Corvette C4 with L98 and flat tappet cam

Joined
Dec 23, 2021
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Hello there!
I'm the happy owner of a 1986 C4 with L98 (cast iron), flat tappet cam, 79k miles and is running fine afaik. I have to change the oil but i'm very doubtful on what should i go for.
I live in Italy so it's not easy for me to get access to spare parts. hence i would like to maximize as much as possible the good state of its engine, starting by putting the right oil. The engine is not stock but modifications should be very light (maybe 10 hp more than stock). I use it for few hundreds miles per year with no racing, just some pulls from time to time.
I know the previous owners run a blend MOTUL 15W40 and a blend 10W40 SN/CF, with the latter currently filled in.

Beside knowing that i should put the oil recommended by the car manual, i know little about this topic. I read many threads on the forums but i'm unable to get to the final point of which one i should go for.
From what i understood i have to look for an oil which has a good amount of ZDDP, saying between 1000 and 1400 PPM. SM and later are no good due ZDDP level around 600. I'm having a very hard time finding any Zinc additive in EU such as HY-PERLUBE ZINC REPLACEMENT, but I instead found the MOTUL CLASSIC NINETIES 10W-30 (spec sheet attached), which is reported to have ZDDP at 1800 PPM, but seems to be too much (btw the MOTUL oil selector tool suggest me this one).

I would like to kindly ask you what do you suggest, and if the MOTUL CLASSIC NINETIES 10W-30 could be a viable solution when mixed with another oil (which one?) to lower the ZDDP levels around 1300-1400 PPM.
Also, can i go for a sythetic oil with cleaning features, or should i stick with blend to avoid engine oil leaking?

On a side note i read about a forum user always using Castrol GTX on its 85 C4 with heavy mods, and racing it hard with no issues after 100k miles, so I could be just overthinking about the oil decision.

Thank you!
 

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Joined
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Those L98 engines used mild cams that pooped out about 4,500 RPM. Any good 10w30 works great in them.
In 1990 the 1st ZR1 engines came out. The car drove similar to the L98 until after 4,000 RPM when it came alive!
 
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I don’t think 1800 PPM will hurt anything, although that‘s close to as high as you want to go. I don’t know a lot about EU HDEOs, but most USA ones don’t even have high zinc anymore.
 

Jackson_Slugger

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Astro14

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I think that Motul is a great choice. You’ve got a limited selection where you are, and the oil was designed for your application, don’t think you could do any better.
 

FCD

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Hello there!
I'm the happy owner of a 1986 C4 with L98 (cast iron), flat tappet cam, 79k miles and is running fine afaik. I have to change the oil but i'm very doubtful on what should i go for.
I live in Italy so it's not easy for me to get access to spare parts. hence i would like to maximize as much as possible the good state of its engine, starting by putting the right oil. The engine is not stock but modifications should be very light (maybe 10 hp more than stock). I use it for few hundreds miles per year with no racing, just some pulls from time to time.
I know the previous owners run a blend MOTUL 15W40 and a blend 10W40 SN/CF, with the latter currently filled in.

Beside knowing that i should put the oil recommended by the car manual, i know little about this topic. I read many threads on the forums but i'm unable to get to the final point of which one i should go for.
From what i understood i have to look for an oil which has a good amount of ZDDP, saying between 1000 and 1400 PPM. SM and later are no good due ZDDP level around 600. I'm having a very hard time finding any Zinc additive in EU such as HY-PERLUBE ZINC REPLACEMENT, but I instead found the MOTUL CLASSIC NINETIES 10W-30 (spec sheet attached), which is reported to have ZDDP at 1800 PPM, but seems to be too much (btw the MOTUL oil selector tool suggest me this one).

I would like to kindly ask you what do you suggest, and if the MOTUL CLASSIC NINETIES 10W-30 could be a viable solution when mixed with another oil (which one?) to lower the ZDDP levels around 1300-1400 PPM.
Also, can i go for a sythetic oil with cleaning features, or should i stick with blend to avoid engine oil leaking?

On a side note i read about a forum user always using Castrol GTX on its 85 C4 with heavy mods, and racing it hard with no issues after 100k miles, so I could be just overthinking about the oil decision.

Thank you!
Luckily for us in Europe almost any A3/B4 oil is going to have at least 950-1000ppm of ZDDP, most are between 1000-1100, which is enough.

I would use almost any A3/B4 5W-40 or 10W-40, i personally have used Total 9000 5W-40 and i liked it plus it's cheap, i think i saw an analysis of it and it had around 1100-1200ppm ish of ZDDP.
 

Jackson_Slugger

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This era of American cars with very few exceptions were not performance oriented. No need to worry about zddp in that engine.

Not that horsepower and the need for extra zinc directly correspond, but that generation 5.7L made about 230HP (a modest amount) but also made 330 FP of torque. Not shabby at all, but not sure high zinc is really needed in that engine nor most engines...
 

LDM

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Those L98 engines used mild cams that pooped out about 4,500 RPM. Any good 10w30 works great in them.
In 1990 the 1st ZR1 engines came out. The car drove similar to the L98 until after 4,000 RPM when it came alive!
Had less to do with the cams and more to do with the long runner design. The intake just couldn't flow the air at higher RPMs. Great at the low end but definitely not great at higher RPMs. I've had my 89 Camaro up above 90 MPH and it pretty much just falls flat on its face at that point. Getting above 100 MPH takes forever.

As for oil, I typically just run 5W30 in mine. Last oil change was with Rotella Gas Truck 5W30. My Camaros sit in the garage all winter and only come out in nice weather so just about any Xw30 or even Xw40 oil will work just fine. I would imagine the original poster pretty much does the same with his considering the limited miles he put on it.
 
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In late model year 1986 the Corvette offered the C4 Roadster; it has the centerbolt "truck" heads which were an improvement.
Not sure if the roller tappets were included...
 
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