RacePro Engineering

This was our first high-speed testing session of the 1987 coupe which we are building for road racing. Here are the pertinent facts:

72,000 miles, basically stock L98, no leaks of any kind, fresh Mobil1 and K&N filter, good compression across the board, TPIS intake, 2.5" straight pipes from the manifolds back, Sunoco 112, air pump and air conditioning compressor removed, vaccum and smog hoses terminated, Doug Nash 4+3 still present, no dry sump or oil cooler yet. Ambient temp 65 F; Water temp 205 -215 F; Oil temp +/- 245 F. Top speed on the track +/- 130 mph.

There were no symptons prior to blow up. I had just exited a fairly fast right-hander, and was changing up from 3rd to 4th. Strong torque through 3rd gear, suddenly NOTHING in 4th! It was then I noticed a white cloud forming off the tail. I coasted off the side of the track immediately, and the "white fog" was still billowing from both tail pipes, and a very slick water/oil emulsion was dripping from under the rear of the motor.

No, it will not turn over. No, we have not yet removed the head.

Opinions please! Is this as bad as it appears? Worse?? Anyone else have this type of SUDDEN FAILURE with an L98? All opinions, observations, personal experiences, and recommendations will be sincerely appreciated.

Ed LoPresti

Slalom4me

Sorry to read about this mishap.

White smoke generally means coolant.
Stock L98 means hypereutectic cast pistons
1987 means aluminum heads
Mods like TPiS intake (which: MiniRam? or their base and runners for TPI?)
and open exhaust mean that chip tuning has or should have
occured.

Could the driver have discerned any unusual noise immediately
before? Was there a big clatter after the loss of power?

My vote is detonation or head gasket failure. Hypereutectic
pistons do not withstand detonation well and will essentially shatter.
Gasket failure due to galvanic corrosion is en established flaw
in Al-headed L98s.

If there was no clatter after the power loss I'll guess this is a gasket
and that the engine has hydraulic-locked from coolant in the cylinder.
Don't try to turn it over with the plugs in place - pull them, turn it
by hand and watch fluid spray.

If there was clatter, my guess is detonation-related piston failure.
Obvious signs are ventilated block and/or oil pan. The engine may
be locked because a rod is wedged somewhere.

What max RPM was being used?

A bent rod picture posted by 62Jeff. (Background here)



.

John Shiels

could have popped after the corner from oil startvation Plug plags and turn by hand after that pull tha valve covers. Doesn't sound good in any case. 4 years ago I was exiting a tight left hander and mine popped shifting to third. Small rumbule total wreck. Engine, tranny, diff. wiped. No oil on track either but it did stop fast as all locked up.

John Shiels

could have popped after the corner from oil startvation

ghoffman

Well it is almost 20 years old, and L98's don't rev anyway. This sounds like a good excuse for a new crate motor with 2x more power and less weight.

TRACKMAN2

I Trackman Being The Undisputed Champ Of Blowing Motors In Into Tiny Little Peices Guesses That A Good Old Fasion Rod Broke And Caused A Blender Type Thing To Happen Inside You Motor. No Warning Meant Good Bearings Just Broke I Bet You Had Good Oil Pressure At First Then It Slowly Crapped Out..try Victory Racing Engines I Allway Wanted To But Never Got The Chance.. They Are Nice Folks....

Solofast

It done blowed up.... take it apart and figger it out...

All of the armchair quarterbacking won't bring it back, or help you figure out what done it in till you take it apart...

larryfs

white is coolant, and it sounds hydro-locked now.
But white from both tail pipes...... that's a good one.

Slalom4me

Vetracr

Um, lets see, 245 degrees oil temperature. Bearing temperature 300+ degrees = BANG!!

When I blew up my stock 90 L-98 at the track I never heard a sound, just a black flag for smoke. Broke ring lands on 4 GM junk hypereutectic pistons.

Postulating what happened won't help. Pull it apart and find out. Whatever it was, it won't be good.

Larry

larryfs

why do people think bearings melt at 300degrees?????
The combustion chamber temp is well over 1500 degrees !!!

RacePro Engineering

Slalom -

The TPIS is a mini-ram. There is the funny thing: there were no unusual noises before, during, or after the white fog! The motor simply had no power going into 4th, then stopped.
Naturally, we too are leaning toward head gasket failure, and your post helps confirm that.
----------------
John -

As you and Slalom suggest, we shall remove the plugs and turn it over manually. There are no apparent holes or cracks in the block or head, so we are hoping this failure was much less catastrophic than yours, although the circumstances sound frighteningly similar!
----------------
Gary -

The crate motor solution certainly sounds like the least complicated way out. It's just that we were hoping (fanticising) about the "$500 magical fix".
----------------
TrackMan -

Thanks for the Victory Racing Engines suggestion - is there anyone in particular there with whom I should speak, and do you have a telephone number or eMail address?
----------------

Our primary reason for asking for feedback BEFORE tearing into it is that we are new to Chevy engines, and did not want to bypass any steps which might provide a clue to how this happened, and (more importantly) how to prevent it in the future!
In that regard, your observations about the piston material and construction, as well as the head gasket weaknesses are very valuable points!

All other thoughts and observations will be welcomed.
Ed LoPresti

John Shiels

To the below add a diff and tranny ruined how bad could one's luck be it one explosion
55,000 tortured miles video was running when I looked at it. I didn't even get mad after all I did to it. Ed get wrenching so we all know what happen.
http://shielsmasonry.com/enginefailure2.jpg
http://shielsmasonry.com/enginefailure3.jpg
http://shielsmasonry.com/enginefailure5.jpg
http://shielsmasonry.com/enginefailure8.jpg

Slalom4me

I asked about the intake out of curiosity about RPM capability,
a MiniRam would certainly allow the engine to rev above the
prudent limit for a stock L98 bottom end.

No unusual noise throughout the incident is a good sign.

Headgasket failure seems to be an issue that creeps up and
announces itself with symptoms well beforehand rather than
breaking down the front door. Chronic unattributed coolant
loss, blowback out of reservoir, bubbles at rad cap, 'chocolate
milk' in the sump. Any of this sound familiar?

Here are threads with pics$500 solution? - hmmm, maybe. The L31 Vortec engine used in pickups
and delivery vehicles in the late '90's is very similar to the L98,
with the main exception of the need for an intake suitable
to mate to the different heads.

I think a resourceful group could scrounge a suitable L31 and
have it operational for not much money, it would do for testing
and learning more about small block Chevys. Many parts would
transfer over from the L98.

Have a look at this thread. It starts slowly but then builds
toward info that may be useful to you if locating an inexpensive
'mule' to see you through the rest of the season is on the agenda.

L31: Flat or Roller Tappets from GM?

To keep it lo-buck, reuse the L98 heads if possible or install some
iron junkyard dogs until you build the dream engine.

.

varkwso

[.....
All other thoughts and observations will be welcomed.
Ed LoPresti[/QUOTE]

I love this armchair QBing on someone elses broke stuff.

Did your oil level increase? Bad sign. Does the oil look like a frothy milkshake? Bad sign. Water from any plug = bad sign. Is there oil in the radiator? - You guessed it bad sign.

I have been the demise of more than my share of engines - most go out with a whimper - it is almost anti-climatic in most cases. I am guessing yours is in need for an overhaul - you can start by pulling the heads (and being really lucky it is bi-lateral head gaskets) or cut to the chase and pull the engine.

let us know the results - most of us here have felt that old familiar pain in the wallet also!

DOCTOR J

FWIW

As previously mentioned, GM had issues with the gasketing on early aluminum-head
engines. If those gaskets gave ~20 years of service, I'd guess they had gone some past
an optimistic life expectancy. If they are all original parts there are other critical items
that are also a decade or more overdue for inspection:

1. fuel pump
2. elastomer fuel and coolant hoses, vac lines; diaphragm in fuel press regulator
3. timing set

Also, the ECM was originally mapped for a low-rev, intake-limited L98 operation. With
the intake and exhaust system changed, one would expect the engine is seeing much
better cylinder filling, especially at high revs. If it hasn't already been done the fuel and
spark maps need checking - especially above ~4.5K rpm.


In terms of fuel and spark control, the later 727 ECM has been configured to work up
to ~8K rpm:
http://www.thirdgen.org/techboard/di...ve3-patch.html
http://forums.corvetteforum.com/show....php?t=1286666

If you are comfortable with computers and wiring, some people have also moved
up to sequential injection on a traditional small-block platform using an even newer
PCM model:
http://www.thirdgen.org/techboard/di...ion-gen-i.html
That happens to be a truck PCM however, so I don't know off hand how high the
tables go in the rev band.

In terms of repair, seems to me a GM Performance Parts ZZ4 short block was selling
for only a couple of $thousand. IIRC that comes with 4-bolt mains, forged crank,
and improved rods - check their web site.

HTH

RedHotBolt

Ed,

If I was closer I would trade hours of motor building for LoPresti Piper parts!


Just incase you guys don't know, LoPresti IS the name of Speed......in the air anyway.

Jerry

Don Keefhardt

If a rod is sticking out thru the distributor, then the problem is 'ignition'. If it's sticking out thru the oil pan, then it's 'oil system'. Beyond that, you're on your own.

Why so much octane in what is basically a stock-ish motor, compression & timing-wise ?

Longer burn times make everything hotter.

Vetracr

Bearing babbit material is a lead, copper, antimony, etc alloy material. These are all SOFT metals with low melting points. One reason bearing babbit is soft is to trap any tiny particles in the oil. Its a better option than scratching the crank. Look at the bearings on even the cleanest racing engine after a little use and you'll see inclusions in the bearing surface. In answer to your question, combustion chambers are cooled by water, aluminum is a very good conductor of heat and aluminum melts at a lot higher temperature than babbit. Bearings are ONLY cooled by the engine oil and they are hot. The 250 degree oil in the pan is 50 degrees cooler than the oil that has been compressed in the pump and is now being forced through through a .001-.0015" bearing gap. Read Smokey Yunicks engine secrets book. Its worth the read if you build engines.

Larry

gonzalezfj

All true, BUT... modern engines don't use babbitt in the bearings. According to GM Powertrain, the maximum allowable oil temp is 340 F for the LS series engines. Don't know the alarm settings for other versions of the LS family.The high oil temp alarm is set at 320 F in the LS6 and LS7 (C5Z and C6Z respectively).

Compressing the oil (or other liquids) does not significantly increase its temp. Gases increase in temp according to: PV=1/2 NRT. Higher pressure (P) results in higher temp (T) if the other variables remain fixed.

Frank Gonzalez