350 buildup Q's
 

When I bought the Nova it had an unknown '74 350. Didn't smoke and ran OK, but I knew it was a low compression smogger motor with 882 heads. I bought a set of 062 Vortecs (already modified for higher lift) with the intention of putting them on with a moderately sized cam (XE274) and RPM intake for a decent street motor with a little power. Going from 76cc to 64cc seemed like it would add almost a full point of compression. This past weekend I did a leakdown test on the motor to check the rings and got around 10% leakdown on the cold engine. Seems pretty solid. But here's where things get interesting. The motor looked bone stock, right down to the paper gaskets and cast iron intake. After the leakdown test I cracked it open and found out that the piston's aren't the stock ones for the block- they are GM 6271097 4 valve relief pistons with a 13cc dish- the ones at the bottom of this page:

http://webpages.charter.net/beckracing/slvpg55.htm

So the last guy replaced the crappy stock pistons with ones that are even worse. Numbers are still on the block so it hasn't been zero decked. Son of a bitch- looks like instead of a 8.5:1 motor it's a 7.9:1. So I'm trying to weigh my options.

Here's what I came up with:

1.) Continue as I was and gamble on a thinner head gasket (.015) and end up at around 9.5:1

2.) Same as above but back down on the cam size to something smaller due to the lower compression

3.) Stop dicking around and get the bottom end rebuilt with flat top pistons (this will waste what seems like a bottom end that's in good shape).


What would you do? Keep in mind that I'm on a tight budget and time to work on this thing is at a premium.

Stock bore? With a stock bore and an .029 head gasket with the vortecs I get ~9.3 to 1. With the .015 I get ~9.6 to 1. Run it Bill. It'll be a good running small block IMO. :wink:
Edit: I see that the bore is .020 over. Makes it only slightly higher but still in the 9.3 and 9.6 range.

So then what is a BIG cam, and allot of power?

Looks like that cam in a smallish ( under 383 CI) displacement is going to need some pretty high gears ( thinking 3:55s ) and allot of head flow to get it up into the RPMs Is that your plan? If not, you might want to tighten up the duration a bit and maybe even a little bit more LSA. The specs I found on the XE274 have it with 230+ duration on a 112 LSA. That combined with static RC below 10:1 isn't going to have much power down low. That cam probably isn't going to go into any kind of power until your well into the 3,000RPM range.

If this car is going to see more cruising then racing, you might want to rethink that cam before you even start on your CR decision.

How tight is your budget?

http://www.jegs.com/p/Keith-Black/Cl...48677/10002/-1

If I did the math right, with a 62cc head and stock thickness head gasket would put you around 9.7 CR. put that with a cam with 224-228 duration 560-570 lift and around 113 LSA would make power around 2500RPMs and would match up nice with your trans and gears.

Another option ( my favorite ), leave it at 7.9 with the 274 cam, and drop a nice 671 blower on top of it. See, all your problems fixed!

Thanks for your input, guys.

Here's the cam card:

http://www.compcams.com/Cam_Specs/Ca...x?csid=87&sb=1

Pamp,

The rear is a 4.11, with a 2.52 first gear. I know that "big" and "little" are subjective terms when talking cams, I meant "little" in that it was below .500 lift and is in the 280s avd. duration. My budget is pretty small, probably $1000 when all is said and done. Time is the bitch though. I've been strapped for days to work on it and dealing with a bottom end rebuild would suck up the little time I've got. That's not to say that I'm not considering changing pistons and the like, just that I'm trying to stay away from that route if I can.


And as for the blower, that's the first thing I thought of (joking of course). Great compression for that type of thing but too bad they are cast pistons, on a stock bottom end!

id go a step or 2 lower in cam if it were me

my first 350 had a 216/228 cam 454/480 lift and it was a great cruiser got great mileage and reacted nicely to a 150 shot of nitrous. i got that combo into the 11's with a loose convertor and 373's. i had world prod heads and 10:1 at the time. if you HAVE to go something bigger go like a 228/236 split duration.

That's about where I was thinking, Won't bleed off CR, make power/torque around 2,200-2,500 and won't have cam surge issues while cruising.

Ok, so a roots blower is too much. How about this then?

http://www.jegs.com/webapp/wcs/store...-1&showValue=1

Guys, thanks again for your help. I appreciate it.

But the more I think about it, the more I think I'll bite the bullet and change out the pistons. It seems like I'm just band-aiding my way around the obvious.

Looking at something like this:

http://www.summitracing.com/parts/FEM-MHP125-311/

Has anybody heard anything good/bad about these kits?

i had one of their hyper kits with the motor i described above. only thing i DIDNT like in the kit was the cheap head gaskets they give you. other then that it was a great complete kit. hit me up on AOL IM if you wanna chat more

Yeah, I'm not going to be using the oil pump, intake gaskets, or head gaskets. With a thinner HG than the kit it looks like I can get 10:1 or so which is right where I want to be.

Thanks for the AOL invite, I may hit you up on that when I'm not on my work laptop :D

Just to play Devil's advocate. Price out the machine work you'll need, block, rods resized, crank turned ect, and the price of the rebuild kit. How far off is buying something like this?

http://www.jegs.com/p/Blueprint-Engi...55988/10002/-1

Way ahead of you. :mrgreen:

I'm contacting some machine shops today to see what they will charge. If it's more than the price of a short block exchange (either via Summit/Jegs/Pace) then that may be the way I go.

Here's what I found last night:

http://www.summitracing.com/parts/MLL-BP3552/

I'm guessing it may be tough to beat $1500, especially if I factor in the time involved.

Geez, you are like Phil. You instinctively take it apart when things are going good....

The shortblock would save you a lot of time but it is a lot more money. BTK and I just did heads and cam on Joes car, that part doenst take too much time and I cant imagine swapping pistons to be all that much more work. I wouldnt even go with that piston kit since you are considering using what you have now. You dont want the head gaskets, they are probably the second most expensive part in that kit. Get all the gaskets seperately and save a few bucks. Why cant you just put in new pistons and rings and leave the rest of the bottom end like it is? Do you want/need to get 100,000 miles out of it or are you looking to get it done and drive it for a while?
An engine swap in that car really is an afternoon affair if you have a couple of people in that car.

Well, I had planned on doing a heads/cam/intake swap and an oil pan re-gasket since it was leaking and full of sludge. And it was a 165 horse points ignition motor. When I bought the car I knew the engine was an unknown and would need a little work. Looked fine after the leakdown test so I pressed on. I assumed (incorrectly) that it had at least the stock 8.5:1 pistons in it. That's the bitch. Shot my whole plan, and I keep yo-yoing back and forth about what to do next. This is a tide-me-over engine as well. Not the final one for the car.

If it is a tide-me-over I would just change the pistons and re-use the damn bearings just reinstalling them as they came out and put it all back together.

But Scott made a good point, you should have left it together and driven it for the season, :rofl: