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TBI on a bbc marine application. Bad idea?
I was gearing up to try the Sniper system on my 509 with air gap intake but heard that the single carb on a bbc is bad enough at distributing the mixture as it is, but a TBI with its finer atomization compounds the problem. Approx 550hp. Any real world experience on this? |
I can't comment on the fuel distribution issue, but have helped an individual with a BBC and bored out big injector TBI. Ran fine but pulled vacuum at WOT due to insufficient air flow. This even with the bigger bore TBI. Cam and heads were very mild too.
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Originally Posted by Trash
(Post 4627714)
I can't comment on the fuel distribution issue, but have helped an individual with a BBC and bored out big injector TBI. Ran fine but pulled vacuum at WOT due to insufficient air flow. This even with the bigger bore TBI. Cam and heads were very mild too.
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run 2 or 3 tbi's,problem solved.
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I have always wanted to try and run two TBI's on a dual 4 barrel intake.
You would have to be experienced with tuning, or know someone that is. My stock 5.7 EFI Merc has the big block TBI on it. They adapted it to a tiny 2 barrel intake. We will see if it still has vacuum at wide open throttle on my 383. If it does maybe next year I will try and run two of them. |
Don’t use a dual plane intake manifold. |
Originally Posted by sutphen 30
(Post 4627755)
run 2 or 3 tbi's,problem solved.
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Originally Posted by Baja Rooster
(Post 4627812)
Lol. So I’m ignorant on the Tech, but what’s so different between the Merc TB on the Merc MPI and a 4 barrel TBI? Is it the huge plenum or the lack of fuel thingamajiggers in the venturies? |
So this is a project/Topic i have a special interest in and have been doing tons of research on it. I'm a firm believer that EFI is far superior to a carb any day and all day. but i can save that lecture for a different day.
thread i have started on it https://www.offshoreonly.com/forums/...aps-350-a.html gear head EFI will have stock truck bin files and the matching .xdf files
Originally Posted by Paxtonspeed
(Post 4627771)
I have always wanted to try and run two TBI's on a dual 4 barrel intake.
You would have to be experienced with tuning, or know someone that is. My stock 5.7 EFI Merc has the big block TBI on it. They adapted it to a tiny 2 barrel intake. We will see if it still has vacuum at wide open throttle on my 383. If it does maybe next year I will try and run two of them. The unmodded TBI units should be (i can post the math if needed) 5.7L SBC 2x 1-11/16" ~=490 CFM 7.4L BBC 2x 2" ~= 645 CFM a 350 @55000 @ 0.85 VE =~474 CFM No such thing as zero vacuum at WOT in a NA engine. Each piston on it's downward stroke with intake valve open, creates vacuum to pull the intake charge in. Equal pressure on both sides of intake manifold creates NO air movement, it's physics. Holly assumes a 1.5" pressure drop across the carb, so you should not see "0" vacuum.
Originally Posted by hogie roll
(Post 4627811)
Don’t use a dual plane intake manifold. Engine Masters ran into the issue you were talking about. |
My Innovation 540 CI 600HP engines had Holley TBI and they were GREAT!
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Originally Posted by KeatonAZ
(Post 4627934)
So this is a project/Topic i have a special interest in and have been doing tons of research on it. I'm a firm believer that EFI is far superior to a carb any day and all day. but i can save that lecture for a different day.
thread i have started on it https://www.offshoreonly.com/forums/...aps-350-a.html gear head EFI will have stock truck bin files and the matching .xdf files for a stock merc 260hp 350Cu.in motor the 2x 1-11/16" should be fine. The unmodded TBI units should be (i can post the math if needed) 5.7L SBC 2x 1-11/16" ~=490 CFM 7.4L BBC 2x 2" ~= 645 CFM a 350 @55000 @ 0.85 VE =~474 CFM No such thing as zero vacuum at WOT in a NA engine. Each piston on it's downward stroke with intake valve open, creates vacuum to pull the intake charge in. Equal pressure on both sides of intake manifold creates NO air movement, it's physics. Holly assumes a 1.5" pressure drop across the carb, so you should not see "0" vacuum. you can run it on a dual plane, you just need a spacer or a way of balancing the vacuum pulses between the plans ( milling or cutting the interior wall) Engine Masters ran into the issue you were talking about. https://www.youtube.com/watch?v=2sQJPZYSoUI I should have said 100 kpa MAP value. While scanning you should see very close to 100 kpa MAP values at WOT, depending on atmospheric pressure in your area. If you are seeing high 80's low 90's, that would indicate a restriction. |
I just installed and tuned my neighbors BBC street car with the sniper system. We bunged all the header tubes with EGT, went out for a drive with it set on self tune. Other then idle I had todo very little tuning other then at idle(big cam) and balance between cylinder according to the EGT was with in 5%. This is with a single plane manifold cant remember who's.
I was sick and tired of hearing him fire this thing up every morning at 6am, revving the piss out of it getting to warm up so it would idle. I mentioned it to him that he should look at this sniper system by Holley. He ordered one that night and had it installed quickly. Lets just say we both are very happy now :) |
That’s great input, thanks! I can see how in car applications a little restriction at wot is no big deal, but for my application where it’s a glorified wake boat it rarely sees 5k anyways and would prefer the simplicity of a FI TBI. Im currently wrapping up my engine build and was debating going down the long road of $ for timing cover with sensors for $500 now for a $2k+ system later but honestly that would be lipstick on this pig. I love my pig, but I have to stop feeding the trough at some point. Its a bummer that i just gave away a Victor Jr but I have a spacer for the airgap. It seems like every engine masters video I’ve seen they struggle with the dual plane, but they never had the channel or spacer on it. For my build the airgap has proven superior up to about 600hp, so that’s what I’m using. It should make the boat easier around the docks for the girlfriend as well. |
Originally Posted by Paxtonspeed
(Post 4627964)
I should have said 100 kpa MAP value.
While scanning you should see very close to 100 kpa MAP values at WOT, depending on atmospheric pressure in your area. If you are seeing high 80's low 90's, that would indicate a restriction.
Originally Posted by Baja Rooster
(Post 4628008)
That’s great input, thanks! I can see how in car applications a little restriction at wot is no big deal, but for my application where it’s a glorified wake boat it rarely sees 5k anyways and would prefer the simplicity of a FI TBI. Im currently wrapping up my engine build and was debating going down the long road of $ for timing cover with sensors for $500 now for a $2k+ system later but honestly that would be lipstick on this pig. I love my pig, but I have to stop feeding the trough at some point. Its a bummer that i just gave away a Victor Jr but I have a spacer for the airgap. It seems like every engine masters video I’ve seen they struggle with the dual plane, but they never had the channel or spacer on it. For my build the airgap has proven superior up to about 600hp, so that’s what I’m using. It should make the boat easier around the docks for the girlfriend as well. |
I have a DUI ignition currently and happy with its simplicity. I was looking at this kit on eBay but seems like it could end up a nightmare of teething issues for the initiated. https://rover.ebay.com/rover/0/0/0?m...2F192533014532 |
Originally Posted by Baja Rooster
(Post 4628042)
I have a DUI ignition currently and happy with its simplicity. I was looking at this kit on eBay but seems like it could end up a nightmare of teething issues for the initiated. https://rover.ebay.com/rover/0/0/0?m...2F192533014532 picture shows a 6 window trigger but here is what is what it should be https://cimg7.ibsrv.net/gimg/www.off...bfb8969437.jpg https://cimg7.ibsrv.net/gimg/www.off...0c7004a869.gif |
Originally Posted by Paxtonspeed
(Post 4627964)
I should have said 100 kpa MAP value.
While scanning you should see very close to 100 kpa MAP values at WOT, depending on atmospheric pressure in your area. If you are seeing high 80's low 90's, that would indicate a restriction. |
Originally Posted by Baja Rooster
(Post 4628008)
That’s great input, thanks! I can see how in car applications a little restriction at wot is no big deal, but for my application where it’s a glorified wake boat it rarely sees 5k anyways and would prefer the simplicity of a FI TBI. Im currently wrapping up my engine build and was debating going down the long road of $ for timing cover with sensors for $500 now for a $2k+ system later but honestly that would be lipstick on this pig. I love my pig, but I have to stop feeding the trough at some point. Its a bummer that i just gave away a Victor Jr but I have a spacer for the airgap. It seems like every engine masters video I’ve seen they struggle with the dual plane, but they never had the channel or spacer on it. For my build the airgap has proven superior up to about 600hp, so that’s what I’m using. It should make the boat easier around the docks for the girlfriend as well. |
Thanks, Smitty. Everything that I’ve read about the air gap is it’s more impressive than other dual planes and only giving up a smidge on the top end. Mine is a 509 that will probably never see north of 5500, and lives around the 4K range 95% of the time. It’s a 272 Islander and about the 60mph mark the girls start screaming, towels go overboard, dogs start freaking out, etc. I enjoy performance but this boat isn’t doing poker runs anytime soon. |
Originally Posted by articfriends
(Post 4628486)
if your motors a 502 or smaller you'll be happier with that air gap unless your really winging the crap out of it. I'll take the 10 to 40+ ft lbs tq/hp from 2500 to 5500 any day of the week plus much better cyl to cyl afr/distribution. Just wrapped up a sorta zz502 marine engine dyno session for a friend and vic jr wasn't in same zip code tq and hp wise or afr wise (did have small cam).
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