Easily Lower 5.0 Compression

YoshiBluedevil · 07-07-2005

Hey guys!
This is more for future reference than anything else. You can see the motor that I have, but N/A is just not enough for me. A bunch of my friends have turbo DSM's, and it kills me that they keep up with me mostly stock (just AWD and 20lbs of boost). Now, granted, they are lighter then my car ... but still ... come on ...
Nitrous is out of the question for 2 reasons: 1) I dont want to rebuild my motor all the time from blown gaskets and such (plus my chip can advance the timing which i know is a major no-no with nitrous) and 2) my g/f would kill me if she knew I had illegal nitrous =\
I think I am running about a 10.6:1 compression right now, and the builders told me I could only run 5-6lbs of boost, and even that could blow the motor.
What could I do to lower that compression easily, without taking it all out and swapping the pistions? My friend told me about head spacers, but I dont think that could work on a V8 because the intake wouldnt line up correctly. I want to lower the compression enough to run about 15 lbs of boost from either a vortec or turbo/turbos.
Would switching to 1.7 rockers change it? I know it sounds stupid, and I dont think it would, but I just dont know.
Then on top of that, once its all said and done ... SC or Turbo? I love the blow off valve sound (yes I know ... I'm a rice lover ... anyways). Now, a guy I was in college with said his SC had a BOV, which I guess is possible, but is that true or not? And if I go turbo / turbos, does the size of the turbo make a difference as far as how much boost the motor can handle?
Right now, I'd say I am leaning to a SC because it would be easier to install, and work with.
One last thing ... I read somewhere that the compression of the motor affects the gas I shoudl use. I run 93 octane, but the calculation said its Compression * 10, thus 106 octane. There is no way I could afford race gas on a daily driver! lol. Is this true or not?

GTRaptor · 07-08-2005

You can remove the heads and have someone do some combustion chamber bowl porting, this will reduce the compression. How much depends on the heads. I guess the AFRs have enough meat to reduce it substancially.
You can also install thicker head gaskets, check with Roll and Felpro.
Last..pistons.

YoshiBluedevil · 07-08-2005

how thick of a head gasket are we talkin about here? and plus, wouldnt that make the intake ports line up differently, thus hurting my power by killing the air flow? And how "big" of a head gasket are we talkin about here, keep in mind, i want to be able to push like 15-20 lbs of boost max

GhostDog 5.0 · 07-08-2005

The intake bolts into the head. How would that cause any alignment problems?

YoshiBluedevil · 07-08-2005

because if the heads move further up off the block (because one goes up to the right, and the other up to the left), then that would mean the manifold would bolt up a little higher, and the heads would have a little more space between the heads and manifold, AND the manifold would be a little higher off the block. I read something along those lines in some forumn somewhere.

its hard to describe in writing, maybe i should draw a picture next time lol.

anyways. assuming im crazy and stupid ... what gaskets should i get to lower the compression? i have a 342 so its NOT overbored, so im assuming id get any high performance head gasket (and of course new bolts, and then upper and lower manifold gaskets)

anyone know someone who wants to sell a cheap SC or turbo kit for a 5.0??

Tominator · 07-08-2005

Interesting thread.

Most supercharged motors have a BOV. It is vented back into the metered gases and is silent compared to a turbo motor that vents to the atmosphere making the sound that gives ricers a woody no matter the car.

And no mater what mod you decide on, throw that chip out the window!.....or sell it...

Why is N2O 'illegal?'

Either NOS or Super can blow a head gasket...UNLESS...you get a proper tune best done on a dyno. :thumbup

Consider the horsepower you already have. I'd estimate close to 380[possible] at the crank and that's conservative. The 5.0 block is only reliable to something less than 500HP. At that, and sooner with less than a proper tune, you are going to crack the block.

If the motor was built properly the intake was matched to the heads. I'd leave the compression ratio alone and consider other options. Making 350+ HP has got to be hard to get to the ground. Have you considered suspension upgrades?

As far as turbo v. super v. N20, and being one harder than the other to tune properly and thus be reliable, it depends on the setup and the guy tuning it.

You are trying to put 15 or more PSI through a motor that's going to break even if you lower the compression!

Not cool!

A properly tuned super at 5 to 6 PSI will get you close to the 450HP limit for a reliable combo. Proper dyno tune is the key.

No matter the power adder, it ain't cheap! If it is, you'll be posting about a blown headgasket or worse.

YoshiBluedevil · 07-08-2005

well the motor was done in january by central coast mustang, so everythign is new. i dunno if the block only handles 500, or maybe more?
as far as i know, nitrous is illegal in street cars if its hooked up. and id rather not get pulled over then arrested for nitrous.
i need to get my car dyno'd to see the wheel HP ...
u really think 5-6psi (which my motor can handle) will give me ~450 at the crank?
i dont think throwin the chip out is a good idea. i had it custom street tuned by horsepower by hermann. it is made for my car, and my car alone based on 02 readings on his laptop on street tuning.

give me more info!!!! =D

Stangboy5666 · 07-09-2005

Heres the deal with chips. Some (not all) can fry your ECU or at the very least make your run like crap... How is yours connected. Plugging chips into the service port of the ECU is a bad idea. The Ford EEC-IV was meant to be modified (if at all) AFTER the harness that connects all the wiring into the ECU.

The chip, when you go with a power adder, will more than likely throw your car completely out of whack. All your tuning will go out the window and you basically will have to start over. Its a whole new ballgame. Most people who really do a turbo or SC right will do a complete fuel management system, and (someone correct me if Im wrong) that doesnt sound like a good mix with a chip burned for an N/A car.

As far as PSI goes, unless your block is substantially stronger than stock, I dont know if id even bother with a power adder. Your next step should probably be either a REAL strong block, or suspension mods as mentioned above to get that power on the ground. You should contact that place that you got your block from and see what they say as far as hp and power adders.

Also, if you want to get the compression down do it right, I wouldnt mess with gaskets and stuff. Either pistons or probably porting your C.C.'s.

Also as far as preference goes, Im leaning toward turbos right now for a few reasons.
1) Most Mustangs that go with an adder choose a supercharger
2) Turbos dont use near as much hp to actually work. Superchargers take quite a bit of hp just to turn over. I think turbo is a more efficient way to do things. There may be a little lag, but I can deal with that...

Good Thread