More Power?

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71Duster

71Duster

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Here is my current combo, it's a street driven car and full bodied etc. I don;t want any steeper gears then I currently have. I'm looking for more power by tweaking my current combo. Contemplating cam changes and or Edelbrock heads but not sure if there are enough gains with the heads on a mild application.

Thoughts and opinions?

650 Speed Demon mechanical secondaries, on an edelbrock rpm intake

Stock J Heads 2.02 intake 1.60 exhaust and Crane Gold 1.5 ratio rocker arms.

3.55 gears and a 727 with 3000rpm SMR Convertor- stage 2 shift kit from transgo.

It runs a Hughes cam #heh2328al

111deg lobe seperation/installed centerline 108deg
intake lift .506/ exhaust .524
[email protected] Intake223deg/ Exhaust 228deg

Engine is .060 over with Keith Black Hypereutectic pistons on stock rods and a stock forged crank.

Ignition is an FBO box
Distributor was curved by Dave's Mopar in Calgary to these specs.
TTI Headders with an x-pipe into Dynomax Ultra Flows.
 
Heads make or break an engine so it's possible Eddy's might help. Then again maybe just some bowl work and port matching with your J heads would suffice. Are you positive on the valve size? I ask because most J heads are 1.88 intake valves. Only the first year or two were 2.02 valves.

What size engine are we talking and what is the compression ratio? Have you ever ran the car to see what it runs and how much does it weigh?
 
It's the numbers matching 71 block still in the car. When the engine as rebuilt I asked and they said they where.

By air/fuel ratio the tune is pretty on but it seems lacking in the bottom end. Contemplating a chassis dyno tune depending on cost.

In a perfect world and the car being set up right and the engine being what the specs say it is in a 71 Duster in full street dress what should it be good for?
 
Ok. Did you do the compression math when building it to know what the actual compression is as that came make a big diff. especially in making torque. The mechanical secondaries can be somewhat hard to tune with a lower stall and tall gears and a dyno tune can find hidden issues in tuning that can make a great deal in power so I think that's the first thing I'd do. That'll tell you what numbers it's making and give you an idea if something is not clicking. I would think it should be making in the 325-350 hp area. In stock form those cars tuned well would still run pretty stout even if they were lower compression than earlier 340's. Not sure on the exact numbers but I think they were in the high 14's so with the mods you've done and good traction you should be down in the mid/high 13's at least. Again have you ran it to know what it's running? The 1/4 mile speed is generally a good indicator of the HP it's making.
 
Some thoughts:

I agree with Fishy. I'd double check the numbers and see what the actual compression is. The combustion chambers on some of those old heads are HUGE. Also, plug in the specs off the cam card to find out where your dynamic compression is. If its low, you could get a cam ground to crutch it.

You might look into the Indy X heads also. They seem to make pretty good numbers, are cheaper and have an X on them (LOL). Unless they milled the bejeez out of the original heads, the Indys would definitely up your compression, plus you get the more efficient new style combustion chamber.

With that stall it might be hard to pick up umph down low at part throttle.

Steve
 
I have a set of J heads that came stock with 2.02's. A basic bowl porting and gasket match will do very well. A good valve job with a comp. back cutting of the valves and seat area help alot.

Mill if needed. Pay attention to this area. Your ratio should not exceed 10-1. Less is OK. Keep it above an actual 9.0-1 and it will be fine.
 
Unfortunatly I left the compresson math to the engine shop who never provided me with any numbers.

I ran it down the strip once and the first run it boged out do to the heat in the long staging lanes and posted a sad 15.2 I can't remember the MPH the next run with less heat issues it ran a 14.8 The MPH where in the low 90's My 60 foot times where in the second range however.

I broke out on my second run a the 15 was my only test run so I put that as my dial in.
What I find with the car is off the line it's not that stunning, again I know gears would help but to keep it a cruiser with some distance ability I like the 3.55's but it won't even chirp the tires out of the hole.
 
My guess is either that the transition circuit on the double pumper (and maybe the jetting) is way too rich or something is up with your converter.
 
Well those numbers where done with the old 2500rpm convertor I just out a brand new SMR convertor in a few weeks ago, it's help drivability for idleing in gear when cold and has more punch for sure. The carb is the one consistant thing since day one I've had the Demon and it's been a bit of a bear.
 
It's hard to say without the static compression figures... But what I see is the pistons, if it wasn't carefully blueprinted with them and the head gaskets are the std stock replacement you have a static ratio around 9:1. That's low for the cam you have. On top of that, you have a very large double pumper carb on it. The 650 Demon is equal to a 750-780 Holley. IMO, the carb is too large, and the cam is too. It simply will feel soft unless you rev it. What is your initial timing set to?
 
As far as the jetting and the carb goes the engine shop helped tune it with an A/F meter in the pipe and it was on the road.

Everything about the heads is stock nothing special or wild just a check over and repair as they needed the headgaskets are just the standard Fel-Pro's.

The carb was speced out by the infamous FBO I've never been told by anyone before it's too big, I know Demon does wet-flow numbers as opposed to dryflow. I run the car on 91 octane and the initial timeing is at 18 deg.

What sort of numbers would you expect for compression with an aftermarket head assuming it's as low as it sounds?

If I get time this weekend I'll run a compression test and see what numbers show up.
 
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