version. I did a mild runner clean up and blend the chambers, "remove sharp edges" Intake Gasket match. Every thing else bolts up fine. For a smog head the 882's are pretty good, Worked a few also but the first generation Vortec's kick but... If I can help give me a call. For there best performance up grade the exhaust, atleast better manifolds and risers. We did that to them also. JMO
Mike

[Tahiti350]

I'm hoping to upgrade to the better L34 Vortec heads and the Vortec specific manifold this winter, but This is what I have for now. I have been looking at the build-ups in Car Craft and Hot rod, and hope to get around 350-375 hp. May have to do the 383 stroker to get there though.