Large inch NA build
 

First of all....let's not turn this into a p!ssing match that gets locked or deleted...

Thought it would be fun to see what guys would put together for combos and share ideas/thoughts to build a larger inch NA motor.

Let's start with say a 502 mag MPI box stock no mods with 700 hours. What would you do if you were shooting for say turn key 700? Is it feasible out of a gm 502 block?

How big would you go to keep as much reliability as possible? 540, 548, 555, bigger/smaller?

Obviously brand and preference are highly subjective but let's keep this simple and as fun as possible....what do you think for hard parts? Ported aluminum heads? Ported stock heads? Ported/cleaned cast iron heads?

Same for rotating assembly...What's all needed? Crank, rods, pistons, cam, lifters?

And a big question...can it be done at all? Let's throw budget out the window as that's subjective too but to do it right and reliable can you squeeze 700 out of a NA gm 502 block?

Let's have some fun with it...what's everyone's thoughts?

So long as the block passes porosity tests, .030 502 with a 4.25 crank - 540 cubic inch. Factory crank, good rods, AFR 315 or 335 heads, cam to match the flow capability, good single plane with a 1050 Dominator. Should get you there.

I built a pair of 548's that made 700hp. Stock block, Big Al heads and a custom Lunati cam. Topped them with Holley EFI. I really like 555ci or 565ci though in a std deck block.

I have read a few older threads and articles saying boring out to 555 or 565 on a gm 502 block is getting dangerously thin on the cylinder walls? Mentioned something about having to sonic test the block or something? Has this practice changed and not relevant anymore?

Good info so far guys! Hope this turns into a very informative thread that can stand the test of time!

Here you go, you won't have to rev it over 5000 RPM, ZZ632 Crate Engine | Chevy Performance Parts (chevrolet.com)

I'm going a route most wouldn't consider. Looking for max torque all in by 5-5200rpm. Just haven't decided if going 540 or 565. 10:1cr, roller cam, probably solid since I have lifters already. Intake from a Merc HP500. Holley 950 or 1000cfm 4150 with annular boosters. Floteck Oval port heads, 290cc intake ports that peak flow at over 340cfm at .600 lift. Should have a high flat torque curve from 2500-5000rpm or a little longer.

we went the other way with a 540 10-1 solid roller ported heads we wind it up pretty tight up to 7000 running an xr standard length 1.5 with a 26p bravo one prop it sits in a 25 active thunder its been the most reliable and most fun boat i have ever run ......building a lot of torque in the lower rpms is very hard on bravo gears letting it wind up reduces the strain but you need really good guts in it to do it reliably

I had 900 hours on mine. It’s a carbed 540 now. 712 horsepower at 5600 rpm same torque at 4700. Dart cnc 335 heads , dart intake , 850 qft carb. Turning all accys but on dyno headers. Running stainless Gen 3 exhaust. Closed cooling.
you may have to run a larger diameter fuel line and pickup. I went to 1/2 inch. Also , there is no mech fuel pump provision so an electric fuel pump is a must. If you are going carb .. I am using a Weldon A 600 going through the carb to a Weldon return regulator and back to the tank..And you will have to ditch the stock mercury oil filter mount , cooler and lines and go with bigger stuff as well.

Coming from the drag racing world... I know without a doubt... cubic inches rule in the marine world.

I started out with small blocks, and immediately jumped to big blocks. First was a 427... then that ended up as a 511.
Ran a 555 and a 565 in two different cars. They ran great... but the ultimate beast was the 632 I had in the last one. That engine was an absolute animal. Any speed, any gear, any RPM it just pulled like a freight train.

Thing is... if you have to buy a block/crank/rods/etc... it really isnt much more money to go bigger. A long stroke, tall deck combo in my (new to marine stuff) opinion is absolutely the way to go.
To play it safe... keeping the bore @ 4.500" and stroke at 4.500" leaves some meat in the cylinder walls and keeps rod/stroke ratio reasonable... so that said... my vote is for a 572 (4.500x4.500) or 598 (4.600x4.500).

My current boat has a 496/8.1 Gen7 in it... so I found a 535/8.8 PSI engine (also gen7) to build and swap in. The longer 4.5" stroke and +.100 bore will make a huge difference.

Thats just my two cents.

So we're actually talking "large inch SHORT 9.8 deck , STOCK 502 gen 6 block build" to narrow things down a little? There's been quite alot of debate/claims/information thru the years of 'how far you can bore a production gen 6. I will say this as far as boring a stock block to its "end", only do it IF it needs done because of bore wear/damage. doing it to gain 5 cubic inches isnt a great plan.
I had plans on building a pair of maxxed out 548s for my 33 scarab AVS, 13-1 or so compression, try a bunch of different heads and intakes while on my dyno on engine one, etc. Actually built engine one most the way, I had the cncd afr heads and ported promaxx heads to try. Then after dynoing several other E85 engines, saw how atrocious the BSFCS actually were even with the BSFC gain from the compression and abandoned the idea because of fuel tank size/fuel range. Sold that 548 short block to a local mud bogger who had me put his USED AFR 290 heads on it with proform intake/modded 4150 carb. It made about 750 hp on dyno and about 680 torque on E85 with cam that would never work in a boat. Those top end parts were chosen strictly because he already owned them off engine he blew up.
So a ideaL big cu inch engine w stock gen 6 block to me is a optimized 540/548, a 555 to 565 with 4.375 stroke is pushing it. , with 6.385 rod. CH is around 1.270. Yes, a oil ring rail supports needed but skirts are just long enough to get a few hundred hrs out between rebuilds. At 4.375 stroke, your into a 1.190/1.20 ch and piston is getting mighty short, rings are starting to get squeezed into quite a small area. So as far as "practical limit" , keep in mind as stroke goes up, ring life goes DOWN.
Maximum bore, IDK what to believe, a well known engine builder in Tennessee told me in conversation that he doesn't even bother sonic checking gen 6 502s anymore as they all pass and can go to 4.600 , has blown Whippled 4.600 bore gen 6 engines out there making 1100/1200 hp at 14 lbs boost that have hundreds of hrs on them but in different conversation told me you can go 4.600 once in a while but 2 out of 3 blocks wont sonic check good enough to do it. I typically order custom pistons for gen 5/6 stuff I build that has to go past 4.530, as in I did a 4.540 bore 502 whipple engine, it was at 4.530, so I special ordered pistons .010 bigger as to keep bore rigidity//cylinder distortion down under boost. A local shop bored their customers gen 6 502 block to 4.560 or 4.580, was a compression engine. When they were dynoing it, they had rings seated, etc, were doing power pulls. They more they pulled it, the less power it made. Started getting blowby. They tore it down and looked it over, the cylinders were distorting and moving around. I dont know if they saw this while re honing it or with a dial bore gauge but they said they scrapped that block.
The next limiting factor is exhaust BUDGET. Im at that cross roads with my own current builds for my boat. I have seen now that I have dynoed countless engines here that you can make just about ANY bbc make a whole ton of hp, but usable torque, thats a whole other story. A 496 spun hard with big cam/heads can make 800+ hp but torque will be aweful. So as far as exhaust, lets say you pump a 540 up to 750 hp with big daddy cam, unless you have dry, big tube headers in boat, the dismal tq it made is gonna make boat hard to prop and hurt all around drivability and if you slap on a set of imco power flows or stainless marine 1s, gils, you can probably take 50 or 60 hp off that glorious hp number. So now you've shifted your torque peak way up as far as rpm wise . gave up usable tq and now killed off the top end hp with a set of manifolds. This is point where alot of my customers in engine build plans get frustrated. Im at that point myself. Im not gonna put used , matched up headers on my boat but Im not gonna spend 20,000+ on 2 pairs of big tubes cmis new either so.
I was having a conversation with a west Michigan engine builder/boat guy who came to my shop to buy parts last summer. A interesting point he brought up was "square tq/hp", basically if your engine makes 720 hp but makes 620 tq, its gonna be a touchy, turd with tiny prop, real sensitive to load in boat etc. would be fine in a competition boat where you have a trailer full of props, boats light, runs on fumes, etc. Would suck in a typical pleasure boat. So if you have pretty square tq/hp, say 680 tq/680 hp, your boat is going to be better all the way around, the average power under curve will make the 720 hp engine look like a joke. When your wife or Gf says oh yeah, I invited more people to go out on the boat your not going to be wondering if it will get on plane. Ill add more later, Smitty

Smitty,

So, I've got this hair-brained idea (not that I have any immediate plans) of starting with a BigM tall deck, 4.25" stroke, bored to 4.6 (565ci) with 6.7" rods. My math puts CH at 1.575". Too much? 4.375" stroke and 4.54" bore gets you to about the same displacement (566ci), and a CR of 1.3125". It would seem Molnar sells rods of just about any length, that would allow the "fixing" of any CR stack-up. Is it that simple?

Anybody ever done this? Morbid curiosity.....

Thanks. Brad.
(937)545-8991

Yes, Im building a 4.375/4.600 tall deck right now for a non boating application and its as simple as getting pistons with right Ch. If I was going to put a 4.25 stroke tall deck together, Id probably go 6.800 rod length to get some of the mass out of the piston, Smitty

If you really want 700HP with a stock GEN 6 block wouldn't force induction just be a better way?

For a lot of the reasons Articfriends said. You can have a much better TQ curve, less aggressive cam so valve train last etc? You would not have to go crazy on the bore/ stroke combo.

Smitty,

So, what's your opinion on hi/lo limits for CH? Is it a standalone parameter, or does stroke, bore, rod length, etc factor into it?

How much does fiddling with rod length affect cam timing? As I know it modifies piston position in relation to cam clocking position. Enough to worry about?

Thanks. Brad.
(937)545-8991

Building NA engines for boats can be a little tricky. While trying to achieve a certain HP goal, sometimes the torque band is overlooked. The most important piece is cylinder heads, and cam. I will post our performance sheet on our 42 fountain, with 790 hp 565's. If you notice we never reach peak hp. You can also see how hard the boat accelerates through the torque curve. We collect our data through smartcraft, garmin that are linked together. Then apply the torque and hp figures from our dyno sheet.
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Who did your intakes again?

Hogan built them.

I had considered going that route. Just wasn't sure how it would hold up running like that for miles at a time. Also I've got a light boat at 22'6" and about 3500lbs when I go out by myself to raise a little hell and blow off steam. Figured as long as I'm easy on the acceleration the out drive should be ok. Either way there's no Ford 9" of out drives available.

The first engine builder who was a nervous nelly and wanted me to buy the best of the best was having a stroke when we had to go 4.530 on a Big M block.thought there wasn`t eanought meat on the bone
As far as I know 4.600 is the limit ..... Dart sais

If you go 4.600 and it gets hurt you`re out of meat on the bone and you have to buy a new block no ?
Thats the issue I see with your plan Brad.

Dan,

I'm kinda liking the idea of a 4.375" stroke and a 4.54" bore, at 566ci, anyway. Start with a tall deck and use long rods to make up the deck height, keeping the rod angle low, I think one could build one HELL of a big cube, NA torque monster. Or top it with a 3.8 Whipple and REALLY twist an outdrive out of shape. :thankyouthankyou:

<Sigh....> One of these days.....

Thanks. Brad.
(937)545-8991

The length and weight of the boat may be a factor in what size engine you build. I thought Big cubic inch is when you're heading for 800 or so.SAR 820 EFI Marine Engine - Sonny's Racing Engines (sonnysracingengines.com)

always love your input smitty. Really looking forward to seeing what you do with the 33.

I agree, an NA E85 motor is a bad idea in a pleasure boat due to range anxiety.

If I had to have a compression motor in a boat, I’d go with 100LL, maybe spiked with a little additive. You could bump up to 13 to 1. I’d also seriously consider EFI to lean it out a bit at cruise rpm to help your range out.

I think if you’ve got a blower motor, it would be fun to have a set of E85 carbs and a party pulley for your shoot out or poker run days.

If I was building NA it would be straight to a tall deck 632 with SR20s and a profiler sniper ram. Exhaust is still a problem, I’d love to see eickerts/lightnings vs stainless gen 2 vs CMIs dynoed at 1000hp.

I've got to admit. I've never built 550+/-a few that didn't make 1000+ with a Dominator. But those went into race cars for NHRA Super classes. Complete different ball game.

who was this clown?

4.6 is pretty standard now. The bullet boys claim they will go to 4.63.

apparently good machines like a rottler can do .005 or .01 overbores, and line to line coatings can even save pistons

Big inch Sonny's or Musi....mountain motors

Go with the longest rod you can fit without getting into the bottom rings. It'll make more power.

You referencing Sonny Leonard's?

on our 598s the wrist pin is 3/4 into the oil ring groove we use a oil rail carrier to get around it ,it carries the oil ring rails like a bridge

Low deck 598s? I’ve been curious what the rod and CH are on those.

If you put those pistons in a 10.2 how much stroke could it swing?

So your main question, is it feasible? Can it be done?

Short answer, it's just not worth it.

To properly build a reliable 700+hp with good torque costs just as much or more than a blower motor. Especially starting with a used up 502. So why do it?

The only reason I went NA is because my boat originally had 750hp supercat engines, it's a race boat with tractor pipes, and just "fits" the theme. Unfortunately they were extremely expensive and are less reliable than blower motors. We love them though! But we started from scratch, 572cu/in Dart blocks, lots of High end parts, dry sump, etc.

I know you are not going to believe me nor listen, people never do with offshore boating advice. The "Hope" to be able to do whatever they have convinced themselves that they want to do clouds judgement. And unfortunately, most people's budget isn't even close to their goals or dreams.

About 10 or so years ago I was down at Lightning Performance in Easton, IL (grew up 10 miles from there) with a friend who was looking to build a 540 for his Checkmate. After Don gave me the grand tour of the place we sat and talked to Keith Eickert about building a 540 off a standard deck block and he flat out said no. When pressing him on why you had to go tall deck as there are many 9.8" 540's out there he barked back, "Not with my name on them there isn't". Take that for what it's worth when building larger inch N/A marine engines. I was really surprised at 540 cu in he insisted on a tall deck or he wouldn't build it. Maybe he just didn't want to p!ss around with such a menial build and figured insisting on a new block would would discourage my buddy from the build. It worked. :rolleyes:

IMO I have been down this road a couple times and regretted it haha. Leave the 502MPI as it is, buy a 2nd block and build it on the side until it is completed, chances are you wont get it built on one winter if you take your MPI apart, and you will end up boatless for a season. Been there, done that, rushed to save a season and got bit by shortcuts. Just get a nice big-inch shortblock and finish the rest, with cost of some of whats on market, isn't much price difference than you will have with machining costs and time of dicking with old block.

In the end, the only thing you will use on the new build is the block of the original motor. Yes they are expensive, but worth getting another. Leave the original motor on the stand when new one goes in as a backup or if you sell the boat.

Smitty,

I get that. My question is what is the ideal CH? I know too short is bad, due to ring wear and potential for catastrophic failure, and I know too long is bad, due to excessive reciprocating mass. I just don't know what that hi/lo is, and the interwebs is all over the place.

Thanks. Brad.
(937)545-8991

[QUOTE=Brad Christy;4862124]Smitty,

I get that. My question is what is the ideal CH? I know too short is bad, due to ring wear and potential for catastrophic failure, and I know too long is bad, due to excessive reciprocating mass. I just don't know what that hi/lo is, and the interwebs is all over the place.

Thanks. Brad.
(937)545-8991[/QUOTE
theres 2 smittys commenting here, lol.
I wont build ANY endurance engine with less than a 1.270/1.280 ch which is what you need to do a 4.250 stroke on a 9.8. And then, your dealing with a pretty short skirt length. That short skirt length comes at expense of ring seal I'm rebuilding 2 540s right now from.a guy from.Virginia that have excessive bore clearance, taper and piston wear.
I've seen guys claim.400, 600, 900 hr rebuild intervals with 9.8 deck 4.250, 4.375 combos but I have NEVER seen it personally. I have built plenty of 1.270 ch 540 variations, come 200 hours I've seen ring seal issues, on blower engines at 100 hours. sure, if it spent its whole life idling or running 2800 or something I guess I could believe the outrageous hour claims.
On other end of ch spectrum, I don't see a need for pistons with all kinds of extra mass with significant ch, like mentioned earlier, Id go 6.800 vs 6.700 if ch was getting into the 1.500+ range on a tall deck

https://cimg0.ibsrv.net/gimg/www.off...29c1d3d57c.jpg
https://cimg6.ibsrv.net/gimg/www.off...3eaf8dea05.jpg
The 540s I just mentioned had these pistons in them, very little skirt, very lightweight, had no purpose of being in a 5400 rpm low compression 540. I DID not build this or pick them out. They were already so loose on his last refreshen someone coated them to try to "fix" it. Well they did a poor job and the coating came off and went thru the bearings and torched the cranks, 77 hrs since that refresh is my understanding. Cylinders have .0015 taper, pistons are at .008 from a coated spot to tightest spot in bore BEFORE honing, more like .010 ,.011 to a loose spot where coatings missing. I am going next oversize on these 2, getting rid of these. Could have it honed round again which would put it at .012 THEN have bad coating stripped off then pistons re coated a ton, but not worth it. I would on a drag engine that has a 5 or 10 hr lifespan between rebuilds, Smitty

Smitty,

Got it. So, looking at the stack-up, does one want to stop just short of the deck height and machine it to the stack-up, or go past it and use head gaskets to make up the difference?

Building my fantasy engine, this is what I've got so far:

Dart BigM 10.2
Crank - Molnar #454-4375DC8F-6385 (4.375" stoke)
Rods - Molnar # CH6760VTB8-A (6.7" C-C)
Pistons - JE, Chevrolet, 4.530 in. Bore, Kit (jepistons.com) (1.27" CH)

This stack-up stops .0425" short of the 10.2" deck height. Or..... Molnar # CH6760VTB8-A rods (6.76" C-C) puts you .0175" over the 10.2" deck height. I know that we can machine the deck height and use appropriate head gaskets to zero in on the exact gap we're looking for. Which is the preferred approach?

I'm hoping this is valuable info for the OP as much as it is for me, so it's not TOO much of a derailment..... :party-smiley-004:

Thanks. Brad.
(937)545-8991

Almost anything is possible with any combination, but most shelf pistons are based off a set rod length, stroke, and deck height.
Then they derive the compression height.
Check the PDF printed catalogs, way more informative.

IMO, at 4.375 stroke, make a sacrifice on the rod length and go 4.5 stroke. 580CI at your bore. :cheer:

https://cimg3.ibsrv.net/gimg/www.off...535f0b8b82.png

Cheech,

That chart pertains to standard deck blocks. My hopes would be to use a tall deck and use longer rods to minimize rod angle. I was talked off the proverbial ledge on the idea of a 632 for this very reason. I'm just looking for where the conventional wisdom is on where to aim for the stackup. Do we aim high, over the deck height, and use head gaskets to establish final head gap, or do we aim low and machine the decks? I'm sure some of both will be in the final recipe, as I'm sure the 10.2" is not a super precise dimension with a new block.

Thanks. Brad.
(937)545-8991

I'm aware that was a short deck block.
I highlighted the piston number YOU linked in your previous post.
A piston doesn't know what deck height block it is in. The builder does!

Reread this: Take half of stroke listed at that part # you picked out 2.125" + rod length 6.385" + CD 1.270= 9.780"
Just under the 9.8" nominal for short deck BBC. All laid out in those PDF catalogs.
Here if this fits you better here's "tall deck listings".
Just go for broke. 4.375" crank same $ as 4.5" stroke, you're above the 1.270 CD Smitty likes, rod is a menial .165" shorter than a 6.7.
And keep your Procharger regardless!!
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I like where this thread has gone! Keep it coming fellas....I'm not currently building engines trying to meet these goals just mainly opened it up for discussion...

Should we clear up some of the acronyms for us stupid people? CH CD etc?

Is the general consensus that you can't get tq and hp up areound 700 with a GM 502 mag block then? In a 540 or 548 configuration? I read through everything and it seems like the hp is "easy" but tq will suffer...did I read that right?

Thanks for all the replies! Turning into a very informative and fun thread I think!