Guys, I'm looking for some insight. Within the next year, I may start putting together parts for a mild 351 build.

My goal: decent HP(275ish BHP), good TQ(375ish), excellent low end and throttle response with decent mileage in an emission compliant package.

My proposed parts list: GT40 iron heads, 1.7 RR's, short tubes, Bassani Y-pipe, and a single 3" Magnaflow. Pretty much stock everything else(intake manifold, cam, MAF, injectors, tune etc..)

Pros and cons to that set up? The GT40's will hook up to all emissions equipment, correct? And at what point is the fuel pump going to be an issue? Will the truck run well on the stock tune operating idle-4500 RPM's?

By time I get a set of used GT40's, and have them refreshed, would it be more practical to buy a set of new heads, such as the GT40X's or a basic Dart or Edlebrock set? Again, I'm looking for a well rounded package, not peak numbers. Would the GT40X heads be "too big?" As in, I would need 24 # injectors etc..?


A lot of questions packed in there, so don't feel obligated to answer them all haha. Thanks guys.

 

Any smog legal aftermarket head will be compatible with your emissions system.
If you are building a motor for your truck I would consider a slightly larger than stock cam. Your mass air equipped truck with not be affected by the slight change.
Your stock injectors will feed a mild combination just fine.

 

get and aftermarket intake the stock 5.8 truck intake is restrictive

 

Actually no....The Factory setup flow pretty decently...I'd put the money elsewhere....

 

Why no cam!?

Id also port and polish those heads.

 

Back in the day(before there were so many aftermarket intakes available) We used to use the truck lowers on our mustangs. I went low 9's in my mustang with a truck lower, cartech upper combo. So, I would have to disagree with you on that point.

 

I must be missing something here...this is a 5.8L build, not a 5.0. I would agree the truck 5.0L lower is a good piece. I would not say the same for the 5.8L version. Two different animals.

For the goals the OP is looking for I would say a good cam would be a better option than the heads. The rest of the pieces are highly recommended.

 

....Thats the 5.0 lower , the 5.8 lower is alot smaller than the 5.0....Lew

 

If you're going to the trouble to replace the heads then it would be a good idea to change the cam out as well. However, I would lean towards a cam with more lift and keep the ratio at 1.6. Changing to 1.7's changes the valve-train geometry and may require the used of shims. It's not a bad thing, I've just never been a fan of using shims.

Only thing worth doing to those GT-40's is to do a little grinding/polishing on the exhaust ports. Paying someone to up-size the the valves, upgrade the springs, porting the intake and polishing the combustion chambers would be money better spent on a good used set of aluminum heads.

 

Your goals are achievable with the stock heads and a larger cam though I wouldn't talk you out of installing GT40s on a 5.8 either as long as they don't need a ton of work to be functional.. it's just not cost effective when aftermarket heads are so cheap and even the worst of them are much better than E7s. As delivered the GT40s flow about 20% better than E7s which puts power potential over 300hp and with a little work on the exhaust ports that ceiling is even higher, you just have to be careful to get a smog version of the head as some of them don't have the AIR ports at the back. Heads and a mild cam upgrade(Comp 35-320-8) will run with the stock EFI system no problem at all.

 

As long as all the parts you are planning on using have a CARB number you will be fine. all emissions legal parts have a number that means the California Air Resources Board checked it and that it creates the same or less emisions than the limit.

 

LONG TUBES

 

x2....Shortys are for higher rpm/horsepower stuff...Think mustang...lol

 

Thanks guys.

In response to all:

1) I'm not against skipping the 1.7's and doing a mild cam. That's a good point.

2) I'm not trying to cut corners, but I'm also looking to put as little $ into as needed.

3) If I have a set of used GT40's refreshed and ported, I will probably have more $ in them then a basic, but new off-the-shelf performance heads.

4) I'm not against using GT40X's, TFS or Dart's but I don't want to turn around and limit it too bad using the stock intake manifold, EFI compontents, etc...

5) No long tubes, haha.

 

Why no Longtubes. They aren't had to put on, and the stock exhaust is the biggest bottleneck out of all of those parts. I got Pacesetter Longtubes for 230 and kept all my emisions except fort teh AIR as I went with a newer Hiflow 3 Way cat.