? Opinions: motor swap ?

[Jack]

Would like your thoughts-opinions on motor swap & stow:

My 71 has has numbers matching motor & drivetrain. Its original unmolested L48 350 (270HP) runs great, no noise or smoke. OE drivetrain (TH400, 3.08 gear) also great shape.

I just acquired a complete 1974 400" sbc by swapping an extra MSD 6 box & blaster coil I had. I measured bores, rods, mains: all standard; no spun bearings and no cracks in block) This motor has been laying around a junkyard (rust) for many years and will need boring (looks like +0.020" over will do it). I'm thinking of 5.7" or 6" rods and just enough cam/heads/pistons to make about 400HP/450TQ w/ about 9.5:1 CR. I can build the 400+.

I'm thinking of pulling the good original L48 350 and stowing it for posterity. Replace with above 400+ so I can play with the car's accelerator without worries of damaging original motor. I can R&R the motor.

What do you think of this motor swap & stow approach for this car & driver?
JACK:gap

 

[goingballistic]

I am in the process of doing exactly that. I bought a 350 from a 74 Nova and am crating the original matching 350 from my 81.

It's a project I started last year with my boys and so far have about $3.5 K into the motor. Essentially gutted the block and started from scratch, bored 60 over, new cam, crank, 6" rods, intake....you name it, it's new. I'm trying to find a set of heads from AFR right now and it's a pain as AFR had a manufacturing problem so the heads are 10-12 week lead time which is cutting into my summer driving.

If you are going to crate the original and rebuild, do your home work up front on the rebuild and decide on what you expect to get out of the motor. Spend some time talking to a few reputible shops in your area and get some feedback about your ideas. I originally thought about external balance and bought a crank for that and since decided to go internal balance so basically I ate the new crank cost..........wife was not happy . Plan the lead times and the $$$$, it's getting into the hot season for motor work so there be a machining wait. Good luck.

 

[Grizzly]

Store Numbers Matching Engine

If I was in this situation this is exactly what I would do.

Two things I have always wondered about, if we are worried about numbers matching, how much of the drivetrain should we pull? Maybe an NCRS judge can help us.

Secondly, what should be done to the orginal motor before storage beyond fresh oil? I was thinking that spining it with a drill motor every so often would get the oil up in the motor.

 

[AKRAY4PLAY]

yard the old stuff and build a fun motor!! i love my 400sb. no need to go as crazy with the build as i did. the difference between a 350 and a 383 is almost the same jump as a 383 to a 400. go with the long rods, 6.0" work the best. .030" overbore pistons are more common than .020". is the block a two bolt main?? two bolts are stronger than the stock 400 four bolt. that block sounds worthy of building and your car is more than ready for some HP.

 

[Jack]

yard the old stuff and build a fun motor!! i love my 400sb. no need to go as crazy with the build as i did. the difference between a 350 and a 383 is almost the same jump as a 383 to a 400. go with the long rods, 6.0" work the best. .030" overbore pistons are more common than .020". is the block a two bolt main?? two bolts are stronger than the stock 400 four bolt. that block sounds worthy of building and your car is more than ready for some HP.

It's a 2 bolt. Yep, 30 over more common/available than 20. Haven't decided on the part numbers yet ... probably use 6" rods ... but I'm thinking if the pistons I'll want are available in 20 ... that'd leave more liner in the bores ... the overall ci diff between 4.145 & 4.155 is only about 1 or 2 ... insignificant for me. Dunno which pistons I'll need yet ... doubt I'll buy pricey Ross, JE etc ... have had good luck w/ SpeedPro Hyper ... worked well for a mild 388 I built. Buddy of mine has a BARREL full of used nascar pistons that cost a lot at one time ... seems like most of em have a dish and but are probably 4.155 ... no clue of compression height ... I might just look again & see what's there.

For now, I'm trying to decide if swap & stow is right ... if so, then I'll spec out the 400 build.
JACK:gap

 

[goingballistic]

Jack one thing to consider. I crated a motor for a Jeep 360 I was rebuilding and shipped it New York when I moved here from Vegas. It was two years later when I actually got around to doing anything with the block and it was a major hassle due to cooling and reheating over the two year span, essentially chucked the block and restarted.

I'm crating this motor ( the original matching ) for the next owner. I am doing that because I think it may bring a better selling point for the car, if I decide down the road to sell it. I've talked to several other people here and they would have no interest in the original block anyway so now I'm questioning my decision. I would assume a "purist" may want it for restoration but not sure why anyone would buy an '81 with a 450HP motor and replace it with the original anyway, I'd be interested in finding out some feedback from people on this board as to what the percieved value is of the original motor as part of the sale even though it's not in the car. That may help you make the decision.

Cheers.

 

[stearnman]

Did you think about this as a "long term" possibility? Once you get the 400 working (whether you swap it in your existing '71 or not), dropping it into another project car...Corvette or other GM. I know, the long term project will be much more time...money...time...money...etc...but it will (eventually) give you the best of both worlds: unmolested and monster!

 

[Grizzly]

Jack one thing to consider. I crated a motor for a Jeep 360 I was rebuilding and shipped it New York when I moved here from Vegas. It was two years later when I actually got around to doing anything with the block and it was a major hassle due to cooling and reheating over the two year span, essentially chucked the block and restarted.

I'm crating this motor ( the original matching ) for the next owner. I am doing that because I think it may bring a better selling point for the car, if I decide down the road to sell it. I've talked to several other people here and they would have no interest in the original block anyway so now I'm questioning my decision. I would assume a "purist" may want it for restoration but not sure why anyone would buy an '81 with a 450HP motor and replace it with the original anyway, I'd be interested in finding out some feedback from people on this board as to what the percieved value is of the original motor as part of the sale even though it's not in the car. That may help you make the decision.

Cheers.

That all depends on how long you keep it. Just look at the change in the value of the earlier Sharks over the last few years. I personally believe that the last couple of years of the C3s were the best looking of all the C3s. Finally the '81 was the last year of the carb, and that would be a selling point for me. I've heard some awful things (real or imagined) about the crossfire. The whole idea of having the orginal engine and a hypo beater in the car I would find rather appealing and would be willing to pay a premium for.

 

[WayneLBurnham]

You, Sir, are obviously possessed of godlike wisdom and superior tastes!

I personally believe that the last couple of years of the C3s were the best looking of all the C3s.

I was TICKLED my project '75 already had the late C3 nose and tail on it! I would have done that myself if they didn't! Don't get me wrong I like all of them, but I find the all-glass/no-metal, somewhat spoilered rear to be the epitome of the concept. Other than I can't SEE to backup at night with the top up, I even like the bubble conversion/no backup light option the previous owners foolishly did! (Now I have to come up with some other nifty place to mount some lights so I CAN see at night.... )

 

[73orange]

Motor Swap

I think the whole motor swap is nuts. I don't quite understand why you have a concern as you put it, "play with the accelerator without damaging the engine". You've got a '71 270 horse engine for crying out loud, it's bullet proof. Morons blow up engines, plain and simple. Do you actually think that you could put your foot in the accelerator to the point where you'd blow up the block, so the numbers don't match? Highly unlikely. I've got an L-48 2 bolt that I'm rebuilding and the numbers match. I haven't touched the bore or stroke, but I'm in the process of rebuilding the heads, and replacing the cam, intake, and exhaust, to something hotter (more like yours), so it doesn't run like a detuned smogray. Think about it....if that engine with its matching numbers has been driven hard its whole life and hasn't broken yet, what makes you think it's going to break now? When my project is done the numbers will match (which means nothing unless you're planning on going to Bloomington) and it will be more fun to drive than before and I'm not going to worry one bit when I put my foot into it, because it's a Chevy engine.
I figured since most everyone is in favor of the swap job, you needed to hear from the other side. Go to the performance store with a big bag and fill it full of goodies and build that block. If you want to do anything, swap out the rear for a 3.55. Then when you're standing around with the hood up, you can say your numbers match.

 

[Koop]

You have a 350 and a 400 that need to be rebuilt.

350 Block + 400 Crank, get some aluminum heads, roller cam...

By the time you build a serious motor it may be more cost effective to buy a GM crate motor.

 

[Jack]

Koop: I have the experience and sourcing to build a reliable long rod 400+ for about $1K-$1.5K ... far less than a similar crate. If I couldn't do it, I'd be the first to suggest crate. I'm starting with 50" over a 350; got the whole 400 by trading $150 worth of stuff. Many good folk don't have the time/place/tools/know-how to rebuild ... for those I usually suggest a crate. BTW, when having late breakfast after Sat nite race ... sitting w/ racer who works for a local race shop ... a retired farmer overhears our bs & asks what it'd cost to have his 79 chevy pickup's carbed 305 rebuilt ... racer says they get about $2500 for a rebuild (too high!) ... I think I convinced the farmer to go to his favorite GM dealer & order a brand new, warranteed Goodwrench 350 for about $1400.

Orange73: Blown motors are not expressly the result of idiocy. L48s are very good motors, but they ain't bulletproof ... not even those (like mine) that have not been driven hard their whole lives. If wanted to pump up the original motor I'd do so ... I built a very nice 388 from L48 that remained matching & had deceptively mundane outer appearance. 3.55 rear gear is nice ... but I choose to cruise below 3K revs ... more inches (~50) will do 'bout the same thing using same old gear. There ain't a thing wrong with the original L48 ... I'd like to keep it (stowed) that way ... then I can horse around with lots more grunt. I have the option of completing a 400+ build at low cost & at my pace ... while continuing to enjoy driving the car ... then making a quick swap. Later, if resale or judging requires it, I can put the good original matching motor right back in. Such convenience is not likely if I built up original motor (been there done that). BTW, if you stick a bunch of cam/compression on top of 30-year-old rings and bearings ... you may be back into the motor sooner than later.

One & All: thanks to each of you for your input ... I've made up my mind to go ahead & build the 400 ... and do a swap & stow.
JACK:gap

 

[AKRAY4PLAY]

Jack,
don't forget pictures and new tires!!! ope the build goes smooth, Brian.