Just bought a 400 small block ( 1975, 2 bolt mains, 817 casting), this thing looks to be in immacculate condition-just stripped it down and the cylinder walls, and main bearings all look good. My plans for it so far include boring .030 over, complete Brodix top end with 67cc heads, dynamic compression ratio of about 10.2:1, and a rotating assembly with a 6" rod. Looking for any suggestions. This will be a full roller setup, looking at retro-fit. I'm basically looking for help calculating the deck height, gasket thickness, quench, ect..., as I have little experience with those values. I will be installing forged internals, anyone have expereince with scat or eagle cranks?

 

Way, way, way, too much compression, unless it is to be a dedicated race engine, never to be run on anything other than race gas. You don't mean a 10.2:1 static compression ratio by any chance, do you?

RACE ON!!!

 

Really, thats too much compression? I was under the asumption that with the aluminum heads I could kick it up a little without detonation. I was planning on running 93 octane or slightly higher.

 

It may seem strange....but with 400's getting pretty hard to find.....you might look into a .020 over bore if it will take it and use some of the good lightweight forged pistons like from Wiseco, Probe etc instead of taking it all the way to a 406. There just isn't much room left to clean it up later if something happens.

I'm guessing you mean 10.2 static compression..NOT dynamic...there's a big difference. 10.2 static will be fine.

If your 400 crank is OK, I wouldn't be too scared of it. I've seen those OEM cast suckers take a lot of RPM and nitrous and still live fine. Past that, the door is wide open on cranks. SCAT seems to come in very close on measurements on cranks....both Eagle and Scat do well on rods. Whatever you do stay away from CAT brand....generally junk. You might also look at Callies and Lunati for good stuff.

If you go aftermarket, try to get an assy that will internal balance..just makes it easier.


JIM

 

Yeh I was definately going to get an internally balanced setup, what range of dynamic compression ratios should I be looking for?

 

Probably not much over 8.0:1.

RACE ON!!!

 

My experience with 400 blocks is that they're hard to keep cool. Make sure you have enough radiator.

 

What kind of Brodix? What's your application? Street or race?

When I first did my 400, I tried using Brodix -10's, kept the runners kinda small and used a more conservative roller cam. The result was a motor that was too torquey... it was to hard to hook up when coming off the corner.

What I ended up doing was to increase the duration about 10 degrees more than what I thought I needed. It was much easier to drive after this.

There's alot of stress on the rods in a 400... the longer stroke enables a lot more piston speed than the 350. I've used the Lunati pro-mod rods with good result... they're realitivly in-expensive and able to handle a moderate horsepower build with reliability. The choice of crank (and main caps) really depends more upon your intended hp and rpm range. More than 6.5k? More than 7k?

I'd second the vot on the .020 overbore... save a little meat for the next rebuild.

Be careful that you work over the oil drains in the Brodix castings... my first set had drainback issues that contributed to oil starvation in long corners.

As far as the compression (static vs dynamic)... what he's saying is that you can run more static compresion if you use a larger duration camshaft vs. using a small duration cam... with the larger duration cam, much of the compression is defeated by the large overlap period.

What is your expected RPM range?

As for the machine work... take it to a shop that builds performance motors and they'll answer all your q's. Most folks cut the deck to 9.00 inches. If low rpm running and idling is expected, then it's be worthwhile to drill the block/heads for steam holes.

 

The overlap period has nothing to do with the difference in static vs dynamic compression ratios.

RACE ON!!!

 

CFI-EFI...


I think sometimes you and I are the only ones that keep telling folks that. But it doesn't help when the latest Kevin McCleland article in Hot Rod tells folks it does!!



JIM

 

Thanks for the posts, the intended use for the car is purely street performance, It wont ever see any heavy track usage. As far as RPM, redline would be set at 6500, and I am looking at the brodix Track 1 package. They will have the steam holes drilled, as this car will see plenty of cruising. I realize that the machine shop can tell me all, I'm just trying to get a handle as I hope to something. I know that most poeple get the deck clearanced 9.00, but how do I figure out the deck clearance-for example .020? Before assembly of the short block. Thanks again for all the help.

 

You don't. That is why a good engine build requires multiple "trial assemblies". It's easy to add up the compression distance of the piston, the rod length, and the stroke, to determine the center of main to top of the deck height, of the block, but in the end, you are crazy if you don't check it first, yourself.

RACE ON!!!

 

For an explaination of how the cam effects cranking compression, dynamic compression ratio, and why overlap isn't a factor, go HERE.

RACE ON!!!

 

Oh yeah, I plan to check everything upon assembly-several times. I just figured out that using a 3.750 stroke, 6.000 connecting rod, and a piston compression height of 1.125-it would take a deck height of 9.00 to have a clearance of 0.000,-I would much rather have a clearance of .020-which would work better with the rest of my application. Is it possible to have a deck clearanced to 9.020-I know it depends on condition of the block-but what is the stock deck height.

 

What you said here-makes perfect sense and that is what I have always been taught, I completely agree.

 

Then you understand why a "dynamic compression ratio of about 10.2:1", would require a static compression ratio of 12:1 - 15:1, depending on the cam shaft used. And why I said, "Way, way, way, too much compression, unless it is to be a dedicated race engine, never to be run on anything other than race gas. You don't mean a 10.2:1 static compression ratio by any chance, do you?".


The blueprint deck height of a SBC, block, is 9.025". Few production engines are that short.

RACE ON!!!

 

At our shop we figure the compression height of the piston and the rod lenth AND ADD HALF THE STROKE not he full stroke as posted.

Guys that deck there block last and the cylinders were bored first they were bored of an unsquared deck which is not the way to do performance machine work, We machine alot of blocks and ship all over the country and the world and no problems so far and we have not had to trial fit any of them so far. And if we had to trial fit every rotator in every block we would have to shut the doors as we would never get anything done in the shop. All our work is done on a HAAS 4-axis CNC machining center.

If you have the proper measuring equipment and the proper machines to do the job right this should not be a big issue.

I have seen the local jobber shops have fit every thing up to deck the block which is very time consuming and most of them have no fixtures to do the job correctly and base there 45's of the original decks which we find are not very close sometimes on the factory blocks.

 

Of course it is half the stroke. I was just giving a quick example of how the deck height could be ball-parked. It wasn't a tutorial on exactly on how it is done.



Most of us don't have production equipment in our home garages. It is difficult to measure a crank throw, connecting rod, center to center, or the compression distance of a piston at home. I for one have the block squared, then bored, and then I start with a trial assembly. I don't have these machine tools at home, so I have to rely on a machine shop. Maybe for your commercial enterprise, you can't afford to trial assemble your engines. Foe my hobby, I can.



I'll run right out and pick these up, on your recommendation.



What is THAT supposed to mean???

RACE ON!!!

 

Alright guys, I've got a handle on this issue for most part now. Next step is to talk to my machine shop, and order some parts. I have just two questions left, how accurate are some of the engine measurement calculators that are available on-line; such as the ones on the Keith Black website and, what basic tools should I have to assemble this motor (I realize that wrenches and sockets are needed-but i'm wondering about things like a piston ring compressor or micrometer; those things that are needed for an engine assembly). Thanks again for all your help.

Andy

 

Quote:
Originally Posted by BLOCKMAN
At our shop we figure the compression height of the piston and the rod lenth AND ADD HALF THE STROKE not he full stroke as posted.

Of course it is half the stroke. I was just giving a quick example of how the deck height could be ball-parked. It wasn't a tutorial on exactly on how it is done.




Quote:
Originally Posted by BLOCKMAN
Guys that deck there block last and the cylinders were bored first they were bored of an unsquared deck which is not the way to do performance machine work, We machine alot of blocks and ship all over the country and the world and no problems so far and we have not had to trial fit any of them so far. And if we had to trial fit every rotator in every block we would have to shut the doors as we would never get anything done in the shop. All our work is done on a HAAS 4-axis CNC machining center.

Most of us don't have production equipment in our home garages. It is difficult to measure a crank throw, connecting rod, center to center, or the compression distance of a piston at home. I for one have the block squared, then bored, and then I start with a trial assembly. I don't have these machine tools at home, so I have to rely on a machine shop. Maybe for your commercial enterprise, you can't afford to trial assemble your engines. Foe my hobby, I can.




Quote:
Originally Posted by BLOCKMAN
If you have the proper measuring equipment and the proper machines to do the job right this should not be a big issue.

I'll run right out and pick these up, on your recommendation.




Quote:
Originally Posted by BLOCKMAN
I have seen the local jobber shops have fit every thing up to deck the block which is very time consuming and most of them have no fixtures to do the job correctly and base there 45's of the original decks which we find are not very close sometimes on the factory blocks.

What is THAT supposed to mean???

RACE ON!!!

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If your going to performance work it might as well be done right the first time as we get blocks in the shop that have been machined by a local shops that do not do performance and you can tell the decks are not square as the go of the origanal decks instead of doing it right then they bore of the unsquared decks which does not make for a good running engine in the end as compared to one that has been prepared correctly. As we charge thar same to deck a block as the local shops but its done to blue print instead of guessing and its much faster as well.

And if you need part numbers for any of the equipment we have let me know so you can go out and pick these up LOL.

And that was a bad example of how to calculate a deck heght as I already got an email from some one here thanking me as he was coming up with some big numbers for his combo.

At our shop we don't have to trial fit any rotators as we know what we need for a deck height with out fitting everything up and blocls that we machine for other shops and engine builders they tell us what they need and and so far we have no problems with anything that has gone out the door.

MACHINE ON