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DC18
12-17-2008, 12:36 AM
Have been looking at performance exhaust. I have serched these forums and other forums. What I'm looking for is this: Ehxhaust that will deliver H.P. and torque, no worries about burn through, no worries about metal cracking. The engine is stock for now (350 Mag, B1 1.65, Mirage Plus 23P ( blueprinted) 69.1 mph (gps). However the built engine as follows, World Motown block w/splayed 4 bolt mains, Eagle forged crank and rods, AFR heads PN 0991 with PN 7511 valve upgrade, Comp cam PN 12-416-8 grind # XM264HR, can spec, lift IN-.488 EX-.495, duration @.050 IN-212 EX-218, lobe center angle 112 with center line of 110, comporesion 9.5-1, 850 cfm t-body and a cingle plane intake. (hope the guys at Barry Grant do the Aero-Ram for efi soon). On my desk top dyno, see below.
RPM POWER TORQUE
2000 149 390
2500 193 405
3000 244 426
3500 301 451
4000 358 469
4500 412 480
5000 457 480
5500 488 465

Boat should do 80 + mph pretty easy.

MOP
12-17-2008, 09:43 AM
How many cubes will it end up being, and 850 on a small block is a ton of carb a 650 is a better all around carb that will take little to nothing off top end. I have a 750 on a 383 SB my mistake it is a bit to much! Back to your exhaust question, many have found little to no real gains just great Bling. Not saying headers are not part of a good package and that you won't eek out a few ponies, but what really counts is torque. There are some dyno charts up on Boat Freaks with headers in many types and price ranges, true they are BB charts but look them over you may be a bit surprised. Many will tell you build for best peak power @5000 as the drives do not like higher RPM's. My engine came out real close to the desk top dyno numbers, but built for a different purpose with lower HP.

P.S. you must be using the speedo not GPS, with 1% slip plugged in the prop calculator you would be spinning a tad over 5,800 to make 69.1 that motor just does not have that much snot!!

Phil

BigGrizzly
12-17-2008, 10:40 AM
MOP, you missed the 1.65 ratio, I get 5600 rpms about 7% slip. However In a 16 or 18 Donzi the 69 will not happen with a stock 350 mag, carb or MPI. I agree with you the carb is too big. The other thing is with the numbers you won't see 80+ in a small Donzi, regardless of hedders. At 69 what rpms are you turning? It would be helpful. That efi system still has a flaw in it. What I see here is a drag car engine that won't work in a well boat. The numbers you posted are similar to a ASA engine we dynoed a week ago for lethal injection. A tad short of the one we dynoed. I don't want to hurt your feelings, just trying to ready you for disappointment. Good luck.

MOP
12-17-2008, 02:51 PM
Randy I tried it again on a different calculator and came up with numbers similar to yours, I was thinking about the same thing "Car Motor" but with a little help from gents like you he should be alright!

Phil

BigGrizzly
12-17-2008, 06:50 PM
The engine will run pretty well idle ok but will be a little thirsty, especially if he puts that carb on. You have been there and heard it " I just hopped up my engine and it still doesn't do 80". Most times it is slower then stock or only a couple of mph faster. I listenrd to Comp cams once and it was my undoing. boats are not their thing especially on Fords. They actually told that my 71 Mach1 had too much compression- I had knocked 2 points down from stock go figure:shocking: When I put it in the Corsican it went 52 with a 351 Ford Cleavland? So I called my old friend Babe Erson and he laughed, and told he send me something, if I would try some other stuff just to prove he was right. Now over ten miles per hour faster and his first cam was the right one. That was over 15 years ago. He still sends me a Christmas card with a boat drawn as his signature.

BUIZILLA
12-17-2008, 07:02 PM
:confused: not sure I completely agree with the dyno graph, for a 264 cam that things climbing awful hard at 5500... there are suspiciously repetitive 60hp jumps too... not likely..

BigGrizzly
12-17-2008, 07:12 PM
I was waiting for that to come out.

DC18
12-17-2008, 10:47 PM
How many cubes will it end up being, and 850 on a small block is a ton of carb a 650 is a better all around carb that will take little to nothing off top end. I have a 750 on a 383 SB my mistake it is a bit to much! Back to your exhaust question, many have found little to no real gains just great Bling. Not saying headers are not part of a good package and that you won't eek out a few ponies, but what really counts is torque. There are some dyno charts up on Boat Freaks with headers in many types and price ranges, true they are BB charts but look them over you may be a bit surprised. Many will tell you build for best peak power @5000 as the drives do not like higher RPM's. My engine came out real close to the desk top dyno numbers, but built for a different purpose with lower HP.

P.S. you must be using the speedo not GPS, with 1% slip plugged in the prop calculator you would be spinning a tad over 5,800 to make 69.1 that motor just does not have that much snot!!

Phil


MOP, you missed the 1.65 ratio, I get 5600 rpms about 7% slip. However In a 16 or 18 Donzi the 69 will not happen with a stock 350 mag, carb or MPI. I agree with you the carb is too big. The other thing is with the numbers you won't see 80+ in a small Donzi, regardless of hedders. At 69 what rpms are you turning? It would be helpful. That efi system still has a flaw in it. What I see here is a drag car engine that won't work in a well boat. The numbers you posted are similar to a ASA engine we dynoed a week ago for lethal injection. A tad short of the one we dynoed. I don't want to hurt your feelings, just trying to ready you for disappointment. Good luck.

Cubic inches are 350. The throttle body is actually a 800cfm. The desk top dino program I used is Dyno2000 and is pretty accurate. As for car engine, talking to Comp Cams, the cam I have listed is supost to be a Marine EFI cam. As for the mph, at 69 mph (speedo not gps) the rpm's are 5000. You won't hurt my feelings, thats why I am asking questions, so I won't be disappointed and do it right the first time. The engine is stock now, but want to get more performance (speed) and keep it dependable. I have also considered going from EFI to carb. Current H.P. is 330 at the crankshaft. A small block likes to breath so I am looking for good exhaust.
I do realyize that more torque is better, thats why I configured the engine the way I did. By the way the compression ratio is 9.5-1. All your help will be used.

Stevo440
12-18-2008, 11:54 AM
Wow those HP & TQ numbers seem awfully high for a NA 350 with a cam with 212 duration at .050. If it was a BB they might be in the ball park. The HP is still climbing at 5500, does not sound like it would work in a boat unless your planning to turn the outdrive into the 6000 rpm range and higher and that is a no no.. Like everyone said above car engine technology (high rpm engines don't work real well in normal boat applications), build power peak for 5000rpm, advance cams, use wider lobe separations, keep duration on the lower side, carbs/TBs on the smaller size, dual plane manifolds, not single plane, build a package that complements/matches all the pieces, the engine and components need to work together/teamwork not as stand alone parts. Good luck in your adventure a head....

Steve

BigGrizzly
12-18-2008, 12:02 PM
My suggestion is wait for the Stainless Marine, especially with a 350 to 400 small block, no question. As for the comp cams listing, I will not bad mouth them, so I won't say anything. As for the compression My Ford has 10.5 and the blower chevy has 9.5. The problem with Desk top dynos is just that they are Desk top. Unless you put it on a dyno, with a capable operator they are just numbers. Even Real dyno number are not without scrutiny. Big numbers don't always relate to top speed. To do 70+ it will take more then 330 HP. Ask the board members.

BigGrizzly
12-18-2008, 12:18 PM
In case you don't know years ago Steve got into a New Jersey discussion with a famous carb tuner who wrote a well received book and won. Could not rest telling the story

DC18
12-18-2008, 08:22 PM
Wow those HP & TQ numbers seem awfully high for a NA 350 with a cam with 212 duration at .050. If it was a BB they might be in the ball park. The HP is still climbing at 5500, does not sound like it would work in a boat unless your planning to turn the outdrive into the 6000 rpm range and higher and that is a no no.. Like everyone said above car engine technology (high rpm engines don't work real well in normal boat applications), build power peak for 5000rpm, advance cams, use wider lobe separations, keep duration on the lower side, carbs/TBs on the smaller size, dual plane manifolds, not single plane, build a package that complements/matches all the pieces, the engine and components need to work together/teamwork not as stand alone parts. Good luck in your adventure a head....

Steve

Advise well taken. I will get better info reguarding the engine. I will call some marine engine builders for advice. I will be looking for the headers.

DC18
12-18-2008, 08:24 PM
There will be a set of Stainless Marine exhaust in the Registry auction after Christmas..
Will be watching.