quick question, this has been driving me nuts, iv read all i could and still didnt find an answer!

Is the l98 In the 91 Corvette a two bolt main or a four bolt main?

Also how much horses can the factory engine take before being pushed too far

 

2 bolt.

nitrous shot?

 

ya thats actually one of the things that i thought about

 

4 bolt splayed > 2 bolt > 4 bolt oem



Correct me if I'm wrong, but this whole 2 bolt vs 4 bolt is way overhyped.

 

Iam sure its 4 bolt main and 1-piece rear main seal, but not splayed thats for sure, someone correct me if iam wrong. stock bottom end will ewasily handle upto 400Chp, with all stock cast internals. Upto 100 shot will esily handle on stock engine assuming its healthy, 150 with timing retard, fuel pressure bump to some more if u have AFPR otherwise add some race fuel, 1-2 step colder plugs and spray in 3rd gear (auto) not at launch.

I assume its a low mileage otherwise may be 75-100 shot.

 

 

Well as they say(I`m not sure who they are)a picture is worth a 1,000 words.

 

A factory 4 bolt main is most definitely stronger than a 2 bolt main.

 

I have yet to see an l98 4 bolt main block. I have never owned a 4 bolt, only 2 bolt mains. I occasionally install studs in them, but have had no issues running them. Best et on my car was 10.97 with a 150 shot.

 

i know i had a choice on my 400 to go 2 or 4 bolt, they say on the 4 bolts, the end 2 bolts go through the "thinner" part of the block, making the 4 bolt main more vulnerable to blowups than the 2 bolt, i went with the 2 bolt, never seen one "blow" in that way in 30+ years though.

 

Many racers consider around 500HP to be the absolute cut-off point for two bolt mains. And that's assuming a well designed and built engine, aftermarket cap hardware and that you won't be revving it to the stratoshere. If you feel you need 4-bolt or just want the extra margin of safety, simply have splayed caps added, unless you run across a good deal on a four-bolt block. If you're really building seriously, splayed is of course the superior design of all of these choices.

 

If you really need a super strong block for l-98 and nitrious GM makes the 1-piece rear seal, splayed main cap Sportsman Bowtie block If you figure machine work to rework your stock block there not that bad of deal.

 

Is there any issue with the non-splayed 4-bolt breaking at the block webbing due to the holes being too close together? Or is that just some ill-conceived rumor?

 

Any links to this block? Want to read about it?

 

There are no 4 bolt L98s made.

 

L-98s are 2-bolt main blocks. Myself, I wouldn't worry about 550-600HP NA with a 2-bolt block. If it had good parts with a good balance job, and of course, machined and put together properly. I think with a big shot of NO2 or a Blower/Turbo, I'd do the splayed mains. JMHO

 

For some reason, factory 2 bolt main blocks seem to hold remain straighter (main saddles) over time, as compared to factory 4 bolt blocks.

 

Not on a 350. Only the 4 bolt 400's had any problems cracking the outer holes.

On a continuing note about how much HP a stock 2 or 4 bolt block will live to:

Sometime ago in the late 70's to early 1980's we ran stock 4 bolt 010 prouduction 350 blocks (and factory GM steel cranks) to eventually well over 650hp and 7000-8000 rpm in our late models with out any problems.

About 5-6yrs later when the raised runner 867 heads came out the Hp went to over 680 and the cranks started breaking. Of course we were using the very heavy Carrillo rods with the huge "winged super speedway caps" on them which contributed to some of that I'm sure but the stock 4 bolt blocks were still doing good (which was good for us as we got a weight break for running under 362 inches, Rodeck/Donovan blocks were illegal and astronomical $$$ wise, Bowtie blocks were expensive and required alot of machine work to prep as they came from GM with 2 bolt caps at that time). We upgraded cranks to BRC 4340 cranks (still standard weight 52lbs) and got by with the stock 010 4 bolt blocks (with careful machining and blue printing) until the Dart Buick heads arrived and once we figured out a camshaft and port package that was pushed 700hp... well then we started having bad main cap walk problems with the factory 4 bolt blocks and caps and had no choice but use the Bowtie block with splayed caps.

Now the last time we built a real racing engine with a prouduction block was nearly 15yrs ago. Really light weight steel rods and 30lb cranks didn't exist at that time and by the time they did (Crower was one of the first in the 1990's) we had already moved on from building small 4 inch bore motors anyway so stock blocks were not an option for us anymore.

But I do have a very old 331 inch Comp Eliminator motor still running. It has a stock 4 bolt 010 prouduction block and is pushing 700hp with no problems, but its a short stroke, alum rod motor and dosen't run for extended time like an oval track engine.

We never built any real high HP oval track 400 block based engines. I have built a few "budget" 421 and 434 inch bracket motors for people and limited them with heads and camshafts to about 600hp using stock 2 bolt 400 blocks and main studs. The first one of these stock 400 based engines I ever built broke the main caps in half and lost oil pressure after a few dyno pulls in the 720hp range... we learned our lesson in a hurry on that one.

Stock 350 2 bolt blocks are indeed good to around 500hp with main studs and good machine work. Converted to billet splayed caps they would be good to what ever HP you could make with a small bore engine IMO. I've seen a few turbo motors go past 900-1000hp for short peroids of time, I even know a guy with a Littlefield 14-71 on top of a converted 350 2 bolt block I did for him in his mud rail. Of course at that level you really should be buying the best stuff you can afford but hey you do what you can do.
Will