Dr Jekyll

Hello all, I recently had the Vette at the local Chevy deal for a new oil pan gasket. I asked the Technician to let me know was this a 2 bolt main or 4 as I have read everywhere L98s were all 2 bolt mains. He calls me back when he has the pan off and said it has whats called a "main cap" on it and a deeper pan to allow room. Ok speak english please. In a nut shell the original owner had this installed to take the L98 from a factory 2 bolt main to what amounts to a 10 bolt main. He explained it to me like this. A way to make a 2 bolt main block even stronger than a typical 4 bolt block is to use a "main support". This is a brace that bolts across all 5 main caps, thus tying them all together and creating a 10 bolt main engine. The theory behind this is simple, if one main cap tries to walk, move, flex or come-off, it has to take all of the others with it at the same time because they are all inherently attached to that main support. It disburses the load across all of the main caps evenly. One can't move or come out without taking the other 4 with it because the brace ties them all together. He believes the original owner had big plans for this car but never followed through. So cool for me my lower end is stronger then a 4 bolt. Other then that mod he found nothing else on the engine to suggest its other then bone stock. Anyone ever heard of this being done? I'm please because I have plans to supercharge this car next month and was concerned it would come apart and could only run 8psi now I think I can push the limits. The GM tech agrees. He also added that he has indeed seen L98s with 4 bolt mains. There are freaks out there. Two ways to know 1st run your casting number through a dealer and 2nd if it comes back as a 4 bolt pull the pan and eyeball it. Who knows some of us could have a freak. The real difference when speaking of a stock L98 NADA ZIP ZERO unless you plan on building it.

five7kid

I was under the impression C4 L98s were all 4-bolt mains, with exceptions that got 2-bolts. But, I could be wrong.

You can't tell if a block is 2-bolt or 4-bolt by the casting number, because 2-bolt or 4-bolt is a machining/parts difference, not a casting difference. They made both from the same casting #s.

If it has a main cap girdle, most likely it has main studs, both in the direction of goodness. It could be argued that factory 2-bolt main blocks are stronger than factory 4-bolt main blocks because the extra two side bolts remove material from the block main bearing webbing, making them vulnerable to cracking. Aftermarket splayed 4-bolt caps solve that problem by putting the bolt holes into the meat of the webbing, and are usually steel rather than cast iron like the factory.

I don't have any direct knowledge/experience of main cap girdles and the power handling capability they provide (probably moves the failure point to a different part of the factory block), but I would imagine your engine's PA limiter would not be the 2-bolt main caps, even without the girdle.

DMITTZ

Its cool that a P.O did some upgrading on the bottom end of your motor.

I would still be concerned about how well the factory pistons and to a lessor extent connecting rods will hold up to 'pushing the limits' of F.I

Maybe the previous owner upgraded the pistons when they put in a main stud girdle, who knows?

Another thing to watch with F.I is piston ring gap if your going to be pushing the limits... I think usually dedicated F.I engines run a larger ring gap (with forged pistons), but I will defer to other who know more about F.I on that point...

If it were me I would be a bit cautious not to run to much boost until I had prepped the motor for it, IMHO.

Best of luck on the F.I upgrade hope it turns out well regardless what boost you decide to run.

WVZR-1

OP - If this build actually has a "girdle" it would be I believe almost mandatory to do a P & G check to see just what the cubic inch is. It would seem odd that a PO would do only a girdle. Maybe inspect the cylinders with a bore-scope and see what's visible there and check all casting information on the cylinder heads and block.

There should be several facilities that can offer P & G.

If you're unfamiliar, some info:

http://www.precisionmeasure.com/test1.htm

If you challenge a seller of a "big bore/stroke" advertised combination to a P & G before buying, if it ain't he'll turn "beet red" and RUN. If he doesn't then he just don't know and is stupid OR maybe it really is ...............

You likely didn't see it either so ........ maybe you've been "storied".

DMITTZ

Actually using a bore-scope, to determine bore/stroke and maybe see if any of the other internals are upgraded is a good idea. Certainly would be nice to know exactly what your working with before you try 'pushing the limits' of F.I

WVZR-1

Bore-scope only is used for visuals. Does no dimensioning! Without a disassemble a P & G is the only way to check CI. I have no idea what it would cost today but in the '70s we saw a P & G very often. You win and it was mandatory.

five7kid

I must be missing something. Why would displacement be a concern in this case? Are you thinking he was sold a C4 with a 305? I don't see any claim for it being big stroke/bore.

DMITTZ

Sorry, I did not mean to spread confusion, based on the above info I thought that WVZR-1 was saying that in addition to checking internals, bore scoping can check dimensions as well, that way you would know if the P.O had bored/stroked the motor when they did the work to the bottom end... I obviously misunderstood.

But having a bore scope done to see if any of the other internals have been upgraded still sounds like a good idea, as long as it's not too pricey, that way you would know if you already have upgraded pistons etc.. since the P.O obviously did some bottom-end work to the motor. If you can determine exactly what you have you will have a better idea of what the limits of the motor are, just my thoughts.

Chris Nieves

I am pretty sure they are all 2 bolt main's from the factory. I've only seen factory 4-bolt mains in trucks.

I have had a splayed(original 2 bolt main that has new holes drilled for the outside bolts at an angle for more clamping force in conjunction with aftermarket main caps) 4 bolt main 357 with over 800RWHP that was pulled apart after 5000 miles and was doing great. This setup is stronger than factory 4-bolt main blocks.

OP, any pictures?

WVZR-1

No I didn't BUT if the PO went to the expense to do a "girdle" it could certainly be something greater than the 5.7 also. I also mentioned the OP being "storied" by the GM tech which sounds more likely. I doubt there a way to "as the OP mentions" include the #1 and the #5 main cap into any type of a 10-bolt girdle.

The tech's wandering the shop and look what I told this guy!

I get the splayed etc. no problems BUT if the OP believes the tech then ..

Dr Jekyll

Thanks for the input guys, As to a picture no I wish I had now with some of the comments. I did notice a drip on the garage floor this morning so I will be taking it back to be looked at. If they pull the pan again I'll be sure to snap a pic of the "main support" As far as a P&G goes I'm not wasting my money on that. I am planing on doing a compression test this weekend if it comes back anything other then the stock specs I'll consider it for sure. I have owned many 350+hp cars and this Vette doesn't have the pull of those cars so my gut tells me its just a plain stock 240hp. All numbers match on this car its not a swap motor or a 305. Now as to being "storied" that's laughable. I seen the "main support" with my own eyes and it does in FACT include the #1 and the #5. Do some research you might well learn something new...I highly doubt the GM tech who has been working on my 2011 Camaro SS and Tahoe would suddenly decide lets screw with this great customer and risk his reputation and career. I am inclined to believe the factory trained GM Technician with 20 years on the job. But thanks for your input just the same. I'll post some pics of the Supercharger install and the dyno pulls before and after. Thanks again for all the comments.

WVZR-1

I'm quite familiar with HUGHES -

Is the oil pan baffle still used with this product? It's interesting for sure and it would be great if you're NOT faced with having to do another R & R of the pan so that it could be captured in a "snapshot".

It's odd still I think that a previous owner would do this on what you mention is a "numbers matching" seemingly stock build.

Who's product do you believe that yours is? Is yours "studded" or bolted?

*** I actually found a similarly attached 10-bolt girdle on an SBC so it's certainly possible. I can see that it certainly should maybe require likely a different pan. The one I spotted maybe wouldn't but the baffle would have to go away. I have my doubts as to it's effectiveness other than "walk" - it would require very precise machining I'd think to allow proper torquing of the mains and likely specialty bolts OR more practically the use of studs. I don't know that I'd consider it a "value added" but certainly wouldn't maybe be considered a detriment.