I have a virgin 4-bolt smallblock 400. I have set an appointment with a local machinist to build this motor. Is this block capable of handling 500 natural, 650 hp with nitrous? What should I be asking the machinist. I've asked about sonic testing and he said its a waste of time and money on a 400 block. What about filling? Should I be looking at using another motor instead? I'm gonna spend alot of money on parts and don't want it to be wasted by a block thats gonna blow apart. Give me some advice please. Thanks.

 

Why did he say it was time wasted? the block is the base for any engine, if it fails, it can damage a lot...on a stock engine I would say the same as every other part doesn't cost much but if you're going to put in the parts to get 500hp, then its worth testing. And yes 500hp can be attained with that block.

 

He was talking about something between each bore, webbing or something that makes sonic testing useless on a 400 block. He said this was unique to 400 blocks and that if it was any other block it would be worth it to sonic test. He said once I bring the block in and they start boreing it they would be able to tell if the block was any good. This is a very reputable local machine shop. I couldn't bring it in this month because they are backed up with engines from some offshore boats and some NHRA cars that will be competing at the end of the month.

 

I agree with Lohkay, whu would he say it's a waste of time - especially with an SBC400 block. SBC400 blocks have relatively thin cylinder walls as is, add an overbore and they get even thinned obviously. Most engine builders do not recommedn anything more than a .030" overbore on a production SBC400 block. It is really is a 'virgin' 400, which is very rare these days, not to mention a 4 bolt, it probably won't be a problem. But if it has been overbored, I think sonic checking the thrust sdie of the bores is a good idea. There's no point in spending the money on a block if it's cylinder walls have .090" thick thrust surfaces, which is entirely possible.

I would express those concerns, and see/hear his response. Unfortunately, thanks to the low margin these guys have to work on, thanks to places like Jeg's/Summit, most machinists only make money on machine work. Therefore, their income and profitability depends on volume. Spending time on sonic checking and baselining a block before he even turns on his Sunnen, is probably wasted time/lost money to some machinists.

If you are going to spend alot of money on parts, as you said, you certianly don't want to a block that is thin and and could potentially crack under the loads of NO2. A block is like the foundation of your house - it sucks when they crack.




[Modified by Monty, 2:57 PM 11/8/2001]

 

SBC400 blocks have simaesed bores, meaning the water jackets don't totally encircle the entire cylinder. The area between adjacent cylinders is solid - while this adds strength and rigidity, it creates potential cooling problems, which are easily addressed.

The area of the bore you should be most concerend about is the thrust side of the bores.

I'm sure it's just a matter of miscommunication. But I do have to say that it's a little too late to find out the block is trashed after you've already got it on the boring bar! Imagine the call from the machinist -"Well, your block is trashed, the cylinder walls are too thin. By the way, your bill's $165 for boreing/honing with torque plates."

 

thanks for the replies. I'm gonna call him again and ask more about the sonic testing. I've been plugging stuff into desktop dyno 2000 and I'm thinking I can get 500 natural hp and 700 with a 200 shot of nitrous added on.

 

January 2002 issue of CHP has an article on how to get @520 hp @ 6200 rpm out of a 406. The two things that I would change on their build would be single pattern cam of maybe 244 -246 and raise the compression a full point to 10.8 or 11.2 with thermal coatings. Drop the 825 carb in favor of a 750 speed demon. Maybe go 111 LCA just to be different.

By the way the article used the same heads I have. The only changes i have is the coatings and bigger exhaust valves 1.625 for NO2 use. You can get 2.08/1.625 or 2.10/1.6 to fit in the chamber.

To get 500 or 700 hp you need a good crank. Get a 3.875 for the same price as a 3.750. Only go internal balance and ask about running 350 journal sizes.

 

gkull- what heads do you have? I don't have that issue yet, can't find it on the news stand. I already have brodix track1 heads. Can you post more info on your engine.

 

I also have a 79. I drive it all over so my parameters were: It needs to go 300 or more miles on 25 gallons of 92 without octane booster. I have lots of money in a 700R4 and a 4.11 rearend. So I don't want to be rpm limited. The motor has to handle 7500 rpm any time and last a reasonable amount of time. The bottom end needs to handle 800 hp on NO2 or a Blower.

So to do that you need the lightest internally balanced forged crank and pistons. I decided to try High tech coatings to get the most out of the cubic inches. So I used piston,chambers, and exhaust valves with thermal bariers. Moly skirts. the under side of the pistons and crank were oil repellant coated.

825 cfm demon carb on a Weiand team - G The intake and heads were bolted together for porting. Dart Pro-1 215s with titanium 2.08/1.625 steel exhaust. 1 3/4 hooker S/C heads ported to bigger exhaust ports. Full 3 inch exhaust W/O cats. 10.84 c/r 238/246 .635/.644 with 1.65/1.6 steel RR.
Solid roller with all the goodies. 383 ci.