Interpreting a Sonic check - help!
 

I have loaded a Sonic Check sheet from a shop in Albuquerque on my .030 over, 390 FE block, into my gallery. I want to find out if the block could be bored to 4.13" so that I could use a 428 1UB crank I bought to make it a 428.

I need some help in determining if this is practical or not.

My choices, in order of preference, are:

1) Bore the block to 4.13 and use my refurb'd stock rods, forged pistons, and the 428 crank to build a 428. Plan to use a Hyd. roller cam (KC or Crane) and lifters with E'brock heads and HS roller rockers.

2) If the block won't go to 4.13 safely, bore it .040 over, buy a Scat 4.125 stroker crank, rods, forged pistons, and the same Hyd. roller cam, lifters, etc. to build a 430 cu in engine.

3) Bore it .040 over 390 bore (would be 4.090") and build it as is with 390 crank (refreshed), new forged pistons, E'brock heads, Hyd. roller cam, lifters, etc.

Questions I have are..... Will the block safely go to 4.13? Usage will be strictly spirited street driving with rev limited to 5,800. If not, what would recommendations be for the choices above (or ????? )?

The car weighs 2,700# with a 3.00, 9" Ford rear end and a Richmond 4+1 race course tranny (1:1 5th). Goal is about 450 - 480hp with comparable torque. I will not be racing this car and overheating at my location wouldn't be good (7,000ft, temps to 100F in the summer).

I would appreciate feedback and suggestions from the experts on this forum.

Thanks.

Paul

It looks like your thinnest cylinder after an 0.080" bore (4.13") would still be a little over 0.11x". A lot a people say to look for 0.100" minimum thickness. I like to see a little more (0.125"). Some of your thinner measurements are on the thrust side of the piston, not a good thing. I know that there's something mystical about the "428", for bragging rights. I'f it were me I'd go for a 0.40" overbore, stroke the snot out of it (4.25") and go fry some hides! ....and best of all, feel good about the nice thick cylinders that's maintaining proper piston geometry and an engine that's not boiling over at every red light..

Posted test sheet so others with more knowledge than me can look at it here in the thread.

http://www.clubcobra.com/photopost/d...onic_Sheet.jpg

Ron :)

Thanks Ron..............n/m
 

n/m............

Actually.......
 

Undy,

Since the 390 is .030 over now (4.080) and .050 over more would make it 4.13, the thinest wall would be .125 (1/2 of .050). The shop that did the sonic is a reputable race motor builder (albeit small blocks) and he recommended to not go below .100 wall thickness and, since mine wouldn't, to go for it.

I'm concerned about overheating too. I live in a small town with a stop light at every corner so getting from one side of town to the other is an exercise in potential overheating. I seem to have solved that with my current set-up but this would take me backwards.

Stroking the .040 over engine with a 4.125 Scat cast crank and associated rotating gear is the most costly solution but certainly has the best chance for HP and TQ as well as cooling. You're probably right.

Thanks.

An 0.050" overbore to 4.130" is going to remove 0.025" from the cyl wall, so subtract 0.025" from any of those dimensions on the chart to give you the wall thickness remaining at those points. eg 0.150" - 0.025" = 0.125" thickness. Then comes the 'fudge' factor, how much corrosion in the water jackets, were there any thinner spots than those points checked etc etc. I would play it safe myself & settle for less cubes, just BS everyone that its a 428.

Jac Mac

my bad, didn't read about the existing 0.030" over-bore..:o

Looking at the readings you probably could do the 0.050" bore and have enough wall thickness. The readings reflect a reasonably consistant thickness throughout, not enough to cause worry about thin spots. Casting porosity would be the main thing that I would worry about. If I really wanted a "428" so bad I could taste it then I'd probably go for it. The more "rational" (Who's rational?? That's why we choose the cars we do) approach would be the minimum bore required to clean everything up and get a "main-stream" size/mfr piston at what ever stroke you decide to go with.

The issue of a thin wall isnt really overheating by the gauge. When they are thin they can overheat, but generally its just localized to one area and doesnt do much on the gauge

What it can do is split or erode the cylinder where that water is superheated

More likely than that, on a thin cyl, is that the bore that doesnt keep shape as it gets thinner. An unstable bore isnt good for making power.

With that being said, I think .125 should be fine, it is my minimum, but I always go for the minimum overbore on a street motor for long term ring wear and as strong of a bore as I can. SO I try not to approach it if there is a way out

BTW if you go Diamond pistons you could go with any size you want, including .035, .037, .039 etc. Doug Garifo from POP can easily get those and they arent really that much more money than the common sizes. I ended up going .047 on my center oiler for just that reason.

I am with Undy, minimum bore change is best, and if you want more cubes go with the stroker, the rod/stroke ratio is almost identical with the 4.125 arm, so you will get the benefit of more cubes without the side loading (you can even go 4.25 arm it reduces the rod ratio a little, but it also gives a few more cubes for no added cost) and you can stay with a good solid bore.

Again I am not afraid of .125, but boring it less than that also leaves one more rebuild if things get ugly ;)

Diamond only charges an extra $45 for the odd bore sizes. The only trick there is that Scat won't run the odd stuff through their system for drop ship orders - - so on the stroker combo you end up paying for shipping both ways. Not a big deal if you're local to your vendor - but more coin if you're not...

Not sure I follow, are you buying Diamond pistons and the crank/rods through SCAT as a package?

I believe that if I want the odd piston size, dealing with Diamond is the way to get them. I don't necessarily have to buy the pistons that are in a "kit" if they won't fit my bore size. Whoever I buy the stroker kit from can get the pistons from whoever will supply what I want, within reason. Diamond is much better to deal with when it comes to odd sizes and configurations. They don't call things "special order" if they can modify the slugs they have. I called them today and they are very accommodating. Because of this, their prices are better too. Barry can correct this if I've missed it.

FWIW..... I'm not local to anyone. I live in small town, high budget Santa Fe, NM. All the benefits of a small town with the costs of a big city like LA. Hmmm.

Paul

Paul thats exactly how I have done it. I also like that they have some flexibility on dish size etc. Pretty flexible company and easy to deal with.