PI Heads vs Ford Racing Cylinder Heads

Midnight2V said:

Gentleman, I have these heads. I have had them on my car in unported condition, then in NA NA Ported , FRPP intake, Comp 270 AH and Built short block at 10.0:1 compression 332HP 359tq @ 5800rpm

add an intercooled Paxton Novi 2000 @ 14 psi 546hp 498tq 6900rpm at 160 degrees inlet temp and 16 total ignition timing.

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Good info Midnight. You are running a Paxton Novi using 10.0:1 compression? I thought that would be too high.

sneaky98gt said:

Why are they not as good for supercharging? I've read somewhere that they flow better than the PI heads. And that the compression bump in the PI heads is not a good thing for supercharging either. Thanks for your help.

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I too had a set of these heads.

I didn't use them as my engine builder( still a current Ford Engine Engineer ) didn't recommend using them for what I wanted to do. If my car was going to be more of a strip car than daily driver, we would have used these heads as they would make a bit more power.

That said, the SVO head is a slow burn head compared to the NPI and PI head which are a fast burn. With a SC and pump fuel, you won't be able to run a lot of timing that these heads( SVO ) work best with.

In stock trim or ported trim, a PI head flows very similar on the exhaust side to that of the SVO. On pump fuel with a SC, a PI head can have more timing added to it before it pings than a SVO head can. On the same street setup, a PI head will make more power/torque than a SVO head will with a blower on pump fuel. If you are looking to build a race engine and running race fuel, the SVO head will be the better power making head.

Yes, I run 10.0:1 compression. Detonation is not an issue because I run a centrifugal blower. A roots or a twin screw will create full boost at virtually any rpm. When you combine high compression and high boost at low rpm, it will promote very high chamber temperatures. When you have a slow piston motion (low rpm), you increase risk of auto-ignition, also known as detonation. As rpm climbs, this changes, inlet temperature, F/A ratio (always a concern), and ignition advance become your critical factors. Because a centrifigal blower typically only makes significant boost beyond this danger area (unless you are running a wastegate controlled setup for high boost at any rpm), it is not only feasible but, in fact, practical. At low rpm, the blower is basically just an accessory load and the high compression will actually help it respond down low as well as increase high rpm performance. This is why the Lightning and the Terminator, and the GT and the GT500 all use low compression.

As to the SVO head being suited for "race only", all I can tell you is that the term daily driver applies to whatever you are willing to put up with in your car. My car has been my daily driver since day 1. I happen to think it is a very tolerable setup. But that is just my opinion, and when you come right down to it, the definition of a daily driver is just that, an opinion. Prior to adding boost, i was getting nearly 30 miles to the gallon....when i didn't drive irresponsibly, i still get roughly 25mpg in boosted form. No rocket science to it, I simply removed every restriction i could think of in regards to the engine being a glorified air pump. These heads, along with everything else, took me from epa 24 mpg to 29.8 by my figuring.

As far as i can tell, yes, the FRPP hi flow intake manifold has been discontinued and there are no units available that I know of. I don't know about the Bullit. I do know that neither are listed in the FRPP catalog. But the Trick Flow intake is a virtual clone of the Bullit, which is in turn a FRPP intake matched for PI Heads. The SVO heads can be port matched to either of these intakes. I am actually very excited to see anything on the new BBK DSI manifold. BBK took the concept of the FR500 Duel Runner manifold and applied it to the 2V heads.

Also, if you want these heads, get them now. They are no longer in production and when the units that are still available are gone...that is it.

Thanks for all your responses, if you have any other questions, I am here. If I missed any of your questions I will try to get to them soon.

Interesting to note, the Hi flow intake was discontinued shortly prior to the TF intake being released as a virtual copy. Now here we are with TF releasing a cylinder head with many "striking similarities" to the SVO design, and Ford halts production of the SVO casting. HMMMM...me thinks.....

To TJG, yes I agree with your comment about ignition timing. This is the one point I know of that the PI head has an advantage. Due to spark plug locations, the PI casting places the the plug closer to the ideal flame kernel location and can get away with more aggressive timing. This was a compromise in the SVO due to moving the intake valve center line closer to the bore center (which was also done in the PI casting), increasing the valve size, and enlarging the inlet port.

sneaky98gt said:

So you wouldn't recommend these on a daily driven car? Would you recommend the PI instead? If I'm looking for good power-making heads that don't cost an arm and a leg, what would you recommend?

I've basically decided that sometime I want to put a different set of heads on the car. I'm not too concerned with P/P the NPI heads; doesn't exactly fit within my budget and isn't that much better over stock. I like PI because it is more of a budget oriented power adder, for me anyway. I just don't really like the idea of the higher compression, with the possibility of a supercharger in the future. The FRPP head looks good too, but I'm not sure about how good it will be in a daily driven car.

My ultimate goal is too have a daily driven N/A car that has the ability to at least run close to an LS1. I guess that would probably be around 300 hp, maybe a little less would make me perfectly happy.

That being said, if I go with the PI heads, will porting and polishing them cut down the compression? Should I P/P the FRPPs? Should I not P/P either one? Or should I give up on the idea of running with the LS1 N/A?

Thanks so much for all the help.

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Personally, if you plan on staying N/A, I would go with the SVO head over the PI head and build a higher compression ratio shortblock.

Budget N/A, it is tough to beat the horsepower increase of the compression bump that the PI head adds to a NPI shortblock. If you don't have the funds to do what I recommend above this, then go with PI heads.

If you plan on going with a SC, I would go with the PI head over the SVO. I would only go this route if looking at a Centrifugal( CF ) SC. You can run a higher compression ratio with a CF SC compared to a Roots or Twin Screw SC. I would not be afraid to throw a S-Trim @ 6PSI on my 10.5:1 Compression Ratio Big-Bore.

If looking at a Roots or Twin Screw SC, you are better off with building a lower compression short block and use PI heads.

You pretty much have to decide what you want for sure before you chose the head you want.

That is my thoughts.

Here is the issue, you already have a pi intake, if you haven't done any work to the intake to match the heads i would just get a set of pi heads, some good springs and a cam to run it out to 6500 rpm. This will give you 10.2:1 compression. Its cheap, its easy and its been done. I'm not saying it's cliche, I am saying many have gone before and made the mistakes already, so there is a large information pool to draw from. Parts, labor, and tune will set you back maybe 2k and you will end up with 275 to 295 at the wheels, better fuel economy, and a big toothy grin. Want more? throw an intercooled V2 or an s trim on there and you can get 425 to the wheels with maybe 10-12 pounds of boost. Safe, reliable and fun.

If you want to get a little more exotic, and you have the cash, then sure, get a pair of the SVO heads. This will give you 9.1-9.2:1 compression. But know in advance, you will have to machine the heads to the intake bc matching it the other way is a nightmare with those composite units. If you don't already have them get a long tube exhaust system, the pi exhaust manifold does not match the SVO exhaust outlet, it bolts up, but the shapes are off and you will get zero exhaust scavenging as well as a new restriction. You can always get the TF intake and port match that way, or you may find a FRPP take off. This way is much more expensive. and we have just scratched the surface.

Here is a novel idea. Karkraft.com sells tumble port cobra heads ("C" castings) for the low price of 475 a pair completely assembled minus cams. grab any 99 and up 4V exhaust system, a set of cams, timing cover and gaskets, and a positive displacement supercharger (like a terminator cast off from a blower upgrade, tons of them everywhere). Your compression is going to be about 8.7:1, perfect for a positive displacement unit. stay at or around 8 pounds of boost, unless you feel lucky. Upgrade your fuel system to support and at some point throw a bulletproof rotating system in it so you can turn up the boost.

Well, there are a few possibilities. Just look at what you have or are allowed to spend, and figure out what is going to give you the best bang for the buck. Just remember, you are never done modding. So always keep in mind what you will want to do in the future and plan it out accordingly. For example, don't throw a set of heads on and then decide to add an intake or cams later. Save money by planning out your labor costs and take advantage of everything you can.

I hope I have helped, and not confused. Good luck, have fun, be safe.