4.6 question
 

ya so my car has this bad knocking sound and it gets loud around 2200 rpms or just when iam at a constant speed, so i took it to get looked at and they said the rod is bad in piston 4 .....they said they could patch it and i was wandering what that means???? also they said they could rebuild my motor but i would like to know if i can put in a bigger motor in it and how hard would it be to put a Cobra motor in it???? or should i just drive it tell it just doesnt work ???also if you know anything on replacing the rod and piston how hard is it for me to do it myself? Thanks

Cobra short block is the same as a GT short block, the internals are different. You could put in a Cobra short block and bolt the stock heads to it. Or you could just buy a whole cobra long block, but thatll be expensive.
What shop is this?

Its a shop here in Mesquite ...called mesquite car care ....how much do you think a cobra short block is and do you know if i would have to put in a new wiring system or get a new computer or anything????? Thanks

sounds to me like a bad rod bearing. Seen it a lot and the symptoms are just like taht... bad knock that shows up around 2k...

I don't know of ANY way to "patch" a bad rod or bearing. Your crank will need to be machined and the rod bearings and main bearings replaced (also possibly a rod but I doubt it).

Find a good used shortblock and have it swapped in. You can put a real bigger motor in it... like a 5.4 (check out the 5.4 swap thread in this forum), or you can swap to a cobra motor, or just pop for a built shortblock. In any case, it's gunna be pricey. Start at a grand and go from there.

I would STOP DRIVING IT, don't even start it. Each time you let the motor turn over you allow more damage to accrue.

If you use a real cobra short block your compression will be in excess of 12:1 and you won't be able to use pump gas anymore. You'll want a mustang GT shortblock (or any 4.6L shortblock from your period car, 96-98, 99-04, etc..).

Hope this helps.

You wont have to do anything wiring wise with a new short block. But to keep it cheap and simple Id just go with a stock iron block built, or find a good used one. Or you could go with an aluminum block, but thatll cost more.

I believe with PI heads and the cobra short block his CR would be 10:1, with NPI heads it would be 8:8:1. You want lower CR for forced induction.

cobras used domed pistons (all the cobra engines I've had apart). small dome but it was there. since flat tops bump compression to 12.4:1 on PI heads and 11.7:1 on NPI heads domes would be higher by about .5. Virtual Engine 2005 seems to come up with the same math as my Probe catalog.

http://www.modularpowerhouse.com/for...428#post512428:dunno:

greenbird was correct on his math...but that was for different starting and finishing components. my math is right. I've double checked it. If you want the compression ratio for any combo, then give me the:
head type
bore
stroke
block type
piston dish

I'll use standard numbers for the HG and deck height. So far I've been right on my compression numbers 100% of the time.

BTW... to clarify an earlier statement. All <03 cobras used domed pistons. The 03+ had a nice dish but you don't see many people swapping for a 03 bottom end without the top half too.

Ok, I have no idea, just posting what I found.