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Carb spacers for performance

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bill_k

Regular Contributor
has anyone ever installed carb

has anyone ever installed carb spacers and got any type of performance gain?? Motor being lets say a 97 5.7L 4bbl thunderbolt V
 
"Ayuh,....

I think the only

"Ayuh,....

I think the only measurable Gain will be the financial sheet of the seller of the part...."
 
"Not worth the effort.

The

"Not worth the effort.

The biggest bang for the buck when doing performance upgrades here are a few that I have seen/done.

If you purchase a new aluminum dual plane intake ( rpm gap, from edlebrock) and the 5.7 LX style flame arrestor ( it is twice as thick as the standard) That alone will give you a 15 to 20 hp gain. That is the only difference between the standard 260 hp and the 270-280 hp Merc motors from the factory. Carbed only!!

If you do a part number search the 20 hp difference is only the intake and flame arrestor. I did the research once............

The next level would be to go bigger on the cam keeping the new intake and flame arrestor. A small change in the cam would easily bump you over 300 hp.

A carb spacer alone will not get much for you. Infact it may cause off line stmbles due to the increased distance the atomized fuel has to travel. Putting the carb further away from the vavles typically helps with top end performance and not low end. The gains if any would be only at the top."
 
"what do you guys think about

"what do you guys think about this idea:

Take an 87 model 260/5.7 Add a set of vortec heads and a dual plane aluminum intake, a 350 MAG cam, and a 350 MAG flame arrestor. what kind of horse power gains do you think this combo would bring"
 
"In a boat I think 275HP is ab

"In a boat I think 275HP is about the most you would EVER get with a stock bottom ended 350 with non vortec heads and 300 hp or so is max with the Vortec heads. Cam changes are pretty ineffective for an engine running a max speed of 4600 rpm. The stock Mercruiser cam is already doing all you need for that rpm.

a 350 turning 4600 rpm can only eat so much fuel and move so much air. If you keep adding more fuel, the mixture gets rich and you lose power. That's why boaters build 383's....more torque at lower rpm..you need the extra 33 cubes of stroke to make the torque.

The only way these performance goodies work on 350 cubic inches is if you put them in a car and turn the motor higher rpms.

Here's where the rubber does NOT hit the road:
A stock 260HP marine engine IS ALREADY a 300HP engine in the Summit performance world....if you put a Mercruiser engine on a dyno and spin it 5300 rpms, guess what you get?
300HP

So if you go shopping and see promises of wild HP with bolt-ons, ask to see the dyno sheet...what you will see is most bolt ons simply make a 350 breathe better when you rev the engine higher than it was intended."
 
"How about a 6.2 MAG MPI rated

"How about a 6.2 MAG MPI rated at 320 propshaft hp? Same block and weight. No carbs to dick around with.
Or if you really want to get going how about a blown 502 putting out 700 hp or so?

Any other marginal hp gain items will not be worth spending any amount of money on IMO. why?
Because the speed you gain will only be the square root of the hp gain.

To put that in numbers, if you increase hp by 50%, you will only gain 22% in speed. So if you were making say 50 mph before with 260 hp, you should get 61 mph after with 390 hp. And you will be burning 50% more gas to do it.

That is why it typically takes huge hp in a boat to break 80 mph.

If you get your 350 up from 260 hp to say 290 hp with the changes you are suggesting, this will get you a whopping 5.6% gain in speed. Is that worth the effort to you?

Rod"
 
"Almost forgot, the heads and

"Almost forgot, the heads and the machine work were free, the intake runs about 175 bucks, and the labor to change it out is also free, doubt i will put a pile of money in a cam for a 21 year old engine. so really what is 3-5 mph per hour costing me? oh yeah about 175 bucks"
 
"not sure about the hours, it

"not sure about the hours, it has no meter. its no slouch for its age. it fires everytime and runs like a top. has good oil pressure and stays good and cool. my family owns a garage and machine shop so if i pop its top im able to do a rebuild fairly quick and inexpensively"
 
i wish i could afford a new co

i wish i could afford a new concord mach II with a small block MPI. My buddies dad has one and it will freakin' haul ass. it will come past mine like im tied to a tree. he's probably getting around 65mph or so but as we all know thats moving pretty good on the water
 
"I swapped a 320 hp 6.2 MAG MP

"I swapped a 320 hp 6.2 MAG MPI into my 20' Mirage last year in place of a 180 hp 4.3. Great swap and really woke the boat up.

I know I am getting somewhere over 60 mph, but every time I get a little over 55 mph the pitot tube fitting blows off the drive leg, and I lose all indication of speed. Need to sort that out somehow.

Regardless of top end, the boat is much livelier out of the hole and pulls like a bear. I run a 21" High Five SS prop with a 1.47 Alpha Gen II drive. The boat weighs about 2600 lbs empty.

Rod"
 
"Rod, rap a cable tie around t

"Rod, rap a cable tie around the plastic and that may help. When I used to break them when forgetting to disconnect them when removing the outdrive I would secure them with a small cable tie till I could buy a bag of replacements.

David, There is no differenc in the cam shaft between a standard 260 hp 350 and the 270-280 hp 350 Mag. The only difference is the intake and flame arrestor. I have looked into this a long time ago and actually researched all the part numbers.

Hystat, You are very good with your explanation!
But I see no issue with spinning the Alpha at 5500 or so. I myself always considered the 4400 -4800 rpm limit a fuction of reliablity not power.

Most small block v8's (350) style typically have a red line of 5500-5800 rpms. I belived that the lower marine spec for rpm's was a safety margine biult in for reliablity.
I could be wrong.........

That being said a factory 260 hp Marine block is in reality a 260 hp truck base motor. That 260 hp spec on the motor is at red line rpm's.
I think it just happens that the HP curve flattens out at and above 4600- 4800 rpm due to the cam as you said.

You can purchase a better cam that will give you the same basic rpm range but higher lift and durations thus more power. So running at 5000 to 5500 I do not see it as a issue as long as the OWNER understand that at those elevated rpm's the motor life span will be reduced! OH and fuel comsumption will.....well lets just say you will be able to watch the guage move...........LOL

I am not sure but if the base block is not a VORTEC you can not swap vortec heads to a earlier style motor. It has to do with the intake to head angle and I also belive the mounting screw hole angles..........Its been so long I forget........
I play with Harley's these day not cars or boat motors. Although I still do some repair work but mostly just for friends."
 
I think it might also be the g

I think it might also be the gimbal bearing that is the rpm limiting factor...it looks like a medium speed straight roller bearing and it's just in grease. If could seal that bearing and pressure lube it with engine oil...hmmmm
 
""my family owns a garage

""my family owns a garage and machine shop"

Will you adopt me? I want to improve my 175 HP 4.3L non-vortec engine for $175 too.
biggrin.gif
"
 
Kghost:

Wouldn't that b

Kghost:

Wouldn't that be great! You just keep posting your diatrides that get on some folks nerves; they stimulate conversation. Your vast experience and knowledge are a great addition to this board. Maybe add some softer comments to help the sensitive readers that feel insulted by the verbiage of them. Glad you are among us.

P.S.

The only reason I have so many posts is that I retired @ 55 and needed something to keep me busy during the boating off season; it has turned into a daily ritual as I TRY to help people w/their problems.
 
"GUY,

Did you mean "dia

"GUY,

Did you mean "diatriBes".

Yes I ramble on sometimes and I do have a habbit of telling it like it is.

There is much danger when giving instructions to people who are trying to fix there own problems just to save money. Some of this work is very dangerous as we all know so If I cop some attitude it is usually for a good reason allthough many may not understand it reading it in print.

I guess to many years of, to quote another poster, "rookies like me". I get frustrated trying to type an explanation to someone when you are not sure they even understand what it is you are saying.

I will try to tone it done a bit and drink more beer before replying....................LOL"
 
"Just so you guys know im not

"Just so you guys know im not trying to be a smart-ass, Im just saying I am blessed with the facilities and equipment to tinker and experiment without sinking a bunch of money into it. Sorry if I crawled under anybodys skin"
 
"That's OK! Get under my

"That's OK! Get under my skin; hell, I may walk faster and longer than to/from the mailbox. So, are you going to adopt me or not? ROFLMAO
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"
 
"Guy,
I wasn't sure what

"Guy,
I wasn't sure what to think about Kghost either when he first started posting but he seems to know his stuff. Some of the best marine mechanics in our area are the grumpiest, honeryest, crusty old salts you've ever met. And I would happily take my boat to them first thing before some smooth talker trying to spare my feelings and drain my wallet. I guess it's the nature of the trade. Keep up the informative posts Kghost. It's just another layer of expertise that makes this board the best."
 
"Guy,
I would adopt you if

"Guy,
I would adopt you if i could but with the second baby due in december i am out of bedrooms. And also I do appreciate the help from everyone on here. It keeps speed freaks like myself from running out and making stupid mistakes without putting a little thought into the task at hand and ending up with a pile of broken stuff.

Kghost,

i dont think you are salty, just a straight shooter. Not a bad quality to have in todays world. I appreciate your insight as well"
 
"I need more beer or I may sta

"I need more beer or I may start to tear up.........................
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"
 
So after all of this posting d

So after all of this posting does the carb spacers make a difference LOL J/k (I just had too)
 
NO It will not make any positi

NO It will not make any positive difference.

But a few cold beverages might~~
 
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