7MGTE MK3 vs Small Block 400 MK3

[Doward]

Correct, the LS1/LS2/LS3/LS6/LS7 are all aluminum V8s of varying displacement.

The LS1 is simply the most common.

Another option, is the 5.3L vortec - it's an Iron block based off the LS1, with heads that will outflow the LS1s, with some port work. 5.3L heads on an LS1 will also increase the LS1s compression ratio (which is great, if you have a huge cam like the MS4)

Tell your dad to get an LS1/MS4 cam combo. Get a carb, tune it, and enjoy all the lumpity-lump he's been missing, but with today's technology (well, except for the carb. I hate carbs, sorry)

 

[IJ.]

LS6 and a standalone ecu =

 

[KicknAsphlt]

Lemme ask this - why a 400? I prefer a 383 (stroked 350) on the street. If he's already got that 400, that's one thing. If he wants something seriously fun, tell him to pick up an LS1 for that MKIII, and actually be LIGHTER than stock!

*edit* Also, you can get a carb'd intake for the LS1

400's a better motor. If you actually get the '400' block casting, it's already designed for the longer stroke of the 400 crank. In the 350 block, that extra stroke will put extra side-load on the pistons, and your motor won't last much more than 50-60k before you need to tear it down. Granted, some of that can be eased a bit by using a 6" rod vs. the 5.7 rod, but not completely. Plus, the 400 has bigger crank journals than a 350, which is also better for higher-hp apps. Oh, and IIRC, the 400 block was the block that NASCAR ran for a while, not the 350 casting.

 

[KicknAsphlt]

The LS1 is just a lighter version of the same - 2 valves per cylinder, pushrod, with a big lumpy thing in the middle of the block

It's the extreme weigh savings + INCREDIBLY well flowing heads stock that make me suggest it!

Basically, tell him it's a 350 with AFR heads stock

Otherwise, 383 is where it is at. 4" bore + 3.75" of stroke FTMFW. The Chevrolet 400 small block developed a reputation for overheating.

Hell, finding a 400/455 Pontiac motor would make for a hell of a fun MKIII as well! One of the more compact designs - Pontiac has neither a small block nor a big block - the external dimensions of the block are the same, from a 326ci motor to a 455ci motor.

LS1 is not the same as the older blocks. It's a completely different design aside from the basic v-shape and 8 cylinders. Oh, and 383 has a 4.030" bore too... :icon_cool

As far as the overheating thing, I'm sure that was probably true back in the day, but engine and cooling technologies have come a long way since then, so I doubt overheating would be a problem now with a 400.

 

[KicknAsphlt]

Correct, the LS1/LS2/LS3/LS6/LS7 are all aluminum V8s of varying displacement.

The LS1 is simply the most common.

Another option, is the 5.3L vortec - it's an Iron block based off the LS1, with heads that will outflow the LS1s, with some port work. 5.3L heads on an LS1 will also increase the LS1s compression ratio (which is great, if you have a huge cam like the MS4)

Tell your dad to get an LS1/MS4 cam combo. Get a carb, tune it, and enjoy all the lumpity-lump he's been missing, but with today's technology (well, except for the carb. I hate carbs, sorry)

Where'd you read that the LS1 is an aluminum block? LS1 is cast-iron, LS2 is the alum. variant of it.

 

[Doward]

You're right, the 383 is technically a .030" over 350 + 3.75" stroke.

LS1 is all aluminum. LOL, I can show you via a magnet if you'd like, on my buddy's '00 Camaro SS.

Also, the 5.3L vortec is the cast iron LSx block - don't confuse the 5.3L vortec (aka the 5300 Vortec) with the 5.0/5.7L vortec motors - these are GenI blocks with Vortec styled heads. The 5.3L and 4.8L for that matter, are GenIII blocks (LSx) in iron.

The LT1 was iron block/aluminum head. LS1 is all aluminum. As for the LS1 being the same, I mean as far as basic 'how it works' - The LS1 is basically a re-designed chevy 350. It's nowhere near as radical as the Northstar, for instance!

The 400ci SBC has siamesed bores - in a high power application, this causes an overheating problem, unless you facilitate very efficient cooling.

 

[KicknAsphlt]

LS1 is all aluminum. LOL, I can show you via a magnet if you'd like, on my buddy's '00 Camaro SS.

Also, the 5.3L vortec is the cast iron LSx block - don't confuse the 5.3L vortec (aka the 5300 Vortec) with the 5.0/5.7L vortec motors - these are GenI blocks with Vortec styled heads. The 5.3L and 4.8L for that matter, are GenIII blocks (LSx) in iron.

The LT1 was iron block/aluminum head. LS1 is all aluminum. As for the LS1 being the same, I mean as far as basic 'how it works' - The LS1 is basically a re-designed chevy 350. It's nowhere near as radical as the Northstar, for instance!

The 400ci SBC has siamesed bores - in a high power application, this causes an overheating problem, unless you facilitate very efficient cooling.

Well....color me pwned....LOL! I blame myself though, really....for not double-checking shit I hear....D'OH! Then again, I haven't really looked at Chebby stuff in years, being a Mopar Guy and all....HA! Thanks for the corrections...learn sumthin' new every day. :biglaugh:

 

[bmoss85]

i personly like the 400 over the 383. alot guys around where i live run the 400 in there circle track cars. ive only built one 383 and it was a pita but the guy had alot of work he wanted done to it.

 

[Doward]

The 400's fine, as long as you take care of the cooling issues. A lot of circle track guys put steam holes in the head to help with the heating.

IMHO, the 383 is the best bang for the buck street motor.

 

[bmoss85]

you can buy a 383 kit pretty cheap, the 383 that i built was just a pita. it was 2 bolt main, so i put in 4 bolt billet splayed caps and there were alot of clearance issues with pretty much everything, alot of grinding on the block. im sure its not a pita for someone who is a more experienced machinist. i think that the kit the guy bought was only a coupe hundred bucks and the caps i think he got for like $60 or something. i think we ended up with like 12:1 compression ratio if i can remember correctly. its been over a year since that motor was built. so yeah i guess thinking about the 383 is the best bang for the buck doward. especially since 350's are a dime a dozen.

 

[thebuddrik]

an old buddy of mine said when he built his 400 that he had to but some kind of holes in the head to help with cooling. i guess that is what he was talking about. it never over heated. that thing was a BMF. at idle it sounded like an airplane!

 

[Doward]

Steam holes.

A lot of circle track guys put steam holes in the head to help with the heating.

Start with a roller 4 bolt main late model GenI block, 383 cast iron kit, cam in the 224/230 range, with around .540-.570" lift, with a set of AFR 195s (or just a set of Vortecs, if this is a low budget build) and enjoy 500+ hp on pump gas.

 

[williamb82]

LS1 is not the same as the older blocks. It's a completely different design aside from the basic v-shape and 8 cylinders. Oh, and 383 has a 4.030" bore too... :icon_cool

As far as the overheating thing, I'm sure that was probably true back in the day, but engine and cooling technologies have come a long way since then, so I doubt overheating would be a problem now with a 400.

if anything, id build a 377. use the 400 block and use a 3.5in stroke crank for it. they do sell them, cast and forged. id prefere the 400's 4.125in bore (4.155" if you go 30 over) with the shorter stroke. itll rev alot better and have a smoother powerband overall. im thinking of doing this when its time to rebuild the 400 in my 64 c10 shortbed fleetside. but first i need a new cab and other stuff for it. the 400 is running perfect as is.

 

[JMDigital]

So what is the weight of a 7mgte ? Will a 350 or 400 sb be close to the same? I am thinking about the diffrence in the 2 and what changes may need to be made to the spring setup..??

 

[Poodles]

old school iron block and heads build would be quite a bit heavier than a 7M...

dunno about an iron block and aluminum head build, but as already mentioned, an LSX series engine is all aluminum and would be lighter...

 

[JMDigital]

UPDATE - He purchased a 350 from GM. Alum Heads. Will get more info tomorrow. Can someone tell me the gear ratio on the rear? He has an 89 auto, and needs the info on the rear to see if it will work for him. Also would the ratio be diffrent in the 5speed?

thanks for the support on his build...

 

[Slow66]

Should be a 3.73, assuming it was a factory turbo car. Autos and 5sp had the same ratio.