More HP Top end for 96 5.7 mercruiser

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

Moore's book, while outdated a bit is dead on for relatively simple things like this...

you can go nuts on cam options, but remember that most people tend to overcam and unless you hwant to take forever to get on plane, you need the torque down low.

first and foremost, you need decent exhaust if you're going to look for power - and I'm talking about the manifolds, a spendy proposition. The only way to go cheap is to pick up longer stainless risers for the merc manifolds. They still have the wet joint leak possibility but will help a lot with reversion (much larger cam then stock and you run a real risk of sucking water back up from the exhaust into the cylinders, water doesn't compress like gasses do, you get the picture). cheaper, can weld extensions onto the riser to let the water mix further down the tube - no gaurantees on this one.

Revolution and kodiac are supposed to be a decent product, and on the order of a grand for new manifolds and risers,

next is imco thumperpower aluminum, good for some weight loss and ,maybe a little more expensive, plus imco makes great products overall,

then come emi's set up, stainless marine, imco powerflows, and dayna in the 1500 - 2500+ range, tubular headers more like 3000-6000. if you think it through and take time, you can get lucky on this though - I scored polished imco powerflows off a guy in nevada (never been mounted) and the matching risers off ebay, combined under a thousand. just be careful, a mistake here can turn your engine into an anchor in no time.

Some possible options (backyard hack who did a lot of research before building current engine).

mkos set up with the stock vortec heads and crane cam, edelbrock performer intake and 600 cfm carb of your choice would net a nice power increase for modest money. In my hands the edelbrock marine carb (1409) is relatively cheap (ca. 300) and a snap to tune - it should also be jetted real close to right straight out of the box for your engine. quadrajets do great when set up and holleys, others, too. (this wold also be great with the comp cam mtnrt recommended)

Next step up might be worked vortec heads or world products or dart heads with wedge combustion chambers and in the same chamber volume as your stock heads. You're talking about a thousand for new heads already assembled. 180 or 190 cc intake runners, aluminum at a little higher if you boat in freshwater only. same cam and intake or airgap rpm might make some difference, with the modified vortecs you can run a little more lift / duration where the valve lift counts by adding 1.6:roller rockers. You could also think about goign with a comp xm270hr

next step would be a set of good aluminum heads like afr 180's a little more cam, something like the next step up in lift and duration in the same or similar crane series, comp cams extreme marine xm276hr, edelbrock airgap performer rpm, etc...

Just some thoughts, bottom line is that if you don't have experience in fitting everything or a lot of patience and willingness to dig and learn, it would probably be money well spent to engage a machine shop that builds amrine engine sif you want to do much at all....

if you really want to hit the 70 mark, plan on 5k + with a good engine builder that's built marine engines and a 383 stroker engine.

and yes, cast components will work if you aren't running hard and fast all the time. I have this little problem.. I can't seem to run anything below half throttle for very long...

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

Reason I ask is because I am used to auto engines where anything under 500 hp you can get away with cast parts instead of a forged setup. However I realize the rpm/ load range of a boat is way different than a car. Also Im big into mustang 5.0's and a few companies (Edelbrock, Holley, Trick flow, AFM) sell dyno proven complete bolt on top end kits. Basically if you have this engine bolt it up an tune as stated then you will have xxx HP... Thats something I was looking for anyone know of a kit like this? I found one on jegs made by edelbrock and they told me it was for a 350, but when I called edelbrock that said those were BB heads no SB. Thanks guys I am new to boatiing.

Sorry didnt catch your other question... most of those engines won't work in a boat 1. because they don't have the necessary torque down low and won't idle down to where you need to shift into gear - lots of folks thet over this by bypassing the cutout and starting in gear. not too practical if you do a variety of boating. 2. because of the reversion issue, if you have too much cam overlap and stock exhaust, the engine will suck water back up out of the exhaust and basically eat itself. and finally, the exhaust on a boat just doesn't flow as well as a car unless you spend big dollars...

 

[Mkos1980]

Re: More HP Top end for 96 5.7 mercruiser

Ditto to the above. I found Dennis Moores book on ebay for 25 bucks a few months ago. Excellant read. Once I saw he had listed the LT4 HotCam, as a marine friendly cam, I was all over it as my combo has made super power with the carcraft buildups. I copied the combo 100% from the book - the exhaust manifolds and I can tell you it idles and drives like stock. But nail the throttle around 3,000 RPM and hold on lol. I ran the 62.33 though stock aluminum GLM manifolds. I'd love to get my hands on a stainless marine setup.

Its very possible for you to hit 70 with the stock shortblock. Your hull is alot faster then most, esp mine. Heck, some of the stingrays with 4.3's are pushing low 60's. There a guy on another site that had a 355 but with AFR heads a bigger Hyd roller cam. He was running 73-74ish. He moved to a 383 and moved up to 78-80. i think his was a 20ish footer.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

ditto on fast hull...

re: moore's book, the only copies I could find last year when I wanted it were like 200 bucks. I ordered it from interlibrary loan (for free) and copied the pages I needed....

I also concur that you should be able to get over 70, but I think sone of the stingrays mkos mentions are a good bit lighter than your hull. Don't get me wrong, that's a great set-up, but it is tougher and will handle a little more "chop" than some of the really light hulls. It'll also take a little more hp to push it that fast imho.... I went with the relatively mild 383 with a very stout bottom end rather than a 350 / 355 so I can idle at 500 or 600 rpms, AND run it hard for long periods of time without worrying about it coming apart. Note that I went with a well-known marine builder (especially known for building bullet-proof offshore race engines). He said we could get away with cast components if i wasn't going to run it real hard or / and if I could live with the fact that it wasn't going to last as long as a factory engine. The way we went he thought there was no reason it won't go every bit as many hours as a new factory engine - even if I run the snot out of it, just so long as I keep fresh oil in it and keep the oil temp down. We offset some of the 383 torque / alpha drive potential problem by running a top end that leaves the lower end of the torque curve a little soft in order to spare the outrive a little strain on take off. That also gave more peak horsepower / top end...

I will tell you that I got some crazy advice from crane cam's tech support folks and that the tech support folks at com initially recommended a combination of parts that wouldn't fit with my heads... we got it worked out, but my point is, a good, experienced builder will catch that stuff where I may not have and a tech service dept certainly won't... and I've built my share of cars, motorcycles and other toys...

if you decide to go for a lot more power, can't say enough good things about the afr heads... as you probably realize, the heads usually wind up setting the level of horsepower that you can expect to get out of an engine...

Ditto to the above. I found Dennis Moores book on ebay for 25 bucks a few months ago. Excellant read. Once I saw he had listed the LT4 HotCam, as a marine friendly cam, I was all over it as my combo has made super power with the carcraft buildups. I copied the combo 100% from the book - the exhaust manifolds and I can tell you it idles and drives like stock. But nail the throttle around 3,000 RPM and hold on lol. I ran the 62.33 though stock aluminum GLM manifolds. I'd love to get my hands on a stainless marine setup.

Its very possible for you to hit 70 with the stock shortblock. Your hull is alot faster then most, esp mine. Heck, some of the stingrays with 4.3's are pushing low 60's. There a guy on another site that had a 355 but with AFR heads a bigger Hyd roller cam. He was running 73-74ish. He moved to a 383 and moved up to 78-80. i think his was a 20ish footer.

 

[MikDee]

Re: More HP Top end for 96 5.7 mercruiser

Sorry guys... I am running a turbo 21pitch ss prop, 5.7 350 not the mag (260hp) it has and edelbrock performer intake and a 600 cfm edelbrock 4bbl carb. Other than that it is stock. I can run 60 on gps currently on a light chop at 4800 rpm that was with 2 ppl and half tank of gas and a cooler full of beer hahah.

Well, you could always just put in the reasonably priced 350/290hp GM factory hi-perf L82 cam, and BOOM! gain 30hp, no extra parts, or machining, no muss, no fuss,,, going to 9.5-10X1 compression, you'd gain another 25-30hp, and with Vortec heads, another 25-30hp, and finally with 1.6 roller rockers, even a bit more.
This is what I call practical engine building on a budget. Unless you wanna go wild, It's your call.

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

Well, you could always just put in the reasonably priced 350/290hp GM factory hi-perf L82 cam, and BOOM! gain 30hp, no extra parts, or machining, no muss, no fuss,,, going to 9.5-10X1 compression, you'd gain another 25-30hp, and with Vortec heads, another 25-30hp, and finally with 1.6 roller rockers, even a bit more.
This is what I call practical engine building on a budget. Unless you wanna go wild, It's your call.

Do you have part #'s for this? Something Id be very interested in looking into although I fell your estimates on power may be high... Also what kind of torque to you gain from these parts? Thanks

 

[John_S]

Re: More HP Top end for 96 5.7 mercruiser

Those parts will require significant machining/modification to work together. The cam plus 1.6 rockers will require clearance on stock vortec heads. ie a change in seals, springs, and/or machining. Not sure if you want that high of compression, but with your dish pistons it will require machining to get it. I also feel that the hp increase is optomistic and not as additive as suggested. For the gains you are looking for, aftermarket heads will be more attractive than modifying the heck of stock vortec heads.

Stock vortec heads/intake, and a flat hyd cam that will stay under clearance spec, will probably get you 295-305hp at prop from about 250, but you also will not be near your 70mph goal, which is a rather high bar to clear.

 

[MikDee]

Re: More HP Top end for 96 5.7 mercruiser

Do you have part #'s for this? Something Id be very interested in looking into although I fell your estimates on power may be high... Also what kind of torque to you gain from these parts? Thanks

Those parts will require significant machining/modification to work together

Wrong, maybe just adding the rockers would? but not the cam

I also feel that the hp increase is optomistic and not as additive as suggested

I don't think it's optimistic to gain a true 60+ hp when it all comes together.

Cam #3896962 on this page: http://www.gmpartsdirect.com/performance_parts/store/catalog/Category.jhtmlCATID=826.html

This is the cam that Uraijit has in his 350/290hp motor, and also the one that Rapido uses, and a few other engine builders use, it adds 30hp to the 350/260

There are other cams there, even a marine cam, that's not as hot, but without changing springs, or anything, IMO this is the best one.

1.6 rockers are only a suggestion, Vortec heads are good for about .480 lift from what I've read, yes, if you decide to use them it may need machining with these?

John, From what I read, Vortec heads are about a 30hp bolt on, and I'm sure they're more plentiful, & cheaper then aftermarket heads.

 

[Mkos1980]

Re: More HP Top end for 96 5.7 mercruiser

You can get 550" safe lift from bone stock vortec heads with Comp 918 Springs, and 787 Comp retainers. No spring seat mods or valve guide mods eather. Compression stays the same as if you had 217 heads as well.

 

[MikDee]

Re: More HP Top end for 96 5.7 mercruiser

You can get 550" safe lift from bone stock vortec heads with Comp 918 Springs, and 787 Comp retainers. No spring seat mods or valve guide mods eather. Compression stays the same as if you had 217 heads as well.

Yes, This is a known fact at the S-10forum, it works on the 4.3 Vortec V6 as well, where I hang out occasionally. A lot of the guys over there are doing this exact same thing when they get the late model Vortec roller (balance shaft) Comp cams with .500 lift. But why go through the trouble, & spend the extra dough when you can get some decent power with common factory bolt on parts, unless you've got a burning desire to get the biggest, & baddest, thing available, and got the $'s to spend? If that's the case, More Power to ya!

 

[John_S]

Re: More HP Top end for 96 5.7 mercruiser

Your minimum additive hp was 80hp, which IMHO is high even if you milled the heads. Keep in mind the Mercs 6.2L has a cam comparable to this, vortec heads, and with the extra displacement & MPI, is only rated 320hp at prop. You are basicly saying that if you up the compression on the 350, you will get more hp (250 + 80 = 330hp) than what the added displacement & MPI would provide.

I also think 30hp is slightly optomistic for the cam. A 25hp is more realistic over the marine cam. The 350/290hp is a crankshaft hp, not at the prop, and is not a certified number.

If you gain X hp by adding XX cam, and you gain Y hp by adding YY heads, does not mean if you do both, the hp is additive.

And I said "Stock vortec heads/intake, and a flat hyd cam that will stay under clearance spec, will probably get you 295-305hp at prop". Your cam w/1.5 rockers and vortec heads fits that description.

 

[Mkos1980]

Re: More HP Top end for 96 5.7 mercruiser

Always thought about that and I said you know what. If I'm going through the trouble of all this for a cam swap I might as well add something big and bad I bought all my stuff used except the valve springs and from going from flat tappet to the hot cam prob ran me 250 bucks differance.

 

[MikDee]

Re: More HP Top end for 96 5.7 mercruiser

Your minimum additive hp was 80hp, which IMHO is high even if you milled the heads. Keep in mind the Mercs 6.2L has a cam comparable to this, vortec heads, and with the extra displacement & MPI, is only rated 320hp at prop. You are basicly saying that if you up the compression on the 350, you will get more hp (250 + 80 = 330hp) than what the added displacement & MPI would provide.

I also think 30hp is slightly optomistic for the cam. A 25hp is more realistic over the marine cam. The 350/290hp is a crankshaft hp, not at the prop, and is not a certified number.

If you gain X hp by adding XX cam, and you gain Y hp by adding YY heads, does not mean if you do both, the hp is additive.

And I said "Stock vortec heads/intake, and a flat hyd cam that will stay under clearance spec, will probably get you 295-305hp at prop". Your cam w/1.5 rockers and vortec heads fits that description.

Ok fine, I don't know about you?, but I'm old school and was around to remember when the L82cam first came out around 1968, it was used in the 350/350hp corvette motor, with the famous "double hump" heads, 11x1 comp, a factory high rise alum manifold, and a holley carb, later on they dropped the comp. ratio to 10x1, and called it the 350/330hp, nowadays the marine version I mentioned at 8.5X1 comp is 350/290hp.

Now the previous similar L79 cam #3863151 was used in the 65' corvette 327/350 with the same "double hump" heads, 11x1 comp, high rise alum manifold, and holley carb. Both the 327/365hp, & the 327/375hp, carb, & fuel inj. respectively both used the old hot "30/30" (valve clearance setting) solid lifter 287 degree, .485" lift cam

The L79 was also used in the 65' Chevy Nova 327/325hp motor, this was basically the 327/300hp 10X1 comp. motor, orig. cam # 12364051, and the only thing added was the L79 cam for instant 25hp.

I know you're gonna tell me, "Oh that's not crank hp!" Well back then, that's the only type horsepower we knew, take it for what it's worth, and that's not from a book end of history lesson

 

[Mkos1980]

Re: More HP Top end for 96 5.7 mercruiser

Keep in mind the Mercs 6.2L has a cam comparable to thisQUOTE]


Believe it or not, the cam used in the 377CI 6.2 Black Scorpian roller motors is the Crane Compucam 214/220 which we were talking about earlier. Now in the 6.2 Blue Scorpian motor which is part of the "Blue Series" Hi-Po mercruiser engines, I'm not too sure about. I tried to find specs on this motor but I cant seem to locate any.

 

[John_S]

Re: More HP Top end for 96 5.7 mercruiser

377 Black Scorpion: I: 0.510 E: 0.530 w/1.5 rockers, dur@0.050 I: 222, E: 230, HP@prop 350

6.2L MPI: I: 0.472 E: 0.480 w/1.5 rockers, dur (can't find right now) HP@prop 320

Mkos: the lift on both cams exceeds the 2032 we were talking about. I have heard that the cam in the more recent 350Mags (mid W serial numbers & up) is equivelent to the 2032, but have not seen specs from Merc to confirm.

The Black Scorpion is probably this cam:
12370846 Hydraulic Roller Design
This hydraulic roller design contains eccentric for mechanical fuel pump. It is for off-road use only. The duration at .050" tappet lift (intake/exhaust) is 222/230; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 509/528. Valve lash is zero/zero and lobe centerline is 112 degrees.



Mikdee: yes, they were at crank, and accuracy was not as important as marketing. ;0 Also, that was with dual exhaust and not limited to 5000 rpms. IMHO, it is much more applicable using stock/known/spec'ed marine engine configurations from the last 20 years, vs muscle cars of 35+- years ago.

 

[MikDee]

Re: More HP Top end for 96 5.7 mercruiser

Mikdee: yes, they were at crank, and accuracy was not as important as marketing. ;0 Also, that was with dual exhaust and not limited to 5000 rpms. IMHO, it is much more applicable using stock/known/spec'ed marine engine configurations from the last 20 years, vs muscle cars of 35+- years ago.

Dual exhaust don't have anything to do with it, that would apply to any perf engine going thru-prop exhaust we're discussing here, so it's a moot point, and yes these cams I mentioned will probably pull to 6k rpm, that's why we prop down to the rpm we need.

I doubt because they're older design, they're less applicable, or not good anymore, as I said Jasper, & Rapido, and other engine rebuilders commonly uses them in their performance motors, this same cam is in Erick Green's motor, & Uraijit's motor, from two different engine builders. You can't deny it is an easy, inexpensive, decent power boost, using all the original factory engine parts, without going crazy It all depends on what the orig. poster wants to do.

Here look at the cam specs for yourself, I rest my case:
http://www.jasperengines.com/pdf/Chev-350-Marine-325-05.pdf

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

whats a good set of resonably cheap heads? Or where is a good place to get a nice used set... Boat is strictly fresh water so aluminum can be considered.

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

bump goining with edelbrock performer manifold, 750 cfm edelbrock marine carb, l82 cam possible... need a set of heads and combo may change depending on the heads.

 

[wca_tim]

Re: More HP Top end for 96 5.7 mercruiser

bump goining with edelbrock performer manifold, 750 cfm edelbrock marine carb, l82 cam possible... need a set of heads and combo may change depending on the heads.

standard vortec heads are decent - especially for the money.

Of the others, I've had good luck or know someone who runs and likes world products and dart heads.. and of course, afr is the hands down power maker for reasonably priced street heads.

the cast style wp or dart heads can be had set up for under a thousand.

If you need cheaper than that, probably vortecs are probably the best bet...

what are you going to do for exhaust? would suck to spend the coin on the top end only to hydrolock the engine and break something.

 

[jared_blown5.0]

Re: More HP Top end for 96 5.7 mercruiser

ttt