73 340 SB Rebuild, Need Help Selecting Parts

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Scottd9990 said:
My 340 is a 4.04 bore, still stock bore. I am thinking this engine is not that warn out but just sat for a very long time. There is very little wear anywhere that I can see and this jives with the odometer reading of just 3047 miles. Could this just a low compression 1973 smog motor with old seals and stuck rings? Bought the car from the original owner (85 years young). So considering all this, did the plan change?
Plan A:
What would the cost be to freshen up this old 340 and what would you do to it? Cost?? Now, compare the 340 engine say spending $3000 total to freshen it up to this idea (see below)
Plan B:
So I am think about possibly doing this:
1. Maybe buying the 408 short block listed at Jegs and Summit. $ + shipping $2500.00
2. Working my heads and using them: Free
3. What cam would be a nice addition to this mix? $250
4. Gaskets, seals stuff needed: $250.00
What would this motor run like? About ?? HP and TQ?

How would this work with my basically stock converter and rear gear. I do like the gear as it's almost perfect for autox in first gear. Nice wide range from 0 to about 55 mph @ 5500rpm.

What's the good and bad about this idea. I am somewhat limited in total funds and this is my toy car to wife limits as well. I am trying to get a freshened up motor done for around $3000 out the door. Is this possible?
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I would not expect you to be anywhere close to $3000 if you spend $2500 on the short block unless you sell the 340. And if you are really going to hammer on this block, then I am skeptical on any mass production bought short block.

If you need to stick with that budget, then you can do a lot if you can do most of the work. Some rough numbers which are just pulled out of my head..
1) Tear down and inspect the block, have it cleaned, measured, and see if it will hone OK with no new boring. If boring is needed, go .020" over. $200-500
2) Buy new Speed Pro L2316F pistons; the L2316F pistons will not require a rebalance of the crank. I can only see them in .020" oversize not standard at this point. This will get your CR up to a real mid 9 range, and that will be good. $450 with rings
3) Keep crank as is and check. Hope all is OK. Have rods checked and put in new rods bolts. $200-$250
4) New main and rod bearings, cam bearings, decent timing chain, oil pump shaft, and oil pump. $300
5) New stock lower gasket set with 1121G thin head gaskets. $100
6) New damper for reliability $250

If you can assemble yourself, then you are in the $1700-1800 range with forged pistons and a high quality damper for revving, and that is less than for the short block with ??? pistons, and no or standard damper.

Now you have the cam and springs and lifters; plan at least $300.

Assume the valve train does not need a lot of work and you run heavy duty stock rockers. $180

Now you are at about $750 left for the heads. If the miles are really low, I'd hope that no guides are needed. If so then you are home free with a few hundred bucks of head work. You can port yourself as you seem to have indicated.

400 HP? I doubt it; the heads don't have it without some work; if you you could kick in another $750-$1000 budget, then you are at a new bolt-on set of really good heads. But focus on torque, not HP, for what you are doing. That will all be in the cam selection and tune. I'd stick with the DP carb for sure and reconsider the torque converter and move up a step from the stock one.
 
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nm9stheham said:
I would not expect you to be anywhere close to $3000 if you spend $2500 on the short block unless you sell the 340. And if you are really going to hammer on this block, then I am skeptical on any mass production bought short block.

If you need to stick with that budget, then you can do a lot if you can do most of the work. Some rough numbers which are just pulled out of my head..
1) Tear down and inspect the block, have it cleaned, measured, and see if it will hone OK with no new boring. If boring is needed, go .020" over. $200-500
2) Buy new Speed Pro L2316F pistons; the L2316F pistons will not require a rebalance of the crank. I can only see them in .020" oversize not standard at this point. This will get your CR up to a real mid 9 range, and that will be good. $450 with rings
3) Keep crank as is and check. Hope all is OK. Have rods checked and put in new rods bolts. $200-$250
4) New main and rod bearings, cam bearings, decent timing chain, oil pump shaft, and oil pump. $300
5) New stock lower gasket set with 1121G thin head gaskets. $100
6) New damper for reliability $250

If you can assemble yourself, then you are in the $1700-1800 range with forged pistons and a high quality damper for revving, and that is less than for the short block with ??? pistons, and no or standard damper.

Now you have the cam and springs and lifters; plan at least $300.

Assume the valve train does not need a lot of work and you run heavy duty stock rockers. $180

Now you are at about $750 left for the heads. If the miles are really low, I'd hope that no guides are needed. If so then you are home free with a few hundred bucks of head work. You can port yourself as you seem to have indicated.

400 HP? I doubt it; the heads don't have it without some work; if you you could kick in another $750-$1000 budget, then you are at a new bolt-on set of really good heads. But focus on torque, not HP, for what you are doing. That will all be in the cam selection and tune. I'd stick with the DP carb for sure and reconsider the torque converter and move up a step from the stock one.
Click to expand...

The Mopar Performance 300hp crate engine was just a mass production stock short block and 380 hp crate engines were basically slightly modified mass production stock short block that just used a larger cam and a few other parts. Both engines were simple carb engines too. I know of a 380hp one that has at least 500 passes and about 25k miles on it without any issues. It runs 4.30 gears and has been driven from WI to the Mopar Nats about 10 times also.

Just saying...
excuseme.gif
 
Good info!! I am leaning that way right now. New is new and I like knowing it's good to go!!
 
Scottd9990 said:
Good info!! I am leaning that way right now. New is new and I like knowing it's good to go!!
Click to expand...

Good luck finding a new 360 crate motor though. You'll have to search high and low because they stopped making those years ago.
That was why I gave you a recipe to build one that will have even more power.

What kind of budget do you have to play with?

Scottd9990 said:
What could I sell my 340 for??
Click to expand...

That all depends on what you decide to do. If you buy a 408 short block you'll only be selling a short block. Since it's a standard bore 340 with a cast crank most people would want the block to build a 416 or larger stroker. First you'll need to come up with your plan.
 
I've seen complete 340's that had no guarantee of running or not being worn out, but are complete and not blown up, and the asking price was $1000-$1200 in my neck of the woods. Finding a good block that is not all rusted up and can be bored on the open market for $300 is a good deal. On the other hand, I found a $50 360 LA block within 100 miles.

My concern over crate motors is not knowing or having any control over the build or parts quality. Yeah, you can mess up your own build fer sure! But you can control each step and each dimension too.

A crate motor or short block has some attractiveness if your engine building experience is limited; a good part of the work is done. But again, you give up some flexibility in the dimensions and such; for this app, I would be paying very close attention to the dimensions that control CR; IMO, moderately high CR without going too high is important for that broad torque range but not detonating.

I can see folks making either decision and making it work. I take a certain satisfaction in building from a minute level of detail but not everyone gets satisfaction out of measuring and managing things to that level. I do feel that good detail work produces better results and a stronger build.
 
nm9stheham said:
I would not expect you to be anywhere close to $3000 if you spend $2500 on the short block unless you sell the 340. And if you are really going to hammer on this block, then I am skeptical on any mass production bought short block.

If you need to stick with that budget, then you can do a lot if you can do most of the work. Some rough numbers which are just pulled out of my head..
1) Tear down and inspect the block, have it cleaned, measured, and see if it will hone OK with no new boring. If boring is needed, go .020" over. $200-500
2) Buy new Speed Pro L2316F pistons; the L2316F pistons will not require a rebalance of the crank. I can only see them in .020" oversize not standard at this point. This will get your CR up to a real mid 9 range, and that will be good. $450 with rings
3) Keep crank as is and check. Hope all is OK. Have rods checked and put in new rods bolts. $200-$250
4) New main and rod bearings, cam bearings, decent timing chain, oil pump shaft, and oil pump. $300
5) New stock lower gasket set with 1121G thin head gaskets. $100
6) New damper for reliability $250

If you can assemble yourself, then you are in the $1700-1800 range with forged pistons and a high quality damper for revving, and that is less than for the short block with ??? pistons, and no or standard damper.

Now you have the cam and springs and lifters; plan at least $300.

Assume the valve train does not need a lot of work and you run heavy duty stock rockers. $180

Now you are at about $750 left for the heads. If the miles are really low, I'd hope that no guides are needed. If so then you are home free with a few hundred bucks of head work. You can port yourself as you seem to have indicated.

400 HP? I doubt it; the heads don't have it without some work; if you you could kick in another $750-$1000 budget, then you are at a new bolt-on set of really good heads. But focus on torque, not HP, for what you are doing. That will all be in the cam selection and tune. I'd stick with the DP carb for sure and reconsider the torque converter and move up a step from the stock one.
Click to expand...
I do have some local help in re-building my 340. I am going to rebuild what I have. I like the above plan and will see how it turns out.

Pulling the block out next weekend and sending block, crank out to machine shop. Will look at block clean up deck it ?? bore and whatever the crank needs. I would like to bump compression and go with better heads.

I will just sell my heads and go with Edelbrock alum heads with 2.02 valves.

Also sell my intake and do something else. ????

Thank you all for the great advice!!
Build:
Pistons: Speed Pro L2316F
Rods: stock with new bolts.
Edelbrock Heads: 60775
Cam:
Rockers: ?
What else other than engine rebuild kit?

Good plan??
 
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Is your intake the performer 318/360? If so, a performer rpm would be a better choice, or even a old edelbrock ld340 if you can find one. I would not use that particular piston in your case, I would use a Keith black KB243, lighter, tighter fit in bore..... otherwise everything else looks ok....Aluminum heads are a plus, get compression in the 10.5 or so range...custom grind solid flat tapped would be nice also
 
What machine shop is going to do the machine work? I see your in Concord also, I can tell you the one to use.....
 
replicaracer43 said:
Is your intake the performer 318/360? If so, a performer rpm would be a better choice, or even a old edelbrock ld340 if you can find one. I would not use that particular piston in your case, I would use a Keith black KB243, lighter, tighter fit in bore..... otherwise everything else looks ok....Aluminum heads are a plus, get compression in the 10.5 or so range...custom grind solid flat tapped would be nice also
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I too prefer the KB243's, and lighter pistons WOULD be a small advantage in auto-x as it takes considerable rotating weight out of the drivetrain, allowing faster revving and acceleration. But, the forged Speed Pro part was suggested to avoid the cost of rebalancing the crank in order to stay within budget and focus $$ into heads and breathing. The KB's drop about 180 grams of weight per piston + pin, and so a rebalance is needed. A typical rebalance of rods, pistons, and crank can run in the $250-350 range locally, and more $$ in some areas I suspect.

There is a fair amount in labor that goes into the weight matching process.It is a process that takes care and precision. The jig to be able to measure big and small end weights can be tricky and has to be right. So this is not an amateur job. If the OP wants to understand the and precision put into it to save some cost, weight matching of the rods with new KB243 pistons will involve:
- Borrowing a decently accurate gram scale and going to the machine shop and comparing it to theirs with a few pistons and rods to insure the 2 scales are calibrated to each other
- Weigh all the rods: total weight and both big and small end weights. This requires a precise jig.
- Using the lightest end weights as the target weight, grind material off of the bottom of the caps and up top to get all 3 weights to match across all 8 rods; total, small end, and big end
- The KB243's will be closely weight matched and for this use, I feel any piston can be put with any weighted match rod and be good enough.
- Give the numbers to the machine shop so they can compute what is called bob-weight and then balance the crank and damper and flexplate together with that bobweight.
- This effort should save cost in the balance process, in the range of 60% + or -. But again..... it is not for a first timer, IMHO.

Or get the the SCAT rods as mentioned before that are all weight matched. But this is all pushing the budget up and up. So, back to the suggestion of the forged Speed Pro's, forego balancing, and live with the extra weight on the crank.

It's just another example of how every step up on performance costs more and more.
 
I am for the Speed Pro pistons and skip the re balance process. Now I will need a new balancer and flex plate, will that change re balancing??
 
Skipping the ballance job isn't a great idea in my opinion, the factory ballance job wasn't that great, and changing pistons can't help the situation. I'd save a few more dollars and put the light pistons in, along with a replacement I beam rod, and take weight out of the rotating assy.
 
Scottd9990 said:
I will just sell my heads and go with Edelbrock alum heads with 2.02 valves.
Edelbrock Heads: 60775
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Scott, you want to get 60779's; the 60775's are listed as having springs for roller lifters; that is not where you are going, I don't believe.

BTW, your best deal on these heads are mail ordered from Autozone, believe it or not. Sign up for their online notices and you will get their discount notices. I see 15 to 20% off the cash price a lot, and sometimes 35% off which is in the form of a gift card to yourself. You will pay your sate sales tax if Autozone has any physical presence in your state, but shipping is free. It is a good deal.

If you use the 60779 closed chamber Edlebrocks, then some review of CR and piston to head clearance is needed. The reason is because the Speed Pro pistons will stick about .017-.018" above the deck (sames as the earlier high CR 340 pistons). If too thin a head gasket is used, then there is real risk of the piston hitting the closed part on the bottom of the head. You will want to use standard Felpro head gaskets (about .051-.054" thick, not the thinner Felpro 1008's, nor the even thinner 1121G's. These standard Felpro's, will give a gap around .033" to .037"; you don't want it any smaller. You will want to check this VERY carefully when you go to build. You can fix it if too tight with taller Cometic gaskets but they are not cheap. Approx $200 per pair, but reusable. Or see how much it would cost to have a bit milled off the piston domes.

And because the piston to head clearance is tight, then make sure each rod length is checked as part of machine shop work. And if the block is decked, then keep it minimal. I have assumed a standard block height of 9.600".

You will end up with right at 10:1 SCR with this combo of parts..... ought to be torquey!
 
replicaracer43 said:
Skipping the ballance job isn't a great idea in my opinion, the factory ballance job wasn't that great, and changing pistons can't help the situation. I'd save a few more dollars and put the light pistons in, along with a replacement I beam rod, and take weight out of the rotating assy.
Click to expand...
You are right on all counts, and that is exactly where my son and I went on his 340 build: KB243's, SCAT rods, rebalance. It is a $$ decision here, I think. And the OP is keeping the revs under 6k, which helps.
 
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Scottd9990 said:
I am for the Speed Pro pistons and skip the re balance process. Now I will need a new balancer and flex plate, will that change re balancing??
Click to expand...
The balancer/damper and flexplate are specific to the '73 cast crank 340, with a specific amount of imbalance to help the overall crank balance. If you get the right parts, it will not change the overall balance.

You can likely get by with the flexplate with a careful inspection at the hub for cracks, BUT the B&M flexplates are about $100 and are a bit of a good insurance policy. What you use and can get depends on the tranny model and if the torque converter has a weight on it or not.

The damper being replaced with a better one is a good investment IMHO, 'specially with repeated high revving. The old ones have hardened rubber that can slip or break out, and won't properly damp crank vibrations anymore.
 
One thing about the scat rods, they give you the big end weight and small end weight on the box......so the requirement for a jig to balance the rods is not necessary...
 
So the ole 340 is out and on the stand. Been doing a ton of digging to figure out best options here to get my car back in the SCCA events. I have decided that I am going Magnum 360 swap and hopping up the stock magnum with heads, intake and cam. I have found a suitable low mileage Magnum 360 locally for $500 and will be selling my 340 complete ready to be re-built. My 340 is standard bore, so can't be that bad!! Look for the listing soon on the For Sale tab here. I was thinking 400 for the complete block, heads, intake was a pretty fair price. Am I crazy?? More?? Less?? What Say Yee??

Scott
 
I'll take it complete for $400 if that is for real and save you the trouble LOL. (What the hell am I doin'? I really don't need it!) But in all fairness, I expect you can get more than that. Heck, you can't find good 340 blocks for much less than $400 unless you are lucky. The 1.88 heads and kinda 'enh' heads however IMHO.
 
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