need some advice on engine set up

[Tahiti350]

I'm making changes to the 350 Chevy in my Tahiti. '78 Tahiti 18ST with a OMC 800 I/O, 1.36 gears, swinging a 14.25 X 21+ SS 3 blade. Last GPS recorded pass was 59.3 MPH @ 4400 RPM, but it turned other non-GPS pass minutes later at 4600, which would be 62 MPH with the same corrections
Below are the current and planned builds, along with the Dyno 2000 numbers for each, please let me know whether the new set up will work or if it's too high in the RPM range for the I/O.
Current:
350 Chevy, mostly stock 882 heads w/78 cc chambers, small dish pistons w/estimated 9:1 compression (running steel shim head gaskets with .022 crush), Performer RPM dual plane intake, 600 Edlebrock carb, cam equivalent to the Comp 280H, factory HEI, OSCO risers and OT pipes.
Dyno 2000 puts the current trim at 334 ft lbs @ 4000, and 305 hp @ 5500, with 279 ft lbs @ 2000. HP and Torque cross at 5200, but I can't turn that high.
Planned:
Same as above except: Trick Flow 215 aluminum heads w/67 cc chambers for an estimated 10:1 compression, 750 Edlebrock carb, and Bassett headers.
With the planned mod's it shows 412 ft lbs @ 4500, and 415 hp @ 6000. with 356ft lbs at 2000. Hp and torque still cross at 5200 RPM.
It might be a little more top end than I can use, but it's still 50 Hp and 70 ft lbs higher at 4000 RPM, so it can't be too bad....
I also looked at what it would do with a single plane intake, like the Torquer I took off, and it went to 426 ft lbs @ 5000, and 442hp @ 6000, so I may have to play with it a bit more to really dial it in.
I know that taking approximately 200 pounds off the back of the boat should help considerably, as will installing my saddle tanks to move the fuel weight off the bow. I'm hoping for 70-75 MPH, without killing my cruisability.
Can I get there from here?

[SmokinLowriderSS]

I get slightly higher HP & Torque figures, but not by much, Maybe a small difference in the porting figures in the airflow files for 882 heads. I double-checked the cam specs, dead on.
The head change, I am not getting NEAR the HP gain you are on DD, here's my differences.
Now;
4,000 259HP/341#
4,500 291HP/339#
5,000 312HP/328#
5,500 313HP/299#
Trick Flows
4,000 269HP/353#
4,500 306HP/357#
5,000 335HP/351#
5,500 345HP/329#
Ahhhhh I just spotted (was reading AS workign in DD) the main difference in our figures. I am running an RPM Air Gap on a 454, and, from all the DD comparison builds I have run, IMO the RPM version of the performer should be run as a single-plane to get the closest figures. I've been running all this with a single plane. Dual plane is supposed to match up pretty close to factory dual plane iron anchor, which is somewhat worse than a standard performer, and IMO a lot worse than the RPM.
You're only turning a max or 4600RPM, so you stand to gain, IMO, 20HP from a couple grand in heads. I don't really think the heads are worth the outlay.
Oh, and the HP curve always crosses the torque curve at 5200 RPM (5225RPM, it's in the math of calculating HP), regardless of what motor it is. Pay no more attention to that fact, it's irrelevant to anything.
Yes, IMO, you're overcammed. I'm running a cam iteration on DD to see if something else would gain you better. 117 thousand operations should take under an hour, I'll be back later.

[SmokinLowriderSS]

Not seeing much change makeable in the cam dept, with the original heads. I'm only finding about 10 pounds torque, gonna try a few things to see just how much I can get ya. Those manifolds might be a hinderance to ya. I'm not very familiar with them. I'm just not seeing any "1-part" changes that are going to net you very much. I'll see what else I can find.

[Tahiti350]

Thanks for all the effort, it's cool that you'd take the time to crunch all this for me. I'm hoping the extra torque above what I have now will help me turn the RPM's up into the 5000+ range. Not sure what it would do but I also have a Edelbrock D-26 (?) dual 4 bbl dual plain, that's supposed to have the same rpm range as the RPM intake. would use 2 50o Edelbrocks on it, if I ever run it. The cam I swapped out was a Comp 274, if I remember right. Nothing wrong with it, just trying to get a little more...
I am swapping the OSCO's for Bassett's, which made a significant difference in the numbers. Using the OSCO's with the new set-up gives me 360 ft lbs @ 4000 and 341 hp @ 5500. The numbers I showed before were for large tube headers w/ open exhaust.
The trick flows I'm looking at are the Kenny Duttweiller ones, and have the following air flow #"s :
Lift .050 .100 .200 .300 .400 .500 .600
Int 29.5 60.3 125 173.6 215 239 243
Exh 18 43 86.5 116.7 144 162 175
Also found an air flow error, had the pressure drop at 25 in H20 instead of the standard 28 inH20, that brought the numbers down some to 390 ft lbs @ 4500 and 360 hp @ 6000....
I can't figure out how to migrate the data from Dyno 2000, or I'd post the charts. Swapping from the 600 to 750 cfm carbs seemed to make a about a 7-8 hp difference above the torque peak.
I played with the different cam profiles I had and the 280H was about the best of the bunch, mine may actually be slightly bigger, it's a Speedpro cam, and the engine builder (of a 400 SBC I re-sold) said it was about 284 duration. I used to have the p/n and spec sheet, but gave them to the guy that bought the 400, then bought the cam back when he went bigger.
Thanks again,

[Tahiti350]

Here's a picture of the OSCOS's and my current exhaust, they don't appear to be a bad design except for the 2 5/8" outlet on the turndowns, just ungodly heavy:
http://www.***boat.com/image_center/...warming_up.JPG

[SmokinLowriderSS]

It's no problem. I enjoy tinkering in DD, and, even without claiming it to be dead-accurate, I think it is a very good guide to the parts interactions.
I was about to say my gut feeling is the exhaust is likely to be hurting you. IMO it is the hardest thing on DD to really quantify accurately.
The head flow numbers fall in between what I have, more than the stock 882'a, less than the Trick Flow's own numbers for 215R's (the only 215 I found @ TF this AM).
For example,
GM 882's, .500" - 205/144
Yours --- .500 - 239/162
TF 215R's .500 - 273 /190
I like the results of those heads better than the 215R's, IMO the 215R's are too big for the RPM you are trying to pull.
Better find 2 LITTLE 4-barrels if you want to try that manifold on it. IMO that'll way overcarb it and you may very easilly loose ground in practical usage, and just burn up more gas. IMO you can't get that motor up to theRMP needed to feed that 350 with that manifold setup. IMO you are best carb'd and manifolded right where you are for maximum usefulness.
I also have not found any cam to be any kind of real improvement, I don't count 5 or 6 HP as a "real" improvement worth the money spent, just not real-world noticable. You are not pushing a racing aplication to locate every last HP.
I am finding nearly ZERO difference withthe Durtweiler heads over the stock ones, once the headers go on. :supp: You can call me confused here.
baseline "stock"
4,000 259HP/341#
4,500 291HP/339#
5,000 312HP/328#
5,500 313HP/299#
Stock heads & small tube headers:
4,000 297HP/390#
4,500 336HP/392#
5,000 362HP/381#
5,500 366HP/349#
50HP @5,000 RPM just from the headers,
New Heads & small-tube headers, no mufflers
4,000 297HP/390#
4,500 335HP/391#
5,000 360HP/378#
5,500 366HP/349#
Loss of 2HP with the KD heads,
I've double-checked the rest of the build info about 4 times, and can't find a reason.
Trick Flow 215R heads with the headers:
4,000 301HP/395#
4,500 349HP/407#
5,000 389HP/408#
5,500 415HP/396#
Gain 77HP @5,000RPM with the TF 215R's and headers.
I'm not liking the results of the heads you are looking at.

[SmokinLowriderSS]

Heavy, Heck, I think the jacketed headers I put on my Taylor last winter weighed MORE than the aluminum logs I took off! :cry:
'Course, I picked up 200 RPM, 50 HP with them.

[Tahiti350]

That's weird that the results aren't matching. The air flow number are from the August Chevy Hi-perf mag, and I found a couple of other errors in the article, so they are suspect :hammerhea .
They did say that they were the best head in the $1000 range ($1026 @ Summit) that they tested. Their 383 (I know different beast) made 496 ft lbs @4000, and 455 hp @ 5300 with a Comp cams XE 274H (230/236 @ .050 & .487/.490 lift) with what appears to be an Air Gap RPM. With more cam and less CID it didn't suprise me that the peak HP came in at 6000 rpm.
I just re-ran the numbers adn double checked the air flow data and now mine is closer to your, definately not what I'm looking for... 362 hp @ 5000, 404 ft lbs @ 3500...
Now I'm confused......

[SmokinLowriderSS]

I'm not a big guru on small blocks, so I have limited insight to help ya with. I tinker mainly with big blocks and kinda have developed a bit of a feel for them I think.

[Tahiti350]

Okay, I think the magazine air flow numbers are bad, so using the air flow data out of the Summit catalog for the Trick flow KD heads with CNC chambers I come up with 435 hp @ 6000, 420 ft lbs @ 4500, 92.5% VE @ 5000, and 363 ft lbs @ 2000.
Using single plane intake kills the low end: 334 ft lbs @ 2000, but jumps the peaks to 465 HP @ 6000, 437 ft lbs @ 5000, and 96.2% VE @ 5500.
I'm using 350 SBC, TF heads PN TFS 30400001-CNC (air flow from Summit below) @ 10:1 for 62cc chambers w/small dish pistons, dual plane intake for the Performer RPM, large tube header/open exhaust for the Bassett's, and 280H cam.
Air flow
Lift .100 .200 .300 .400 .500 .600
Int 64.2 138.5 197.7 237.1 256.8 258.4
Exh 55.9 105.2 145.5 170.7 186.3 195.9
CNC heads are $1199.95. Do these #'s and details help with DTD?