paulmoore

Well, what can I say? It is FUBAR. I have been having problems with the fuel mixtures and a lack of acceleration above 4000 RPM. So after some tweaking, I decided to take it for a road test. Got her up to operating temperature and went out for a ride. Still had the no accel above 4000 thing so I decided to turn around and go back home(I was only 2 miles down the street, on a back road) Anyway, I was in fouth gear at about 1500 RPM as I came up to the stop sign. I hit the brakes, clutch in, and downshifted into third gear. The engne RPM's came up to 3000 RPM, then a whole bunch of CLANG CLANG CLANG and the engine just stopped. So I had it flatbedded home, and took out the spark plugs. The no. 4 plug was obliterated! Here is what happened...













So it seems that I didn't have the required piston to valve clearance and the No. 4 piston kissed the valve and bent it. Then on the next upstroke, it hit the valve again, breaking it off where it proceeded to bounce around like a pinball. So the engine has to come out now, and I have to figure out what I want to do for a new powerplant. Hmm, maybe a 383 stroker is in order!!

jonarotz

iTrader: (26)

WOW!!! That is probably the worst piston damage I have ever seen.
Sorry about your luck.

Scania

Sorry to see that, i hope you can get a new engine soon.

sofakingdom

iTrader: (1)

Looks like a typical broken valve spring to me. Pretty routine and ordinary and commonplace, as far as the results of that. Not even trashed TOO bad... I've seen the cyl so badly blown away by the piston pin that the piston fragments wouldn't even come out whole like yours mostly did. It's FAR FAR worse when it happens in a race car motor at speed. Not that the relative lack of severity of yours, matters too much when the block is still lunched.

There wouldn't have been a clearance problem if the spring wasn't broke.

This is why alot of the old-timers around here, will tell people over and over again, DON'T CHEEP OUT ON VALVE SPRINGS. Not that you necessarily did that, although if they're the stock RPM springs, they're just K-Motions, and therefore not really enough even for that POS RPM cam; but in general, breaking a spring is A VERY BAD THING. You don't EVER want it to happen to you if you can prevent it. Here's a textbook set of pictures as to why.

Don't be surprised if your pics get used to show people who are trying to test the limits of springs, why they might want to re-consider that idea.

Sorry it happened to you.

Air_Adam

I must be getting better at this problem diagnosis thing.... I was just going to suggest the same thing Sofa just did.

I was thinking broken valve spring as well, because it just wouldn't make sense to me that you'd have piston/valve clearance issues with only ONE cylinder, when you have the same pistons, valves, and combustion chambers over all 8 cylinders, and the same size cam lobes for all 16 valves. It would be more like, either all the cylinders would have clearance issues, or none would. Not just one.

rx7speed

jb weld and some duct tape you will be good to go
maybe a little coat hanger to hold the piston to the connecting rod your fine.


also just out of curiosity how abnormal is it that you can open the valve on a head by hand pressure alone?

88 Z28 Guy

iTrader: (1)

Damn that sucks. Ive seen way worse but it still sucks.

IHI

iTrader: (1)

I've seen a few valves pop the bottoms off from having undercut stems with higher spring pressures and also due to inadequate spring pressure causing valves to bounce in the seat, also seen a few hollow stem valves pop the bottoms off as well from both above mentioned criteria as well as just poor valve design in a race application.

While it looks bad, and is bad for that matter since your out an engine, i've seen much worse carniage from the same culprit.

84z28350

bah, what are you talking about...

It looks perfectly fine to me, that will buff out...

SaintedCorrupt

That just means you have a low resistance valvetrain. I wouldnt worry about all the valve bouncing or inevitable eventual fraggin youre going to get down the line.

rx7speed

how long should this fragging take though? it's been like this since I have owned the car so at least I would say 10k miles or so with a few spurts up to around 5500rpms.

slohand

YIKES!!

That R E A L L Y sux. may we now pas the plate.

but, praise the car gods!! i just lost a valve spring and by luck i was doing about 40mph when it went. turns out the valve didn't bend and the piston just has a few "clean" place where the valve was bouning off of it.

this was a crate from scroggin dickie and only has about 30k on it. i called a tech and he claims they don't have a problem with it so go figure. anyway, had the spring back in for a couple of days now and she runs fine again.

strange thing is the car wouldn't idle before and now it does. ???? makin me wonder how long this thing has been going bad.

good luck with the repair, may you have fair weather and a winning lottery ticket.

mw66nova

iTrader: (13)

hey paul, i have 8 of those exact pistons in a .060 over if your lookin', lol!!!

Mcdamit

save what u can u still got a good cam, assuming its roller good lifters and rockers.. and one good head..lol

RWB____s

I can relate to your anguish. (Dead Valve Springs) Same thing happened to me but at 6000+ rpm! Destroyed the block(Piston and Rod went "thru" the cylinder) Destroyed the heads beyond repair.

Token

Oh, that'll buff out

Demon355

iTrader: (1)

lol @ RWB, I saved that picture.

paulmoore

Well guys, I appreciate all the kind comments and offers for parts but I have some good news. No, I didn't save a bunch of money on car insurance by switching to Geico(they are already my carrier ) Currently, I am having a 383 short block being built right now. It will have a 4 bolt main, Eagle forged crank, Eagle forged SIR rods, and forged Mahle pistons with file fitted rings, COMP cams XR288HR-10 camshaft(.520/.540 @ 236*/242* hydraulic roller), double roller timing chain with the cam degreed. On top of it all there will be a set of AFR 195cc street heads, 68cc chambers(10.3:1 compression) Edelbrock Performer RPM Air Gap manifold and 750 CFM carb(not sure if I am going to keep the Edelbrock carb or ditch it for a Holley. Anyway, almost EVERY single 383 stroker kits that I have seen that use the AFR 195 heads and that particular COMP cams camshaft with 9.5:1 compression is making in excess of 500HP/500TQ. Realistically, with all the accessories that are hooked up to my motor and parasitic looses in the drivetrain, I am hoping to get 400RWHP/400+RWTQ. This should be easily attainable, be streetable, and hopefully reliable. I want this new engine to be bigger and better than the last one!!

mw66nova

iTrader: (13)

just my opinion, go with the holley, you won't regret it.

rx7speed

why not the 215cc head? or at least if I remember right that is the size. the next size up

Rob Wade

Don't take this the wrong way.......nicely done!! Anyone can spin a bearing and stuff, but it takes a mans man to fubar one that nicely! LOL

paulmoore

rx7speed wrote:Because I am buillding this motor for torque. For maximum torque production, you need to have port velocity. The 195cc runners will give plenty of port velocity to keep torque production up, and will do it at a relatively low RPM range. Let me see if I can find the dyno chart...

383 cid Small Block Chevy Package
AFR 195cc Street Heads
9.5 to 1 Compression
1 3/4” Headers
AFR FloPower RPM #5028 and 0-4779 750 cfm Holley Carb
Comp Cams Hydraulic Roller Cam #12-433-8
MSD Distributor 36° Timing
93° Octane Pump Gas

THE DYNO CHART FOR THE 383 IS THE ONE ON THE LEFT!!!



I'm not looking for peak numbers either. What I want to do essentially is build the engine to make as much torque as possible at the 5200-5300 RPM range. The reason why is because...

Torque x RPM= Horsepower
5252

So, if I can make 500 foot pounds of torque at 5252 RPM, then I will have exactly 500 horsepower at the same 5252 RPM. Now, take a look at the 383 dyno chart again, looking specifically at the torque made at 5252 RPM. Do you see how the horsepower line intersects at the EXACT RPM? And then look at the numbers it is putting out.

VILeninDM

Torque x RPM= Horsepower
5252

So you are saying you want 500 ft-lbs at 5200-5300 rpm only because then you will have 500 hp. But if you go up to 6500, you can make 619hp with the same torque.

rx7speed

I am curious on one thing. what the heck was the point of trying to teach me the math to figure out horsepower? I'm still trying to figure out what the point of that was and have been since last night. I know you want low end torque thats fine, I know you want to go fast that's fine. but what does that have to do with (tq x rpm)/5252. only reason I can see that is because you want the same horsepower as you do torque but why?

plus with that larger cam and evrything else (other then the compressionw hich seems a tad low IMHO) I would figure a little larger heads wouldn't hurt. but then again I admit I'm not that well versed on AFR products other then most seem to really like them.
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or if you moved the peak horsepower of 500hp down to 1500rpms you make 1750lbs/ft of torque

paulmoore

Well, my main concern is not having to spin the engine up to 6000+ RPM to get the power that I want. Yes, I COULD spin it up to 6500 RPM, and make more horsepower, but how many times are you going to go full throttle on the street and hit 6500 RPM? The only reason why I even brought up the formula was for a comparison, just to show that the numbers were the same at 5252 RPM. Personally, I'm happy with making 500HP/500TQ. And because I know how things work, I can make that power safely at a relatively low engine RPM. This is going to be a street engine, in a street car, and I am willing to sacrifice the extra power I could have got from revving the **** out of it. I feel that limiting the engine RPM to say 5500 will still give me plenty of power, yet still be completly reliable for everyday use. I am looking at this from a longevity standpoint as well.

rx7speed wrote:I'm not going to change camshafts. Almost every single 383 stroker is using this camshaft, and putting out good numbers. Also, the actual compression on my engine wll be around 10.2:1-10.3:1 which I don't think is low. The 9.5:1 compression that you see on the info for the dyno chart is on that particular engine, not mine. Larger heads(210-215cc) would yield a higher overall flow number for the given engine combo especially since it will have more cubic inches, but the immediate tradeoff is that I woudn't make any decent power until 6000 RPM or higher. I am not willing to spin the engine up that high. This is mainly due to the loss of port velocity and lower engine speeds. Torque production drops off until the engine speed increases to where port velocity reaches its peak(usually that point is also the engine's highest VE or volumeric efficiency). That completely shifts that usable powerband much higher, and could possibly make the engine not want to work on the street where acceptable power levels at a lower RPM are required.

On a side note, I don't want you to think that I am trying to *TEACH* you anything. The only reason why I stated the equation earlier was to show the direct correlation between TQ and HP at 5252 RPM, and that if someone built an engine for peak TQ at 5252 RPM, then the HP numbers would be the same. That's all that I was trying to say.

five7kid

iTrader: (14)

Pic links have died.

paulmoore

Ok, well then I guess that I could upload my limit of 3 then...

TigerZ

daaaamn

that sucks man

i hope you got something to drive in the meantime