509 CI BBC Build

[Beachcomberbrian]

I need some help. I’m currently having my 509 bbc twin engines rebuilt. I’m looking to make close to 700hp out of them on a stock GM bottom end. I’m thinking with those numbers I should switch the rods to H beams? Stock GM are I beam. Also looking for advice on a good head and cam package that can make that power. Advice on pistons? Stock Piston compression is 9.6:1. Should I put domes in it and raise the compression? Thanks in advance for any help. I’ve found some good combinations from old hot rod magazine 502 builds but wondering if there’s any major difference when building power for a street car vs a marine engine.

 

[oldschool]

Paging Barry, Obnoxious 001.

 

[4Waters]

Definitely go with H-beam rods and a steel crank, the thing to remember with a marine engine is it is a constant uphill run.

 

[Bigbore500r]

I need some help. I’m currently having my 509 bbc twin engines rebuilt. I’m looking to make close to 700hp out of them on a stock GM bottom end. I’m thinking with those numbers I should switch the rods to H beams? Stock GM are I beam. Also looking for advice on a good head and cam package that can make that power. Advice on pistons? Stock Piston compression is 9.6:1. Should I put domes in it and raise the compression? Thanks in advance for any help. I’ve found some good combinations from old hot rod magazine 502 builds but wondering if there’s any major difference when building power for a street car vs a marine engine.

You need to consider the application and RPM range you will be operating. That will determines how much power you will make out of the motor N/A. Too much camshaft will make it idle too high causing shift issues with a bravo drive, as well as robbing torque below 3000 rpm, which you need to get a boat on plane.

Compression is a function of camshaft selection as well. If you run a larger cam with a late intake closing point it bleeds cylinder pressure and lowers the dynamic (running) compression, which will require you to increase the static compression ratio. But if you cam it with an early intake closing point, you don’t need as much compression. What fuel do you want to run it on?

 

[Beachcomberbrian]

You need to consider the application and RPM range you will be operating. That will determines how much power you will make out of the motor N/A. Too much camshaft will make it idle too high causing shift issues with a bravo drive, as well as robbing torque below 3000 rpm, which you need to get a boat on plane.

Compression is a function of camshaft selection as well. If you run a larger cam with a late intake closing point it bleeds cylinder pressure and lowers the dynamic (running) compression, which will require you to increase the static compression ratio. But if you cam it with an early intake closing point, you don’t need as much compression. What fuel do you want to run it on?

91 pump

 

[nrbr]

Invest in some decent cylinder heads!

 

[vstdispatch]

91 pump

Not going to make 700hp then fyi

 

[obnoxious001]

I need some help. I’m currently having my 509 bbc twin engines rebuilt. I’m looking to make close to 700hp out of them on a stock GM bottom end. I’m thinking with those numbers I should switch the rods to H beams? Stock GM are I beam. Also looking for advice on a good head and cam package that can make that power. Advice on pistons? Stock Piston compression is 9.6:1. Should I put domes in it and raise the compression? Thanks in advance for any help. I’ve found some good combinations from old hot rod magazine 502 builds but wondering if there’s any major difference when building power for a street car vs a marine engine.

I need a better description of what you plan to do. What does your engine builder say to do? I would not be happy if I was building an engine for someone and they were asking someone else what to do with it!

The 502's that I have dealt with came stock around 8.75-1. I have used a completely stock 502 bottom end that held up fine to a very mild blower set up, but normally I suggest going to aftermarket rods with a rebuild just since new rod bolts and resizing will get close to the cost of a set of I beam rods, not to mention the aftermarket rods are bushed for full floating wrist pins.

As I said, I need more information to comment further, but if you are doing a twin engine, big boat, pump gas, , stock stroke, NA engine, I don't think your goal will be very cheap.

 

[zx14]

700hp on stock bottom end will not last very long.

 

[Beachcomberbrian]

I need a better description of what you plan to do. What does your engine builder say to do? I would not be happy if I was building an engine for someone and they were asking someone else what to do with it!

The 502's that I have dealt with came stock around 8.75-1. I have used a completely stock 502 bottom end that held up fine to a very mild blower set up, but normally I suggest going to aftermarket rods with a rebuild just since new rod bolts and resizing will get close to the cost of a set of I beam rods, not to mention the aftermarket rods are bushed for full floating wrist pins.

As I said, I need more information to comment further, but if you are doing a twin engine, big boat, pump gas, , stock stroke, NA engine, I don't think your goal will be very cheap.

28 Daytona. Naturally aspirated. Would like to make about 700hp, it’s a twin.

Currently I have zz502 that have been bored over to 509s. Builder wants to put Big cams and port and polish the stock heads. I’m concerned it won’t make the HP I want if we don’t go to bigger aftermarket heads. I read the specs on the zz502 and it says it has I beam rods good up to 575hp. That’s why I was concerned about running those rods without going to h beam. Just trying to get all my ducts in a line so I can make the right decisions with him.

 

[Beachcomberbrian]

700hp on stock bottom end will not last very long.

700hp on stock bottom end will not last very long.

I’ve been told the rotating assembly
On the zz 502 is really solid. Looking at the specs it’s got a steel crank, forged rods and pistons. Seems like a good start.

 

[Bigbore500r]

The issue with making 700hp out of a 500” N/A motor on pump gas, is that you’ll make that power at near 7000 rpm. Bravo drives don’t like 7000 rpm, and the cam will be too large to idle low enough to shift in and out of gear, or have dock manners. Plus torque below 3500 will suffer.

To get 700hp that is marine friendly, your gonna need cubes and to build a stroker and go 540” or bigger. Your also gonna need quality heads and valve train. That should get you the ability to get 700hp below 6500 rpm peak without killing torque where you need it.

 

[Ouderkirk]

I need some help. I’m currently having my 509 bbc twin engines rebuilt. I’m looking to make close to 700hp out of them on a stock GM bottom end. I’m thinking with those numbers I should switch the rods to H beams? Stock GM are I beam. Also looking for advice on a good head and cam package that can make that power. Advice on pistons? Stock Piston compression is 9.6:1. Should I put domes in it and raise the compression? Thanks in advance for any help. I’ve found some good combinations from old hot rod magazine 502 builds but wondering if there’s any major difference when building power for a street car vs a marine engine.

To be honest, for what you're talking about cubic inches is what you want.

An example is this (not recommending this item per se). It's $15K each but you're going to spend a good bit of $$$ to get what you have, to where you want to go.

https://www.ebay.com/itm/BBC-Chevy-...130528?hash=item4d63fee360:g:6w0AAOSwjghZx98x

 

[Boat 405]

700 Hp is doable but tough with 509 NA.

Id go with a 540 4.25 stroke. A good set of AFR cylinder heads like their 325 heads. 10.5 to compression and a healthy amount of camshaft.

My last 540 made 787hp and 700ft lbs. All done by 6500 rpm with a carb. I was able to make it idle decently to shift my bravo xr drive. 750rpm. With feathering the throttle to get in and out if gear without stalling. If you go EFI. You’ll be good.

 

[Beachcomberbrian]

The issue with making 700hp out of a 500” N/A motor on pump gas, is that you’ll make that power at near 7000 rpm. Bravo drives don’t like 7000 rpm, and the cam will be too large to idle low enough to shift in and out of gear, or have dock manners. Plus torque below 3500 will suffer.

To get 700hp that is marine friendly, your gonna need cubes and to build a stroker and go 540” or bigger. Your also gonna need quality heads and valve train. That should get you the ability to get 700hp below 6500 rpm peak without killing torque where you need it.

Understood. My blocks can only safely bore to a 509. Maybe I need to lower my expectation down to 625hp.

 

[SkyDirtWaterguy]

I’d be calling Alexi @ Boostpower

 

[Xtreme1]

Understood. My blocks can only safely bore to a 509. Maybe I need to lower my expectation down to 625hp.

Sounds like you may not understand cubic inches and how it is figured.. If you want to stay with a 4.00 stroke crank then your builder may be correct. However look at it as theres no replacement for displacement! If your buying all new internals rods and pistons you might as well get cranks too and achieve the desired power while putting less stress on the parts... i.e a 470 cu in bbc at 8500 can make 900 hp but it takes big $$ parts and its going to break. This is not an endurance build. A 540 with 4.50 inch bore , 4.250 crank and a set of 6.385 rods will now get you close to where you want to be at or around 6000 rpm reliably and produce significantly more Torque which is what you should be shooting for not a H.P. number

 

[BamBam]

Your 509 is bored 4.500" with a 4.00" stroke. The suggestion above is to replace your cranks and rods with 4.25" stroke and 6.385" rods (you have 6.135" now) this will create 540 cubic inches and increase the ease of building both torque down low and HP as the RPM increases. We built a 540 (now .030" over and 548) that made 711HP at 6200 (cause we only pulled to 6200) and had over 600ftlbs of torque from 2800 all the way to 6200 with a peak tq of 675. Oh and it runs on 91 all day long. You will also need to invest in good cylinder heads and match you cam. As Barry said, you really need to sit down with your engine builder and lay out what you want. If he knows your target for HP, Torque, fuel requirements and use he will be able to put together a combination that will fit your needs. It's just gonna cost money.

 

[obnoxious001]

28 Daytona. Naturally aspirated. Would like to make about 700hp, it’s a twin.

Currently I have zz502 that have been bored over to 509s. Builder wants to put Big cams and port and polish the stock heads. I’m concerned it won’t make the HP I want if we don’t go to bigger aftermarket heads. I read the specs on the zz502 and it says it has I beam rods good up to 575hp. That’s why I was concerned about running those rods without going to h beam. Just trying to get all my ducts in a line so I can make the right decisions with him.

Try also looking up the new Eagle I beam rods, they claim they are good for 850 HP. I have used about 3 sets of them so far, H beams normally would be considered better, but read the specs for yourself.

As I did say before, I built a 502 for marine use with an 8-71 supercharger, and factory bottom end, held up fine last I knew, it must be about 10 years old now. I also built one that was bored to 516 with a 3300 Whipple on it (not stock bottom end), but that block has held up for 10 years, boat is able to peg a 120 mph gps.

Factory heads will cost some money to port, and then you will also want better valves, so might be better at looking at aftermarket aluminum heads that will also give you a bit more margin against detonation by transferring heat better.

 

[rrrr]

No way I would pay someone to "port and polish" heads in this day and age. Some guy with a die grinder isn't going to make stock heads work as well as aluminum heads produced on a multi axis CNC. Bolt on a set of AFRs and be done with it.

 

[sintax]

No way I would pay someone to "port and polish" heads in this day and age. Some guy with a die grinder isn't going to make stock heads work as well as aluminum heads produced on a multi axis CNC. Bolt on a set of AFRs and be done with it.

I think theres a few different price points here we have to consider. Its totally unfair to compare a set of 049's that have been thoughtfully cleaned up, to a set of FULL CNC 5 axis jobby AFRs. Not everyones building a 1200 hp package. Maybe someone is just looking for a little extra while they're in there doing a valve job or something.

 

[jetboatperformance]

We build these BBCs from balance rotating assemblies purchased from Skip White Performance (Alabama) A decent short block build (Eagle/Scat/Wiesco etc) runs about $1500 includes dampner and flex plate super clean stuff lots of options good service . ( 9.5 or slightly higher) Currently using Maxx aluminum heads and Howards cam components

 

[Ballyhoo]

28 Daytona. Naturally aspirated. Would like to make about 700hp, it’s a twin.

Currently I have zz502 that have been bored over to 509s. Builder wants to put Big cams and port and polish the stock heads. I’m concerned it won’t make the HP I want if we don’t go to bigger aftermarket heads. I read the specs on the zz502 and it says it has I beam rods good up to 575hp. That’s why I was concerned about running those rods without going to h beam. Just trying to get all my ducts in a line so I can make the right decisions with him.

It doesn't sound like you have full confidence in your builder. It might be a good time to contact a few other reputable builders to get some ideas. I did this a number of years ago and its still paying dividends.

 

[fishing fool]

@RaceTec is the person you will need to talk with for pistons....

 

[Hallett Dave]

@RaceTec is the person you will need to talk with for pistons....

When it comes time to freshen up my Foxwell engine I will go with KB forged pistons again.
To each their own.

 

[CLdrinker]

If your motor builder knew what he was doing you wouldn’t need to be asking anyone anything. That’s why he is getting paid.
I would be looking elsewhere for a builder.

 

[wet hull]

Good luck and it's hard trying to figure out what is possible. My engine builder "Flat Top Marine" would not allow me to have a opinion. I didn't get a say in parts or anything else. Built me a 540 N/A at around 650 hp and 9 years with zero mechanical issues.

 

[rrrr]

If your motor builder knew what he was doing you wouldn’t need to be asking anyone anything. That’s why he is getting paid.

I would be looking elsewhere for a builder.

The OP, @Beachcomberbrian, says:

I’ve found some good combinations from old hot rod magazine 502 builds but wondering if there’s any major difference when building power for a street car vs a marine engine.

Hell, yes, there's a difference. If you're using old issues of Hot Rod as a guide to building engines for marine use, you're going to find out the difference when those engines grenade. It'll be an expensive learning experience.

Currently I have zz502 that have been bored over to 509s. Builder wants to put Big cams and port and polish the stock heads.

That statement is so vague, it's impossible to determine what the builder intends or give any advice to the OP about how the engine should be built. I do know one thing. Do a search in this forum and the engine build forum for "ZZ502” and ”ZZ572”. You'll discover why these engines are unsuitable for marine propulsion units unless marine specific parts and clearances are used when they are converted for boating power.

If the builder has any experience and product record building marine engines, he should be able to sit down and show the OP several specific builds, with displacement, compression ratios, induction system, valvetrain, and rotating assembly that accomplish his clearly stated theories and goals. He should have dyno sheets and a customer base that back up his claims.

If he does not have specific experience building marine engines, find someone who does. You don't want to be the person whose engines he uses to figure out what he doesn't know and is doing wrong.

There are many questions that must be considered when building a marine engine. How big is the boat, and how much does it weigh? Who manufactured the drive, and what internal upgrades have been done? What type of hull does it have? What's the elevation of the lakes the boat owner frequents? What is the primary use of the boat? There are more.

The last marine engine I had built was an EFI 540, and before I signed on the dotted line, I had thoroughly examined the builder's shop, talked to his customers, reviewed his build sheets, and so on. After doing my due diligence, I was confident the guy was qualified, honest, and would build an engine that would perform as expected. It did.

You would be surprised at the number of people that listen to a ten minute monologue about a builder's capabilities and then turn over a cash deposit of thousands of dollars. But building an engine is much more than a "big cams and port and polish" philosophy, particularly when it's a marine engine.

Like most things in life, it's up to you to decide if a builder knows what he's doing and if he's on the level.