4.3lx intake manifold question

[Lt1z350]

installing a carb spacer and increasing plenum volume increases low and midrange

BTW, Volvo Penta manifolds and Edelbrock manifolds both come out of the exact same casting boxes at Buddy Barr castings.

Not sure what your issue is with your motor, however I suspect tuning and potentially carb issues. cant swap manifolds and not tune the carb.




the motors with higher power have vortec heads



what is is you are trying to do?

if you want a bit more power, swap to vortec heads and a vortec intake and properly tune the carb

if you want a go-fast boat, pull the V6 and install a V8

I did a ton of research on the vortec heads vrs this casting number on this boat. These are not the swirl port heads that cannot flow air but the heavy duty gm castings that were marine specific. They flow way better then then the earlier castings and what I found were specific to 94/95 only. Alot of the s-10 guys like to use them over the vortec as their is a pretty big list on why you dont just stick the vortec on a non engine. For one the pistons are different each one matches the coubustion chamber of the head. So not so much actual performance is gained. i verifed this on the piston part numbers from my 94 motor to a 96 and up piston part number. But besides that some guys that did even the early heads to a votec said most gain they saw came only in higher rpm. Im going to v8 swap this boat so to me I didnt see the 10 hp coming from this swap worth it. I keep getting conflicting info on if this is 180 hp or 190 hp if it s prop rated or engine rated so really hard to know what the whole package would net on it. But My goal is an aluminum 5.3 motor that makes in the 350/375 hp range so can stick with the alpha drive which I have seen this done on even higher hp when guys take a 350 and go out to a 383. I know that is pushing it so 350 Im sure at the same weight this boat will be plenty fast and Ill be very happy with it. I talked to Ken about the prop and said even on this 1.84 drive a 14.25/24p will probably net 60 mph at 350 hp. To me on a 19.3 Im good with that as can then cruise comfortably around 40/45. This is a long lake so if put in where I do and want to hit up a few restraunts at night its quite the run at 30 mph.
I got to source a lot of stuff for that so why I want to get this thing right plus then better resale for someone that wants a 4.3

 

[Lt1z350]

If a bit more initial timing helps the Bottom End, then just change the advance curve of the Distributor to limit Centrifugal Advance. The OP's engine sounds old enough to have a Mechanical Advance Distributor. Heck, my 2002 Volvo 5.7 has one.

This thing has that thunderbolt IV on it and what I have found is a point and shoot for setting up timing. I found 8 degrees btdc if someone can verify this for me great.
So as I had posted before I just added some on the water and was alot better on my last run home for the day. i couldnt get a good top speed it was pretty rough at that point but hole shot was even better I felt and was already good. Im up by 15 mph or so on plane less then 3 second. This was all about how it feels dragy at wot like engine struggles. you can drop the throttle back quite a bit and maintain that 42/44 mph on it like so much dead throttle hiolds that 4300-4400 on this prop anyway. Like not enough peak hp in my eyes.
Anyway I put new plugs in it marine ac delco 43s a hotter petronix .6 ohm (matches factoy ohms exactally) 45,000v coil on it and checked the timing as per where I stuck it and it felt good so far. I have not been back out yet just messing in the garage. Well as of now it looks to be right at 8 degrees and if thats spec then they had it too low some reason. The guy had the balancer tab marked at 4 degrees so his mechanic was not doing this correctly if actual spec is 8 degrees where it is sitting now.
It has sierra wires on it and a good brass terminal cap with zero wear so saw no reason to replace any of that right now.

 

[Lt1z350]

installing a carb spacer and increasing plenum volume increases low and midrange.

I did think about doing the spacer but found the edelbrock intake on amazon as a return for 280 bucks vrs 350 most places so saw that as good enough deal to just give it a try.

BTW, Volvo Penta manifolds and Edelbrock manifolds both come out of the exact same casting boxes at Buddy Barr castings.

This one I have comming is a ton different then the one I showed on the top in the pictures with the open plenum style. Edelbrock actually chewed me out sort of in an email back to me as I said there is no good proving info out there on this setup. They told me that they pulled off one of these early styles of intakes and gained 18 hp at 7000 feet elevation on big bear lake some test they did back in the late 90s I guess. But of course you dont get this info posted anywhere so who knows if true or the guy pulled it out of his behind as I put him on the spot with not having good info. What is posted with the intake makine 202hp 280 tq looks like it was done on an s-10 as motor had 1 5/8 headers on it. To me that is not apples to apples when comes to us trying things on marine vrs auto.

Not sure what your issue is with your motor, however I suspect tuning and potentially carb issues. cant swap manifolds and not tune the carb.

So I did break down and go through the carb put a kit in it and could tell it had never been opened before. I worked at a couple speed shops when younger. Always been into hot rods and projects besides being a master tech and building transmissions/rear ends/ transfer cases for 25 years. So im really good with all this kind of stuff. Know the affects of tuing cams carbs timing. I actualluy tune for a living on line now for late model gm vehicles. So im really good with something IF I know the platform other wise it comes down to trial and error or relying on great people like yourself that will share findings.
But as per my carb the floats were way off no min and max set on it. I put the edelbrock kit in it for the 1400-1409 carbs which I found matched up to these style on the boat a square bore carter. It is not a q-jet so having building edelbrock in the past felt good on it. I was temped to buy a holley as know those a lot better.

the motors with higher power have vortec heads

I did a ton of reseach on this with the s-10 forums and most that changed from this 94-95 year non swirl port heavy duty casting said the actual vortec didnt help enough to warrant all the money and work. This casting has 30 percent higher flowing then the 93 and down castings I found and a better exhaust port. This winter I might pull them and do a little port work and freshen them up. I did a compression test and its 160 across the board so bottom end seems good and sealed up. I get a little oil on one plug so probably a valve guide seal so when season is over might clean up the bowls and that will gain any small losses to a later vortec. I want this motor right and good to sell when I do a v8 swap so dont mind a little effort and work to make if good for the next guy when sell it.

what is is you are trying to do?

if you want a bit more power, swap to vortec heads and a vortec intake and properly tune the carb

if you want a go-fast boat, pull the V6 and install a V8

Just make the boat run right really at wot 4300 rpm seems a little low for the 44 or so mph I saw but his was on lower timing so possibly on smoother water next time out with the correct timing it might feel better. I have since done a coil new plugs and refresh on the carb. I need to verify the 8 degrees of timing on it though for thunderbolt 4 setups.The wires and cap look really good.

I got the intake on the way it was cheaper as an amazon return what sold me on it was when had carb off I found the intake gasket sticking into the port 1/4 of an inch on the port bank the two ports ajoining each other. So its been off and not put back on correctly. So since I need to fix this anyway I decided 280 on the edelbrock was worth a try. I do hate the choke setup on this carb its the heat riser one doesnt work worth a crap when its dead cold so debated a new carb with electric choke on it.

As per the v8 thing I am going to start sourcing an aluminum 5.3 as it will be the same or less then a 4.3 that is all iron. Build it up to around 350 hp and enjoy that as I really like how this boat runs and handles. when I looked it up on nada before buying it I did it as a 1995 which this is the 94. Chaparral 1930 sst and in 95 v8 was the base engine 94 it was the 4.3 so seems it was considered a little under powered so they started with v8 as base engine the next year.
The boat is mint everyone thinks its a 2005 or newer and no one thinks it was 94 model so I feel its worth the sawp and hanging on to it. I looked at a 95 crownline with a 5.7 that ran 55 mph had the same alpha drive on it but the boat was a tank at 20.3 feet listed at 3300 lbs. With trailer it was sqautting his f250 when took it out and boat was not as quick as this 4.3. It had more top end but lazy to get there 260 hp I think. So all the added weight to that boat I decided to just stick with something like this and update it how I feel fit as many say sell it and get the v8 in one.
The LS motor is so much more advanced then most marine motors at least in the 60k and down range as the high end ski boats get them. buddy has a 100k plus 06 malibu I think with the ls6 405 hp in it and just spent 5k on some clutch that they use vrs the normal out drive.
So to wake this up with some technology should make it such a good boat. FIberglass floors in this old I saw that as a win the boat is built very well from what I can find and my knowledge anyway. I didnt see finding a better model to do this all to in time as probably be a two season getting it all together as I have found when get in a hurry I over spend. So if get it as I find it then wont hurt so much lol

 

[Lou C]

I think you’ve got something else going on there. I have a pre Vortec 4.3 with the standard cyl head design and with the 4bbl Quadrajet & a 15.5x15 prop (heavy 20’ boat) it easily pulls up to & slightly over 5,000 rpm.

 

[Lt1z350]

I think you’ve got something else going on there. I have a pre Vortec 4.3 with the standard cyl head design and with the 4bbl Quadrajet & a 15.5x15 prop (heavy 20’ boat) it easily pulls up to & slightly over 5,000 rpm.

Mine pulled fine to 5000 rpm with the 14/19p so that tiny 15p I’d hope at least that which they do say is too many rpm. Affective range is 4500-4800 rpm. Since going to a 19p 4 blade prop I’ve lost more rpm then expected. I also tried a 13.25/24p 4 blade stainless steel as on my bass boat and it was 42 mph at 4500 rpm. While it’s smaller it is 24 pitch. Pitch and size both seem to play a pretty big part on max speeds/rpm.

 

[Lt1z350]

So here is a quick shot on edelbrock. Runners are all the way up to plenum. Stock has one open larger runner no divider to the cylinder head. This design is to build more torque proven on any v8 engine combo. It’s also taller I think 2 inches so will add to peak rpm hp. It’s a proven design just hope to see a decent difference vrs the stock iron. Hopefully if nothing else this will answer a lot of questions as most doing this come from a 2bbl and of course say improvement is huge.

 

[Lou C]

When discussing max rpm remember that the engine manufacturers give their ranges for the boat being loaded as typically used. That is if you are out testing all by yourself, you are lightly loaded, and in that case you should prop it to get closer to 5000 rpm to allow for increased loads in the boat.
If you got 5000 with the 19 pitch prop why not stick with it?
I used the 15 on mine because a 15x17 gave me 4600 and the range on mine (loaded typically) is 4600-4800. After weighing the boat and trailer I found that the combo was 5050 lbs! the trailer is 850 so the boat is about 4200 lbs. So to lessen the load on the little 4.3, I went with the 15 pitch and lost some top end which I don't really care about anyway, I'm in a coastal region where you can hardly ever run at WOT anyway. More concerned about lessening the load on the engine than top speed.
Lower than optimal WOT max rpm causes elevated combustion chamber temps, and exhaust valve tuliping, and low compression. The closer you get to 5000, the less strain will be on the engine every time you pull the boat up on plane. In addition to that, no matter what the engine manufacturers say, you can't easily hear pinging or detonation in marine engines, so I use 93 octane gas whenever I gas up at the local gas docks. No knock sensor on these old engines, so err on side of caution, for long engine life.
The Edelbrock manifold looks great, I thought of upgrading to that if I repower with a 4.3. However when I found out how much this boat actually weighs, I think it needs a 5.7 lol.

 

[nola mike]

So here is a quick shot on edelbrock. Runners are all the way up to plenum. Stock has one open larger runner no divider to the cylinder head. This design is to build more torque proven on any v8 engine combo. It’s also taller I think 2 inches so will add to peak rpm hp. It’s a proven design just hope to see a decent difference vrs the stock iron. Hopefully if nothing else this will answer a lot of questions as most doing this come from a 2bbl and of course say improvement is huge.

Do you have a zoomed out shot so we can see it vs. the original?

 

[Lt1z350]

When discussing max rpm remember that the engine manufacturers give their ranges for the boat being loaded as typically used. That is if you are out testing all by yourself, you are lightly loaded, and in that case you should prop it to get closer to 5000 rpm to allow for increased loads in the boat.
If you got 5000 with the 19 pitch prop why not stick with it?

Boat was realy slow to get up on plane with that prop on it. If you just nailed it the prop cavatation was terrible so had to roll on it slow.

I used the 15 on mine because a 15x17 gave me 4600 and the range on mine (loaded typically) is 4600-4800. After weighing the boat and trailer I found that the combo was 5050 lbs! the trailer is 850 so the boat is about 4200 lbs. So to lessen the load on the little 4.3, I went with the 15 pitch and lost some top end which I don't really care about anyway, I'm in a coastal region where you can hardly ever run at WOT anyway. More concerned about lessening the load on the engine than top speed.

I see your point on all that for sure why I wanted to see if cleaning up some things I could get a little more rpm from this prop as its so good and fast to get up on plane with 2 people and 3/4 tank was how it was for testing it at first anyway.

Lower than optimal WOT max rpm causes elevated combustion chamber temps, and exhaust valve tuliping, and low compression. The closer you get to 5000, the less strain will be on the engine every time you pull the boat up on plane. In addition to that, no matter what the engine manufacturers say, you can't easily hear pinging or detonation in marine engines, so I use 93 octane gas whenever I gas up at the local gas docks. No knock sensor on these old engines, so err on side of caution, for long engine life.

It turns out I was actually right about what the manual says and the previous owner had timing set too low. I am about 9 degrees right now and no pinging and I read the plugs after a very hard day on it with 5 people and full of fuel pulling adults on the tube at 40 mph at times. I did run ethanol free 93 in it that time out also just to be safe. Will post full resutls shortly.

The Edelbrock manifold looks great, I thought of upgrading to that if I repower with a 4.3. However when I found out how much this boat actually weighs, I think it needs a 5.7 lol.

Im going to do the 5.3 or 6.0 aluminum motor eventually this is temp fix and more then anything testing hopefully to help others that question the change. my one port the gasket is not aligned and its got slight oil leak behind distributor so needed a reseal anyway. I figure its comming off so why not go ahead spend the 280 bucks and run this other one for a while. If helps the boat a little and helps the community on if its really worth it or not im good on spending the money plus adds a little value to when I sell this motor after the v8 swap. All lakes here an no salt so good on the corrosion thing. If it is a true 20hp as clamined this will help enough to pay for its self.

 

[Lt1z350]

Do you have a zoomed out shot so we can see it vs. the original?

When I get other off I’ll do a direct compare on it all for everyone to see. Design wise it’s just newer better technology vrs what they ran when the iron intake was designed and then never changed for any of the newer motors. So the cast iron is truly 80s Marine technology and really built around lower hp platform. The edelbrock is built around v8 tech on what was learned in street performance where torque and hp is important. Then applied to a 4.3 that fires different then a v8 so a little change on runner design I was told by tech in some recent emails.

 

[Lt1z350]

Sorry forgot to post last results. So last time I worked on it I put new gm 43 marine plugs gaped to .045 not factory .035 the ones I pulled the ngk were more like .030. Also cleaned and threw a edelbrock kit at the carb. Set floats and idle to 19 inches vacuum 650/700 rpm.
I also installed the pertronix 45k volt coil which helps support this .045 gap. Also set timing to 9 degrees on the gun running 93 no ethanol fuel which was mixed with 1/4 of 87 e10.
3 adults 2 kids 3/4 tank fuel not glass moderate chop and I had the top up so more drag. 43 mph 4500 rpm. Old previous was with 1/4 tank and two adults too not up about same chop. 42 mph 4300 rpm. So it’s making more power for sure. Been bad weather so haven’t got back out yet with just the two of us but I will before swapping the intake. I need a new baseline for 2 people and same weight no top up.
The much better part of Saturdays test was pulling a tube. 2 kids or 1 adult 19-35 mph over an hour of beating on the boat it barley used 1/4 of a tank. A ton of wot hole shots running it hard and fast with dragging the tube I could hear the 4bbl open when around 30-35 and the tube out back. So feel like the fuel useage is a lot better. More spark hotter timing way more complete burn less waste. Even with the tube and 200 lbs of adult on it the hole shot was very fast this prop has turned out to be great.
So far every change has been very positive and if this intake can get just a little more from it I’ll be pretty happy on the whole setup for the time being.
Found a 6.0 ls from a caprice cop car those are 355 hp stock so a freshen up dod cam delete and a decent marine cam 375/400 will be easy with most likely tq in the 400s. But gonna freshen up the motor all that so going to be a slow project as it can hit 5k rpm and 50 mph on this setup with 2 and the intake I’ll be happy as loaded it doesn’t seem to care too much with this prop.

 

[Lt1z350]

So got back out with just my wife and I again back to same conditions or as close as possible anyway to the first few prop tests prior to carb coil and plugs. So 2 people 1/2 tank and moderate chop not smooth at all. 46/47 mph at 4800 rpm. I checked my plugs no signs of detonation at all and maybe on the lean side as they are pretty clean. The coil .010 gap increase and carb clean up seems to be worth a good 4 mph and 400 rpm.
So got intake off cleaning it all up. Looks like it was pulling some oil in two ports at bottom of intake runners. Valve covers also has some leaks so debating throwing 1.6 rockers at it at same time. Yes it skews the intake results but covers can come off with out removing the exhaust with intake off so that’s a big plus.
If I do it I’ll put on the comp roller tip 1.6 as fit under this plastic cover and they are 170 new for 16 of them.
8-10 hp max from that and the intakes claimed 18hp a 25 hp gain should put this boat at my goal of 50 mph but most likely over 5000 rpm. So just have to see how this shakes out as then might need the 21p if too far over 5k or limit it. I’m sure if it’s 5200 it will be ok just don’t keep it up there long periods.
Here is a few more pics of the intakes. If anyone likes to see anything just ask as it’s apart at moment. I’m going to research this head casting a little more also.
As can see this manifold the runners are much shorter the edelbrock is also 1/2 inch taller from floor to carb mount but over all it about the same height. They moved the exhaust cross over lower so lowered the floor it looks like. I’m gonna block it and go to a electric choke as this one doesn’t even work right anyway.

 

[jimmbo]

If you see any gain at the top, you will likely see a drop in low end torque, compounded by any increase in Prop Pitch.
When it comes to boats, Displacement and Torque Increases are far more noticeable than HP increases. And what flies well in Street engines is often worth zilch in a Marine Engine, as the Operational Parameters and Requirements are quite different.

 

[Lt1z350]

Well i just did two street tricks with the coil and the plug gap increase and added 4 mph and over 400 rpm. The manfold isnt all about hp its gaining 50 lbs in torque below 3500 rpm according to the dyno graph they sent me. Hp and tq is the same add and what ever your applying it to will go faster from a stop and or top end. All of that depends on what part of the rpm range its gaining and its also possible to add torque and hp at the same time. Its called picking your mods wisely. I have a car or truck on a dyno ususally 3 times a week. Street or track picking up under the curve is always more important then peak power. This is why adding the plug gap and making a more complete burn of the same fuel made it both go more lean and added quite a bit of power to the motor all the way to 4800 rpm. I started with a boat on this same prop that didnt want to go but 41 mph and 4300 rpm at best. a few little tricks and now at 4800 and probably 47 mph. I didnt use the gps this time as was a little rough to try to keep the phone in one place so used the speedo which I know roughly the error of it when its showing 45 mph its a little low.
Good or bad ill post the results of the intake and rockers come next week as info a week of rain here it looks like so hopefully by the weekend.
Ill also say that going to this 4 blade hustler prop has really made this boat so much faster from a stop. Anyone that thinks they have a good hole shot on a 3 blade is missing out. I tried the neighbors expensive lazer 2 stainless steel 19p and it was lazy from a stop and still didnt net but 45 mph. took to 22 mph or around to be on plane and fell off by 19 mph. The hustler is up by 15 or so and I can slow it to around 18-17 before it really wants to fall off. So can easlly crusie 19 mph on plane. For 150 bucks with a new hub I couldnt ask for a better prop so far as now tried a few of them from cheap to expensive.