Hey guys,
my paint and body guy gave me a 402 block in excellent shape, some 396 heads, and the rotating assembly. I want to build this engine to be a monster. I know all about the replacing a small block with a big block woes... I am set on a big block. Whatever I have to do to make it fit - I'm gonna do it.

My question is this - does anyone have experience making power with a 402? My paint and body guy seems to think I'll be able to make 500+hp by boring and stroking it. Is that possible?

-Here are my plans so far:
-Crank - Install Scat 454 crank to make the engine a 427 (is that right?)
-Block - Bore the block .60 over to make a 466 (is that right too?)
-Pistons - Flat top or pop-up. Not sure what I need to use. Any help here would be appreciated!
-Cam - I really like the Thumpr series cams. Can you make power with them?
-Intake - Not sure what to use. I am more interested in stump pulling power, but some top end would be nice. Not worried about fitting under the hood. I have a 3" over stock cowl induction hood in the plans.
-Carb - I don't want to drop a couple G's on fuel injection, so I'll be carbed. What size will feed this engine?

Thanks for any help or advice you guys can give - especially guys that have built one of these. Like I said earlier, I am more interested in light to light stump pulling power, but a little top end to keep up with my buddy's 1999 LS1 370hp WS6 TransAm would be nice.

OK, just found a bore/stroke calculator. Looks like a 454 crank in the 402 block will make it a 427c.i.. Then boring it .060 over will make it a 440c.i.

 

With a 454 crank and standard bore your CI is 428. With a .030 overbore you are at 434. The 402 is a .030 overbore 396 block. Don't know if you can or would want to go .060 over. I think the 396 (402) block is a little different design and might not take a .090 overbore. Be nice to have the casting numbers on the heads. You need all specs ( bore, stroke, deck height, gasket bore, gasket thickness, head chamber displacement, piston dome CC) to determine actual compression. Also need Rear end ratio, trans type and gearing and your driving style and goals (highway cruiser, 1/4 mile, mixed highway and city with occasional trip to the track) along with actual compession to determine cam choice and type. First thing you need to nail down is a budget. Pistons choices and manufacturers will be limited with the bore and stroke you are using. There are a lot better options than the thumper series for producing power. They are really designed as a cheap option for a close to stock build and compression to make it sound like a race engine. Fools the guys when you pull into the car show not a real good choice for a true performance build.

 

I doubt that you'll find off the shelf pistons for this combination, and custom pistons are going to cost more than a used 454 block.

 

Keith Black makes off the shelf pistons for that combo. KB361
The only drawback is that they are hypereutectic, not forged.

 

Yes, here is a budget kit. Don't know who makes the components though. Forged crank upgrade available.
http://www.speedomotive.com/ps-75-7-...roker-kit.aspx
Here is another one. Not too confident in the KB hyper pistons.
http://cgi.ebay.com/ebaymotors/BUDGE...Q5fAccessories

 

My budget can be spread over the course of the next year, so a real number is not that easy to nail down. I can say I don't want to spend more than $3000, but in reality... I will spend what i need to within reason. I'm not good with setting a number and staying under it. I would pay for porting and polishing, block machining, etc. I do not want to pay for stuff like balancing and blueprinting. So, a basic garage build on a big block with good parts.

My goals for driving are as follows - I live 60 miles from work, and will most likely be driving my Vette every day during the summer. Gas mileage is not a consideration. I drive through Colorado Springs on my way to work, so light to light performance would be nice. I will most likely never take this car to the track. I don't really care about time slips - I want to feel and hear the power.

The reason for saying I want a Thumpr cam was because of the sound. I LOVE that lopy idle. I know that you can't get that unless you pretty much have a full on race engine, and that does not fit within my driving requirements. I want something that is goign to start every time for me and take some abuse without breaking every time I put the hammer down. If there is another style of cam that will provide that 'nasty' sound without sacrificing driveability, then I am open to it.

I was doing some research after I posted this - You're right about the 402 block - it's a .030 overbore of a 396. I guess I would only be able to bore it another .030. So, actual bore will be 4.155, stroke will be 4.00. Don't know deck height. I know I will probably use dead soft copper head gaskets unless there's a reason not to - not sure what thickness they come in. Heads are 97cc chambers. Gasket thickness and piston dome displacement were some of the suggestions I was looking for. Rear end ratio is 3.08. Tranny is a TH400 with a Transpack installed. I will probably be putting a 700r4 in at some point, but the TH400 will suffice for the next year or so.

 

63 mako is kind of on the right track. IMO it is not worth the time and effort. I've given away 396 H-P short blocks.

396 4.094 3.760 B&S
402 4.125 3.760

The longest stroker crank that you can put in the block is kind of limited to 4 inch and with an over bore to 4.155 you can get a 434 ci.

454's a plentiful and so a re 4.25 stroker cranks to make nearly 500 ci BBC

 

Yah, but this block and heads were free... I'm not talking about dumping serious money into it. I guess you could call this a budget build with no ceiling.

Here in the Springs, I have been looking for a 454 block. The only one I have seen in the last few months went for $750 with rotating assembly and heads and needed a rebuild and boring.

You guys are saying it's not worth putting any money into a 402?

 

It's like building a 305 instead of a 350 or 383. It won't cost that much more to go with a 454, and you'll be much happier in the end.

 

How much is a used 454 block going to cost? If the non-standard purchased parts for the 402 block cost more than that amount from the standard parts you have to buy for a 454 block, getting the 454 is a much better deal. You are still getting an extra 50 cu. in. for nothing! Since you don't know anything about the 402 block [or the used 454], you will have to have the block magged and measured to determine what machining must be done to it, in either case. And, if you are going to build a high-revving engine, it will need to be balanced; not doing so would be foolish. Find a good 454 block that is not cracked/damaged and not previously bored, have it machined the way you want it...then have fun building it!

 

I've heard that KB pistons are not good. They expand at a different rate than the cylinder walls, right? And they're brittle...? Do they work fine as long as they're not in a high stress environment? I seriously doubt my motor will ever see over 5k rpm.

 

OK, so lets go a different route here. Lets not bore and stroke it. If I use the 396 heads (97cc chamber), and stock 402 rotating assembly, is it possible with a cam and head work to make over 400hp? The block is not bored, and the pistons are cast. Will they hold up to 400hp?

 

If you are dead set on building this the only pistons available put your compression over 10.5 to 1 with the iron heads you have. You also have a 3.08 gear. This and wanting a rough idle makes cam selection difficult. You need enough duration to run pump fuel with iron heads and also be in the operating range that works with your gearing and automatic trans. This cam has the right operating range for your rear end gearing, will get you pump gas compatable and still have a lope due to the overlap with the slow factory style ramp rate. It is a solid flat tappet and will need periodic adjustments. The slow ramp will cost you HP compared to a modern ramp rate cam but also be more durable. If you use this spring for the EDM lifters and use the high zink oil.
http://www.compcams.com/Cam_Specs/Ca...px?csid=4&sb=2
I would also recommend as others have that you look aroung some more for a 454 block. You will spend the same money on machining, same on rotating assembly, same on valve job and parts and can go with less compression to better match your gearing. More CI also will give you better torque at the bottom end to help pull that 3.08 gear and you can get more HP for less $ and still use your factory rear end. Doubt you can build the 402 matching the parameters you have strong enough to run with your buddy with the LS1 without different heads and/ or a roller setup.

 

Your at mile high elevation better start thinking on how to get more thin air supply into the engine.

Instead of more money spent for another engine, porting heads,
expensive cam setups.

Do a regular rebuild spend the money on some form of forced air
pressure. Everything in a big block is much stronger then a small block even the oval port heads flow decent air in compairison to what came on SBs.

Lets say at my elavation 500 FT, I spent $800 to $1000 for a cam makes another 40 hp at your elavation that same money outlay might get you 25 hp, your a good candidate for forced pressure.

 

You're going to build an engine from a used 402 block...without checking it for cracks and having it measured for cylindricity, taper, out-of-round, size...then you'll put iron 396 heads on it, stick it together with a 3:08 rear end and go racin'!! Well, good luck. I don't think we can argue with a plan like that!

 

My only comment is that I had a 402 in 1980 that screamed and smoked every 428SCJ and Mopar that came near it. And that was stock bore and stroke. It can be made to run! The 1970 402-375 was underrated and actually pushed over 400hp. Find an old chevy engine guru and let him tweak it up if that's what you want.

 

Psssst.... {the engine type/size is not the problem...}

 

Hey man... who said anything about not getting the block checked? I said I didn't want to pay to have it balanced and blueprinted. I'm not a moron... of course I'm going to have it checked out.

I also said nothing about racing. I think I actually said I didn't plan on ever going to the track. Please don't make uninformed assumptions about me or my stuff.

 

True... I'm a dealer for ProCharger bike superchargers. Maybe I'll see if they'll work me a deal on a generic BBC setup... that would be fun!

 

If you buy the stroker kit I listed above and use this cam with new retainers, springs, EDM solid lifters, pushrods, timing chain and gears, head bolts Main bolts, complete gasket set you should be fine rebuilding the rest of the stuff you have. You will end up with a 400 to 450 HP 434 CI big block that will run on pump fuel and have the proper operating range for your rear gears and vehicle weight. A new 2400 RPM stall convertor would be a good move also. You can not take shortcuts. All measurements must be taken, all machining needed must be done. Everything needs to be checked and double checked. All torque readings on bolts must be correct. Heads must be rebuilt. The KB piston rings will have to be installed exactly according to their instructions. You will need a new carb. A 750 would be fine if you are not pulling over 6000 RPM. You will need headers and a decent exhaust. If you try to use the old pistons and rotating assembly and just throw bearings and rings in it good luck with that. If you do the above I think you can do the motor in your budget. It won't be a full race build but you can't run a full race build given your parameters. It will be a fun big block with decent streetability and good durability in your budget.