Rebuild Thoughts? Pros vs. cons?

[Strable781]

Hello.

Getting ready to pull my 03 cobra motor to fix cylinder 8 low compression issue. Block is getting bored .020” over with 10.6:1 flat top pistons. Car is staying on 93 pump gas, 80# injectors with dual 340lph pumps with a 2.3 whipple, 2.75” pulley and stock lower pulley, should be 15ish psi i believe? Stock heads, stock cams. I really dont care about power numbers as i just want to get the car running right, but i would like to know if someone has an idea for what the car should make power wise as i cant find much info on this combo or any reasonable expectations. What are the things i should watch out for with this combo/upping compression? Let me know. Thanks.

 

[03' White Snake]

That’s a lot of compression for 93.

I’m running 10.3 and my tuner said that is too much for 93. I’m on E85 full time. My tuner says 9.5-8 is the best CR and makes the most power.

 

[01yellercobra]

I'd drop the compression about a point if you're sticking with 93.

 

[Strable781]

Got it. Ill opt for 6cc dish pistons instead. Should drop the compression about a point or so. Appreciate it.

 

[Blkkbgt]

I'd drop the compression about a point if you're sticking with 93.

Why?

Everyone these days seems to be running higher compression and lower boost psi these days.

 

[Blkkbgt]

The only thing I have to add is don't instantly jump to .020 over pistons.

Have the bores measured and see if you actually need to go that far. More meat in the cylinders is seldom if ever a bad idea.

Something I've learned over the years of getting ****ed by machine shops is run away from anyone who instantly says you have bore the cylinders 20 or 30 over and won't even measure for taper before.

If the bores are straight and have little to no taper you can often get away with a .005 cleanup and a custom piston.

This is usually a sign of a bad shop with bad equipment and they want room for error because they aren't getting or able to get consistent bores.

 

[biminiLX]

Why?

Everyone these days seems to be running higher compression and lower boost psi these days.

Was going to ask the same but it depends on several factors.
First I’d discuss with your tuner.
Second if you’re stuck with 93 but don’t drive a ton of miles, definitely consider a modern octane booster so you can enjoy the compression for off boost driving and more power boosted.
Third would you ever run e85 or non 93 pump?
Good luck man.
-J

 

[Strable781]

Was going to ask the same but it depends on several factors.
First I’d discuss with your tuner.
Second if you’re stuck with 93 but don’t drive a ton of miles, definitely consider a modern octane booster so you can enjoy the compression for off boost driving and more power boosted.
Third would you ever run e85 or non 93 pump?
Good luck man.
-J

Yeah ive always considered running e85. Just the fact of availability for me and more so the fact that i dont want to add the steep price tag of a e85 capable return fuel system to my build. Im not trying to make uber power. Just good, upgraded, reliable power on pump 93.

 

[Strable781]

The only thing I have to add is don't instantly jump to .020 over pistons.

Have the bores measured and see if you actually need to go that far. More meat in the cylinders is seldom if ever a bad idea.

Something I've learned over the years of getting ****ed by machine shops is run away from anyone who instantly says you have bore the cylinders 20 or 30 over and won't even measure for taper before.

If the bores are straight and have little to no taper you can often get away with a .005 cleanup and a custom piston.

This is usually a sign of a bad shop with bad equipment and they want room for error because they aren't getting or able to get consistent bores.

I agree with you. .020” over is what im budgeting/planning for the build as i can get these parts off the shelf and not have to wait for lead times or pay custom piston prices. When I contacted my machine shop i said i was planning on .020” over but to let me know how their preliminary measurements came out and revise my plan if needed. I dont find it worth custom pistons for the power level ill be at with my plans now. I can have modmax pistons and rings here in under a week and thats all i really need.

 

[Blkkbgt]

I agree with you. .020” over is what im budgeting/planning for the build as i can get these parts off the shelf and not have to wait for lead times or pay custom piston prices. When I contacted my machine shop i said i was planning on .020” over but to let me know how their preliminary measurements came out and revise my plan if needed. I dont find it worth custom pistons for the power level ill be at with my plans now. I can have modmax pistons and rings here in under a week and thats all i really need.

Take a look at JE. They offer minor changes to their off the shelf pistons for a low price.

Additionally you can look at Icon. They have an off the shelf .010 over piston. Modmax doesn't list them but their catalog and summit do.

 

[MG0h3]

Isn’t Gibtec like a go to now? Lot of noise about them at a good price and custom fit.

E85 is one of the best mods you can do. I did it for like 1150. Level 1E with 465s. Deleted Fores relay that they call a controller and ran 2 $7 40amp relays. Didn’t do rails at the time.

2.75 is going to put you well over 15psi which with higher compression, will require more than 93.

Boost and compression just compound one another so higher compression means less boost or the sooner you’ll need more octane.

I would also strongly suggest doing cams with the engine out. Bit of an expense but way better performance. I’d only go custom from Todd Warren or the like.


Sent from my iPhone using svtperformance.com

 

[badcobra]

If you were truly interested in 'reliability' as your main goal, then you would be making the switch to e85. I also agree with the others that you are making a mistake going right to .020 over. The price for a custom piston is barely different and so what if you can get pistons next week? Your block won't be done next week and ready to put together, it will be many months. Slow down and do things correctly, you're going to be down for a year anyway.

 

[PC03GT]

Isn’t Gibtec like a go to now? Lot of noise about them at a good price and custom fit.

E85 is one of the best mods you can do. I did it for like 1150. Level 1E with 465s. Deleted Fores relay that they call a controller and ran 2 $7 40amp relays. Didn’t do rails at the time.

2.75 is going to put you well over 15psi which with higher compression, will require more than 93.

Boost and compression just compound one another so higher compression means less boost or the sooner you’ll need more octane.

I would also strongly suggest doing cams with the engine out. Bit of an expense but way better performance. I’d only go custom from Todd Warren or the like.


Sent from my iPhone using svtperformance.com

Yup, a 3.0 pulley with stock lower is 18psi

 

[01yellercobra]

Why?

Everyone these days seems to be running higher compression and lower boost psi these days.

It's just what I would do. 93 octane doesn't have as much wiggle room with timing and boost as E85. I think a lot of the guys going to higher compression are running E85 full time.

As I said, just my opinion. It's a lot easier to add a couple degrees of timing or another pound of boost when needed vs reducing compression when you realize you're hitting the limits of the fuel.

 

[DSG2003Mach1]

It's just what I would do. 93 octane doesn't have as much wiggle room with timing and boost as E85. I think a lot of the guys going to higher compression are running E85 full time.

As I said, just my opinion. It's a lot easier to add a couple degrees of timing or another pound of boost when needed vs reducing compression when you realize you're hitting the limits of the fuel.

once again, this

Im a little over 9.5:1 because I run around on 93 all the time. We have E85 here but not other places I go. Same reason I didn't have a bunch of head work done, cheaper and easier to add a little more boost

 

[DCguy]

If youre pulling the whole thing apart anyway id def have the heads gone through and freshened….valve job, new seals, guides, lifters/lash adj if needed, etc. Depending on what heads you have should also replace the exhaust valve seats as theyve been known to fail. Ford recalled a bunch of them.

I went down the path of pulling motor and embarking on rebuild. Ditched the iron block for Teksid aluminum for the 80lb in weight savings.

If staying on 93 with factory ECU stick to 9.5:1 or lower like most have said. The tuning window is much more forgiving and youre only giving up like 20hp at low boost.

 

[Blkkbgt]

It's just what I would do. 93 octane doesn't have as much wiggle room with timing and boost as E85. I think a lot of the guys going to higher compression are running E85 full time.

As I said, just my opinion. It's a lot easier to add a couple degrees of timing or another pound of boost when needed vs reducing compression when you realize you're hitting the limits of the fuel.

I understand. I was was simply curious because I am planning a higher compression build in the future and don't have easy access to E85.

My plan currently is just under 10:1 and a little octane booster to up our shit 91 to 93.

I am trying to run lower boost psi to keep IATs lower.

 

[01yellercobra]

I understand. I was was simply curious because I am planning a higher compression build in the future and don't have easy access to E85.

My plan currently is just under 10:1 and a little octane booster to up our shit 91 to 93.

I am trying to run lower boost psi to keep IATs lower.

Depending on your care level for the state you might consider a stand alone. I don't know if you were able to keep the knock sensors when you did the swap, but with a stand alone you can dial in the sensitivity. Mine has already saved me once when my tune went wonky.

 

[Strable781]

Thank you all. You have made me all the wiser. I appreciate and will consider all of your input.

-Bill