How to tell a Chevy 400 from a poncho?
 

Well, I may have a good deal on a 400 engine, from a -76 Pontiac Bonneville brougham. As far as I know, this car should have a Poncho engine, but the seller claims it's a chevy.

Now, he lives quite far from me, so I haven't seen this engine in person, but I told him I could probably find out how to conclusivly state if it's a chevy or not, with the help from you guys from thirdgen.org.

So, how do one tell these engines apart?

www.mortec.com

check the serial number..

It's EXTRMEMLY unlikely that it's a Chevy.

A Pontiac motor will have the battery & starter on the left, a Chevy on the right. A Pontiac motor has an intake that sits up above the block, with a sheet metal cover over the top of the block, and a space between them; a Chevy motor has an intake that meets the block. A Pontiac timing cover is cast aluminum and the water pump is a little flat thing that covers over part of the front of it; a Chevy water pump looks like it stands up on 2 legs away from the block, in front of a sheet metal timing cover.

That should be enough to where you can tell them apart from a couple of hundred yards away.

*shrug*

they, uhhh... look totally diffrent.......

that would be my first clue... :D

It'll take day's to read through all that info on that site, and I probably won't get this guy to crawl to the back of his engine block to look for numbers hidden by grease and dirt.. this is a car that's sitting outside, and it's 15 below zero with lots of snow here..lol

I was hoping for something a bit faster.. like the dipstick location, or perhaps the number of bolts on the valvecover, or maybe the size and shape of the valvecovers... Perhaps something with bolt location to the exhaust manifolds..

Granted, this info has to come from someone knowing a poncho engine, but there ought to be several of those here on thirdgen.org, shouldn't it?

Well, Me myself would probably be able to see right away that it isn't a chevy, if it's not. But I havent seen the car, I need to tell him, by a cellular message, what to look for.

I think I will go for the starter thing.. you say that a chevy 400 have the starter on the passenger side like a 350 or 305? If so, and the Poncho has it's starter on the driver's side, I will tell him to look for this then..

the easiest physical way to tell if it's a pontiac or a chevy, is by the timing cover/ waterpump. if it has a bolt going from the waterpump to the intake.. it's a poncho.

if it has an aluminum timing cover, and the waterpump mounted high.. looks similar to a ford cover... it's a poncho. more than 4 botls in the waterpump.. a poncho.

fuel pump on the driver's side.. poncho. all the spark plugs pointing "ford style" out of the heads.. poncho.. passenger side oil filter... poncho.


any of those questions would be good.. the easiest one would be the oil filter i guess..

not to hijack the thread.. but performance wise..
IS there a diffrence between poncho/chevy 400's ?

Is the bore/stroke diffrent?

Pontiac 400 is (bore/stroke) 4.121 x 3.75, Chevy is 4.125 x 3.75. As for the performance you can build a pretty mean pontiac 400 but dollar-to-HP you'd be A LOT better off with a chevy ...SBC parts are a dime a dozen.

An even easier way, is simply by looking over at the distributor. Chevy distributor's go 'through' the intake manifold, whereas Pontiac distributor's don't.

That's what's great about Poncho's, you never have to remove the distributor (and deal with re-timing the engine) whenever you want to change intakes..... :D

The quickest way to tell is to look at the heads. More specifically, the exhaust ports. Pontiac exhaust ports angle downward. Chevy exhaust ports come straight out the side. Also, Ponchos have a head bolt going right between the two middle exhaust ports. If you need a visual, go and do a search on ebay. There's always pictures of both Pontiac and Chevy heads.

I have a Poncho "big block" in my 68 Firebird. All of the above are correct. Mine's actually a 455, but visually, they look the same.

Anyway, I'd say the easiest quick identification is the distributor location. Like the guy above said, the Poncho distributor does not go through the intake like the Chevy.
But at first glance, you'll see many differences. The heads look completely different, although the valve covers look just like a small block Chevy's. The Poncho heads are larger. The exhaust ports are much lower, BELOW the spark plugs. So the exhaust is not competing for space with the spark plug wires like in a Chevy.
Another way is to look at the intake, which is spaced above the block. It looks kind of like an air gap manifold.
The entire front of the engine looks completely different. You'll notice that too. It will look "non-Chevy".
Pontiac motors tell their displacement right on the sides of the block below the exhaust manifold right in the center. It should say "400" if it's a 400.

Performance can be excellent with a Pontiac motor. But there are a few points to address when rebuilding one.
1. Raise the compression. Mid-70's Ponchos had horrible compression ratios. Edelbrock makes a good Poncho head with 87 cc chambers. Or you could take a 6X and shave it down to 89 cc's. Those flow better than the ram air heads.
2. Replace the rope seal. They always leak, no matter how good you prep them. Just get a modern rubber seal for it instead.
3. BUY AFTERMARKET FORGED RODS. USE ARP FASTENNERS. Ponchos had weak rods, but stock rods WILL live reasonably well with ARP fastenners if you're on a budget.
4. Consider stroking the 400 to a 428 or a 455. 455's are real torque monsters with a decent compression ratio.

The Pontiac 400 has a superior rod/stroke ratio to a Chevy 400 due to nice long rods. You can improve a Chevy with longer rods, however.

There is a company that makes conversion kits to allow a traditional Pontiac engine to fit a third gen F-body. But you WILL blow up your stock rear end. These motors are real thumpers. I'm also not sure how well it'll pass emissions. But they are dimensionally smaller than BBC's, so they should fit pretty well.

Turned out to be a poncho.. it had the cast aluminum timing cover... Well, i need to look a bit more for a 400 engine I guess...

I'm hoping to getting a chevy 400 engine, and not try a engine family swap, cause thats really over my head.

Had a bad experience with a Harley scratch built bike, who took almost 8 years to complete, because of my lack of fabrication skills, and general lack of funds to pay to get those hard things done.

So I'm thinking staying smallblock chevy this time, not complicate things too much unneccisarily.

What car do you want to put a Chevy 400 in?

My -87 Formula :-)

This one:

The best way to tell a chevy 400 is to check the left and right side of the motor and see if the side round outward. On any other small block chevy the block will be flat from the back to the front. but the sbc 400 have two round places that stick out because the cylinders are bigger than the block. But dont be quick to think it's not because many people bondo the sides b/c of race restrictions. I just planted a .060 400 in my iroc, they are great motors. Hope it helps man.

Nice lookin' ride. Are those rims 'shopped?

Yep, they're photoshopped onto the car with a little lowering at the same time. I just thought it looked kinda good, so I have been keeping using that one. Nice kit you have... :-)

Should'nt you also have a NOS kit wired to that "Turbo boost" button? ;-)

I'll attach 3 pics of a poncho 400 so you can see what they look like compared to the typical sbc. I will say pontiac had their act together and built these like a brick chit house, tons of factory goodies!!

notice oil filter location and how the exhaust ports on the heads point down in the above pic.

this is one we threw together for my buddies 66 goat. First and hopefully last yak motor we'll ever work on!!

mb