[gkulland]

I have a 1973 with a 340 and am thinking of getting the Edelbrock Performer RPM power package. It sounds like a good package but I would just like some opinions/testimony to the package.

[dave-r]

It will work. It will give you more power.

[Eddie]

I have a 1973 with a 340 and am thinking of getting the Edelbrock Performer RPM power package. It sounds like a good package but I would just like some opinions/testimony to the package.

Your 340 is a good motor. But there are a few things you can do to help it along. I assume since your looking into a 340 engine package that a re-build or engine resto is in order? If so the Ed's package is a good one. There are some that are a bit better though. What are your plans for the engine? racer or street? The 1968 340 is a much better engine due to it's higher comp. ratio and camshaft plus it had a 2.02 intake valve compared to your 1.88 intake. By 1973 the 340 had been 'converted'(some use the word emasculated) to a lower comp. ratio, softer cam, bigger carb. It was in it's last year. I would try and re-create a 1968 340 engine! If you plan on re-building it a new set of pistons with a higher compression height to get the comp. ratio up in the 9:0-10:0 range will give you some torque. Your's was a 'meager' 8:5 to 1 if you were lucky! Then a new fast rate of lift,(Engle, Scott Brown, Comp Cams, Ultra-Dyne, Bullet, Crane, ect many choices here), would also get you more power then the stock juice stick you have now. On to the heads, you would be much better off buying a set of Ed's heads, or Indy/Brocks,(Modified Indy edelbrock castings), or a set of Mopar perf. ones either way you'll have more airflow and better valves, giudes, ports ect or re-work your old castings but be prepared to pay as much for re-conditioning your old heads as a new set of ready to bolt on heads as described from the aftermarket. The intake manifold should be changed to an Edelbrock Performer RPM AIRGAP. This manifold is a jewel. It doesnt give up anything to the single planes and makes more torque/ Power from the start of the RPM band to 6,000+ RPM's,,finish it off with a Thermoquad or Holley/Edelbrock 650/670-770 CFM Carb. Headers would be nice or factory manifolds and duals with free flowing exhaust system 400 H.P and the same torque should be pie. I ran a 340 in the 70's and now have a modded 360 in my truck and have usedmany of the parts listed above. They are strong power plants when used with the right COMBINATION of parts, the secret is not to over-cam especially with a low comp. ratio,(stock 1973 ratio), if you DO use your stock ratio, there are some special grind cams that make use of your meager ratio and will still make decent power. Pat runs a 340 so does Jon.

[gkulland]

Thanks eddie, I am going to rebuild the engine and am browsing to get pistons to get me up to a comp 9.5. I have heard nothing but high praises about the airgap manifold, needless to say im sold. Cams are a dark area for me, but reading and talking to people a lot helps. HAGO.

[Eddie]

Here is a site that can help you on camshaft selection. http://www.webcamshafts.com/pages/cam_glossary.html it will also give you an understanding of how a camshaft works in a V-8 4 cycle engine. Nothing effects engine operation as much as the camshaft. And if all else fails there is a MoPar Camshaft 'guru' who can pick the perfect cam for your engine and application, his name is Scott Brown and his number is 1 -616-499-6223 I just recieved a cam from him and he'll make sure you 'pick' the right one. I wouldnt just 'pick one'. I would ask a knowledgeable person before ordering any parts. It's the 'combo' that 'makes' the engine!

[patrick]

I have a 1973 with a 340 and am thinking of getting the Edelbrock Performer RPM power package. It sounds like a good package but I would just like some opinions/testimony to the package.

I would listen to Eddie and, Dave. They do know, what they're talking about. My #'s 340, was built by some caring, rich parent's, of the previous owner. I have no idea of the exact specs. the motor is but, it run's very well. They spared no expense. I had some tuning issue's but, got turned on to Don at F.B.O. He got me super close and, Eddie fixed me with the turn of a scew driver. What messed up the tune of the car was, I got rid of the header's. Car was still, a bit lean. It runs hot and, fast now. Even with the stock head's. Smokes the tire's through, all three auto, 3.23 gear's. Still have a suregrip issue. Clutches, I'm sure. Getting ready to install some T/A exhaust manifold's. That will open her up, again. And, I'll have to retune again but, it's a labor of love. The Eddelbrock package is, a sweet way to go though.

[Jon]

You may be able to get away with 10.5 to 1 depending on the fuel availble over there. Mine is right on the verge of pinging at times with the 91 octane sold here. I understand if you go aluminum heads it allows for about 1 point higher due to heat transfer. Eddie probably knows for sure.

Hey pat, I didn't forget about checking into those exhaust manifolds. The guys wife is ill and I didn't want to approach the issue right now.

Jon

[Eddie]

10:5 to 1 with closed combustion chambers and no more than .060 quench at TDC, should be fine with 92-94 Octane gasoline and alloy heads should be no problem.

[dave-r]

I agree. But I would have thought 40 thou quench would work better and still be OK?

[Eddie]

Yes Dave. It would be much better. A zero deck piston height,(as measured from the piston pin centerline to the top of the piston head and the top of the block/cylinder), a .040 gasket which would give both piston to head clearance and have excellent quench. I put the .060 measurement up because this is the outside limit. You have to have at least .030 piston to head clearance, more with alloy rods and forged pistons,(due to piston rocking at TDC). The 'quench' factor is usually embraced by Pro Engine builders as between .030-.060 this way you can tell the machinists what you want in regards to gasket thickness, piston deck height, block deck re-surfacing, and the type of gasket you wish to use ectt If he does choose Edlebrock heads, they make the 1968 340 which had a positive deck height,(.040 If I remember right), open chambered heads, which have fallen out of flavor due to the flame travel inefficiency with 'domed' pistons and open chambers. Sorry to have rambled on

[Jon]

What is a 340 fitted with from the factory in 1970 with X heads?

[Eddie]

'Fitted" I dont know what you want answered Jon, you mean the pistons compression height? The factory pistons were 'in the hole' a bit, probably around .030-.040 or so. They relied on chemical enhancement,(octane), instead of combustion efficiency,(closed chambers and squish or quench), because it was much cheaper to machine and produce it this way. The only 340 engine to my knowledge that used a positive deck height,(the piston top sticks above the block deck), was in 1968 ONLY. This design has fallen out of flavor with most engine combustion chamber designs which favor small chambers, and dished or reverse domed pistons). This design is also more 'detonation, pre-igntion resisitant due to the 'cooling' effect of the colliding flamefront and gasses.

[Jon]

Yes, that's what i wanted to know. Thanks.

So say a 10:1 compression ratio on two similar engines is not comparable unless the same head and piston designs are used. (as far as combustion, detonation, performance, etc...)

[Eddie]

Yes, that's what i wanted to know. Thanks.

So say a 10:1 compression ratio on two similar engines is not comparable unless the same head and piston designs are used. (as far as combustion, detonation, performance, etc...)

Your'e welcomeYes, as far as my limited knowledge can assume. If I were Gkulland, I would investigate the addition of a stroker crankshaft. It's hard to beat the torque of a 416 stroker! This is the power you will feel as you leave the line. But a Eds headed 340 with a good cam will also pull very hard too. Jon,I can remember some of the older V-8's that had a two-barrel carb, "closed" exhaust system, hot underhood air, heavy car, that would 'ping' with anything over 30 degrees at 2000 RPM's The chamber designs in these new alluminum heads are really sweet. Efficient, smaller, fast burn, so it's easy to build compression with a flat top piston, which is key to good torque. The newer GM LS series of engines and the Gen III Hemi accel at this design. The Eds 340/360 Heads are heart shaped closed fast burn blah blah. It would be hard to find a better dual purpose head,(180 CC to 200 CC intake port). The Magnums are nice but have a weaker stud mounted rocker system compared to the old MoPar shaft mount which the eds 340/360 heads possess.

[Jon]

My thought is instead of the next valve job on the X heads, just bolt on aluminum Edelbrocks in combination with my stock 10.5:1 (Speed Pro) pistons. That should alleviate any worry of detonation, and increase horsepower to boot.

Probably need new rockers and pushrods also??

[dave-r]

Forget about compression ratios when worrying about detonation.

What you need to worry about is cylinder pressure.

Cylinder pressure is not just about compression ratio. There are other factors that have as much to do with what the pressure ends up at.

Number one is valve timing.
In general, the bigger the camshaft you use, the less cylinder pressure will be because of the early/late intake valve opening/closing points.
So with a bigger cam you need more theoretical static compression ratio to make the same cylinder pressure.

A second factor is cylinder head material type.
Aluminium heads cool the cylinders faster because of their fast heat transfer. Heat is directionally proportional to pressure.
So with aluminium heads you need to also increase the static compression ratio (by one full point) to maintain the cylinder pressure.

Other factors such as exhaust efficiency, carb size and intake manifold design also effect cylinder pressure.

Of course increasing cylinder pressure makes more torque. So you don't want to avoid it completely. You want more pressure but without the detonation.
This is where fuel quality, quench, rod to stroke length ratio, piston speed, cylinder design, ignition timing etc all come in.

[Jon]

Great info Dave. If keeping the same cam just replacing heads (to aluminum) the net effect should be less cylinder pressure. However if the Edelbrock heads flow better would that increase pressure again?

Like I said it's right on the verge of pinging now. With cooler weather like we had yesterday (plus month old gas) I noticed a bit of detonation when stomping down on the throttle to pass.

[gkulland]

Thanks for all the useful information!

I have another question though about cylinder heads, I found out that my motor was built in 67 and I looked up the numbers on the heads and I believe they are "X" heads with the larger intake and exhaust.

SO, would it be worth it to buy new heads or just fiddle with the ones i have now?

[dave-r]

Great info Dave. If keeping the same cam just replacing heads (to aluminum) the net effect should be less cylinder pressure. However if the Edelbrock heads flow better would that increase pressure again?

Like I said it's right on the verge of pinging now. With cooler weather like we had yesterday (plus month old gas) I noticed a bit of detonation when stomping down on the throttle to pass.

If the Edelbrock heads have a smaller combustion chamber it might work out just the same.