5.0 Questions

1990_LX · Oct 2, 2010

Well I'm pretty much a lurker, I never really post but now I have a reason to. I got a 5.0 out of a Grand Marquise with low oil pressure for free. I'm fairly sure it is out of an 87, but being it is out of a Grand Marquise and not a Mustang it doesn't have forged pistons, does it? I haven't taken it a part too much yet but I have been told that it has cast pistons and they don't have valve reliefs and that would mean the biggest cam I could run is a HO one. I'd like to run a little bigger cam since I'd like to find some GT-40 P heads because I read a write up on them on 5.0 and Super Fords site and they said that the smaller chambers result in higher compression. Are they worth the extra trouble of needing special headers over the non P ones? Based off the hearing I need different pistons I'm not sure what would work for me. The cars going to be N/A and probably nothing more then just some bolt ons but some people still suggested buying forges pistons. I'm trying to stay on a small budget so I was looking at Hypereutectic pistons due to the fact that they are 1/3 the cost of forged. Do you guys think they would work fine? These are the ones I was looking at that Summit sells....

Speed Pro Z8KH273CP40 - Speed-Pro Piston and Ring Kits - Overview - SummitRacing.com

List of questions for those who don't like reading..
1)Would an 87 Grand Marquise have forged pistons or not?
2)GT-40's or GT-40 P's?
3)What would be a good cam with a carbed motor and said heads with maybe a little porting?
4)Are forged pistons worth dropping $500 on or would hypers work fine for me?

1990_LX · Oct 2, 2010

Also, wouldn't a gear drive from a 351 fit a 302?

RatStang · Oct 2, 2010

I won't bother answering the questions posted one by one because it sounds like the motor is in need of a rebuild REGARDLESS.

Since it's a rebuild, you can put whatever pistons you like in there. Pick your compression and cylinder head then go from there. You don't need a gt40p head to raise your compression. If you're going to spend money on heads, get yourself a nice set of aluminum heads then purchase your pistons to get you into the compression ratio you're looking for.

Since you're buying pistons, you can purchase them with whatever valve relife setup you like. Purchase them to be the best match for the valves in whatever head you get.

Your cam choices are then only limited to the combination you put together.

As for your last question... Personally, I don't think that I would buy forged pistons unless I were intending forced induction for nitrous. Hyper pistons are great! They're lighter too. Lighter rotating assembly means faster rev and more power (comparitively everything else being equal). They also have a tendancy to seal better due to having tighter clearances.

1990_LX · Nov 5, 2010

Bumping my old thread here with a couple more questions. I took the 86 motor apart, the crank has some nasty grooves worn in to it. I have a crank in nice shape, but it's out of a 79 302(or it could be an 80 but I think it's a 79 since is weighted differently then the 86). Can I use the 79 crank as long as I run the correct flywheel and harmonic balancer? Also, I'm going to be running a carbed, does anyone know of a good diagram for wiring it up to a 2.3 auto car?

Rick 91GT · Nov 6, 2010

You will need to have the rotating assembly balanced with the different crank and pistons, it is not as easy as swapping balancer and flywheel. The rods,rings, bearings and pistons are all matched to a specfic crank.

The 87 should have forged pistons but for what you are building it really doesnt matter...

cam choice comes down to the exact combo you will run, although I can tell you youll want a nice dual plane intake and a 600-650cfm carb

1990_LX · Nov 6, 2010

I have a Edelbrock Performer 289 intake and a Holley 600cfm 4bbl....would that work out fine, or at least until I could afford to upgrade the carb?

bwguardian · Nov 8, 2010

You are better off with cast pistons for your application.

The GT40p heads do not need the special headers...I use the MAC shorties with 90* spark plug boots on mine in addition to having to ding one or two primaries.

As far as cams...I run the E303 on mine and am happy with it as it is a weekend car.

That 600cfm carb will be all you will need for that engine...I would spend the money and get another intake, like the one from Ford Racing or an Edelbrock Performer RPM.

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