[AnglicoGT98]

How high can your Compression Ratio be before you need to worry about runner really high octane (High meaning above 91-93)? I know after the PI swap my C/R will be about 10.4:1. But plus a turbo with 5 psi my C/R will obviously raise, so when do I need to worry about special fuel?

[Boomer]

You will be okay, you will have to pull a bit of timing but it should be okay. You may want a tune for "special" fuels for at the track.

[memphismustang87]

Does the DiabloSport Tuner not set it to run best at a 93 octane? Just wonderin, cuz my hypertech tuner did. It would make a pingin noise if I used lower.

[1slo5.0]

10.4:1 with a forced induction is asking for problems...

[SWEET2KSTANG]

on a very conservative tune, it will be ok. you will have to make sure who ever tunes it know exactly what they are doing. that is a lot of pressure in the cylinders.

[AnglicoGT98]

What do you think my C/R will be after the turbo? And it would be a conservative tune. I don't want to go over 400HP. I want 370-390. Which should put me at about 4-5 psi. Definately not more than 6.

Darrell - I was reading a post from a little while back where someone said they heard that a PI swap + FI will cause problems. And I believe ver batim you wrote, "Someone fed you a line of crap".

[SWEET2KSTANG]

cylinder pressure will go up quiet a bit, and 5-6psi is hardly worth the $$$. if it was me, i would invest into an all motor set up. guys that do a p.i. swap with vt heads, cams, and header back have seen 99rwhp. throw that with cai, t/b, plenum, udp's, mid pipe, cat back, and a hell of a tune you can see around 350rwhp.

[AnglicoGT98]

My dilema is that I already have EVERYTHING for the PI swap...lol. I wasn't planning on going FI for a while. But I fell into some cash, and I have turbo kit put together dirt cheap. So I would really like to boost it. And you can only get so far on a N/A engine before it starts to cost an ass load of money. I was also going to get forged internals in about a year so be able to handle more HP. I've been told by a couple of shops that 10.4:1 is the highest I'll see before the turbo. And just like you said, with a conservative tune, high octane gas, and they are estimating about 14*-18* of timing I should be okay, even if I want to run it hard.

But I want to get everyone's side of the story before I jump into it.

[1slo5.0]

Originally Posted by AnglicoGT98 What do you think my C/R will be after the turbo? And it would be a conservative tune. I don't want to go over 400HP. I want 370-390. Which should put me at about 4-5 psi. Definately not more than 6. Darrell - I was reading a post from a little while back where someone said they heard that a PI swap + FI will cause problems. And I believe ver batim you wrote, "Someone fed you a line of crap".

Refresh my memory. What do you mean FI? Fuel injection or forced induction or what? People loose me with abbreviations because they could mean anything. How do you know you are at 10.4:1 anyway? Is that what it calculates out to be or is that what someone said? I could have swore the guys I talked to around here said per measuring and the mathmatical formula the compression comes out to be around 9.6:1. I could be wrong though. Its been along time since I've heard anyone make that swap around here.

[Boomer]

One thing being overlooked here is 10.4:1 is only static compression ratio, you can go over 400 easlily with 5lbs. The combo will determine a lot of what power you will make. It will be safe if the tune is "safe", you are going to be running less timing to make it safe. The diablo software in capatable hands is a very good tuning device.

[AnglicoGT98]

Yeah sorry about the abbreviations. I was using FI as Forced Induction. I was using 10.4:1 as the highest my compression ratio would be. I don't want to plan for it to be 9.7:1, buy all the shit, and then find out it is too high. You know what I mean?

What do you mean by static compression ratio? I assume it means when the car is static and not at WOT, like idleing or something?? And if I hit 400HP with only 3 or 4psi (just an example) then that's all I would go for. The amount of boost the car has isn't my goal. It's the 400 horsepower mark that I'm after. And FYI, this WILL be intercooled.

Will running colder plugs help anything??

[ModMustang97GT]

The normal compression on a PI engine is around 9.5 but due to a different design in the 96-96 pistons. With the same heads and everything Our cars actually make about 10.2-10.4:1. The forced induction is doable with any compression really, you just can't run high boost. There are TT NSX's with 11:1 stock compression, plus turbos at 8 psi. When you add boost you are creating higher compression. But, if you read the articles posted by MM&FF. They have tested compression ratio's related to boost. With the same artificial compression (teh compression after applying the boost) you will make a set range of power. However, the limitation, is that with a lower compression engine and more boost, you can get away with lower octane fuel. But with a higher compression engine you have a much higher chance of detonation, and there for less timing so slightly less power.

[AnglicoGT98]

Just spoke to the shop that would be tuning my car (Mustang Specialties). The tech over there said realisticly that a my '98 with 70K will have a 10:1 no higher than 10.2:1 after the swap. If I don't go over 5psi Intercooled then I will be okay. They said they can tune it to run on 93 octane and pull timing so I won't detonate. He also said that I can have combustion chambers opened up a little bit to lower the C/R a tad if I really wanted to. And I trust this shop 100%, they sponsor my cousins 7 second 5.0.

[SWEET2KSTANG]

Originally Posted by AnglicoGT98 Will running colder plugs help anything??

any time you start running a power adder or push more through a stock power adder, you are suppose to change plugs. colder and a copper version.

[AnglicoGT98]

So NGK Iridium would not be good for a power adder? I saw these plugs that run 10* colder or something...would that be more ideal?

[1slo5.0]

Originally Posted by AnglicoGT98 So NGK Iridium would not be good for a power adder? I saw these plugs that run 10* colder or something...would that be more ideal?

Spark plugs have nothing to do with temperature. A colder plug disipates heat faster than a hotter plug. It doesn't make the engine run colder.

[AnglicoGT98]

I know it doesn't change engine temp. What I am asking is, an Iridium plug would not be as good as a copper plug that is said to run colder or do iridium plugs already run colder??

[Boomer]

Iridium are junk IMO on a modular. Static compression ratio is taking all the numbers and crunching them, dynamic compression the actual base compression when figuring for timing events. Valve overlap will lower dynamic compression.;

[AnglicoGT98]

Okay that makes sense. So what would be the best thing to pick up? I guess I'll go with those plugs I saw that are copper and say they burn 10* colder than stock plugs.