I have a 2-bolt main LT1 block that I am converting to 4-bolt main...any suggestions on what type to use??? I have seen Callies 4-bolt main caps, Oliver 4-bolt main caps???

I saw those are SUPER expensive also, so I was looking for a GM part number for some LT4 main caps since they are 4-bolts, but I dunno how much cheaper that is if any...

Any suggestions for me???

Thanks

 

Technicality, but there's no such thing as an LT4 cap... since there's no such thing as an LT4 block. There is a 4-bolt main version of the LT1 block that was used in all the Corvettes, which happened to include the LT4.

All that said, you need to decide if you want the "straight 4-bolt main" conversion, and utilize GM LT1 4-bolt caps, or do a "splayed 4-bolt main" conversion and use the 4-bolt caps from the sources you mentioned, or Pro-Gram. Hard to believe anything from GM would be "cheaper" than the splayed caps you mentioned.

It can be argued all day whether the straight or splayed conversion is the best... depends how much metal get taken out of the block webs by each method, and where it is located. As a point of reference, one of the most powerful LT1 engines ever built was done with a "straight" 4-bolt factory LT1 block. But I'm not sure what caps he used in the 1,125HP application. I'm running the Pro-Gram caps on my 800HP nitroused LT1. The Pro-Gram caps were $182. But you still need an ARP main stud kit, and the special bolts to hold a windage tray, then the added cost of the machine work to fit the caps into the block, drill/tap the extra stud holes, and align bore the mains.

 

I have the GM nodular iron "straight" 4-bolt caps. Last years combo was 733rwhp (M6) and it worked fine. Next year is gonna be 100-200hp more, so we shall see.

Rich Krause

 

Thats what I needed to know!! I figured the GM caps were going to be expensive...I only plan on making about 450rwhp so I think it is still in question whether I even need a 4-bolt main or not, but just to be sure, I am going to spend the extra money.

Thanks guys!!

 

450 rwhp?

I wouldn't worry about a 4-bolt main cap. Especially if that's all you ever plan to do. I'd stay with the 2-bolt and use studs.

Yeah, you're always gonna get less movement with a 4-bolt cap but I don't see that being a necessity @450rwhp..... just something that'd be "nice" to have.
I've had n/a bracket race motors that were in the ~500 rwhp level with 2-bolt mains and the bearings never shown any signs of premature death. However, I did notice abnormal bearing wear with an increase in rpm (700 more rpm) and some 30 more hp. So there is a time when you really need more... just gotta pay close attention to what's going on inside the engine. An oil filter is a great tool in that sense.

-Mindgame

 

If you're going to 4 bolt mains just make sure they are splayed and not straight. Thats really all that matters.

Oliver and Callies are both reputable companies.

 

To my knowledge, and based on examination of the LT1 block, this is not necessarily an accurate statement. Boring for the splayed bolts MAY remove metal that weakens the webs of the block. Which type of bolt/block/cap combo (and its the combined strength of the components that is important, not the strength of one individual component) is stronger is a function of the design of the block, and there is no hard and fast rule. The guys that built Geroge Baxter's engine are not dummies... and they chose the stock 4-bolt block with straight bolts. They recommended the same to me, but I couldn't find a 4-bolt block, and "settled" for the splayed conversion. Remember... GM designed the LT1 block knowing they were going to use straight bolts for the 4-bolt blocks, and put the metal there to accomodate it.

Without a rigorous finite element analysis of each 4-bolt configuration, I wouldn't feel qualified to state what you did.

 

The guy who does my shortblock has built 100's of SBC race motors. He prefers straight caps for production blocks, splayed for Bowtie or aftermarket. I tried to talk him into the splayed caps, but he was adamant. Like Fred implied, he pointed out that the stock block was cast with straight caps in mind. Still, both certainly work. I wouldn't lose any sleep over it but would also say the extra cost of the splayed mains is not necessary.

Rich Krause

 

For the newer/thinner blocks, I agree that the straight-bolt cap should be used. Almost anyone you talk to with experience will tell you about bore distortion using splayed caps on these blocks. No secret as to why they'd be adamant in using straight-bolt caps over splayed.
On the older blocks, especially the 400, it's always been somewhat common knowledge that the 2-bolt blocks were better than the 4-bolts... only because the outer bolts on the oem 4-bolt blocks are notorious for cracking out the main webs when you start putting alot of power through the block. That seems to suggest that they were more an "afterthought" than anything else. The cure... use a 2-bolt block and install splayed mains. Guys have been doing this with older blocks for years and the data seems to suggest that just in bearing and crank life.... the move is a good one.
On any block that doesn't show bore movement with the press of a finger.... splay is the way to go. Open for debate but isn't everything.

-Mindgame

 

Actually I was planning on 450 rwhp NA and I would later add a 150 shot of nitrous on top of that (a ways down the road)...I just don't want to have to tear it down again when I decide to so I figure better safe than sorry.

I will probably stick with the straight caps as that is what the majority of you are telling me to go with.

Thanks!!

 

My engine builder did the same thing this year. I talked to him about splayed caps and he stood firm that straight was the only way to go with a factory block. If I would have gone aftermarket on the block he would have gone splayed. I personally went with the Olivers, but only because they are manufactured right in town.

Q