How can I get more power from a 428CJ?

[ERA427]

So I (with my ERA 427) am running a stock 428 Cobra Jet build with headers/pipes, and Holley 750. I’ve got a 3.54:1 rear, and a TKO 5-speed. I don’t take it to the track. It all runs great (starts right up, idles fine, good throttle response, never stalls, and sounds healthy at all rpms).

Now, I know most of you would say “don’t mess with it!”


But “if” I wanted more power, what do you all think would be the best place to start? Is there anything that wouldn’t come with a bunch of drawbacks?

1st and 2nd gear seem to have all the power I could put onto the pavement. 3rd is good, but 4th and 5th gears feel unimpressive. Or another way to say it is that 0-50mph is good enough but from 50 up, I wish it felt like it had more kick. No, I don't "need" the power for anything. I just want it to pull better at higher speeds without giving up on the low end.

I'd prefer to add power as opposed to change the rear gear.

I like the authentic-ness of my build so I’d prefer something that isn’t obvious upon quick inspection.

I’m not expecting any easy answers. But wondering if anyone has done any mods that didn’t come with a bunch of new problems. Is there a "single" upgrade that makes any sense?

For example, is there a different cam that is simply "all around better" and doesn't necessitate a all sorts of other mods to make it work well?

[undy]

Give us a baseline as to where you're at now with the engine, cam, heads, intake, CR, displacement etc... That will give a starting point.

[ERA427]

It's totally stock as far as I know. It's a 1969 428 CJ. It's got the CJ heads, with PI aluminum intake, Holley 750. I don't know the cam but I did speak with the original engine builder who didn't recall changing it. So it should be in that 410HP/455lb/ft range that most people seem to think is what a stock 428CJ really had - plus the headers which would add a bit to that figure I believe.

[ERA427]

I'd love to know if there is something that would add about another 50hp, that wouldn't have significant drawbacks to the low end pull.

[blykins]

Well, a cam is going to pick it up more in the upper rpm range. It will essentially shift the hp curve to the right. That means you'll lose some of your bottom end, but you'd gain top end.

Head work would increase power everywhere and would let your cam work easier, so the power would stay with you more in the higher rpm ranges.

Do you have a budget figure in mind?

[ERA427]

no budget in mind yet. Which type of head work are you referring to? What would you expect the net effect (gain) to be and what would that cost?

I'd like to keep the heads since they are real CJ heads.

[blykins]

Porting the heads. Depending on who did it and what kind of budget you have, you could gain 30-40 hp.

[ERA427]

how much $$$ does that typically cost? Does it require taking the car to someone, or sending the heads somewhere? Does it also require modifying the intake manifold?

[blykins]

$600-$1000 depending on who does it and how extensive of a job it is. You would have to pull the heads and send them off. The intake would benefit from matching the ends of the ports to the heads.

[DanEC]

A true CJ motor is a pretty nice motor and yes, the restoration examples I saw at Keith Crafts shop were pulling down about 410 HP stock according to the dyno operator. You might consider a set of Edelbrock heads and just put your original CJ heads away someplace safe. Fairly easy bolt on change.

My heads are 1961 390 HP heads (as in 390/401 HP) that Keith Craft ported and put larger valves in. They are very close to the same as your heads now except for maybe a little additional porting. I asked the dyno operator how much additional HP my engine might have made had I gone with Edelbrock heads and he guesstimated about 30 - 35 HP based on his experience.

Something to consider.

[ERA427]

interesting - thanks. Sounds like a lot of $$ and work for 30-35 hp. Nothing's ever easy here is it...

[blykins]

Horsepower isn't cheap and a 30-40 hp gain isn't anything to sneeze at.

Almost anything else you do will either move the powerband up extensively, or cause you to have to change a lot of parts.

One thing that you can look at it is your timing curve. A distributor with total timing in sooner than later on a lighter car will make the engine feel snappier.

[JBCOBRA]

+1 one on the timing.
...in the summer when it is really hot out, your engine is not going to feel as snappy compared to nice cool spring or fall weather.

[ERA427]

I like the timing idea. I have a Mallory ignition. How do I get the timing optimized? Is there a way to do this at home or does it require some specialized technology to perform an analysis? I live in the Boston area. There is a dyno place in town. I wonder if they could be a good starting point...

[ERA427]

either way - sounds like I need to read up on this a lot more before messing with my problem-free engine.

[JBCOBRA]

Mason Racing Ignitions in Swenksville Pa. re-worked my distributor for optimum curve, re-bushed etc... for very fair money. He has a distributor dyno too and dials it in. It was interesting to watch him work his magique.

[blykins]

A dyno would be the best scenario, just to see what the engine likes. It will probably like anywhere between 36-38 degrees total timing, all advance in by about 2700-2800.

If you're mechanically inclined, it's something that you can do in about 10-15 minutes with a few hand tools and a timing light. Mallorys are a little more involved to change the timing curve than an MSD, but it's still easy.

[ERA427]

JBCOBRA - I assume that you took the whole car in there and had him tweak it? What was the net effect and how much did that cost you? Were you having problems before or just making sure you were as optimized as possible?

[olddog]

I never hear much talk about intake charge temp around here, but this can be the cheapest Hp you can buy. Air density is proportional to the absolute temp (use the Kelvin scale). If your under hood temp is 140 F (assuming your carb is pulling in under hood air) and you can reduce that air temp to 90 F, air density increases ~9%. So a 335 Hp 428 would get a 30 Hp increase. Now the air temp that actually matters is after it is pulled into the cylinder, and the air temp increases coming through the intake manifold. So just because you drop the air temp entering the carb by 50 F, it doesn't mean there will be a 50 F drop when the air gets to the cylinder. Also a 335 Hp 428 is a number that was corrected to what the engine would have made at sea level and I think 70 F air, so you most likely are not producing 335 actual Hp where you are at.

But the bottom line is that a good air gap type intake (not sure about availability for FE) and getting outside ambient air to the carb can be a big help. This is not going to break the bank and requires little modification to the engine.

Point #2. Most engines have not been tuned to get the correct AFR and best timing. There is usually Hp left on the table that can be grabbed by a good Dyno tuner. Dollar per Hp gained may not be so cheap, but after an intake and routing cool air to the carb would be a good idea anyway.

[DanEC]

Originally Posted by ERA427

either way - sounds like I need to read up on this a lot more before messing with my problem-free engine.

There is a lot to be said for a problem-free FE engine. Some careful tuning with the distributor and carburetor might be your best bet.