Pi Head Swap: Worth The Effort?

Discussion in 'SN95 4.6L Mustang Tech' started by bhuff30, Oct 11, 2013.

  1. I am considering the PI head swap for my daily driver: 97 GT, 217k miles. She already has a PI intake, PI cams and some other basic bolt ons (OR H-pipe, underdrive pulleys, upper plenum / 75mm TB, drop in K&N, tuner). Only current issue on the top end is some slightly old valve seals that occasionally leave a puff of blue smoke at a long stop light. Timing chain guides were replaced at 175k, so I don't worry about the timing set too much.

    In the garage, I have a low mileage Romeo PI engine with a smoking problem. From testing, I think it's a blown head gasket, or maybe a ring pack issue. I will be tearing down the engine to part it out anyway, so I will have the heads literally in hand.

    So is it worth the effort? The gains would only be 5-10hp, even with my other mods? The time required is around 12-16 hours to do it yourself? I guess the only cost would be the FMS head change kit at around $120. Seems like too much work, so I am thinking it makes more sense to sell the heads, and use the time and money for the roadster instead, so I'll be curious your replies.
  2. I'll leave a longer reply later tonight when I get time.

    But short answer? Yes.
  3. Doing a quick search, it looks like the power gain may be closer to 15 hp. Of course, torque should be up throughout the range due to the increased static compression. I will probably hold onto the heads and look for a good chance to install them.
  4. They will probably add more than 15 hp because I think you will get more compression. PI heads on a non-PI bottom end usually make more power than a full PI engine. And since you already have them you might as well get them ported by a good company. They will make a night and day difference with a good stage 1 cam. If you upgrade the springs and go with a stage 2 cam then you will gain even more!
  5. To add, if you take your time (if it isn't your DD and you can spare downtime), then why not just build a short block. You already have the block. The GT crank is good for probably like 700 or 800 hp. Tear that block down, get it machined, add some H-Beam rods and forged pistons with a good 9.0:1 - 9.5:1 compression ration (if planning to go FI) or like 10.5:1 - 11.0:1 (if staying NA). Then get the heads ported, add some aftermarket cams, and do the engine install. You may be looking at spending about $2500-$3000 but that engine will be rock solid and a beast.
  6. She is a daily driver, so I don't want to put big money or effort into the project. Yeah, an aftermarket cam might give me 30hp, but at $600, I will pass. Then again, 15hp for the cost of a $120 head change kit sounds pretty good.
    My money and effort (in terms of cars), is getting wrapped up in the FFR.
  7. Alright, 2 days later, I finally get the time, haha.

    I think you're going to see a good bit more than 10 horsepower. I think that the better heads, bump in compression, and (I'm assuming) tune afterwards, you'll see more like 20-25 on the tires. Basic bolt-on (CAI, exhaust, tune/timing adjuster), PI head-swap cars will make 260ish on the tires (amirite? @Winters98GT ). At the same time, I remember someone on here a WHILE ago had a 100% full bolt-on, PI cam/intake setup with NPI heads that made 225 on the tires. That's 35 rwhp. So I think you're selling yourself short on how much you'll pick up.

    Granted my case is under boost, I picked up a TON of power simply by going to PI heads. My semi-old setup (blower, blower cams, NPI heads, intake, exhaust, tune) trapped a best of 112 mph in pretty decent weather. When that motor popped, I went to a full PI motor on the exact same components, and it went 118 mph in similar conditions. So even without the bump in compression, I picked up 6 mph in the 1/4 just from PI heads. That's a solid 60 rwhp.

    And on top of all this, just how much do you think you could get if you sold the heads? I know in my area, you'd be pretty lucky to get $150 for them. I see complete top ends going for $250. For the cost of a head-changing kit, I'd definitely say go for it. Also, if you wanted to save a few more bucks, I've read many times now that you can re-use the head bolts at least one extra time. So you may could pass on the head-changing kit and just get the gaskets.
  8. It depends how much you want to put in the engine, but if you just want to rebuild it throw some 4v rods and pistons in it. Makes 11.8-1 comp runs great off pump gas/e85(with tune).
  9. Sneaky, thanks for the info. A gain of 20-25hp would be great, and certainly worth the time and effort.

    Rusty, your 11.8:1 compression setup runs fine on premium? what cam are you running? I can see it working with an aftermarket cam where the cylinder pressures are a little lower, but probably not on a PI cam. Anyway, I will stick with 10.5:1 CR of the PI heads for now. If I ever need to replace the shortblock, I may pull a teksid and run it as is with flat tops.

    I started tearing down the PI engine and managed to twist off a valve cover bolt in the head. That should be fun to remove. Hopefully I can swap the heads in sometime before the end of the year. Again, daily driver, so probably around t-day or x-mas.
  10. My old car had stock cams. Perfectly fine on pump gas. You have to run really high timing to get one to knock. I have a race tune that will barely knock, and its like 26-27deg. at WOT. Stock timing on 96-98 cars are like 10-12 at WOT.

    Ive built 5 of the 4v rod/piston with pi head engines. Its a very fun/cheap engine. Even more fun on a 125-50 shot!