355ci vs 383ci

[NormRinker]

Hey all,

I stopped by a reputable local racing engines shop today, and I asked the owner some questions. I wanted to inquire about machine work on my 350 2 bolt mains block, and the answer was 4 to 6 weeks wait time on block machine work. Wow! They must have this nice back log of work there. The price wasn't cheap either for their complete block preperation job, but I guess they're not worried about it with their customer base and the back log that they have.

His suggestion was to go with a 355 instead of a 383 for its lower oil operating temperature. He said I can still get the power that I am looking for out of the 355 with ease. It would be nice to be some where in between 300-350HP range which is a bump up from the stock 250HP rating. He proceeded to show me a couple of built 355's that dynoed at 550 plus horsepower. He's been building racing engines for the local racers for more than 35 years now.

What's your take on this? I am still undecided between having either a reputable local shop or myself do the build on my exisiting engine or to buy assembled long block whether it be new, custom, or remanufactured from GM, engine builders, engine remanufacturers, etc. I have a 2 bolt main roller lifter block that I am not sure about for the 383 build or to even rebuild. Decisions to make...

Thanks, Norm

 

[Coors]

Re: 355ci vs 383ci

If it has a long duration cam-no. Has to be a marine/ truck cam.

 

[QC]

Re: 355ci vs 383ci

Do you recall what RPM those engines made 550 hp? To me this is much more about budget and compatibility with the existing application. What do you need and how much do you have to spend on it? Unless you are planning some longevity challenge I think we're splitting hairs here . . .

 

[NormRinker]

Re: 355ci vs 383ci

QC,

The RPMs must have been way up there for the 550hp end result. Not what I want. He was just making a point about 355 being capable of putting out some power that there are other possible ways for more power than the stroker way.

What would you do with about $3k and an existing '98 5.7L Vortec (roller-lifters) engine with the 2 barrel carburetor set up and a blown head gasket? Rusted cylinders with a bore job at the mininum if it can be done. Also, keep in mind switching over to the 4 barrel intake set-up is desired. I want more power than the stock rating at 250hp. 300-400hp would be nice! :-D

 

[NormRinker]

Re: 355ci vs 383ci

Imported Coors,

How long of a duration is too long for marine use with stock OEM MerCruiser exhaust manifolds and risers through the transom exhaust system?

I have some Corsa Quick and Quiet non-switchable diverters I can add on later doing the side-exit exhaust set-up on top of the exisiting through the transom system.

Thanks!

 

[Coors]

Re: 355ci vs 383ci

Basically anything over 112 overlap, as the exhaust is open while the piston is in intake stroke. Works good on a car at full throttle, but a boat has water all in the exhaust area. Been there for major $$$, I know. And a boat engine is always under a load, and under 4600 rpm. A 383 torquer like Bondo-o says ia better.

 

[HT32BSX115]

Re: 355ci vs 383ci

There's another issue also....

Those engines make all this HP with high compression and fairly wild (non-marine) camshafts. Those kind of camshafts may suck water into the exhaust system.


Most lakes only have regular or mid-grade fuel and octane booster doesn't always cut it.

You may have problems if you run one of those engines on regular. Fuel injection, Cubic inches and or turbo/super charging is about the only way to get HP with regular gasoline. And even that may require in increase in octane.


You might want to make sure they will guarantee the performance on regular gas.

 

[NormRinker]

Re: 355ci vs 383ci

Imported Coors,

I believe you about water reversion issues. Do you know of a good 383 combo you would suggest? Parts, camshaft spec's, etc? To be throwing some ideas around.

Thanks!

 

[NormRinker]

Re: 355ci vs 383ci

HT32BSX115,

I wasn't implying to run one of his racing engines in my boat. I was only stating that he said 355 will work perfect in my application with some improvements done to the stock 350 configuration without much changes in the oil temperature verus going the 383 stroker way. I went there to ask about doing the machine work.

What is an ideal compression ratio for marine use with a slight improvement in performance but staying with let's say 89 octane pump gas?

Thanks

 

[8AteEight]

Re: 355ci vs 383ci

Id say to go with the 383 combo too. Youd want to stay at 5500rpms and below. but making that much power, that low in the RPM band, is just a lot easier with more cubes. Plus, theres a TON more torque down lower, and Id think youd be a lot happier with it. And, if your running on pump gas; stay at 10 to 1, or lower. Even at 10:1, youll want a really low temp thermostat.

 

[HT32BSX115]

Re: 355ci vs 383ci

I asked similar questions at a local machine shop also.


I guess another question might be what transom/drive are you putting this engine in front of?

If it's an Alpha you'll have a roughly 300hp limit.

I think the Bravos are good for around 400hp or so.

I don't think many stock Mercruiser/Volvo engines are over about 9.5:1......They're completely electronic (spark control/injection) They prevent detonation with knock sensors by controlling the timing.


I found a longblock BBC engine HERE and it indicates with 9.6:1 it requires 92 octane....... maybe smaller engines don't require high octane with high compression?

I have never seen 92 octane at the lakes around here. It's probably available but it sure is a pain to have to haul gasoline when it isn't!

In any case, your engine probably has a raw water cooled oil cooler. I doubt oil temp will be a problem.

HT32BSX115,

I wasn't implying to run one of his racing engines in my boat. I was only stating that he said 355 will work perfect in my application with some improvements done to the stock 350 configuration without much changes in the oil temperature verus going the 383 stroker way. I went there to ask about doing the machine work.

What is an ideal compression ratio for marine use with a slight improvement in performance but staying with let's say 89 octane pump gas?

Thanks

 

[NormRinker]

Re: 355ci vs 383ci

I asked similar questions at a local machine shop also.


I guess another question might be what transom/drive are you putting this engine in front of?

If it's an Alpha you'll have a roughly 300hp limit.

I think the Bravos are good for around 400hp or so.

I don't think many stock Mercruiser/Volvo engines are over about 9.5:1......They're completely electronic (spark control/injection) They prevent detonation with knock sensors by controlling the timing.


I found a longblock BBC engine HERE and it indicates with 9.6:1 it requires 92 octane....... maybe smaller engines don't require high octane with high compression?

I have never seen 92 octane at the lakes around here. It's probably available but it sure is a pain to have to haul gasoline when it isn't!

In any case, your engine probably has a raw water cooled oil cooler. I doubt oil temp will be a problem.

I have a Bravo III drive behind the boat, so that's good for handling a little bit more HP. 93 Octane is readily available for me because the boat is trailered. It has a 75 gallon tank so it should last a full day's worth of boating or more.

Don S. made a good point in one of my other threads. You're sacrificing the dependablity aspect of it if you're out to wring every last bit of HP out of it.. I will need to make my decision sooner or later.. Mild build-up, or buy new stock engine..

I didn't know there might be an oil cooler on my boat, so I would have to check again to see. I also didn't know that there is a knock sensor on the engine. I didn't pay attention to the details like that.

Thanks!!

 

[HT32BSX115]

Re: 355ci vs 383ci

If you're using a bravo III you're good for about 400hp.

Do you know the ratio? If you post the model/serial numbers Don can tell you exactly what you have.

If you want more performance you could opt for a 454 or 502. In fact I am going to either buildup a 502 or find one in a year or so to replace my 454.

I have a 1.81 ratio Bravo III.

Your's is probably 2.00:1 or 2.20:1 model if it's behind a small block.

depending on the year of the engine, You also probably have a rev limiter too....Is it fuel injected? The model /serial numbers will also determine what the max rpm is.

 

[John_S]

Re: 355ci vs 383ci

The Bravo III and large gas tank indicates a large, heavy boat. If so, go with the 383 for the extra torque, lower in the rpm range.

 

[Bondo]

Re: 355ci vs 383ci

While I agree that Abunch of HP can be built with a 350,.....
But,........You'll build More Usable HP with a 383......

And,.... I've never heard of a 383 running Higher oil or water temps than a 350 worked at the Same rate..........

And,..... While a SBC can turn Well over 5000rpms,......
Dependability goes downhill Quickly, for not only the motor, but your Drive as well when you try running the High side of 5000rpms......

To build serious HP,+ Torque,..... There's No replacement for Displacement.......

I'm Still putting together a 383,.....With a set of Vortec heads at a tight quench,... a Cam in the 214 to 218 range,....Compression ratio around 9.5 to 10:1....With a 4bbl. carb,.......
I'm expecting near or over 300hp.......At Less than 5000rpms......

As noted,..... The Cam's LSA has to be kept between 109*,+ 112* to prevent Reversion......

 

[John_S]

Re: 355ci vs 383ci

Norm,

You should post what type of hull you have and weight, along with your current performance specs (time to plane, WOT rpm/mph), and what you are trying to achieve. A BB may be the only answer to get what you might want. In that case, you might have to cost compare to selling and buying a more sutible boat.

PS: As far as heat goes, the more hp you get out of the engine, the more heat you will have to deal with. At the equivelent hp, I don't understand why a 383 would be any hotter than a 355. Additional compression ring friction from the longer stroke? Assuming you are keeping the engine builds to something reasonable for a boat, probably minor, and within current cooling capability.

 

[SuperNova]

Re: 355ci vs 383ci

I have built 18 383's to date. A couple for cars, a couple for trucks, a couple for boats and a couple all-out race setups. They definitely make a lot more power than a 355, but there are some additional considerations as well. If you rebuild your 350 the expense will be significantly lower than putting together a good marine 383(expensive crank and rods and pistons). If you go with aftermarket heads, 4-bbl intake and 750 cfm carb on your 350 you can stay with 9.5-1 comp and a reasonable 216* cam and hit over 300 hp fairly easily. The 383 will cost more than 3000 to do properly.
--
Stan

 

[John_S]

Re: 355ci vs 383ci

Stan,

I am not picking here, I just like discussing this stuff! Given he is already into it for pistons (has to bore because of rust), assuming he will go with decent quench style ones, are we only talking about the cost of crank and rods? He has been talking cams for both the 355 and 383, too.

I am curoius about your after-market heads comment. I would think he could hit 300 hp with the 355 with just the cam and 4brl. He might want to do a little work to the vortecs, but wouldn't think it requires a head change. If he has to push above 5K rpms, I could see some benefit of better heads. Have you run the newer small port cast-iron bowtie vortecs? I would be interested in your additional comments. Thanks.

 

[Bondo]

Re: 355ci vs 383ci

are we only talking about the cost of crank and rods? He has been talking cams for both the 355 and 383, too.

Only the Crank,....... Rods are the Same,+ the originals can be used.....

 

[SuperNova]

Re: 355ci vs 383ci

Well, basically an engine is an air pump. The more air you get in and out the more potential there is to make power. The biggest restriction on a SB chevy is the intake tract. Most of the stock heads have 155 to 165 cc intake runners. To make decent power with a SBC you need at least 180cc. Even a ported and polished stock head only goes about 170cc. You also don't want to go too big, because you'll start sacrificing low rpm velocity for high rpm flow, and that'll cost you power down low because the fuel will drop out of the charge and puddle on floor and walls of the intake tract. The second consideration is combustion efficiency. Each drop of fuel is worth X btu's. If you can only extract .5X btu's versus .8X btu's, which engine will make more power? So the two real world factors affecting engine output are breathing(how much fuel and air can we move) and efficiency (how much of that fuel and air are we converting to power). Aftermarket aluminum heads are very well designed to do both, assuming you pick the one with the correct attributes for your particular application.

AS far as expense for the 383, as I said there are some additional considerations involved to do one properly, and a JC whitney stroker kit doesn't get it done. First, with our head discussion, that 383 needs to breathe deeply to make significant power and if you use stock length rods, 5.700" the piston dwell at TDC is too short and the rod angle is too steep to make efficient use of the combustion pressure, you end up making a hot exhaust charge and that's about it. Second, piston speed increases dramatically in a 383, which means they are more prone to piston scuffing and the ring package is much less stable, leading to more blowby and more burned oil. That is why they must be done correctly. Lastly, there are clearance notches that must be machined into the oil pan rail area that leave only a few thousanths of an inch of metal between the cooling jacket and the inside of your engine(where the oil is). On a raw water cooled engine, it rusts thru rather quickly. I'm sure you can imagine what happens then.

For my money, I'd spend it on the best heads and intake I could get. The stock roller cam is already a very good piece, so I wouldn't change that. And just do the required rebuild on the bottom end.
--
Stan