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Discussion Starter #1 (Edited)
Help me with the "science" of a car intake vs boat intake. GN7, I'm looking at you.

Here's what I'm needing help with. Does a jet boat "load" the engine enough differently than a car to "shift" the powerband of the intake it needs?

Not sure if that made sense...so I'll try to ask another way. Say the engine in my jet boat only runs 6000 rpm, then do I get an intake for a car that is perfect for the 6000 rpm range, or does it shift up?

I ask...because I have a 383 LS1 in my boat. With a Performer RPM and carb, it revved 5700-5800 rpm, a Super Vic and carb, it revved 6000-6100 rpm. Now, with a Fast 90 intake (that is usually great in the 5500-6000 rpm range) it'll only rev to 5500 rpm. - it'll "flash" to the 6200 rpm rev limit, but then get pulled down to 5500 rpm. I'm 99% sure the issue isn't the tune, so I'm wondering if the intake it just a bit undersized?

The intake that I *think* would be good has an optimum rpm range of 7000-8000 rpm - and I know my engine will never be able to spin over 6000 rpm. But...I'm wondering if that might actually be perfect?
 

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northern member
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what carb ? try a super sucker on the victor :))THumbsUp
 

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mo balls than $cents$
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Canuc he is efi. i do agree on the intake.do that super victor with a elbow for your tb.may have to change rails tho :(
 

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fockin efi :angry::stir:;) put a carb back on .
 

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don't know efi , but think the fact that the carb on the victor pulled 5-600 more rpm says you want the higher rpm efi manifold . that or the tb is just too small ??? where's Beer 30 :D
 

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Here's what I'm needing help with. Does a jet boat "load" the engine enough differently than a car to "shift" the powerband of the intake it needs?

Not sure if that made sense...so I'll try to ask another way. Say the engine in my jet boat only runs 6000 rpm, then do I get an intake for a car that is perfect for the 6000 rpm range, or does it shift up?

I ask...because I have a 383 LS1 in my boat. With a Performer RPM and carb, it revved 5700-5800 rpm, a Super Vic and carb, it revved 6000-6100 rpm. Now, with a Fast 90 intake (that is usually great in the 5500-6000 rpm range) it'll only rev to 5500 rpm. - it'll "flash" to the 6200 rpm rev limit, but then get pulled down to 5500 rpm. I'm 99% sure the issue isn't the tune, so I'm wondering if the intake it just a bit undersized?

The intake that I *think* would be good has an optimum rpm range of 7000-8000 rpm - and I know my engine will never be able to spin over 6000 rpm. But...I'm wondering if that might actually be perfect?
Here's my 2 cents. Steelcomp may have more to say because flow is his thing, and he understands jets better than I do. I know the basics of a jets power band.

A car can utilize a over rpm, in the manifold and cam. It has gears, and a "over" rpm can land it back in the power band on a shift. High stall converters can tolerate manifolds and cams that would suck in the same engine with a tight converter and tall gears.

A jet can tolerate a manifold aimed at higher rpm power than say a heavy I/O. It literally blows thru the low end drag. Where a single plane manifold in a I/O may be a pain in the ass, and hurt planning, the jet blows thru that point almost on the hit. It CAN BE like a dyno that doesn't start loading the engine until X RPM is reached. But once it does load it, its pretty much fully loaded. Its the reason the Fast 90 gets pulled back to 5500 after an over rev.
the max load that engine can tolerate is 5500 with that impeller cut.
So a car engine that may have a manifold that is suppose to give up at 6000, may actually rev to 6500 because the gearing and load in less than high gear. A car engine that may only turn 6000 in high gear flat out on Bonneville salt, can easily turn 6500 is second. The "over rev past the manifold/cam peak can allow it to fall back to inside the meat of the curve on the shift.
The jet is in high gear the second the pump sees full load. You are already in high gear. Its kind of like taking a Powerglide and running it in high gear only, but with a loose converter that allows the engine to rev into its power band and pulling the converter the length of the track. The RPM will be what ever the power verses the converter and gearing, and will pretty much pull the same RPM start to finish with maybe another 500 on top end.

So, in short, where a big heavy I/O might love a dual plane and 850, the jet might run better with the same engine, and a single plane with a 950.
The boat itself plays a huge part too. Heavy verses light, no different than a car.

Heres the biggest issue I see with the manifold you mention. The LS is not the number one engine on the planet for carb manifold selection. The BBC is probably number one. If not, it is a very close second to the SBC. Huge selection. Carb manifolds for the LS tend to be geared towards serious HP, or they are street manifolds.

Its a tough one to call. Up side is, the single plane for the LS1 is probably RPM rated at 350 ci, not 383. Like reading a cam catalog and seeing a cam that is 3500 to 7000, and you stick it in a 572 and it lays down at 5500.
If the manifold was 6000 to 7000, I would say I see no problem. But a manifold rated for 8000, on a LS1 makes me wonder about its cross section and plenum area. It could be a loser on a 6000 rpm jet. But then, they seem to love tunnel rams even more so than a v drive.

You say the Fast 90 falls off early. Ever consider the throttle body size? Specially with a 383.
You say the Super Victor turned the Rs you are looking for. Are you now trying to match that with a EFI and found the Fast 90 didn't hit the number?
I would still question the throttle body size, however, I am pretty sure when you hit the wall with a tuned port manifold, its pretty much finished. Again, unless you are choking it with a too small of a throttle body.
Curious, what does a 8000 RPM EFI manifold look like if it doesn't look like a single plane (Super Victor)carb manifold with a throttle body???
I dunno, I think I will throw this ball in Mr Steels court and see what he has to say. First thing he is going to ask, WHAT IS THIS MANIFOLD?

I just remembered why I love blowers. This N/A stuff can be tricky. :D



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Discussion Starter #7

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That's about what I expected, as opposed to the long runner Fast 90.
The Edelbrock Proflo is not unlike a T ram with a larger plenum and relatively short tapered runners, the Victors are basically the same as the carb manifolds.
The Pro 'Flo probably has a wider power band than the Victors. It would probably have better manners and overall drivability over the victors in a car. . Would it be better in a jet. You got me. My gut tells me no. In a heavy I/O, probably. Jet seems like it would drive right passed any low RPM benefits it might have over the Victors.



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Discussion Starter #9
I really have more to say about what you posted earlier than I will right now. Just not in the condition right now...but...

The Pro-Flo XT has had good reports of being good across all powerbands, but it seems like in general - jet boat manifolds don't follow suite with everything else.

One of my big debates is the Super Vic vs Hi-Ram. So the story goes...above 7k rpm the Hi-Ram is better than the Super Vic. But...I only turn 6k rpm - but in a way, it seems like jet boat engines "like" manifolds that would be considered outside their rpm range?
 

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mo balls than $cents$
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I like the rams out now but like you posted when are you gna need that much intake? Prob can find a nice used super vic efi intake on yellowbullet ls section for sale sticky ;) elbow for your tb cheap there to.
 

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Not the first time someone has experienced your results. Wont be the last either.
Check this out, then stick with the carb. Or trade off some power for the placebo of supposedly better manners. Or spend a lot of $ & time trying to equal the carb when you may never quite reach it.
Pro Systems - Under The Scoop
 

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I've bought many carbs from Pat.

I'm not completely sold on what he has to say in that article. NASCAR went EFI and they wouldn't give up 1/2 of one HP for anythng. Including fuel economy. For the sake of discussion lets say he's right. I don't think the OP had a pro systems carb on it. I don't see an out of the box carb out HP an EFI system. Both being matched well to the engine. Pat's blueprinted state of the art carbs only out performed by 5% by his claim.

I think his throttle body is too small.
 

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NASCAR went EFI because they restrict HP to a certain amount and when restricting HP and trying to win, then yes EFI and MPG will win. FormulaZR is looking at Max HP.
 

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NASCAR went EFI because they restrict HP to a certain amount and when restricting HP and trying to win, then yes EFI and MPG will win. FormulaZR is looking at Max HP.
He's looking for an intake manifold. But apparently he needs a Pro Systems carb also. ;)
 

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I tend to agree with Infomaniacs prior statement, the FAST 90 has a 90mm throttle body. No matter how big the injectors you put in it, it is limited by the throttle body.
 

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Canuc;2738898where's Beer 30 :D[/QUOTE said:
I would think the 90tb would be MORE than enough for a 383.

My thought would be loss of velocity? Like running headers with primary tube that are too large - the flow "slows down" due to it tumbling around in too large of a "hallway".

I've seen a 502 on a dyno where they were chasing every last HP. They left the TB bolts loose, got the engine to full song, and then stepped up and REMOVED the 90mm throttle body. No change. So, I personally wouldn't believe it the TB itself.

I know the first picture Holley ram intake is a formidable piece. Standard issue on the COPO Camaro. Plus, I just saw one first-hand on a 5-seat sand-car. I had a GM ECM reflashed at a local LS performance shop. He has two dynos and is constantly tuning LS-powered stuff. Anyway, this sand car had an LS7 + stroke to 440. Don't know who's cam, but with 2 76mm turbos, on E85 and water/meth spray via this intake:


It hit 1250 at the wheels. So, I don't know how much it makes WITHOUT the turbos, but sure worked for that setup.
 

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I tend to agree that the Fast manifold at some point where a larger throttle body is of no benefit and on serves to loose resolution, it will happen with a smaller TB than the Edlebrock or Holley. Its not designed around RPM. Its the "dual plane" of EFI manifolds.
If I was building a max effort 427 LS, I would probably be all over the Holley. But on a 6000 RPM 383 LS1 in a jet, I wouldn't care to be the one that says its a better choice than the Proflo, or even the Victor. I am just not all that confident to choice. I can only say I can see where the Fast was the answer.
Either Andrew's experience with different EFI combos, or Steel's with the effects of the plenums and runners and being a jet would have a much better idea than I would.



I've bought many carbs from Pat.

I'm not completely sold on what he has to say in that article. NASCAR went EFI and they wouldn't give up 1/2 of one HP for anythng. Including fuel economy. For the sake of discussion lets say he's right. I don't think the OP had a pro systems carb on it. I don't see an out of the box carb out HP an EFI system. Both being matched well to the engine. Pat's blueprinted state of the art carbs only out performed by 5% by his claim.

I think his throttle body is too small.
I have heard this same claim about Nascar's switch to EFI and not losing any HP. But they ALWAYS manage to fail to mention that aside from the fact that they are not dealing with the pressure drop/restriction of a venturi OR that the air is dry NO FUEL taking up precious space thru the throttle bores verses a carb throttle bores, THEY STILL INCREASED THE SIZE OF THE THROTTLE BORES A 1/16 AS WELL!!!! as well as increased the restrictor size on the restrictor plate races.

Did they bother to test a carb at those sizes, and does anybody know what those results were? Not that I ever heard of. Only that they gave them more throttle bore to get them back to where they were.
I also find it very interesting that if they moved the injectors any closer to the throttle body, they might as well run a TBI. Some speculate that they are that high due to vaporization, others to induce fuel cross talk in the plenum under the TB. What ever, the injectors are MUCH closer to the TB than they are to the head, and it a known fact there is fuel cross talk taking place under the TB. It all adds up that they are trying to mimic a carb with a EFI.



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I have heard this same claim about Nascar's switch to EFI and not losing any HP. But they ALWAYS manage to fail to mention that aside from the fact that they are not dealing with the pressure drop/restriction of a venturi OR that the air is dry NO FUEL taking up precious space thru the throttle bores verses a carb throttle bores, THEY STILL INCREASED THE SIZE OF THE THROTTLE BORES A 1/16 AS WELL!!!! as well as increased the restrictor size on the restrictor plate races.

Did they bother to test a carb at those sizes, and does anybody know what those results were? Not that I ever heard of. Only that they gave them more throttle bore to get them back to where they were.
I also find it very interesting that if they moved the injectors any closer to the throttle body, they might as well run a TBI. Some speculate that they are that high due to vaporization, others to induce fuel cross talk in the plenum under the TB. What ever, the injectors are MUCH closer to the TB than they are to the head, and it a known fact there is fuel cross talk taking place under the TB. It all adds up that they are trying to mimic a carb with a EFI.
:))THumbsUp :D
Maybe the OP can change the TB and get back with us & report if it gained all of the rpms back to even equal what the carb did.
 

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:))THumbsUp :D
Maybe the OP can change the TB and get back with us & report if it gained all of the rpms back to even equal what the carb did.
Good point.
 

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:))THumbsUp :D
Maybe the OP can change the TB and get back with us & report if it gained all of the rpms back to even equal what the carb did.
Good point.
Without know what the size of the TB, it is very possible that the TB is whats limited the FAST. We have all come to that same possibility. But like Beer said, that manifold is going to hit the wall sooner than the Holley or the Proflo. After that, you can rip the TB off and toss it, its not making any more power.
Was the manifold already maxed out in the TB department, don't know. I am no cam expert, specially when it comes to long runner efi manifolds, but I question the wants of a long runner efi manifold verses a Victor and a carb.



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