454 rebuild with blower... Pistons and clearances.
 

My 454 B&M 250 project has really started to get moving, and in the process I've come across some stumbling blocks. I found that four of my pistons showed evidence of detonation; definitely one for sure (#3... Slight erosion around the intake area at the crown extending to the top ring) with the other three having blemishes in the crown's face. Needless to say, these won't work with the blower. My bearings all came out looking good, and my crank should require polishing to put it back together so that's good!

My question centers around pistons: what to use and how should I have the block bored for proper clearance? My plan is to run less compression than the original LS6 pistons provided. I figure a flat-top with a zero deck, .040 gasket, and a 120cc chamber will give me right about an 8:1 compression ratio, maybe a touch over would be good for supporting 9-10 pounds of boost with aluminum heads.

The block will go to the machine shop this week to have it cleaned, sonic checked, decks trued, and finally bored and honed. I'm hoping that I can go with a .060 over piston to take advantage of the extra cubic inches as well as unshroud the intake valves of my heads. If I was to use a JE 139478 piston, ould it be safe to say bore it to 4.31 (if it checks clear), and then finish hone the bores to 4.315 to give the proper piston to wall clearance (assuming .003-spec'd piston clearance plus supercharged and cold water application). Thinking that ring end gaps should be set at .022 on the top ring and .025 on the second (plasma-moly rings). I guess I'd need to have the pistons in-hand first.

Looking for some advice from the experts here. Thanks!

Tom piston manufacturers have different piston to wall clearances. And if the Pistons are coated that changes things also. As far as ring gap you really need to go by the manufacturers suggestion on that one and even more importantly the block needs to be honed a certain way depending on which style ring you are using. This is crucial to ring seal. .060 overbore is not going to unshroud the valve that doesn't start happening till about .250 I personally wouldn't put 8:1 in a 454 with a blower it's gonna be a complete turd down low. And lastly if you want to bore your block .060 it needs to be sonic tested to be done right.

the Merc 525SC only had about 7-1 and they ran well...8-1 will be fine with the blower

Closed cooling or open? Thermostat?

Merc 525sc couldn't get out of its own way.

How would you build this?

I figured lowering the compression and turning up the boost (which would start low... figured it would start to build boost around 3K) would make up for the .75 lower ratio.

Raw water cooling. Not sure on the thermostat. Our water temps in the summer are generally in the 70's to mid 80's at the most. I'd probably run it with a restrictor but open and flowing all the time.

I seem to remember the guys from b&m to prefer around 7.5 to 1 and overdriven blowers with the 250 , on a street car would make for a glorious tire frier and suprisingly reasonable inlet tempatures.if you have aluminum heads get the block deck nice and flat and go mls gaskets and closed cooling should be able to make a reliable 550 or so hp with right cam and decent exhaust im building same thing now with flat tops and large ovals 122cc have some good 250 blower tech specs and extra parts also .pm me if you like ill share more about what ive learned about the ole original 250

This is how I would do it not that I'm an expert
9:1 so it's not lazy, using the speed pro pistons with raw water cooling and no thermostat, .006-.007 piston to wall clearance. I had an issue, with .004 scuffing pistons with iron heads and a 174 blower.

Bench racing with a friend of mine here suggested sticking around 9:1 with high boost numbers and the aluminum heads. He made over 700 with his 496 using pretty much the same setup. I guess I'm being too conservative?

Any particular reason to go with a Speed-Pro over a JE?

I'm on the hunt for probably closer to 650 to do what I want to do. I've collected a lot of parts... complete roller setup , heads. The rub was that I ran into unexpected issues with the short block hence having to redo it all. Bob Madura had pretty much told me that with a roller upgrade and 6-7 lbs with my iron RHS heads that we would be close to my goal if not beyond it with the 250. Needless to say, this has grown into quite the project.

I'll send you a PM. Thanks!

In this application I would really prefer the je pistons and tighten the clearance a little. But budget wise speed pro's are a dime a dozen and can work if everything is prepped, measured and assembled properly. If the budget fits go with srp or je pistons. There are better options than those but unnecessary for what you're doing.

Hey Tom. I wouldnt try 9-10lbs with a 250 blower.

Keep the bore size as close to standard as possible as to keep the walls thicker. The gains really arent worth it to go from a 454 to a 468 unless you absolutley need to.

I'd shoot for around 8.5:1 to 8.75:1 static, the right cam, 5-6lbs of boost, and go have fun with it. Low compression and big boost only works when you have enough blower to do so. Like lets say you did 8:1 with an 8-71, 420, then you can put some boost to it. A 250 trying to make 10lbs on a hot 454, is just gonna superheat the air and promote detonation. 6lbs of boost from an 8-71 will make more power than 6lbs of boost from a 250.

So go for a hone and truing of surfaces then? The bores look good (some scuffing in the cylinders that had issues... looks like it overheated if I had to guess) and still show a good crosshatch pattern. I really wish I didn't have to take this baby apart. The rod earing were great, and I don't recall having a crank installed in a block that felt so easy and smooth to turn. Make some wonder if the engine was gone through previously. Or if it's even the original short block.

I know this probably comes off as me being all over the place... the short block being an issue really screwed things up plan-wise.

Boost-wise, what's the most I should be on the hunt for with 93 and aluminum heads? It will be run on my friend's dyno so we'll be making sure she's tuned properly. Not going to leave anything to chance there.

My old combo which ran GREAT!!!!! For 3 years before I sold it:
Gen. 6 454 .030 trw 2399 Pistons 8.8 compression
Bullet hyd roller .640 lift
Merlin iron heads 120 cc chamber 345 intake runner, 2.30 intake valve
Blower shop 250 No intercooler
Single dominator 1050
Thunder bolt 4 with V6 box
700 hp , 5800 rpm 5 lbs boost

7.5-8 compression with small blower will be a waste of time. Think of what that engine would make for HP if you remove the blower , 400 tops
In theory if you add 14.7 lbs of boost you double the HP, so at 7lbs you add 50% more. That makes the engine 600 HP , now take the parisitic drag of blower and heat caused by spinning that little blower SO fast to try and make 7 lbs. that's another 50-75 HP loss. So you left with 525-550 hp. Besides the HP numbers the engine will not be efficient at all.
The engine your looking for has been built for the last 25 years by every engine builder there is. Learn from other people's mistakes and successes.

If they can just be honed, nothing wrong with that.

The 250 blower I wouldn't take past 6-7psi . I think you'll hit 650-700hp with those RHS heads, right cam, 6-7psi.

As for the 525sc being a turd, or not a turd, I guess that's opinion. But 525hp from a supercharged 454 isn't exactly killing it in the power department. While a very reliable piece , it wasnt a powerhouse by any means. But look at what was there. No compression, mild flat tappet, gm iron heads, tiny blower. Now take that engine, give it some compression, cam, better heads, better blower, and now youre making some horsepower.

:readinghelp:Great thread I'm thinking of doing the same next winter. Keep the advise coming please, especially from the ones that have been there done that.

Very much looking forward to getting this thing built and run on the dyno then finally in the boat enjoying the end product.

I'll say though that I'm probably overthinking a lot of this.

Lots of good points so far , prob should settle on your pistons and rings before you sweat the cylinder finish any more .prob wouldnt wouldnt theorize psi numbers too too much either .
a clean easy 5 psi through a efficient combo is as good as or better than 8 psi through a smog motor with a cam where the 3 psi extra is just bottlenecked boost and extra inlet temps really .
start looking for some extra pulleys now if you have the splined blower snout

As soon a i find a 3.25 pulley mine is going together . With port fuel injection . Have a old 4 hole nos sprayer that i was thinking about fabbing up a alcolol inj sys above the throttle body like we had on a old datsun drag car running 25lbs boost not sure how the rotor lobes would like that though

i just finished a build very similar to what you are doing,it is scheduled for the dyno wednsday.it is 1 of 2 for another oso member.it is standard bore 454,8.5 to 1 compression ratio,afr 305 heads and a bob madera cam.it has wet exhaust so the cam is pretty conservative and it has to run on 89 oct fuel.it has a 177 blower that makes around 4 lbs boost.i am looking for 625 to 650 hp but more important to the owner is reliability.add in,it has scat h beam rods with arp 2000 bolts because they did not cost much more than rebuilding the stock gm rods with new bolts and they are a way better rod.also has morell hyd roller lifters.imo this engine should go 250 to 300 hrs before it needs the isky valve springs replaced and hundreds of hours before needing a refresh.i will let you know how it does on the dyno if you are interested.edit in,im no expert but i did stay at a holiday in express last week.

With the gas prices down so much ill bet everybody now wishes spec for
93 octane . Who knows how long these prices will stay though.is this going to be run on dyno with wet exhaust ?

billy,very well said and imo that was good reliable power.just think what that small engine would have made with the addition of some afr 305s.

no,it will have the dyno headers with egt,s and a/f ratio hookups.the engine is speced for 89 oct because that is all he can get at his marina.

the 525 sc actually had a static ratio of 7.5 to 1.with the junk flat tappet cam and gm iron heads im suprised it made 525 at the flywheel.

Agreed.

I have a couple of pulleys now. I'm picking up additional pulleys as I see them come available.

This sounds like a great combo and similar to what I'm after. Looking forward to seeing the dyno numbers!

tom,the dyno sesion got bumped to today,just got back.it made 690 at 6000 rpm with a safe tune.i was expecting 625 to 650 so i and the owner am pleased with the results.

Just curious what kind of torque did it make?

667FT lbs

Mike,

What did you use for pistons in that 454?

race tek.not off the shelf,they were not cheep but worth every penny imo.

Yep, the owner is very pleased.

Very nice . With good headers looks like your in ilmor v10 and the blue whipple motor territory .should be a runner

Well, everything went to the machine shop today. We're on our way!

Initial thoughts are that 1) the block is in great shape and we're pretty confident that a hone is all that's needed, 2) pistons are good with the exception of the one. The other two can be cleaned up, 3) the condition of the parts overall was very good showing minimal wear, and that this will be considered a refresh vs any real rebuild. All great news!

I should have everything back in a week or so. Then it's off to assembling everything.

The cool thing is that the machinist was commenting on how great all the parts were. He must have said it like 10 times!

tom,what do you have for rods?

FYI,,race tek is the old owner of je piston so he is not new in this game..he had a claus that he could not make pistons when he sold out so now he is back into the game making a better quality piston with out the long wait times...yet! when you have the block honed make sure the machine shop use's deck plates to true up the bores..

not bad rapping j&e but the race tek is a really nice piston they had my custom 1 off pistons to me in 2 weeks.

Factory 454 mag 7/16.