lt4 vs lt1 block for fi

When choosing a block for a forced induction setup, is it better to find an lt1 block and convert it to 4 bolt mains or to start off with an lt4 block to begin with (or does it really matter)? Aiming for 600 rwhp.

i have heard that if you use a 2 bolt main and convert it to a 4 bolt that is stronger then a factor 4 bolt, now this is hear say never done any reseach.

my current block is a 4 bolt main but I want as little downtime with the car as possible but finding another 4 bolt main has been kinda tough. I had heard that 4 bolt 'splayed' can be better but haven't found any hard evidence of this.

I wold venture to say that the majority of people making significant HP with an LT-x motor have used an LT-1 block and machined the block to accept the splayed 4-bolt conversion main caps. Either are typically very reliable for big HP motors and are not the weak link in an LT-x build.

LT1 block is the same as an LT4 block.

Some argue that a splayed 4 bolt is stronger than a stock 4 bolt.

you might want to ask Advanced Tech the question on the power limits of a 2-bolt vs 4-bolt and see if your designs fall inside our outside those ranges. Boost really isn't the issue as much as raw torque and the unbalanced vibration. From your desired state of 600 RWHP, you're probably pulling 500 Ft/Lb torque and may create havoc for a 2-bolt.

DelSoto,

Search the Advanced Tech section and you can start to form an opinion. Vizard and others tend to relay that 500 flywheel HP is the safe 'limit' for a two bolt Mouse. My un-scientific notion is that 600 crank would be ok for a street car with studs and real careful setup, etc.

To go out and find a 4-bolt LTX block will likely take more time and about $200-300 more than a 2-bolt block. That is roughly half the cost of converting a 2-bolt block to splayed caps - with 3 steel caps of course. The downside could be finding a real good shop to do the conversion - correctly.

People have made big power with both straight mains and also splayed outer bolts. Some have said that straight-4 is stronger on a production block (not necessarily true with aftermarket blocks) and some say that angled outer bolts tie into the oil pan rail for more rigidity. But, you need meat in the area of the angled bolts....if your breaking into water jackets or tying into thin areas then how far ahead are you? I've read that flat bottom splayed caps are better than stepped caps. You machine the block flat and your cross-car register moves way out to the pan rail. Seems that with all of this, any solution will still allow for main-cap-walk at real high power levels. Apparently walk can occur with either straight or splayed outers (fore-aft movement of the cap). One option could be to dowl the main caps to prevent this motion. HOWEVER, the major concern will be cap-cracking between dowl and bolt hole so.......do your homework if you're going consider this.

Oh, and to answer your specific question, I say either block will ok on the street at 600hp. Your budget & project timing will dictate.

One last comment - the above information is worth about what you paid for it. :D

Regards,
Scott.

Thank you....great information here!

LT1 block is the same as an LT4 block.

+1.

The appropriate question is... "corvette vs f-body bock for fi"

i thought all f-body lt1s were 4 bolt mains??? my dad got a GM short block for his 95 TA and they told him it was 4 bolt mains.what would was that motor made for?

Corvette = 4 bolt mains
F-body = 2 bolt mains

Reportedly, GM put a few 4 bolt blocks in f-bodys because they ran out of 2 bolts.

OHH yeah he told me he got a corvett lt1 but i thought it was the same thing any other changes? mines siting with huge blow by time for some forged speed pro pistons.

The block and related parts are not typically a problem unless you are planning a very high power setup. I have used each of the following with no problems: factory 4-bolt, factory 2-bolt to ductile iron straight 4-bolt GM cap conversion (ductile iron caps no longer made by GM), factory 2-bolt to steel cap conversion on all 5 with splayed center caps. I think the last was overkill. All of these blocks had a 1/2 fill however.

Rich

How would the have filled block run on the street. Wouldn't oil temps be dangerously high? I have heard people do 1/4 fills on a dd with no problems. So would it be worth doing the quarter fill or half fill? for an almost dd?

If you fill to the bottom of the waterpump you shouldn't see much difference in coolant temp. An oil cooler is recommended however.

-Scott.

Works fine on the street.

Rich

Rich,

Curious if you measured oil temperature with the street fill. I've heard that a cooler is recommended, but not seen data to support.

Thanks
Scott.

No, but the car isn't driven hours on end either.

Rich

i have a 4 bolt block sitting in the garage. motor came out of my old 97 SS it was the stock motor. i also have a 2 bolt block sitting next to it :)

97SS0594,

PM sent :D