Just installed my wideband finally, and thought it'd be a good idea to do a compression test since my SVT will be going boost hopefully in a couple months.

so if your looking at the motor going from left to right (1-4), compression is as following:

cyl 1: 90
cyl 2: 120
cyl 3: 110
cyl 4: 120

cyl 1 looks weak compared to the other 3. I'm gonna be doing a leakdown test w/in the next few weeks to see if my rings are still good. But what do you guys think? is cyl 1 toast? would you boost on it? I bought the comp turbo from Tom, and was planning for 280ish on 91oct and about 300-320 on 100oct.

I'm gonna do some pulls here in a little bit to see what my afr's are. Still untuned. not sure if afr's would tell us anything, but I figure the more info, the better. I'll post up what they are when I get back.

thanks in advance for any help.

that is a bit low to boost. i would talk to tom

Hmmm...that's low. The most you want is a 10% difference between any two cylinders. So 120 - 90 = 30. (30/120) x 100 = 25%. I know it's not what you want to hear, but that is out of spec without a doubt. I agree with leak down test. I just did a compression test today as well and Cyl 1 is 10% less than 2 and 3, so luckily I am just within safe bounds. Let's see what others have to say, though.

Ok, starting @ 5k, WOT afr's are 13.0-13.2, and then right about 6k through redline it drops to 12.7-12.9. That's for 2nd, 3rd, and 4th gear.

that may be a little lean but tuning will add more fuel.

that may be a little lean but tuning will add more fuel.

That's what I thought. And actually, just did a few more 4th gear pulls, afr's are 12.5-12.7 from 6k to redline.

You need new rings..... trust me.

You need new rings..... trust me.

I was afraid you were gonna say that. If I do rings, I mine as well slap some lower comp pistons in there. How good are stock rods? How hard is like 350 on 91oct? I'd rather not do a returnline, just max out the stock fp (or upgraded pump), and 60# injectors. Don't want anything insane, just something quick on the streets and a beast at road racing events.

Yep. 25% difference is no good.

13.2 AFR is perfectly fine for N/A. That's what I'm tuned to when my dang car is running right.

Edit: your post just popped up. I priced out a rebuild. With Eagle rods, Supertech pistons, and all the other bearings and seals, it's about $1500 in parts if you can do it yourself.

350 on 91oct is pushing it but it's possible.

well, if you wanna just re-ring it, you can, but you can't run aftermarket pistons on the stock forged rods cause no one makes pistons for the svt's rods as the wristpins are different sizes i believe.

They can be made to fit. Tom says it's not ideal, but it can be done.

Yep. 25% difference is no good.

13.2 AFR is perfectly fine for N/A. That's what I'm tuned to when my dang car is running right.

Edit: your post just popped up. I priced out a rebuild. With Eagle rods, Supertech pistons, and all the other bearings and seals, it's about $1500 in parts if you can do it yourself.

350 on 91oct is pushing it but it's possible.

What cr pistons were those? And yea, my buddy would do the build for me.

And how would 350 be pushing it?

8.7:1. That's with Zetec head gasket. With SVT gasket, it's 9.25, which is good.

http://www.massivespeedsystem.com/supertech_massive_speed_custom_pistons/supertech_massive_speed_custom_pistons/mcen84771_87/i-292046.aspx

91 oct is crap; especially in Kalifornia. It can be done, though.

8.7:1. That's with Zetec head gasket. With SVT gasket, it's 9.25, which is good.

http://www.massivespeedsystem.com/supertech_massive_speed_custom_pistons/supertech_massive_speed_custom_pistons/mcen84771_87/i-292046.aspx

91 oct is crap; especially in Kalifornia. It can be done, though.

hmm. Interesting. Stock on the SVT is what? 10.2:1? And idno about a head gasket making a .525 cr difference. What about the 9.0:1 probes from cfm?
And does anyone know the weight difference from these pistons/rods compared to stock? Any gains in quicker revs?

Yes, the head gasket makes that much of a difference. That's why it can be dangerous to put a Zetec head gasket on an SVT. The valves get mighty close to the pistons. I'm sure Massive has put in the time to do the compression ratio calculation.

Re-read the Massive info. The different compression ratio's are dependent on the cylinder head, not the head gasket. The pistons if installed in a regular Zetec motor give 8.7:1 compression, but if installed with an SVT head they are rated at 9.25:1. I assume those numbers are with using the gasket designed for the particulare head (zetec on zetec, svt gasket with svt head.)

Deal with C-F-M or McNews on pistons , I send everyone the C-F-M or McNews , they seem to know what there doing

The head gasket on the Zetec and SVT is diff thickness , Idealy for a DD you want to end up in the 9.0-9.2 range on compression when all finished , there is many ways to come up with that

Tom

well, if you wanna just re-ring it, you can, but you can't run aftermarket pistons on the stock forged rods cause no one makes pistons for the svt's rods as the wristpins are different sizes i believe.

...All my shop did was just press them on. No work that i know of needed. Im running svt rods and probe pistons. Tom said svt rods would be good to 350ish, figured that is my turbo limit too and my goal is only 300. Good enough for me.

What is gonna happen if you boost is what happened to mine. I had a bit low on one cylinder and eventually it just kept wearing down. Mine was a bit more of a difference than yours though if i remember. Can do a quick check and put a bit of oil in your cyl before you do the test, if it jumps up a ton, your rings are worn and most likely your problem.

The real reason ppl dont keep using svt rods is b/c the eagles are so affordable. The reason I didnt was because I managed to save a bit going with the svt. If I was to redo it i would probably consider the eagles a lot more.

I also agree with tom on those shops. Personally I only have used CFM but love them and will pretty much only use them for aftermarket if I can. Never had an issue with things that they sent me.

Not tohijack the thread. I have probe pistons 8:2:1 pistond, ford racing head and svt head gasket. What kind of compression do u think?

91 oct is crap; especially in Kalifornia. It can be done, though.


So true....

I was talking to Brad at FSwerks the other day and he said they tested ALOT of different stations, verdict: 91 isn't always 91 in Cali.

Not tohijack the thread. I have probe pistons 8:2:1 pistond, ford racing head and svt head gasket. What kind of compression do u think?

I don't know the piston deck clearance and I had to take a guess at your piston dish displacement, but using an online compression calculator, you should actually be very close to 8.2

my compression was 180,180,165,180. guess what happened to my motor after about 8 months of 14psi and LOTS of track time....
mine was zetec tho. but still the point.