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how to increase power of 5.7L 2BBL?

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cforcht

New member
Hi all, I'm needing some advice.

I have a 1996 Starcraft 22' cuddy with a 5.7 2bbl. alpha one gen2. it runs well, has 150 psi on all cylinders. running a pertronix electronic marine dist in it also. Ive had it two years now and I would like to up the HP and looking for cost effective ways to do it. I considered going EFI but OMG that seems to be pretty pricy, so Im looking to the old school method. 4bbl carb, intake and cam. now for the questions.
merc or aftermarket intake?
square bore or spreadbore?
which carb? holley quadrajet edelbrock etc
and what kind of lift and duration cam can I use without having to machine the heads for bigger springs or create more problems.
and finally what kind of HP can I expect to gain?

option B is to drop a 383 in it. but then the same questions for parts would apply as well. but more costly since I would need to rework the lower end or buy a short block.

I have plenty of street performance experience and building engines, mostly big block though. but marine seems to be entirely different so I felt asking more marine savvy guys than myself would be my best bet.
 
cforcht said:
Hi all, I'm needing some advice.

I have a 1996 Starcraft 22' cuddy with a 5.7 2bbl. alpha one gen2. it runs well, has 150 psi on all cylinders. running a pertronix electronic marine dist in it also. Ive had it two years now and I would like to up the HP and looking for cost effective ways to do it. I considered going EFI but OMG that seems to be pretty pricy, so Im looking to the old school method. 4bbl carb, intake and cam. now for the questions.
merc or aftermarket intake?
square bore or spreadbore?
which carb? holley quadrajet edelbrock etc
and what kind of lift and duration cam can I use without having to machine the heads for bigger springs or create more problems.
and finally what kind of HP can I expect to gain?

option B is to drop a 383 in it. but then the same questions for parts would apply as well. but more costly since I would need to rework the lower end or buy a short block.

I have plenty of street performance experience and building engines, mostly big block though. but marine seems to be entirely different so I felt asking more marine savvy guys than myself would be my best bet.
Click to expand...

My take?

Option "A".

1. Carb: 4 bbl carb, Qjet or Carter (Weber, Eddlebrock) are fine, but marine grade ONLY. Spreadbore / square bore your choice.
I think spreadbores are great in a car when you are loping around at 1900 RPM, but in a boat, how often is that? Your
secondaries would be opening sooner than a square bore, in a boat. Some folks have problems w/ Holleys on boats, but others
love em..
2. Manifold: If you have closed cooling on engine, then aftermarket aluminum manifold like an Eddlebrock. If raw water cooled,
then Marine iron manifold or one of the very pricey lined aluminum marine manifolds.
3. Cam: I would stick with a Merc or specialty marine cam. Longer duration cams can introduce undesirable exhaust reversion problems
(ingesting raw water into engine). Lift, on the other hand, is OK, as long as it's isn't too crazy, needing specialty head work and
special pistons for valve clearance.
4. HP gains: That is very subjective, indeed, as no 2 are the same.

Option "B":
Nothing replaces cubic inches (except a tight budget).... LOL (I have a 25 1/2 foot Chaparral cuddy sport boat with 454 Mag w/ a Bravo 1, so I'm a little bias'd)
 
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2X on option B...

I would not spend the time on the manifold swap as you aren't likely to see any major improvement.
 
oh my thats quite a screen name LOL im sure there is a story behind it somewhere. your explanation of the square vs spreadbore makes sense. never considered it that way. and yes I know whichever I go with I want a marine version. as for cooling I have raw water not closed system. and have found mention of the aluminum ones needing to be a marine app as well or there are corrosion problems. cams are always a slippery slope. what works for one guy doesnt always work for another. same goes for HP gain. I was just looking for a ballpark. mostly so I could compare cost to hp gain versus the plan B route. I would love a big block but dont really want to replace the outdrive as well. Ive read the Alphas dont hold up well to the big blocks. and then of course I dont need to replace everything like manifolds, pulleys brackets etc. if I stay with small block.

so based on the input I have gotten its pushing me towards option B. which is kinda why I posted. I wanted to see if it was worth the effort of doing manifold cam swap for any real gain as opposed to going with the 383 option. thanks for the advice guys. guess Im looking for a 383 now.



the golden rule applies. there is no replacement for displacement.
 
I assume we're all assuming you have a stainless prop already. If you have aluminum now, going to a SS prop and a 4 barrel might make enough of a difference to make the boat more enjoyable. One or the other by themselves not earth shattering, but SS props are much more efficient than Al.
 
ya know thats a very good point. I have changed props a couple times now, trying to find the best one for my boat. all being aluminum for cost factor. but have yet to get one in stainless. why oh why did you have to post? I was all set to order a 383 long block tomorrow. still leaning towards that anyway. in light of that. how will that affect my prop sizing. Im running a michigan match 15D x 16P 4 blade now. boat runs at 38 mph by GPS at 4800 rpm
 
If you were to sell your long block motor, minus the exhaust manifolds, oil pan, and accesories. Leaving the ignition and intake in place I bet you could get ~ $1200-~$1500....for a running motor.

You can get a remaunfactured 383 ~ $2500 -$3500 long block.

You would need to get a intake, a carb, a good marine ignition replacing the thunderbolt V with a all in one.
New timing cover, A new Oil pump (with brazed pick up to pump body) There may be more stuff needed but you get the idea...
Exhaust manifolds, engine water pump, all accessories behind motor, (fly wheel, coupler, bell housing etc etc) would be transfered.


I would say a Edlebrock Air gap ALUMINIUM and a Barry Grant marine carb would be a good addition

if you have the cash then a simple all in one thottle body injection system with a self learning ecm.........

I think it would be easy to accomplish 320-350 hp with a carb and intake on a 383 without to much difficulty.

Barry grants web site does not show marine but does manufacture and sell them.

It looks like he developed a spread bore design so maybe he has one in a marine version...........






http://www.usengine.us/marine.html

https://www.sandjengines.com/rebuilt-marine-engines/CHEVROLET#

http://www.demonfuelsystems.com/Index.asp

http://www.jegs.com/i/Mallory/650/YLU624AV/10002/-1?parentProductId=748619
 
cforcht said:
oh my thats quite a screen name LOL im sure there is a story behind it somewhere.
Click to expand...

Screen names do have a funny story to them sometimes.
My 04fxdwgi (if that is what you were refering to), is the model number of my Harley Davidson.... Nothing special, unlike some other screen names that we have all seen. hahahaha

As you stated, Alpha's are rated to around 300 HP, but there a ton of Big Block powered Alpha's running around due to the Bravo's not being around when the 454's started going into pre-Bravo Mercruiser setups. If you don't push em hard, they'll be OK. The 383 can easily be pushed outside that 300 HP envelope. I personally believe the gobs of torque of the Big Block is what can kill the Alpha drives.

There is the price point break of getting to where you want to be. I am sure, that given enough specialty parts, such as induction, ignition, exhaust, headwork and props will get you all the power you want, but may just be more costly than the 383 swap out. Plus it may be a bit more finicky, since it's all tricked out.

But remember, after the 383 swap, the prop will still need to be tuned to the final engine configuration to give you that optimal engine RPM at wide open throttle. You'll be making more HP, so wheel will need to be more aggressive so you don't over rev at WOT.
 
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04fxdwgi said:
Screen names do have a funny story to them sometimes.

As you stated, Alpha's are rated to around 300 HP, but there a ton of Big Block powered Alpha's running around due to the Bravo's not being around when the 454's started going into pre-Bravo Mercruiser setups. If you don't push em hard, they'll be OK. The 383 can easily be pushed outside that 300 HP envelope. I personally believe the gobs of torque of the Big Block is what can kill the Alpha drives.QUOTE]

I believe it is all related to the tourque of the big blocks..........I have seen many pre bravo small block mercruiser motors exceeding 320 hp from Merc.
One for example, They had a EFI 350 (based on the LT1) released around 1986 rated at 320 + hp...

even todays efi small blocks are rated much higher than the equivalent of pre bravo. (regardless of where the power rating was taken from [crank or prop] todays are much more powerfull with no issues with the alpha's.

Big blocks have big torque ..........that is what does it......
Click to expand...
 
04fxdwgi said:
Screen names do have a funny story to them sometimes.
My 04fxdwgi (if that is what you were refering to), is the model number of my Harley Davidson.... Nothing special, unlike some other screen names that we have all seen. hahahaha

yes it was your screen name I was referring to. and like I said there was a story behind it.



But remember, after the 383 swap, the prop will still need to be tuned to the final engine configuration to give you that optimal engine RPM at wide open throttle. You'll be making more HP, so wheel will need to be more aggressive so you don't over rev at WOT.
Click to expand...

I was aware that the prop would once again change if I change the HP output regardless of which direction I go. thats why I asked how it would change my prop. meaning suggestions on where I might begin to get one the right size. we dont have big marinas here so the try and buy isnt really an option unless someone does it via mail.

its good to know that the small block will most likely handle the 383 even if the HP is above the 300 mark. I knew the big block killing them was related to the gobs of torque they create.
 
kghost said:
If you were to sell your long block motor, minus the exhaust manifolds, oil pan, and accesories. Leaving the ignition and intake in place I bet you could get ~ $1200-~$1500....for a running motor.

You can get a remaunfactured 383 ~ $2500 -$3500 long block.

this was kind of my plan. but I was going to wait to sell my current engine after I have the swap done. just so I dont inadvertently let something go I need.
as for the injection... its outside my budget range. well maybe not. its outside how much I "want" to spend. the 383 alone will get me where I want to be. I dont need to pull the entire ski team just a couple of them at most. I dont beat the boat and I dont hot rod it. which is somewhat of a surprise even to myself since Im pretty much a speed freak on anything land based.

I noticed the links you posted. I was looking at a long block from raptor engines for 2300 and some change. anyone with experience with them? http://raptorengines.com/index.php?main_page=product_info&cPath=35&products_id=97
this is the one I was looking at
Click to expand...
 
I think it is to radical for your application.

motors with that kind of output typicaly get it at +5500 rpms

you want a motor with the power to be all in under 5500 rpms......

They may offer something a bit less radical........



The best thing if obtainable is like what was suggested.........

A 454 (HP ~ 325 hp or just a bit higher) and bravo 1..........22 ft would then do about 65 -70 MPH.........
 
maybe Im wrong here but couldnt I prop it so it didnt exceed 5k? do keep in mind I dont plan on keeping the throttle pegged all the time. just once in a while. this is the only marine engine they offer in 383 and their price is better than any I have found thus far not to mention their warranty is better too. I could even put a rev limiter on it. but I think propping would be better solution.
 
Yes I would say you are interpriting this wrong.

A motor with high horsepower at high rpm ranges will be low power at lower rpms that you would be operating in.

Stock marine engines have a typical power curve that occurs between 2500 and 5500 rpms even though most never go above 5000 rpm.

Simply propping it down will not allow you to gain the power when you need it.

So purchasing or biulding a motor with max power to be obtained close to 5500 rpms BUT have it come on around 2000 to 2500 rpms is best.

A 450 hp small block motor is designed for high rpm use and power most likely comes on around 3500 rpms or higher....if used in a car you would need a high stall converter if used with a automatic transmission.

Thats my opinion........maybe someone with greater marine motor application can chime in and may add more
 
Old rule of thumb for propping is a 1" increase in pitch will drop top RPM by < > 300. That is a ballpark place to start.

After your build, see where she redlines, then adjust prop pitch accordingly and retest.
 
IMO the 383 is a great swap. Same weight and way more power. That's what I have in a 21' Blue Water, running a 1.47 ratio gen II Alpha. 21" SS HighFive prop.
WOT speed is 63-65 mph.

Rod
 
BTW, your increase in speed will be about the square root of the ratio of the power increase, just so you know.
It won't be linear with the power increase in case you were thinking it would be. Just won't happen.
For instance, say you have 250 hp now.
With a 383 making 350 hp, the power ratio is 1.4; and the sq root of that is 1.183.
So your speed will increase about 18%.

Rod
 
If you are into this engine this far, you'll likely be replacing pistons.
If so, build a "quench effect" into your combustion chamber.
See this thread beginning at post #7.

Say NO to these:


A good Q/E will greatly increase low end torque, and will reduce the liklihood of detonation.
The additional cost is peanuts comparitively speaking.


Watch carefully which camshaft profile you choose.

I prefer the Holley Q-jet replacement, of which is a spread-bore.

If closed cooling system...... you can use an automotive dual plane intake manifold with no issues.
If Raw Water cooled, you'd best use one of the Marine bronze lined dual plane aluminum intake manifolds.

Keep in mind that higher hp and torque begins to push the limits for the Merc A drive.
A well built 383 would be out of the question for an A drive, IMO.



.
 
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