Help with 502 BBC build for my jet boat

[Nikwho]

Hello folks,
I previously started a thread, buy was leaning towards a 468/iron head build. You guys all helped me realize that my goals were not easily obtainable going that route. So, I have made progress! I've been collecting some parts. I've got a 502 longblock with 088 heads. BUT, I just picked up a set of Brodix "Big Brodie" heads. Was told that they flowed 365cfm by the machinist that removed them from another customers build. I belive that they were blended/ported to help flow. Currently the combustion chambers are at 119cc. My 502 has 4 bolt mains (as all do, to my knowledge) and an all forged rotating assembly. The heads can be milled to 110cc chambers. Not 100% certain, but I believe that the pistons are around -3cc dome. Low hour factory 4.470" bore. They are stamped "SRP 75F".

I don't want to land south of the 700 HP range. I'm okay with higher compression and running 100 octane fuel in the boat, if I cannot reach my goals on pump gas. Boat is currently a '74 Tahiti with 12JC pump, but looking for a different hull, more suited to handle the power. Pump will get rebuilt for the power and set up accordingly, but that'll come next.

So, with retaining the stock forged 4" crank and forged rods, and the factory forged SRP pistons, if possible, and utilizing my Brodix BB-2 Xtra blended heads, what is my path to making 700 HP? Seems like it's right on the brink of being a pump gas deal.

What kind of static compression do I need?

Do I need to go to a solid roller, or can I meet my goals with a hydraulic roller camshaft?

Can I do this with pump gas, or do I need to go to 100 octane fuel?

Can I do this with the SRP pistons, or will they be too low compression, even with my heads milled to 110cc?

I'm making serious headway on my build. Will be getting all machining processes done soon. Want this thing wrapped up by February, in the boat testing in March, and ready to run all summer.

Thanks a million for the expertise that you guys are so willing to share!

Nik

 

[Shlbyntro]

If those heads are aluminum, please please please put a closed cooling setup on that engine block. Raw water will eat the aluminum up in short order.

Ps. Big blocks care a lot less about compression than their smaller siblings. Get yourself a nice cam and good high quality externals., and I don't think you'll have any problem making 700hp NA

 

[Nikwho]

In the other thread, where I was wanting to build an iron headed 468 initially, another member reference this article that @cyclone wrote up. I'm tempted to more or less just follow his "recipe", but want to take into account any variance in parts.

If the best route to take is a roots blower, I can say that I am open to it, but cannot afford that this winter. I want to get this thing up and running N/A, and reach 700 HP. If I feel like I want more power later, I'll likely go the roots blower route.

Regarding parts, I have my 502 Gen 5 BBC. Currently has 088 heads. I have my Brodix "Big Brodie" BB-2 Xtra heads. Currently 119cc chambers, can be milled to 110cc. Just sent these heads to a machine shop in Ohio, who is machining my combustion chambers. There was a little bit of pitting in some chambers. It was welded in, and the shop I am using has the ability to CNC cut my combustion chambers. I have two new hydraulic roller camshafts that cam with the engine, but I think that they will fall far short of my power goals. I'll get those grind numbers and specs posted tomorrow, but don't think that they'll be a factor here.

I also have a rectangular port Weiand tunnel ram and two QFT 650 cfm carbs that I would like to make work, since I already have them.

To further complicate matters, I kind of want to keep my exhaust through transom. I would love to keep the logs/snails IF I were supercharging! Otherwise will go through transom headers.

If all things are pointing towards forced induction, I think that I could easily make the power I want that way, and force the air through the logs and snails! If I should run lower compression for now, and choke it up with the logs, with plans to do a cam swap and add a roots blower next year, I'm very open to that!

Whew. That was a lot. My apologies!

 

[Shlbyntro]

You can't keep the logs with that target number. However, I believe Lightning does make through transom headers and there are also some low profile high flow manifold setups.

If you end up not using the tunnel ram, please lmk. Im going to be in need of one shortly for my Hallett build

 

[Nikwho]

If those heads are aluminum, please please please put a closed cooling setup on that engine block. Raw water will eat the aluminum up in short order.

Ps. Big blocks care a lot less about compression than their smaller siblings. Get yourself a nice cam and good high quality externals., and I don't think you'll have any problem making 700hp NA

Good night! A closed cooling system adds a considerable expense to the build! Seems like tons of guys run aluminum heads on the river without closed cooling systems, don't they? This boat will essentially only operate on the Colorado River. I do have a ready to run set of 088 heads, as well as a set of 049's, 820's and a mix/match set of 215/068 heads. BUT, if I were to end up running any iron head, I think that it would be the 088's. But will almost certainly run the Brodix aluminum heads.

 

[Shlbyntro]

Good night! A closed cooling system adds a considerable expense to the build! Seems like tons of guys run aluminum heads on the river without closed cooling systems, don't they? This boat will essentially only operate on the Colorado River. I do have a ready to run set of 088 heads, as well as a set of 049's, 820's and a mix/match set of 215/068 heads. BUT, if I were to end up running any iron head, I think that it would be the 088's. But will almost certainly run the Brodix aluminum heads.

Yes of course you can, but you're talking about much shorter rebuild intervals. The electrolysis will eat the heads from the inside, even in fresh water. Thats why nearly all Merc blue motors are closed cooling. Id be surprised if a raw water aluminum headed big block makes it 200 hours.

The cost isn't that much more, it's really just a different tstat housing and a heat exchanger with some plumbing

 

[Nikwho]

You can't keep the logs with that target number. However, I believe Lightning does make through transom headers and there are also some low profile high flow manifold setups.

If you end up not using the tunnel ram, please lmk. Im going to be in need of one shortly for my Hallett build

Yeah, I'd only look to run the logs/snails if I were to go with forced induction. I've seen guys successfully run them with boost. But, will likely go with a quality through transom header.

I'm pretty pumped on my tunnel ram. It's the nicest one that I've seen in person. Someone did a heck of a job polishing it. It's a rectangular port Weiand (part # 1921).

Here's the two hydraulic roller cams that came with the engine that I bought. I'll pull the numbers tomorrow and post them here, so nobody has to follow links to see specs:

Crane Cams 168731 Crane Hydraulic Roller Camshafts | Summit Racing

Free Shipping - Crane Hydraulic Roller Camshafts with qualifying orders of $109. Shop Camshafts at Summit Racing.

www.summitracing.com

Chevrolet Performance Parts - 12366543 - Hydraulic Roller Camshaft ZZ502/502

Pace Performance offers the best pricing on products offered by Chevrolet Performance Parts. Including 12366543 - Hydraulic Roller Camshaft ZZ502/502.

paceperformance.com

I have a couple sets of 1.72:1 roller rockers, as well as a set of hydraulic roller tappets for the engine.

If I am to go with a roots style blower, I might just run the better of these two camshafts for now, and spend a little more time saving money to buy a nice 8-71 blower. I got a quote from The Blower Shop today. Was about $6,000 all in, with a 16 to 18 week turnaround time. Unfortunately, on my public safety salary, it will take more than 16-18 weeks to earn the money.

But, if the big picture points towards buying a blower, I'll save up and go that route. Like probably everyone else, I've always wanted a blower motor!

 

[Shlbyntro]

Yeah, I'd only look to run the logs/snails if I were to go with forced induction. I've seen guys successfully run them with boost. But, will likely go with a quality through transom header.

I'm pretty pumped on my tunnel ram. It's the nicest one that I've seen in person. Someone did a heck of a job polishing it. It's a rectangular port Weiand (part # 1921).

Here's the two hydraulic roller cams that came with the engine that I bought. I'll pull the numbers tomorrow and post them here, so nobody has to follow links to see specs:

Crane Cams 168731 Crane Hydraulic Roller Camshafts | Summit Racing

Free Shipping - Crane Hydraulic Roller Camshafts with qualifying orders of $109. Shop Camshafts at Summit Racing.

www.summitracing.com

Chevrolet Performance Parts - 12366543 - Hydraulic Roller Camshaft ZZ502/502

Pace Performance offers the best pricing on products offered by Chevrolet Performance Parts. Including 12366543 - Hydraulic Roller Camshaft ZZ502/502.

paceperformance.com

I have a couple sets of 1.72:1 roller rockers, as well as a set of hydraulic roller tappets for the engine.

If I am to go with a roots style blower, I might just run the better of these two camshafts for now, and spend a little more time saving money to buy a nice 8-71 blower. I got a quote from The Blower Shop today. Was about $6,000 all in, with a 16 to 18 week turnaround time. Unfortunately, on my public safety salary, it will take more than 16-18 weeks to earn the money.

But, if the big picture points towards buying a blower, I'll save up and go that route. Like probably everyone else, I've always wanted a blower motor!

Id put one on the Hallett if they weren't so damn expensive! Lol. Im billing mine as a "how to get into an antique hotrod for under $10k." We'll see how I do when the winter is up! Ha.

Good luck on your build! There are a lot more guys around here that know far more about building HP than I do, I've always been more focused on longevity since thats my business.

700 is very attainable NA tho, excited to see your end product

 

[JUSTWANNARACE]

Yes of course you can, but you're talking about much shorter rebuild intervals. The electrolysis will eat the heads from the inside, even in fresh water. Thats why nearly all Merc blue motors are closed cooling. Id be surprised if a raw water aluminum headed big block makes it 200 hours.

The cost isn't that much more, it's really just a different tstat housing and a heat exchanger with some plumbing

Much less electrolysis in a jet drive then a stern drive imo. Biggest thing with alum heads on a jet is restricting flow to build consistent heat. Wide open throttle to idle(without the right restriction) will warp a head in a hurry

 

[Nikwho]

Was looking at this Hydraulic roller from Comp. Pretty similar to the grind that @cyclone used in his 740 HP 502 with AFR heads, that ran on 91 octane and came in at 9.6:1 static compression ratio. For me to hit that SCR, I would likely have to have my heads milled down to 110cc chambers.

COMP Cams 01-461-8 COMP Cams Xtreme Marine Camshafts | Summit Racing

Free Shipping - COMP Cams Xtreme Marine Camshafts with qualifying orders of $109. Shop Camshafts at Summit Racing.

www.summitracing.com

And have been looking at quite a few solid rollers. Just not sure if I need to go solid roller to hit my goal with this combo? I think that in order to get much more power, I'd need to up my static CR considerably enough that I would certainly need to swap pistons. If I have to buy new pistons, I would probably go to at least a 4.5" bore, get up in the 11-12.5:1 static CR range and plan on running 100 octane fuel. Then I could get more aggressive with the camshaft, and run a solid roller.

 

[78Southwind]

I would give Chris Straub a call about the cam.
https://straubtechnologies.com

 

[brgrcru]

Been running aluminum heads for 30 years
On my jet boats . Never a issue .

For super trouble free 700 hp
That 502 can be stroked to a 540 real easy.
Run the brodix heads and a hyd roller
Single 1050 dominator
Pump gas. Trouble free . Just change oil and plugs.


That Tahiti boat and pump will need a lot of work . To reach any speed goals .

Just my .02

 

[Nikwho]

Yeah, I'm not looking to make the Tahiti hull go fast. I've been on the hunt for another hull. Likely a Sanger or Hondo V-drive.

 

[02HoWaRd26]

Bump her to a 540”, your BB2’s and i have no clue on cam, but than add a Holley Sniper up top. You may not hit 700, but I’d bet you get real close.
I would suggest a closed cooling with T-stat as well, even if you did it a little later. A lot think keeping an engine cold is good, well you don’t want it hot either but you definitely want her a good stable 165-170° which can easily be maintained with closed cooling and a t-stat.

 

[Blackmagic94]

Bump her to a 540”, your BB2’s and i have no clue on cam, but than add a Holley Sniper up top. You may not hit 700, but I’d bet you get real close.
I would suggest a closed cooling with T-stat as well, even if you did it a little later. A lot think keeping an engine cold is good, well you don’t want it hot either but you definitely want her a good stable 165-170° which can easily be maintained with closed cooling and a t-stat.

Why do you need it that hot? For one the higher temp is gonna make the engine need more octane. And then you are gonna have to run a water pump with a water pickup etc. a lot more crap for no or very little advantage

 

[hman442]

Been running aluminum heads for 30 years
On my jet boats . Never a issue .

I'm Curious about the aluminum issue in fresh water also. Everybody has aluminum intake manifolds, as well as thermostat housings, fittings etc., are these components subject to the same issues, or is something that just affects cylinder heads ?

 

[brgrcru]

I'm Curious about the aluminum issue in fresh water also. Everybody has aluminum intake manifolds, as well as thermostat housings, fittings etc., are these components subject to the same issues, or is something that just affects cylinder heads ?

All those parts get corrosive over time . Nothing you can really do.
Maybe run it on a hose at home for a bit.
Not really anyway to prevent it
You don’t really notice it until you start pulling stuff apart . By then you need to replace or repair that shit anyways .
For a jet or vdrive running river duty
I just don’t see going with a closed cooling system .
Grew up and have Been running the river 55 years
We Never thought about closed cooling .
Motors are running cold . But again
Never had issues with cold running motors .
Never went through a motor because it was running cold for 10 plus years .
I’m no expert motor builder.
I’m just talking from experience with big hp motors in jets and flats

Keeping it simple seems to work best.
If you don’t want to wrench on it .
Pump gas
Hyd cam
Searching for race gas or high octane fuel (100) sucks
When you are out of it .