Hey guys. so I am knees deep in this boosted 340 project (see signature).

My machinist is working with the block now half filling it. it's a 69 block with a forged crank, eagle H beam rods and forged pistons. I will be using head studs and main studs along with cometic gaskets. W2 econo heads flowing just around 300cfm with boost supplied via an intercooler D1 pro charger. I would love to try to make 700fwhp....enough to get my full interior challenger into the 9's.

I was talking to Dizuster here (who I just want to publically thank for all the help) and he told me that one of the issues he ran into with trying to make big power through a boosted small block was eating up bearings from what appeared to be cap walk. He's also running a cast crank.

Since my machinist may have to align bore the mains to install the main studs anyway, I was thinking that it may be a good opportunity to put in billet caps if this would help. My other option is a stud girdle.

My question is, would either of these really help me with keeping the motor alive? Would they be worth the expense (especially the billet caps which seems to get pricey). Keep in mine I doubt I'd be spinning this motor too high, maybe 6500rpm's at the very most. Certainly not what most N/A small blocks would be hitting to make over 550hp.

Any advice is appreciated!

Buy one of the R1 or R4 race blocks listed in the race parts section now before someone else does
The four bolt mains and the beefier thicker main casting area will hold up way better than any of the original OEM 340 or 360 blocks other than the T/A AAR casting blocks
Especially on your deal

The above would be the best. I've used filled stock block w/ main studs and made about 650hp, but I was pushing it. I still saw some cap walk but the studs helped some.

Big Boost means start with good block like one of the units on here this week--they have thicker decks as well which will aid the big issue and that is the" Only 10 head bolts"--not good with high compression--tuned right with no detonation etc bottom should stay happy but no better cure than an R block for sure!! Good luck let us know how she does

billet mains will help if the mains are cracking. they won't prevent cap walk. a girdle doesn't work on a small block as there is nothing to tie it to in order to stop the movement. on a big block there is a pan rail. on a small block the caps float below the pan rail.

aftermarket block is the best option here.

Why would the machinist have to align bore just to put main studs in?

I believe ARP recomends that due to the deeper pentration of the main studs having different distortion affects on the main webbing
I would use a good dial bore gauge with the mains torque down with the bolts and then install the main studs and retorque the caps with the recommneded torque with the new studs and lube and see if the dial bore gauge shows any difference in the main bores, all five of them If any of them are distorted .0002 or more have it fixed

When you build a house you start with a good foundation just like building a engine you need a good foundation a r block or a Ritter block is the only way to go

Or an X block if you can find one.
Still kickin myself for dragging my feet on a virgin 4 bolt X block I could have had for 1300 bucks. I finally go to get it and he sold it a month earlier.

The problems I had at 650 horsepower was cylinder wall cracking. By a R Block you'll never be disappointed

I've made 600 for many years with a stock 340 block and crank. It did get an upgrade to an R block. There is almost zero blow by even using the old pistons from the stock block , 5/64 rings as well. Same crank since 1985, never wounded the first block. In fact Dizuster rode home in this car when he was born.
Doug

I've had a blown 340 for many years with a stock block and crank. It did get an upgrade to an R block. There is almost zero blow by even using the old pistons from the stock block , 5/64 rings as well. Same crank since 1985, never wounded the first block. Makes around 600. In fact Dizuster rode home in this car when he was born.
Doug

What I did - along with a 1/2 fill.

Hey guys, thanks for the replies and I appreciate the input! I would LOVE to use an R block, but I am putting this setup together with scraps from other projects and despite what seems like an extensive parts list, it is by no means a big budget build. Many of the parts I already had lying around. I was originally going to do an all motor W2 build but got carried away with having this procharger sitting here.

Hell, the R block would cost me more than what I am paying to have my 340 half filled, rebalanced, honed, assembled plus new H beam rods, a roller cam and roller lifters. If I spent 3k on an R block, I'd still have to pay probably another 3k getting it all assembled/machined with my parts. It's just way out of budget, at that point I think I'd be leaning towards a big block.


I want to do a BIG power setup in the distant future. At some point in the next 5 or 6 years I want to tear the whole car apart, back half it, restore the whole body and lay something in it that will be 1000+hp capable. When I take that route, I think I'll likely go late gen Hemi or big block but I am waiting until I have a better place to work than in my tent outside. The setup I am building now I just want to have to get some fun out of for a few years, take to the track once or twice a year and enjoy without spending a fortune. That said, I don't want to blow it up the first time out, but I am also not looking to "invest" in a setup that I probably won't be keeping for too long.

I know there ARE guys here running high 9's and making 650HP plus out of factory LA blocks. I just don't know how much trouble guys are running into when doing this.

It seems like the billet caps and stud girdle may be a waste of money, and I guess there isn't anything else I can do other than the half fill to beef it up. The question now is how long will it last? lol

DVW, Disaster told me about that motor in our PM's. That definitely gives me some hope that this may actually work!

^Exactly. To be more accurate, my machinist didn't say I HAD to have it align bored, he told me that generally speaking if the studs screw in by hand then it will normally all go back together OK with the studs and no distortion, but if not then it will likely have to be align bored. I am just assuming it will have to be until told otherwise but he seemed pretty confident it may not need it. He is going to check it out with the dial bore first to make sure it all works without the align bore.

So here is what I have found in my research. I have several guys who I have spoke with who HAVE gotten their boosted stock block applications to live at well over 600hp. Some of them have run into cap walk issues, some of them haven't (or apparently haven't after running for several years and no engine failure).

I have also heard from guys who have cracked webbings etc...

One common theme I am seeing is that the guys getting these blocks to last are all using very low RPM combos (mostly turbos) that don't need to spin too high to make power which makes sense. I hear of guys breaking them, but honestly (and not to be rude) some of the guys who have broken them don't seem to share too much about how/why it broke after inspection or what the combo was. What is sure to fail on a 650hp N/A 8000rpm motor isn't necessarily sure to fail on a 700hp boosted 6200rpm motor. Even take two 700hp boosted motors, let's face it, carbs aren't the most precise fuel management system and many guys aren't using wideband to tune. The shockwave of detonation can wreak havoc on the block. With my own experiences using late model GM stuff, there are many guys pushing certain blocks to 1000hp with no problems and others cracking them at 600. The end result when things are really torn down always seem to be that the blocks breaking at the lower numbers always had some tuning issues- and this is with late model boost capable fuel injection systems/wideband 02's etc... I can only imagine how many old school boosted/blow through small blocks were killed prematurely due to detonation issues.



One of my questions is with the main girdle. I know Hughes talks it up but a few guys mentioned here that it has nothing to anchor to. If trying to prevent cap walk, wouldn't simply tying all the mains together be enough to help significantly? I feel like it would be harder to 'walk' all the caps together than it would be to move one. Being that cap walk seems to be the major issue the guys who are making over 650hp with stock small blocks are encountering, I am thinking it may not be a bad idea.

IMO, most of the cap walk / block cracking issues are caused by detonation. That's why some SAME blocks live and others don't. I always run well in to the "safe" zone with race gas at water injection.

That's what I was thinking. Getting the tuning right with forced induction, especially with many of these old motors running iron heads and blow through setups, definitely isn't easy. I'd imagine that a lot of failures are from detonation.

I'm going to bite the bullet and order the Hughes main girdle. I can't see how it wouldn't help with cap walk. It may not make a huge difference, but when you subtract the cost of the studs which I was going to need anyway it's only about $200 of added insurance. Of course, now I'll HAVE to align bore the motor...


I'm going to be running E85 which has the added octane and also cooling properties, a large front mount intercooler and timing/fuel controlled by the FiTech fuel injection using a wideband 02. I think the only [censored] in the armor here is the iron heads, but if I can get my compression down enough I think with a safe tune it will be about as detonation-resistant as one can get...I hope lol

Definitely a learning experience for me.