Approximately 10 years ago I had a stock 1973 340 engine completely rebuilt by my local speed shop. I bought the complete original motor for in my ’73 Road Runner, but after finding that it had sand in the oil pan from the previous owner not properly sealing the ports when he sand blasted it to clean it up, we realized that a complete rebuild would be necessary before attempting to fire up the motor. At the time we wanted a budget build and the speed shop happened to have a used B&M supercharger laying around that we ultimately decided to incorporate into the build. The total cost back then was around $4500 and through dyno testing they proved the motor had 371 hp and 402 lb./ft torque (see details of this build listed below). I was really hoping to hit the 425 hp mark so that I could have the satisfaction of knowing that I had a small block motor cranking out around the same amount of hp that was advertised with the stock 426 hemi engines (I know the 426’s were probably advertised lower than what they actually put out), but that didn’t happen.

Now several years later I’m almost ready to put the motor back in the car, which will primarily be used for street use (kind of a pro touring vibe to the restoration I guess). I located an original B&M blower intake manifold because I wanted a nice clean manifold (my custom manifold worked, but wasn’t really show quality) for appearance purposes. I could only buy the manifold in a package deal, and what the seller told me was a 144 supercharger ended up being a 162 supercharger much to my delight. So starts the turmoil in my engine plans. I want to upgrade to the larger blower and I still have the 425 hp goal in my mind. Other upgrades that I have to go along with the engine include TTI ceramic coated headers, Rev-N-Nator electronic ignition, Firecore distributor, coil and wire set, and a Powerjection throttle body fuel injection setup. The engine will be matted to a Tremec TKO-600 5-speed transmission and an 8 ¾ Sure-grip rear end (gear to be determined, leaning towards 3.73 or 3.91). The car also has subframe connectors, an adjustable rear pinion snubber and HD big block leaf springs to handle the increased torque.

Through researching the topic I came across a Mopar Muscle magazine from 1992 featuring the Dick Landy Inc. supercharger engine build. In the article, dLi is claiming 450 hp from a 144 supercharger on a 340 engine with mild porting to stock heads and an upgraded cam, while they claim 500 hp from their high-engery supercharger and moderate porting of the heads. With this in mind I’m starting to wonder why my engine is built nearly the same, minus the porting work, but is producing way less hp on the dyno. I realize that dynos can be calibrated differently, but at 80 hp difference between their engine and mine I’m a bit concerned.

I’m looking for some suggestions on what to do to give my engine a little more power (425-500 hp range) without completely rebuilding it once again. Simply porting the factory heads, upgrading to aluminum heads, and even scrapping everything to buy a long block stroker motor have all crossed my mind. The only consistent thing I know is that I want a 340 block and the B&M forced induction setup that can be run on pump gas (or 92 Super if necessary), everything else could be subject to change. What I need is some input from Mopar engine gurus who know more about this sort of thing than I do. I’d like to get the car on the road next year, so what I’m looking for advice on the best way to liven up the engine without going completely crazy and dumping a ton of money into it. I could really use some guidance so I could quit stressing and pick a direction to take this engine build. Sorry for the long post, and thanks for taking the time to read.

Current Engine Specs.
Engine Displacement: 345 ci
Peak Horsepower: 371 at 5400 rpm
Peak Torque: 402 lb./ft at 3900 rpm
Bore: 4.070
Stroke: 3.310
Compression Ratio: 8.27:1
Crankshaft: Stock, cast-iron
Main Bearings: Sealed Power, 4923MA10, Bi-metal
Connecting Rods: Stock forged
Rod Side Clearance: 0.010-0.140
Rod Bearings: Sealed Power, 2130CP10, Tri-metal
Pistons: Speed Pro, L2316F30, forged
Rings: Sealed Power, E286K30, Iron Moly
Ring End Gap Clearance: 0.026/0.026
Cylinder Heads: Stock 587, machined for larger intake valve
Combustion Chamber Size: 68cc
Intake Valve Size: 2.02
Exhaust Valve Size: 1.60
Valve Springs: COMP Cams 995-16, 1.700 installed height
Rocker Arms: Mopar Performance stock type
Pushrods: Stock
Camshaft: COMP Cams 20-223-3 Hydraulic
Int./Exh. Duration at 0.050 Lift: 224/230
Int./Exh. Max Valve Lift: .477/.480
Intake Centerline: 106
Lobe Separation: 110
Timing Set: Stock
Intake Manifold: Customized low profile single plane aluminum Edelbrock blower manifold
Induction: B&M 144 Roots-type supercharger (2.08:1 drive ratio, approx. 7-8 lbs boost)
Fuel Delivery: Demon 750 cfm blower carb
Ignition: Mopar Performance
Timing Specs: 33 degrees total
Exhaust/Headers: Hooker Super Comp.

Was the original blower the smaller one when it was dyno tested? Peak HP is determined at certain RPM, change he amount of boost and the HP and RPM can and will change The key to making power on any motor is airflow, the more air and fuel the more power you get If I was you and the smaller blower was on the motor I wouldn't change anything on the motor until I ran the bigger blower BTW, I have dyno tested several roots blown pump gas motors, I have seen 100 HP gain by going from 12 % under driven at 7 lbs of boost going to 13 % over driven with 12 lbs of boost with race gas The bigger blower can be ran slower and make the same boost while forcing more volume through the motor at WOT which will make more power Slowing the blower down also results in cooler inlet temps, which is really important to help prevent detontaion. If your not going to use the bigger blower I would change the heads to a good set of new aluminum heads like the Edlebrock or Indybrocks with bigger ports and valves with the sme size combustion chambers as you have now, that will allow more air into the motor as well as help keep the combustion temps in control in the cylinders IHTHs

Compression Ratio: 8.27:1 is low, killing your HP

http://www.uempistons.com/kb_car/performance.php?action=details&P_id=135

not sure what will happen if you go 9.5:1 with a blower and use pump gas...

maybe someone with a blower can give you pointers

personnaly, i'd just stick with what you have, drive and enjoy it

Is the 371 w/ boost? I would have thunk you'd be well over the 400 mark w/ 8psi of boost. If you are running a 5 speed I'd drop down to 3.55's The boost will come in quicker and you will have more of a "powerband" You could also consider going to 1.6 roller rockers. That might help a tad.

1. Your heads are the #1 thing I see holding you back. The larger valves if no porting was done don't do much if anything. Even though there is a pump pushing air through them, having less restriction in the intake ports helps more air get in.
2. I'd agree that even a set of out-of-the-box Edelbrock heads will help in three ways:
a. Easier work for the supercharger.
b. Allow you to run more compression ratio that'll help across the board.
c. Better combustion chamber should help as well.
3. If these changes don't get you where you want, turn the supercharger faster. As posted above, that's the quick way to more power. Use of a larger charger is another way to do the same thing.
4. Keep in mind that pushing harder on the air puts more heat into the air (adiabatic heat of compression) so anything you can do to make the supercharger's job easier helps across the board.
5. The last step is getting the exhaust out. Bigger horsepower means bigger headers.

I don't see why you cannot get an easy 550 crankshaft hp with your setup and my proposed mods. That's just 1.6 hp/cubic inch.

R.

Well for what it's worth....

My dad has been running a supercharged stock block, stock crank, ported iron headed, 340" since '85. The motor is ~8:1 and had a cam very similar to yours in it for most of it's life (finally upgraded to a R3 block, and big solid cam in late 2000's).

At 3850lbs, the car had run a best of 11.60's@117mph with 12~13psi. Now this is with a V671 blower, not the B&M stuff, but you can see the potential and durability is there for what you're talking about.

I honestly would put it together with what you have. If you're unhappy with the results, you can always make changes later, but what you have isn't mismatched really at all. Might have to play around with the boost/timing to get the tune right, but it'll make over 400 with it's eyed closed once you get it right.

Bolt that big blower up and let it rip!

Id love to see pics of your setup. I have a NOS B&M 162 supercharger setup. But I need to build a shortblock for it one day...

Camshaft: COMP Cams 20-223-3 Hydraulic
Int./Exh. Duration at 0.050 Lift: 268/280

That's a typo, right?

I should have clarified that motor was not a blown SB, it is a 496 C.I. 426 style Hemi with a Littlefield 10:71 and two Carb Shop 1050 Dominator blower carbs. Sorry for not being clear to start with BTW, I have built several N/A SB 340 NHRA stocker motors that made 430 HP over 12 yrs ago, more is possible now with the current technology and parts

just bumpt the compression to 10 or so and ditch the blower and make the same power.

Seems pretty lame that motor only making 370/400 a mild N/A build can do that without trying. I think something big is wrong with the motor, cam timing, leakdown...

What manifold did you start with?

Ditch the Fram filter.

one of the key to forced iduction is camshaft
you will need a cam with wide lobe center
112 to 116 degres.anything less will create too
much overlap,meaning you will blow all the boost
out the exhaust.from your post you got the wrong
cam.