PI swap and detonation

[ZmanGT]

I've been sitting on the fence about going forward with the heads swap on my 96. (Anyone have a set cheap?) Big question I have is regarding the resulting higher compression. What level octane are you folks running to prevent detonation? Right now I have to use a mid-grade 87 to prevent pinging. Does the swap drive you up into the 91 range?

Hyland in his book says to cut down the swirl dams to drop compression. I've seen arguments that almost broke out into fights over swirl dams! Anyone go this route? or figure out how much it drops?

 

[TweekedGT]

I've used 91 since my swap. i have put the 87 in once. It didn't ping but i got a hesitstion in my throttle, it would kind of sputter. It seems to really like the 91 vs the 87. A little more costly but safer and better performance in my car. JMO. I don't have a clue what your talking about with regards to the swirl dams though, sorry.

 

[2002BLGT]

personally I would remove the swirl dams , it should cut compression by a point or so atleast ......

 

[ZmanGT]

Appreciate the info. When you look protecting your engine for only a couple bucks extra at a fillup, it makes sense to go with the higher octane. Swirl dams are the "bumps" that Ford added to swirl the gas/air mix in the chamber. Some folks swear that all hell will break out if you cut htem down.

 

[CanadaStang]

I've had trouble with mine pinging after the headswap, when the weather is cool it's fine but on warmer days it pings like crazy, and I'm running 91. I just ordered a 4 position chip from SCT, with:
1) Custom tune with stock timing
2) Custom tune with timing -2 degrees from stock
3) Custom tune with timing advanced
4) stock tune

I was hoping the tune would clear up the lean condition I'm getting, but just in case I ever find myself low on fuel in a small town with no 91, I can just back the timing off by selecting the #2 tune. Or if the custom tune fixes the predetanation issues, I can kick my timing up by selecting the #3 tune.
I figured this way the loss of HP that would result from removing the swirl wouldn't be much different than backing the timing off a bit, with a lot less hassle. Not sure how long it will take to get the sct, if the weather holds out, I may be able to find out how it works before I park the Stang for winter.

 

[ZmanGT]

Sounds like an interesting fix. You have a web site for them? would an adjustible timing set do the same thing for you? Would be a bugger to reset timing for every change in octane though.

 

[Stanglover96]

I bought my PI heads and intake yesterday for 650 used, and was wondering if I used a timing adjuster would that mess it up with the comp ratio being higher after PI swap? Also, what about a set of low compression pistions like maybe blower pistons?

 

[CanadaStang]

Sounds like an interesting fix. You have a web site for them? would an adjustible timing set do the same thing for you? Would be a bugger to reset timing for every change in octane though.

I bought it from Modular Depot, not sure off hand what the web address is, but if you just do a web search for Modular Depot, you will find it. Yup, a T/A would do the same, just not as convenient, and you won't have the custom tune.

 

[CanadaStang]

I bought my PI heads and intake yesterday for 650 used, and was wondering if I used a timing adjuster would that mess it up with the comp ratio being higher after PI swap? Also, what about a set of low compression pistions like maybe blower pistons?

You may not be able to advance your timing much with the higher compression, but every car is different. If you go with the newer stock mustang pistons it will be just like the new PI motor. The non PI pistons don't have as deep a dish in them so thats where the higher compression comes in. If you are planning on adding a blower in the future you will have to go with the PI pistons. I think I'd just look around for a complete PI motor instead of going to the trouble of swapping pistons.