73 340 SB Rebuild, Need Help Selecting Parts

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Scottd9990

Scottd9990

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So here is the story: Yea I know everyone has a story. I have a 1973 Dart Sport that I am building for Road Racing and SCCA Autocross. There is a new Class Called CAM (Classic American Muscle) so I didn't want another Mustang or Camero. Found the Dart in pretty bad condition and started working on it. Chassis is now in great shape and drives on rails. Here is a short video of first run with this car.


Motor seemed so so with low compression, but ran pretty good. Initial compression was not great with the average cylinder was around 125 lbs (wet) per hole, 109 lbs (dry). Had some pretty good oil leaks out rear main so its time. Oil pressure has been good but the engine did tend to run hot around 200.
Tearing down the motor now.

Here is my Goal for this build:
Looking for more of a Road Race setup. Needs to be completely street able. On the Autox course I run mostly in first gear @ 2500 to 5800 rpm peaking out around 55 to 60 mph. Motor spends most of the run around 2500 to 3500 in the turns.

Goal: Build a 375 to 400 hp small block with very wide power band from 2500 to 5500 rpm, Here is what on the car now:
Standard 904 three speed auto transmission with manual valve block and 273 gears, stock converter.
Here is what I have so far:

Heads are PN# 3671587 which should be 340 heads with 1.88 1.60 I think?
Edelbrock Intake# 318/ 360 #2176
Holly 750 dp carb, thinking of going with big 2 barrel say 500+cfm?
Cam: Unknown once block is out will post up here.
Pistons look to be Standard bore: Stamped "STD"
Looking at the Pistons, looks like there is plenty of room to improve compression. Pistons are down in the hole at lease 1/8th inch.

I am no motor builder and don't have unlimited funds to spend, but I am looking for a good quality build at or around 400 hp with a wide power band for road racing.

What parts should I be looking to put back into this motor?

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Same goals, but nowhere near driving the car yet. Going to watch your thread.
 
You need to talk to Autoxcuda. He is a super nice guy and will tell you anything you want to know. His car is total basassary.
 
Excellent idea Bobby. AutoXcuda has been doing this for awhile.

Those heads with a 1.88 intake valve would not be a 340 head. But that valve size maybe OK for what your doing.

I'm not sure how to proceed with the engine build since I do not any of the rules. The only I see is the need for more gear. Get you going quicker.
 
4" Stroker under 500 hp with cast crank is what I did if you are going to rebuild it. Would use Chinese aluminum heads done/messaged by a reputable shop like Brian at www.immengines.com . TTI shorties or Thorley headers, etc, etc.

Or do you need to reuse Pistons and heads to keep cost down that way?
 
You are on the right track with wide torque band: I rallied (SCCA, NASARallySport, RallyAmerica) for a long time and it is the same thing: wide torque band. The low cranking pressure makes sense with those pistons; those look like low compression after market pistons. (With that depth in the hole make sure it is not a 318 !....340 standard bore should be 4.040".)

To get that wide torque band and that power range, you are going to have to push the compression ratio up to around 10:1, get the breathing up, and then use the right cam without too much duration. You should be going to different heads with more breathing to make it to those HP numbers. Or porting yours and opening up the valve sizes. Look at this link for a while to see where your head flows need to be; the EQ or indy-X iron heads, or Edelbrock aluminum head flow numbers in their stock form are where you need to be shooting for.
#1---Head Flow Charts & Comparisons

Both of those above heads have smaller, so-called closed combustion chambers so will make it easy to get the CR up. That is what you will be fighting with those stock heads: the open chambers take a different tactic (lots of shaving and standard early 340 pistons that stick above the deck) to get the CR up and you still cannot get effective quench out of the setup. Quench is an aid to avoid detonation, which will be important here, and also helps combustion efficiency.

For CR in the right range with these closed chamber heads, you need to go with some flat tops and put them near to zero deck. KB243's are one choice; they are hypereutectics and light and I have rallied on hypers with 14-15 psi boost with no issues. There are also Ross pistons for forged units, which would be good for durability in this use, but forged are heavier. Lighter pistons and rods lowers crank stress.

To fight detonation with a shorter duration cam used to keep the low end of the torque band alive, aluminum heads have a distinct advantage. I personally would go straight to the Edelbrocks and minimize the detonation issues and get right to the breathing numbers needed.

I'd be reconditioning the rods, or, better yet, going to SCAT rods, which are lighter.

Look at the oiling mods in the stickies section of this subforum. The high RPM stuff is less applicable IMHO; I think you will need to consider a slightly deeper pan built with baffles to keep the oil around the pickup. And I'd put in an oil cooler and remote filter to add oil capacity and cooling. Those don't cost a lot but add a lot.

The intake and headers are good; just stick with what you have.

One more word; if you sre $$ limited, consider selling the 340 parts and get a 360. There are more pistons choices. The rest is the same cost. I say this because in my view, the ideal engine really only uses your block and crank. If you like the 340, stick with it; those 3 numbers in that sequence truly do have a certain mystique, but the HP does not care what produces it.
 
If you are buying rods, pistons, and boring... It's not that much more for a stroker kit. And extra $ spend per hp/TQ gained from the stroker higher value most upgrades. And you get better drivability at lower rpm to get a specific hp/TQ (valve train parts $ savings). Stokers soak up cam.

This is what I did:

416 from a 340 block

-Scat 4" cast crank balanced rotating assembly.
-9.7 to 1 comp with quench. (Calif. 91 octane)
-Hand/home ported edlebrock head. There are less expensive heads now.
-Hand ported matched M1 single plane (trying to shift power torque curve up) I have a RPM on shelf.
-Comp 274S cam (236/242@.50, .502/.511)
-Milodon road race pan
-TTI full headers. Before they had TTI shorties.
-Oil passage clean ups.
-BG silver claw 750 (wet flow). Might be little too big for farting around running errands around town.


You could run that combo with hyd ex275 cam and stock rockers and used rpm intake. Makes HP by 5800rpm so it's easy on valve train.

HP/TQ-wise.....guys in stock SRT challengers at track can't pass me out of a turn over a long straight.
 
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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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Aluminum heads would be a nice improvement here, not only from a power standpoint, but because it takes weight off the nose of the car....and just like with oval track racing, handling is more important than the HP in my experience........
 
Hi mate, looks like a top combo going on there. I'm doing something very similar to have fast fun family car - the wagon in my picture.

318 heads with 2.02/1.6 valves, ported and decked.
360 block @ .040" over,
KB107 pistons,
Scat cast crank & stock rods,
Crower 31243 cam with .480/.503 @ 227/237 (@.050")
Speedpro hydraulic lifters & stock pushrods,
Rochester Quadrajet & ported Crosswind manifold.

The static compression works out at about 11:1 with the decked heads so it will need a strict diet of 93 (98RON, readily available here).

If I had to go again I'd probably choose a milder, more modern camshaft grind but this one was only $50 so I couldn't pass it up. Either way it'll be a bit of a screamer once it gets going and still have buckets of torque in the good usable 2500~3500rpm range.

The big spreadbore will help up top and down low but might hurt a tad in transition through the midrange.
 
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.
Click to expand...

Crack her open and have a look.

Plan A:
What would the cost be to freshen up this old 340 and what would you do to it? Cost??
Click to expand...

Go to Falcon Global on eBay. Get a 'Master Engine Kit' that contains the gaskets, rings and bearings for the engine. It'll be under $300 I think. Install, good to go!

Plan B:
So I am think about possibly doing this:
408 block / stock heads / cam
What would this motor run like? About ?? HP and TQ?
Click to expand...

Should have an easy 350hp assuming even a modest 9:1 compression and a half decent cam and induction. Could easily be a fair bit more. It'd most likely be a big, lazy torque monster under 2500rpm and then roll over about 5500rpm with a good topend.

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.
Click to expand...

Cam will be your biggest worry with converter and ring gear. 2.92 or 3.23 is a good compromise, anything less than that and you will lose out on response and acceleration a fair bit... although 2.74's are great for highway. Anything under .475 lift and 225 duration at .050" should be quite nice with anything except a 318... then you'd want about .440 / 220' max in stock form.

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?
Click to expand...

Good? New motor.

Bad? Big expense. Lots of work. You already have a good engine from the sounds of it!

I would stick with what you have, tear it down and see what you've got. If the internals are fine then I'd re-gasket, ring and bearing it and run that sucker.

Cheers - boingk
 
boingk said:
The big spreadbore will help up top and down low but might hurt a tad in transition through the midrange.
Click to expand...

I'm not remembering how that particular carb worked. It's been a few decades. Can you slow down the opening and or the opening rate of the secondary?
 
Scottd9990 said:
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?
Click to expand...

I'mnot sure what your machinist shops costs are. They vary to much local, never mind around the country.
The idea of the create chort block is a nice one. Double check with the vendor to as what exactly it is and needs. What balance is it and what flex plate does it require, etc...
Go see a FABO vendor, Pace Performance, member Johnny Pace here is mpost helpful.

I'd look at a cam like Boingk has. OR a slight smaller depending apon the track straight away length. The big cubes eats up a little duration. Knowing your turning a lot requires more torque than HP. Check with the fellas here that race this circuit.

Keep working on your steering and suspension!
 
The big spreadbore will help up top and down low but might hurt a tad in transition through the midrange.

This why I am considering running a large 500 cfm + 2 barrel carb. I have one to try at least and see if it makes good power.
 
If your worried about the carb transition, use a well tuned vacuum secondary carb...and a stroker will make a ton of bottom end torque, more likely to "blow off" the tires and be harder to control than a stock stroke 360......PM if you want to get serious
 
Scottd9990 said:
The big spreadbore will help up top and down low but might hurt a tad in transition through the midrange.

This why I am considering running a large 500 cfm + 2 barrel carb. I have one to try at least and see if it makes good power.
Click to expand...

They don't rate airflow the same way when listing the CFM specification. This link should help to explain the differences. THE CARBURETOR SHOP / Carburetor sizes and CFM

A 500cfm 2 barrel only flows 353cfm when converted to the scale 4 barrel carbs are tested at.

I would definitely recommend a mechanical secondary 4 barrel carb for the precise throttle control needed for autocross. I would stay on the smaller side size wise for crisper response.

A vacuum secondary carb should be avoided because it has a delay when the secondary's open and close. This delay will cause the car to be harder to control in a drift or slide when you need to lift and get back on the throttle quickly which will hurt your times and your ability to control the car under power. You want the carb to immediately do what your foot tells it to do.
 
Good point on the vacuum secondary carb, that i didnt think of, they work good for wot acceleration, but not very good for on/off/on throttle situations......a mechanical secondary would be better, and even better yet, fuel injection!
 
Scottd9990 said:
TNT
You are right on the money of what I need the motor to do
Click to expand...

I autocross too. I haven't raced in a few years but next summer I'll be screwing around doing some autocross in my '78 Magnum for kicks.

That looks like a stock '73 340 engine to me.

Considering your budget I would sell the 340 and buy a the lowest mileage 360 magnum you can find to build. Sell your intake also.

With your budget and gearing in mind keep it pretty simple. Put some Eddy magnum RPM roller heads on it, switch to a performer rpm air gap magnum intake with a 650-750 double pumper. Use a premium double roller t-chain w/ tensioner, have camshaft reground or buy a new roller cam and put some adjustable roller rockers on it with new pushrods too. I would use a HV pump with a HD pump shaft and some oiling mods listed above in sticky thread(not sure how much applies to a magnum engine) and a Kevko oil pan.

You'll need a B&M flex plate meant a 360 magnum and to remove the balance weight from your converter or use a slightly higher stall quality convertor(someone would probably buy your stock one). I'm assuming you use a sure-grip in the rear diff.

That would be a good budget build for you and should achieve your goals. There are quite a few members here who are very knowledgeable the magnum engine swaps that can answer any questions. I would think a 650 double pumper would be my choice in carb size personally.

This should stay within your budget once you add the sale price of the 340 onto it and be a great set-up with the extra power and weight savings.
 
All great ideas TNT. What do you think about the short block 408 from Summit? Anyone run one before??
 
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