ok guys after 4+ years of running 12-14 psi boost on bone stock engine, i had some problems with my 93 fox. engine would over heat even though i have cometic gaskets. it had low oild pressure at idle.i also noticed why there is so much blow by from my breather when i snapped throttle. so to figure out why its over heating, i found #1,2,3,4,5,6 had 155psi compression. #7 and 8 had 125psi. also found during leak down test #7 and 8 had about 70% leak so i figured it had bad rings so engine need to be out for a rebuild anyways.


this is what i found when i pulled pistons out,enjoy:

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i couldnt believe engine had no noises what so ever. in fact right before i took it all apart, i did 1st,2nd,3rd gear pulls under full boost to make sure it over heated under boost.
# 5,7 and 8 had busted pistons due too extreme pressures in cylinders under boost.seems like too much pressure pushing against rings caused ring grooves to just let go. whats amazing is #5 still had 155psi compression ! only 7 and 8 had low compression(125psi)
BTW i found head gaskets were all intact with no signs of detonation at pistons,gaskets,spark plugs,etc. it seemed like under stress block was twisting ,causing head gaskets to leak compression into cooling system.also i pulled main caps off and noticed crank walk at second and middle main cap.seems pretty hammered.

all in all i couldnt me happier. iam glad it lasted that long especially i am really hard on the car. i believe if iam gonna baby it, then might as well buy 4 cyl!!! i had fun with this engine plus it gave me a reson to go to 351 or 351 based stroker.

 

You ran comentics head gaskets, when did the overheating begin? I ran cometics and it leaked from day one of seeing boost. This seems to be a common thing for these type of MLS gaskets to leak. Did you coat them with anything when you put them on? Did you use heads studs?

The motor looks like it did a nice job of holding up to a pretty good beating.

 

i replaced head gaskets with cometics one when stockers blew and i lifted heads under boost. at the same time i installed arp head studs and torqued my heads at 95/100lbft. i did not use any spray and just cleaned deck and heads with green gasket cleaner disc with die grinder. this way i ran 55mm turbo for 2 years and ran 10psi all the time.

last year i went to 70mm turbo with 10psi boost. of course bigger turbo is shoving lots of air volume even at 10psi compared to 55mm turbo 10psi.BUT as we all know boost is addicting so mid summer last year i decided to up the boost to 13-14psi. boy was it fun while it lasted!!!! tires always screamed in 3rd gear while doing 100km/h. by the looks of it seems like block was under MAJOR stress when boost came. poor hyper pistons just couldnt keep up to cylinder pressures above rings. mains were walking.figured once at peak torque ,block was twisting causing head gaskets to leak.

 

Man that's a testament to the venerable 5.0L HO motor! Thanks for sharing those pics!

 

Interesting posts, nice one

I know the 302 is weak in the grand scheme of things, but shit, there not many compact/cheap/common engines that can take such a beating when bog stock.

With the right tune they great value for money if you keep the internals stock

 

to be honest i was really surprised how engine looks internally. cylinders still have nice criss cross pattern. i bet if the engne had high volume oil pump ,bearing would have lasted me a long time.also if it had factory forged pistons instead of hypers,i could have gotten more out of it. like supernatural said its all in the tune. AFR was at 11.6-11.8:1,total timing was 18*, but boy this engine have seen lots rev limit rpms.
only thing that i do regret is not taking the car to the track with bigger turbo.

 

Same exact thing happened to my '93 pistons. The engine ran just fine, but under boost, it would blow white smoke out the exhaust. Once I saw this, I knew something was wrong. Put in some factory forged pistons and hope for the best.

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man that is amazing that 5 did not have ow compression. that is truly a show off the versatiity of the 5.0. thanks for sharing

 

mine had no smoking issues what so ever! keep in mind i was debating to just replace head gaskets initially and run another summer. only thing that directed me into total tear down was 1) low oil pressure at idle 2) noticed blow by @ breather when i snapped throttle. i mean yes 2 cylinders showed low compression but they were still within 30psi then the rest of engine! i have ditched 302 all together and looking for 351 block now.figured might as well put stronger block and stroke it rather to invest in weaker 302 block.

no problem. 5.0 are really strong engine doesnt matter what ppl say.i work for local honda dealer up here and a honda engine can never take that much abuse as much as my car have seen in the past 5+ years of boost. when i turboed my car everyone thought it wont last a year but here iam after 5years with broken pistons which i totally admit is my fault of increasing boost as i simply wanted more out of it . OR maybe i was just looking for a reason to upgrade to bigger engine!!!

 

Either way now you have a good excuse to build a motor to handle he big boost