Exhaust Question

[Onebadcat]

I have a 1975 Tahiti Tornado with a 455 olds in it with wet logs and snails. It has thru hull exhaust with rubber flappers, that basically do not cover the exhaust. I want to build new tips out of stainless, I am a metal fab guy, basically I want 4 inch slant cuts for it. My question is do I need the flappers or not, it seemed fine the other day when I had it in the water, do the snails cause a s trap effect? thanks for any help

[roostwear]

I'll step in since you asked. It's a good idea to keep the flappers... you never know when a wake will push water up over the snails. I can't for the life of me figure out WHY you want to put offshore style tips on a boat so opposite that look. You're not gonna make it a wakeboard boat are ya?

[Onebadcat]

I dont know I like that look, its kind of neat for me, looks more muscular. So you say it is for wakes pushing up through the snails? makes sense at sitting they do not look like they are doing anything. cool thanks for the heads up

[R/C-PILOT]

I have them on mine. Last year, I found the inner flappers burnt up. Of coarse, this was after hydro-locking the motor 2 times. Didn't hurt anything, thank God, each time was at shut down. I now check them, every month.

[Onebadcat]

well I found a set on ebay that gave the idea how to make them, basically i would have a rubber flap inside the slant cut tube. See i am real new to boats and really really new to jet drive boats, I love the idea of a jetboat, less moving parts and v8 power, easy to work on, as i am a trained auto tech as well so it is second nature sort of, except it has been 10 years since i messed with a carb and I rebuilt a Barry grant speed demon and cant to get it right for the life of me, any help on that would be awesome too

[Cas]

I rebuilt a Barry grant speed demon and cant to get it right for the life of me, any help on that would be awesome too
not to worry, you're not the only one unable to get a BG to work right. Summit Racing has dropped all the BG stuff due to too many issues with warranty and lack of customer service.
Just get yourself a Holley and be done with it.

[Onebadcat]

personally I dont think it is the carb, I think it is me not remebering what adjustments to make it run right. It idles awesome, except the idle set screw is all the way out and it still idles around 1200rpm, also it bogs on take off and when coming off throttle it stalls, like I said it has been like 10 years since I messed with carbs, lately it has been nothing but fuel injection I play with, so basically I feel total rookie to this right now.

[roostwear]

I agree with Cas, ditch the BG. When I was considering a carb change I did a little research on tuning a Demon. They are not the same as a Holley (tune-wise) and good or bad, people have a hard time getting their head around tuning a Demon. If the customer service isn't there to help, why beat your head against the wall?

[Onebadcat]

agreed but this is what i have curently, honestly the best luck i have had with carbs have carter or edlebrock performance. On my 72 vette I went through like 3 holleys, and finally got ahold of a edlbrock and never looked back. I bought this BG for $150, put $30 rebuild kit Its a speed demon minus the choke tower and a 850 cfm

[TIMINATOR]

If performance is the goal, there are 2 sizes of snails, most olds motors came with the smaller ones. Install the bigger ones, also the later snails have a step in the outlet to allow use of either 2 7/8" or 3 1/2" exhaust tubing, you can cut off the step and use the big hose and tubing. Rex Marine will sell you the rubber covered flappers (you need them), and pivot axles by themselves. Call with any further questions. TIMINATOR

[bp]

not to worry, you're not the only one unable to get a BG to work right. Summit Racing has dropped all the BG stuff due to too many issues with warranty and lack of customer service.
Just get yourself a Holley and be done with it.
where have you been??? summit hasn't carried bg for 5 years, and it had nothing to do with warrant/cs stuff. jegs sells everything bg makes, and has been for at least 9 years.
demons work just fine. sometimes they work perfectly out of the box (ask sean forrest or brad parrack), and sometimes they need to be tuned depending on the specific application, which is no different than holleys. i've been running 2 mightys for 7 years, and i had issues on and off for 2 years until i learned everything i could about them and tuned them correctly. after months with the same issues, we tried a pair of "tuned" 950 holleys, they had exactly the same problems and ran no better than the 850 demons. now, under load, my engine will accelerate from 1200 to 6200 in 0.27 seconds with no bog and no delay (with data, i can see exactly what the acceleration rate is, and see things that you'd never just "feel"). i'd defy anybody to do that with out-of-box carbs of any make on a unique 538" bbc.
rather than learn how to tune them, you'd have people just toss them in a junk barrel and go spend another 700+ for a holley, or more to buy a carb someone else tuned, when they could just as easily fixed what they have. there's a fellow running river-racer this year, in a little flat, with a single 850 demon. in oregon, it developed a bog so we made a few minor changes and no more bog. in san diego (where the air is a lot different than oregon) it bogged again, so we made a couple changes and no more bog (flats are much more difficult to get rid of a bog than jets are).
so all you guys that want to take cas' or roostwear's advice and throw your demons in the garbage, just let me know so i can be the demon garbage collector... and it'll come back to haunt ya... or, if you just have a question, pm me so i don't have to wade through all the anti demon stupidity.

[Cas]

I didn't say they are/were junk Bob, I just said that many people have had issues with getting them to run correctly. I also didn't say to toss it, I suggested getting Holley.
On top of that, he has a 455 Olds not a "unique 538" bbc" that runs in the 10's or better through the lights. He is also seems to be looking to get on the water with a good running engine and not take 2 years to learn how to get it going without a bog or stalling.
It's also been said over the years that BG's work rather well at wide open throttle but seem to have issues with the individual AF mixture from cylinder to cylinder. When I was looking to get a carb I was told to shy away from the BG for those same reasons.
There is no doubt you, as well as others, have had real good success with the BG's, your records prove it. As far as anti Demon stupidity, there is none from here....ignorance from not personally owning one might be a better description.
He gave some additional info with what is going on and some additional info about himself. That's all good and it's now it's time to give him some help on what to look for and where.

[bp]

steve, you advised him to "get a holley and be done with it", basically because summit doesn't carry them. do you provide guarantees that all holleys work perfectly out of the box??? if he gets a holley, what's he supposed to do with the demon? paperweight??? very shortsighted, and not what i would consider good advice.
my point in even mentioning my junk was, if they can work on that, they can work on anything, even a 455 olds. my combination runs and responds perfectly from 2500, 3000, 3500, 4000, etc. some carbs, regardless of the manuf, are going to work just fine out of the box. some are not. just because a car carb doesn't work perfectly out of the box in a jetboat application doesn't seem a real good reason to just go get something else, and it doesn't mean it can't work if a little effort is put forth. if people can't "get their head around the tuning", all they need to do is ask - they are just as simple to tune as any holley, and in many ways, easier because of all the adjustments that are easy to make.
it appears that this demon was already on the boat when it was purchased. if it's got a bog, which is not uncommon with demons or holleys, the first thing i would do is take it apart, find out which size it is and disect it to determine if all specifications are stock. to do that, get the speed demon spec sheet linked here. if it's not a marine speed demon, find the correct speed demon chart and print it.
http://www.barrygrant.com/demon/default.aspx?page=29
he'll also want to determine if it's a "new" version demon, with the center air screw, or if it's an older model (like mine) without the center air screw. he'll need to use a pin drill set to verify that the bleeds and ifr's are the sizes stated in the specs. without knowing what the starting specs are, it's almost impossible to advise what to do to correct a problem.
the next thing to do is download the speed demon manual and read it, here:
http://www.barrygrant.com/fromBarryGrant/Demon%20Instruction%20Manuals/Speed%20Demon%20Manual.pdf
there is one basic premise that must be strictly adhered to when tuning a demon. the butterflys must be set such that, when in the closed position (against the stop), there is 0.020, or less, of the transition slots visible below the plates. if those butterfly stops are moved at all, in an effort to adjust idle or any other reason, the carb will not transition properly, and there will be a bog/delay/deadspot in acceleration.
with the butterflys set properly, and idle mixture screws at 1 1/2 turns open, the engine should idle just fine. the manual describes why/how to adjust them.
the engine should be tested with the carb in stock specification configuration, set up in accordance with the manual. if there is still a bog/delay/deadspot, we can go from there, and there are some relatively simple fixes.
I didn't say they are/were junk Bob, I just said that many people have had issues with getting them to run correctly. I also didn't say to toss it, I suggested getting Holley.
On top of that, he has a 455 Olds not a "unique 538" bbc" that runs in the 10's or better through the lights. He is also seems to be looking to get on the water with a good running engine and not take 2 years to learn how to get it going without a bog or stalling.
It's also been said over the years that BG's work rather well at wide open throttle but seem to have issues with the individual AF mixture from cylinder to cylinder. When I was looking to get a carb I was told to shy away from the BG for those same reasons.
There is no doubt you, as well as others, have had real good success with the BG's, your records prove it. As far as anti Demon stupidity, there is none from here....ignorance from not personally owning one might be a better description.
He gave some additional info with what is going on and some additional info about himself. That's all good and it's now it's time to give him some help on what to look for and where.

[Onebadcat]

well I rebuilt it myself, which i have total confidence in my abilty there, just never been good tuning it down. I did search google and found something on a corvette forum tuning a speed demon using a vac gauge, really doesnt give numbers what to look for there. My stupidness did not realize there is an idle screw for the butterflies on both primary and secondary. Also I believe it is newer with the Idle ez screw, what is base adjustment for that? it is mechanical secondaries, which i like, I hate vacuum, never any good luck thanks to all that can help. I which I had the money to through injection on this and be done with it, it seems Chevy SS454 pickup TBI will bolt up and work on a 455 what have been reading, but with the cost i threw into redoing the floor I am trying to be frugal,

[Cas]

frugal and owning a boat really don't go together very well :D
Here's another pretty good article to read-
http://www.circletrack.com/techarticles/ctrp_0707_carburetor_tuning/index.html

[bp]

well I rebuilt it myself, which i have total confidence in my abilty there, just never been good tuning it down. I did search google and found something on a corvette forum tuning a speed demon using a vac gauge, really doesnt give numbers what to look for there. My stupidness did not realize there is an idle screw for the butterflies on both primary and secondary. Also I believe it is newer with the Idle ez screw, what is base adjustment for that? it is mechanical secondaries, which i like, I hate vacuum, never any good luck thanks to all that can help. I which I had the money to through injection on this and be done with it, it seems Chevy SS454 pickup TBI will bolt up and work on a 455 what have been reading, but with the cost i threw into redoing the floor I am trying to be frugal,
1 1/2 turns open. open this file and print it for reference...
http://www.barrygrant.com/fromBarryGrant/Demon%20Instruction%20Manuals/Idle-Eze-Addendum.pdf
the article with doug shriefer is good. several years ago, i spent about an hour on the phone with him - he didn't solve my issues, but he pointed me in the right direction to start with. the key starting point which he mentions, and can't be emphasized enough, is that the butterflys must be set with 0.020, or less, of the transition slot showing below the plates. the butterfly setscrews should never be moved, once the plates are in the correct position.
also, if you're going to run it in the driveway to fine tune idle, set it about 300 rpm higher than you want on the water. if the jet is tight, the load on the water will drag the engine down 2-300 at idle. it is essential to get idle set correctly, with the transition slots covered, before any other issue (like a bog) can be addressed. make sure the rubber caps that cover the vacuum nozzles are in good shape, and not cracked/leaking.
another note - it's very important that the carb remains clean, and free of any dirt particles. particles can find their way into the bleeds, which will screw up performance.
when you have the idle set correctly, and the carb is set up consistant with the specs, test the boat to see what, if any, issues come up. if it repeatedly bogs on acceleration, at what rpm does it bog??? cruise it at various rpm, listen for any pre-ignition, and if there is any, note the rpm where this happens. post up the results.

[TIMINATOR]

BGs seem to work fine in a racing enviornment, but tend to be rich in the midrange where a typical boat or street/strip car would run. If fuel economy is no consideration, they can be fine. The 22 Daytona that I just bought has a BG carb on it and the plugs were totally black with the stock jetting, even with quite a bit of high speed testing. I went down by 3 jet sizes front and back, and they are not black anymore, but it still is rich and needs more tuning. I allways preach for the lake boat guys not to take too much stock in what the race boat guys are doing as far as parts and tune, NO OFFENSE MEANT TO ANYONE, but these are different animals. TIMINATOR

[bp]

I allways preach for the lake boat guys not to take too much stock in what the race boat guys are doing as far as parts and tune, NO OFFENSE MEANT TO ANYONE, but these are different animals. TIMINATOR
no offense??? wtf is that supposed to mean??? you insult the hell out of me and half the people i know, then say no offense meant??? well, you DID offend.
the difference here is that i don't have any kind of business, and i'm trying to give advice that i know is sound, rather than just troll for customers, trying to get them to pay for something they can just as easily do themselves.
your opinion about demons IS WRONG, basically from top to bottom. your post offers no helpful advice.
if anyone wishes to question my ability to tune a demon for river or lake use, call steve brule at westech and ask him if i know what i'm doing. http://www.westechperformance.com/index.htm
your effort to make yourself look good by running other people down without any factual basis to back up your slams is lame at best.

[Onebadcat]

cool thanks with the Idle ez info. On my experiences with carbs I have always heard BG being better and easier to set up. Honestly being in the BG it seems way better made, like billet metering blocks and everything smooth. But there is alot to adjust, alittle bit over my head now, coming off with metering rods, diffrent ball game really.People know what they like, some guys are just nuts over Holleys and some have to have blondes.Which is betterI dont know as long as it runs good. I know about being frugal on a boat, kind of a temporary thing, moving money so wife doesnt go crazy, basically I know boats are this way and she doesnt grasp it yet........

[jetboatperformance]

I have a 1975 Tahiti Tornado with a 455 olds in it with wet logs and snails. It has thru hull exhaust with rubber flappers, that basically do not cover the exhaust. I want to build new tips out of stainless, I am a metal fab guy, basically I want 4 inch slant cuts for it. My question is do I need the flappers or not, it seemed fine the other day when I had it in the water, do the snails cause a s trap effect? thanks for any help
Back to the original exaust question ,without regard you should have exaust flappers whether they be internal or external or 3",4" 0r ?? ,they will help the snail traps with the "slow down" surge of water against the transom that occurs on jet boat decel and thus reduce the possibility of hydrolocks and water reversion issues. The small cast units like you probably have were are adequate and work well (when the flappers are correct size and in place)
The "off shore" type 4" Stainless slash and straight cut tips which are necked down to either 3" or 3.5" (to fit your current rizer outlets) have been very popular the past few seasons and been selling well , one of the advantages over and above the "look" is that they will facilitate a small silencer if desired , The internal flappers are also generally "burn proof" and are very effective (they do "clank" some) Like Tim said you may have rizers that allow for easy modification of the outlet to enlarge the size , this is always worth some performance gains IMO on thru hull applications Tom
heres an example
re Demons, although I prefer Quick fuel products (for which were a dealer) , Holleys are my weapon of choice for 30 years , I have had a problem in the past with a pair of Demon T'ram carbs (castings) but also succesfully ran a Demon on my Blown Bahner jet for years
http://i147.photobucket.com/albums/r319/jetboatperformance/Eliminator%20V-drive/ResizeofDSC00317.jpg

[TIMINATOR]

Yours is not the only opinion, neither is mine. My posts are the result of my experiences. I tend not to go off on those who disagree with me, and there are a few of them! I don't believe that I am the only person on these boards that share my experiences with Demons. Read the rest of the posts. Arguing is not my thing. You may have the last word..... TIMINATOR

[bp]

tim, i'm just going to ignore you and your continuing mantra that race boat guys don't know anything.
cool thanks with the Idle ez info. On my experiences with carbs I have always heard BG being better and easier to set up. Honestly being in the BG it seems way better made, like billet metering blocks and everything smooth.
they are well made, and very easy to set up. many of the holley parts will interchange, like gaskets, jets, bleeds, ifr's, squirters, power valves, fuel pump components, etc. i prefer to use the bg bleeds because the tops are slightly different and they conform to the opening a little better, but i've run holley bleeds without having any performance issues.
But there is alot to adjust, alittle bit over my head now, coming off with metering rods, diffrent ball game really.People know what they like, some guys are just nuts over Holleys and some have to have blondes.Which is betterI dont know as long as it runs good.
there are really only a few things that -may- need to be changed from stock configuration. once you get the engine to idle properly as the manual suggests and previously noted, it'll be a piece of cake.
I know about being frugal on a boat, kind of a temporary thing, moving money so wife doesnt go crazy, basically I know boats are this way and she doesnt grasp it yet........
when i bought mine several years ago, to replace old 750 holleys that did not have the tunability of a 4150, the choices were holleys or demons. i went with the demons because 1) they were highly recommended by a friend of mine, 2) the mightys had attributes the holleys didn't (socket bowl bolts, bowl glasses, etc.), 3) they were much less expensive, and 4) very few of the other racers were running demons and i like to be a little different. i knew of 2 other racers that had run them out of the box with no problems. with the issues i originally had, we chased the issues like you would with a holley - results were mixed and at the end of it all, the issues would resurface at the least opportune time. again, choices - replace 'em with holleys, or figure out how to tune the demons. i chose the latter, and am perfectly happy i did.

[bp]

well I rebuilt it myself, which i have total confidence in my abilty there, just never been good tuning it down. I did search google and found something on a corvette forum tuning a speed demon using a vac gauge, really doesnt give numbers what to look for there. My stupidness did not realize there is an idle screw for the butterflies on both primary and secondary. Also I believe it is newer with the Idle ez screw, what is base adjustment for that? it is mechanical secondaries, which i like, I hate vacuum, never any good luck thanks to all that can help. I which I had the money to through injection on this and be done with it, it seems Chevy SS454 pickup TBI will bolt up and work on a 455 what have been reading, but with the cost i threw into redoing the floor I am trying to be frugal,
have you had the opportunity to test this thing yet???

[squirt'nmyload]

damn bob, you get em!! :D :D how ya been buddy? :)

[bp]

damn bob, you get em!! :D :D how ya been buddy? :)
just fine brian. what happened to your steelers?? shoulda kept faneca, maybe ben woulda had more than half a second against a real defense...