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Discussion Starter #1
we have an '88 SC Lemon's car and we just about blew our engine at the 6.5hr mark on Saturday. Rod knock on #1. we're trying to understand what happened.

We had just rebuilt the engine prior to the race (rings, bearings, etc..). it was running fine all day. we were trying to keep the rev's below around 6500 but of course there were some excursions to redline.

my teammate (who has built engines before) doesn't understand what the failure mode might be. on other engines w/ bearing issues they tended to fail immediately, not after 6hrs of racing. he was thinking it was oil aeration because he was randomly reading another forum where an LS engine was consistently dying after 6-8hrs due to air getting in the oil and decreasing the effectiveness of the oil film on the bearings.

my question to the ITX racers is do you run an accusump, how much oil do you use, and have you ever heard of such a failure mode?

the engine is stock SC internals w/ a JDM SC (10psi vs. 8psi) and machined block / head for flatness and to get the compression up from 8:1 to around 8.9:1. otherwise stock.

any suggestions would be great as we're pretty disappointed.

1,277 Posts
There is a lot of things that result in the rod bearing failures. Some of them are pure mechanical that without some coin you are not going to fix. It is why there are more than one aw11 teams out there with “rod” in their team name.

A few of the things in no particular order.

1. Too much oil gets to the head and not in the bottom end where it is needed.
2. Oil has issues returning back to the pan. This is why on the small port motor they added a rather large line connecting the head to the block to drain.
3. The oil passages on the rod are not centered on some, and this causes a slight twist
4. The factory clearance is a bit tight, increasing clearance without doing something to increase oil pressure will make matters worse
5. Oil temp plays a huge role in the protective properties. The cars are known to run very high oil temps. To the point that a 50wt oil is actually something less than 10wt.

These are the biggest things that I know that cause failures. It is why that it is not an instant failure. I have rebuilt maybe a dozen 4AGE’s by now and I have seen probably half of them with evidence of a rod spun bearing.

I run an accusump on my car because of my favorite track (Roebling Road Raceway) has quite a few long high load right hand sweepers that hold the oil away from the pick up. I also like the pre-oiling capability.

So on my lemons car here is what I have done and will do to help the situation out.

1. Debur what I could in the head to make sure the oil is not seeing additional restriction. This includes trimming the head gasket as required.
2. Shimmed the oil pump to increase the oil pressure
3. On the IT cars we removed the factory oil sandwich plate. The lemons car for cost reasons we are keeping it. I shimmed that to increase the oil flow to the motor and not back into the pan.
4. Going to install a oil cooler I got from an RX7 in line after the factory cooler
5. Keep the RPMs Down. We have seen a direct relation with RPM and oil temps. Sometimes it is rather drastic results (~30°) just by lowering the shift point 1k rpm.
6. The car will probably get an accusump later. I have one, just need to get the line which costs money.

Thinking about accusumps, the last race we were at the pressure relief valve randomly failed while the car was sitting on jackstands and I my wife just happened to be sitting and watching us work on the car and she saw it squirt out while we were under the back of the car. It was not even running!

Premium Member
3,509 Posts
I never had an issue with my '85 ITA car (4AGE engine), but my '91 ITA car (5SFE engine) has had multiple rod bearing issues. I installed a 2 quart Accusump after the first one. I'm convinced that the Accusump pumping that additional 2 quarts into the system after the rod failed added to my engine fire (hole in the block, oil sprayed onto the headers).


I also had issue with too much oil in the head when I was running the high flow oil pump, so I drilled and tapped the 6mm oil passage between the block and head with an NPT allen head plug that I drilled to 4.5mm
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