• If you log in, the ads disappear in the forum and gallery. If you need help logging in or getting registered, send request to: webmaster@southernairboat.com

Intake installed backwards

lboxer316

Member
When I had the engine rebuilt the shop put the intake on one way. I had to rebuild it a second time in a year and half....friend tried to be funny and threw a wave at me with a jet ski sucked in and hydrolocked the engine while I was at about 1200 rpm! Had to bring it to a different guy for rebuild and he put the edelbrock 2115 on the other direction. clearly the engine runs with the intake facing either way. Does it make a difference which way it is mounted? I see all these posts about welding up the intake. does anyone have pictures of what they are talking about and how much difference does that actually makes? I have a DD 17' fiberglass boat. after my initial rebuild my engine is very snappy but I lost a lot of top end speed. I did about 52 on the gps.... averaging only 43 now! not very happy about that!!! Any insight is helpful!
 
As you've stated, it will mount and run with it backwards. The only reason I've known for that to be done deliberately was when fabricating A/C compressor mounts in a car, as the 2115 had none. In that case, there may well have been a spacer used to correct the attitude for the carb. Without restarting a debate about how effective a 2115 is at DD RPMs, I don't think there would that big of a difference air flow wise.

The carb pad on most intakes is a little higher in the back in an effort to help keep the carb closer to level when mounted in a car.
If your intake is on backwards, that incline may be compounded rather than corrected. While it may not seem like that would make that big of a difference, if your carb is not filling the bowl it could claim some top end. Have you reset the float level to see if that yields any positive results? What kind of carb is it?

It is not uncommon to mount the carb backwards to simplify the throttle linkage mounting. This typically presents no deleterious effects, but that may well be the with the carb closer to level than what you have now. In fact mine has been like that for years, however the intake is not on backwards.

If you are comparing results of two different rebuilds, your difference could lie elsewhere, but I would probably at least try to adjust the float level and see if you get part of that back. If so, I would probably turn it around.
What carb? How many RPMs? What prop? Is it a 500 or no?

If you have a 17' DD that ran 52 and weren't over spinning the prop, you were doing well.
Your later experience sounds closer to the norm.

As far as welding up the intake, look in from the top and there is a divider under the carb mount.
It does not go all the way up to the carb base plate. The desired objective there is to extend that divider all the way up to the carb base.
Usually done by welding a plate on top of the divider to extend it up to being flush with the carb mount. Can also be formed and poured with melted pistons. This is more work, but looks better when done right. I doubt the difference would be measurable on a stock DD build.

Dammit, found a link after I typed all that. Should have looked a little harder, I reckon.
https://southernairboat.com/phpBB3/viewtopic.php?f=48&t=66529&p=646157

The incline I referenced earlier is visible in that second picture. You be the judge; were it me I'd hold backwards suspect.

cad1.jpg

cad2.jpg

Edit: With a little after the fact Moderator help, these pic were imported from the above thread. Thank-you, Sir.
It should be pointed out for those who don't check the above link that, of these pictures represent the two options as listed above. These are NOT pics of the same effort. The two preceding pics are from welding the divider. The following pic is of having Poured the divider. The later represents a result approaching artwork, courtesy of Sidejobs, who should not go without credit given the results attained.


cad3-800x600.jpg
 
it was a 472 that I converted over to a 500. builder swapped out the 76cc [they cracked] to 120cc heads. it has Holley 600 4bbl carb, 3 blade sensenich ngh running at about 2950. not sure how familiar you are with these props but I am right at the 2 mark on it.
 
Ran a caddy for 10 yrs
It had old 72" 3 bld H series on my 472 was .020 over with a comp cam and 500 Holley 2 brl turned 2900 at almost 3. Ran good for what is was but man that prop would make your ears bleed.
 
Just like Deano mentioned the fact that the intake is in a reversed configuration has NOTHING to do with a decline in power or performance. Mr. Branch has used the reversed mounting of a factory intake to accomplish leveling the carburetor to afford ample fuel. In a DD application the 2115 should not be the first choice as the factory intake typically works better in his years of experience. Unless you have things matched up and mods done there is no need to use the 2115 and the weight savings can be negated by loss of low and mid range power. The strongest non-roller DD Cadillac I have ever seen was Blu's high compression 509 and it ran a stock intake in a reverse configuration that had been port matched. On a Jimmy White 13-6 the 509 with Sensenich Q blades pushed it into the mid 60's confirmed by GPS with 750lbs persons. That is bad azz for a dd car motor :stirpot:
 
Now, your lack of power compared to the original build probably much less of a mystery.
If the second builder did not replace the pistons with the correct ones to much the new open chamber heads, mystery solved.

By design, the compression from the factory is determined by the combination of the heads AND pistons.
The early model (small, closed chamber) 76cc heads produced about 10:1 with the correct pistons.
The later model (large, open chamber) 120cc heads produced about 8.25:1 with the correct pistons.

A common, and nearly always fatal mistake is to mate early heads with later pistons. This results in nearly 13:1 which will run like a stripped-assed ape for a little bit. Then it grenades an it's done. To much compression requires exotic fuel to not detonate.

It sounds like maybe your situation is the reverse of that scenario. IF the builder either 1) reused the pistons from the original build, or 2) replaced the pistons with the same ones, you may now have a situation where you're in the neighborhood of 6.5 or 7:1 at best.
If that is the case, your top end would be radically decreased for lack of potential power output.

The pistons you need with those heads should have a round recess in the center very similar to this:
s-l500.jpg

If they aren't configured like that, they are very likely the wrong ones.

Without looking through the plug hole with a bore scope camera the easiest way to determine would be to get a compression tester and see what you get. AutoZone has a loaner program that I think may let you borrow one, if there is one near you. They aren't expensive if not.

With the early heads and pistons, cranking compression will be somewhere around 170-190 (iirc) depending on other variables.
With the later heads and pistons, cranking compression will be more like 145-165 depending again, on other variables.
If you end up with less than 140ish on a new rebuild, it would be a safe bet the pistons do not match the heads.

When you do the compression test, remove the plugs and make sure you block the throttle plate open to get valid results.
Let us know what you find out, and we'll confirm an assessment at that point. The numbers above are off the top of my head because I'm on the wrong computer, but should be close enough for case of example.

Your 2950 rpms at the two mark must have been on the early build ? or is that what you have now?
Either way, what is the before after RPMs/ pitch mark comparison ?
 
what do you mean by ports matched...if the stock intake is running in reverse configuration do you need the ports matched? not too familiar with this. I will have to look back at old pics and see how that was originally installed... maybe that's why the original rebuilder set it up that way! Ive been running this boat for 38 years and never had problems with it. I might be going back to the original intake...
 
Port matching amounts to an effort to squeeze every little bit of performance out of the engine.
While a little more power is always desirable, that difference will not touch or even dent what you are trying to re-gain.
 
Agree if the pistons were not changed to match the 120cc heads your probably now running sub 8:1 compression and if they made that mistake chances are the cam is not degreed properly. The 120cc heads for DD love a stock 472/500 intake fyi

But hey on a more positive note on a hot day it probably cranks over real easy and wouldn't need premium or blended fuels!
 
I will be putting the stock intake back on the engine. I need to send it out to get sand blasted and inspected... is it worth doing anything to stock intake while I have it at the engine shop? little insight on the current build... 120cc heads shaved down a little to true up. comp valve springs #26918-16....seat load 125 @1.800 open load 367 @ 1.150.. rate lbs/in 372. Elign pro stock cam e-1084-p...see pic for specs. also attached a pic of the pistons that are currently in it. when it was running the rpms were the same for the prop and it's hard to say where the mark was before the last rebuild but I believe right around the same mark. I was running a sesenich 72 lxl 46 before first rebuild on the boat and was over revving that after installing the full msd ignition... currently running the adjustable NGH. not an engine guy... numbers mean nothing to me... I just write the checks! any info is helpful... have not had a chance to run compression test on it yet... hopefully this weekend I can get to that.
 

Attachments

  • Cam.JPG
    Cam.JPG
    2.2 MB · Views: 3,679
  • 2-14-17 009.JPG
    2-14-17 009.JPG
    2.4 MB · Views: 3,679
  • 8-27-13 041.JPG
    8-27-13 041.JPG
    1.8 MB · Views: 3,679
Please clarify. I'm confused. That piston has a broken ring land.
Do you have the heads off ? or is that a pic from before last rebuild? I am hoping it's the later case.

Please confirm this scenario . . .
-> It was a 472, then rebuilt with the set of pistons we are looking at in that pic.
Then you had the mishap with your friends help and it needed rebuilt again.
That picture was then taken before the second rebuild and shows the aftermath of the mishap.

->The 2nd rebuild used the same kind (but new set) of pistons as the original build, and used a
a 500 crankshaft to increase the displacement. You then added the MSD ignition after that second rebuild.

That piston in the photo looks like a KB353 which should be the correct piston for those heads (good news).
However, that particular piston is junk (hoping that was from the last round).
Were they all replaced, just the bad one(s), or did they all survive?

If the above scenario is in fact the way it played out, then life is good and you may only have a tuning issue.
 
Sorry for the confusion. The piston that you see has been replaced. Those are KB pistons in it currently... apparently it was just the one piston and valve that was damaged. just wanted you to see what was in there. Unfortunately I didn't know those were no good.... would have replaced all of them when I was in there again. The msd setup was done prior to the first rebuild actually. What are your thoughts on the cam and head setup? Could the engine be lacking power to turn these new 3 blades as well as it did my old wooden prop?
 
Sorry to have misled, there is nothing those KB353s. Many of us use those deliberately as they are one of few replacement pistons that do not unintentionally cost you a little compression. They claim 9:1 IIRC, which is a little optimistic but you still are way better off than the other replacement alternatives. The KB382s (for the earlier heads) are crap and should've been pulled from the catalog. The have a stepped dish and will break ring lands if you eat a big breakfast and stare intently at them. :?

There is nothing wrong with that head/piston combination. Those heads are less temperamental than the earlier, smaller chamber ones.
You may give up a little power overall, but at DD RPMs that difference is not that big. At higher RPMs (with a gearbox) the difference can become quite noticeable depending on other parts selection.

When you say "Could the engine be lacking power to turn these new 3 blades as well as it did my old wooden prop? that is not really possible to answer because of all the information that we don't have. However, there is no reason that engine should not be able to turn that prop, as far as I know.

Did you switch the prop at the same time as the 2nd rebuild?
Did you run that top speed on the original build with the woody, and then
switch the prop when the second build was completed, which subsequently yielded your 9 mph loss on top end?

I don't think your cam is as optimal as it might be if you were still at the drawing board stage, but it will work.
I don't think I would credit all of your loss to that cam, although part of it may be.
 
The ngh prop was installed during the first rebuild so I have no comparison with the wood vs composite on that rebuild. I don't have any records of mph with the old wood prop. just after the 1st rebuild with the ngh it was in the low 50's. I had less than 12 hours on the 1st rebuild before the engine was comprised. what do you think about the original intake going back on this setup... or should I have the edlbrock intake altered?
 
The stock intake works very well for a DD.
It will work even better with a 1" spacer, as it is lacking plenum volume.
That is what I've run on mine for years, and debatably works as well as the 2115. It's definitely heavier though.

Given the ROI for 2115 upgrades with a DD, I opt to spend that time & money elsewhere.
My opinion would be save the 2115 for if you decide later to upgrade to a gearbox. It will work better above DD RPMs.
 
Now that's it's a new day and have had some sleep; what really happened becomes more clear given
that we now know what parts were involved and have a chronological sequence of events to work with.
It also simplifies things to leave the woody completely out of the equation, since it predated anything in this storyboard.

In the beginning, at your first rebuild while your engine had early, 76cc heads, that first builder screwed the pooch when he used those KB pistons. Those pistons are intended to be used with the later 120cc heads and produce about 9:1 only in that case. With the early heads that you had at that time, they produced 13:1. This far exceeds any expectation of staying together for long, absent exotic fuel use. Your first rebuild actually fell victim to the exact scenario I described earlier:
Deano said:
. . . A common, and nearly always fatal mistake is to mate early heads with later pistons. This results in nearly 13:1 which will run like a stripped-assed ape for a little bit. Then it grenades an it's done. To much compression requires exotic fuel to not detonate.
A man simply can not swap pistons back and forth between open and closed chambered heads for this reason.
This was why I elaborated earlier, and pointed out how compression is determined:
Deano said:
By design, the compression from the factory is determined by the combination of the heads AND pistons.
The early model (small, closed chamber) 76cc heads produced about 10:1 with the correct pistons.
The later model (large, open chamber) 120cc heads produced about 8.25:1 with the correct pistons.
So . . . what we know now, is that the first rebuild was running on borrowed time right out of the gate, and it was pure coincidence that your friend on the jet ski was a smart ass right when it decided to let go. It would have done the same thing without his involvement.
This also explains your comparative lack of power now. When you clocked 52 on that big ol' boat, that engine was in the "running like a stripped-assed ape" mode, and was in fact self destructing while making that effort. 12 hours is longer than most like that last.

Now after the second rebuild, you have an engine that was at least assembled with the correctly compatible parts and may very well be fine for the long term. The reason I qualify that statement is this; those other seven pistons were exposed to the same abuse as the one pictured. I don't know what lengths your second re-builder went to determine the health of those that survived. Maybe they are fine, maybe they are wounded. It would have been preferable to replace the whole set, but in actuality may not have been necessary. :dontknow:

The one thing that is for certain is that you are not going to regain your lost performance with your current stockish build.
It can and could be done, but without a defined need to go 52 instead of 43, I would call it a day or get a smaller hull to push around.

What to do now? Presumably the engine is still together (ie. you haven't removed the intake yet)?
I personally, dislike taking apart a running engine unless there is a well defined need. As such, if it is still together, I would leave well enough alone and run the 2115 that's on it. The difference is not large enough either way to make me want to buy a new bathtub to put under the stock intake, especially on a 17' hull where the difference will be even less noticeable.

Were I you, I would very diligently perform a cranking compression test and see what I get. My wild ass guess is that you will be around 160ish, although what is more important is consistency. If there is much variance then you should do a leak down test, which could show
that your loss is past the rings, which may be a red flag to your piston's health. If there is only minimal difference in comp readings (it should only be minimal on a fresh build) I would take that as a good sign and run it. Naturally keeping clean oil/filter will help. I would probably run a bit of Lucas in it as well, just for the extra piece of mind.

One last note: When you do your comp check be sure to record and save your results. Given the unknown condition of the pistons, if it seems down on power later, you'll have a benchmark to compare to. Not that you need to forever hold them suspect, but if you check it whenever you change the oil, you may head off a problem and then not need to worry about it after two or three oil changes.
 
Little more confusion I need to correct... first rebuild DID have correct heads to pistons. the original engine had the 76cc and pistons kinda like you had showed earlier but with twin recesses. my first rebuild had the 120cc installed with the picture of the broken piston that I showed and intake installed backwards. with the 120 heads and correct pistons I was doing 50 before the title wave. 2nd rebuild still have the same 120 heads and pistons on there but had a head job done... put the heavier spring in it, had it decked, etc. I was told the springs were too light and may have been causing the valves to stay open at wot. all new rings were put on the good pistons. intake installed facing correct direction. right now the engine seems to be running good but I always have a hard time leaving good enough alone! Right now I have those super traps hanging right off the headers as seen in the pic... originally it had a single muffler that was in the center of the boat that both pipes went into. The engine is considerably louder now than before and I want to put some form of mufflers back on it. supertraps are not cutting it anymore. I have time and money to waste on this thing! I want it to be right and last me another 30 years!
 
The cam has a bit more duration for a 472 than I would recommend for a DD and is a split pattern. The 120cc like a single pattern cam but that said it will probably work just loss of torque at lower rpm range.
 
lboxer316 said:
Right now I have those super traps hanging right off the headers as seen in the pic... originally it had a single muffler that was in the center of the boat that both pipes went into. The engine is considerably louder now than before and I want to put some form of mufflers back on it. supertraps are not cutting it anymore.

Boxer, no offense, but this is a hard thread to follow and I am really confused (as I think others are). Any chance you can summarize the changes since the boat ran right?

For starters now, that you pointed them out, get rid of those Super Traps! I mean, those things are for motorcycles and little cars that make fart sounds. Those things must make your ears ring and are not much better than a banana in your tail pipe for flow. Your motor is constipated. I don't know where you run, but the first thing I would try is taking those supertraps off and running open headers for a run and see if she don't run better!:violent1:

Then put a decent exhaust system on the motor, there is a reason that boat originally had a 2:1 exhaust package, it helps build low end torque. On a 2:1 set up, go with a 3" muffler. Dual exhaust is easier and will work, just don't oversize them (2" to 2-1/2" max). Go buy 1-2 SST Magnaflow mufflers and break out the welder. I bet you find a bit more torque vs. the open headers (and a lot more vs. the supertraps) with a much more enjoyable ride.

https://www.magnaflow.com/automotive-performance/mufflers/xl-muffler/

There are only 2 kinds of jet ski riders, pricks and chicks.

Chose Chick :thumbleft:
 
Slidin Gator said:
Boxer, no offense, but this is a hard thread to follow and I am really confused (as I think others are) . . .
Don't feel like the Loan Ranger, brother. :roll:
Even resorting to laying out a best guess scenario based on available information and asking for a confirmation, does not reveal relevant or complete information. This thread reads like I've been trolled, as the information changes post to post. I've decided to not play anymore, life is to short.

Given the time that I've already devoted to try and help him though, I will make this last post before I become a spectator (if that).
You sir are correct, his engine needs to breathe deeper than it can now. You also make a very specific suggestion that I will confirm.

Boxer, you should run 2.5 inch exhaust out the back, using a pair of #13216s that Gator pointed you to.
I've done this, and it's a time proven combination that will provide the back pressure you need without being overly restrictive.
It will also quiet it down very nicely, if that matters to you. That was one of my goals and they fit that bill.

Those God forsaken SuperTraps are junk. I dare not ask where along the way you changed the exhaust (that was never mentioned).
That is not relevant now, but that difference could very well be a lot (if not the majority) of your power decrease, as Gator implied.
Had you supplied all the correct information on the front side, we probably could have arrived at that in a couple posts.

IMO, if that's a back flame arrestor, it needs cleaned desperately. If it's an 'air cleaner' it may have been cool when it was new but at this point should go somewhere else with those SuperTraps. A standard round 12-14 by 2-3 plain jane air cleaner (whatever you can get local) will let it breath much more effectively and likely keep your friends wake out of the motor.

If you're wanting to spend some money and do some wrenching, I suggest you search for Buddy Branch's phone number and buy one of his DD cams. I believe you already have enough spring. You also need to install new lifters as part of that effort if you do opt to go that route.
 
Back
Top