new 408 low dyno numbers

[rhauf]

Hi everyone, i just built a 408 with the fallowing:

95 roller block
crane roller cam with 224/232 duration 5.40/5.63 lift 114 LS
Edelbrock RPM heads w/ 2.02/1.60 valves, 185cc runners
forged pistons 10:1 compression
edelbrock 750 carb
summit intake (looks like edelbrock clone)
mallory distributor/electronic
shorty headers
dual exhaust 2.5"

and after completing it i took it to be dyno tuned since it wasn't running too great, and was pretty dissipointed when we could only get about 210rwhp and 270ft/lb torque out of it... so i took it home and regapped the plugs to .032, and upgraded the fuel pump (i think it was running out/running lean dyno showed it around 14) it definitely runs a bit better now, but not a massive improvement. the timing is set as advanced as i could get it without ping, and i have played with it some too. i have also tried rejetting the carb richer. i was expecting around 400+ hp out of this when i built it, is there something seriously wrong here? are the heads i chose junk? what would a realistic estimated horsepower be for a build like this? any help is appreciated, thanks!

 

[dodgestang]

That's a small cam
Need a larger gap on the plugs.
I have 'rumors' that edlebrock carbs are very reliable but never been a favorite when wanting to make some big power numbers. Is it a VS or DP?
Stick or auto?
What was the RPMs you where seeing the numbers at?
What size is the fuel line to the tank? The sender in the tank? The line from the pump to the carb?
Did you confirm you are getting a full WOT when you push the pedal to the floor?

 

[mrmustangman357]

That's a small cam

Did you confirm you are getting a full WOT when you push the pedal to the floor?

very important. what is your total ignition timing and did you degree the cam? also what trans and rear axle is this?

 

[69gmachine]

Your expectations are very reasonable for your combo. Something is definitely wrong, either with how it was assembled (lost compression due to bad ring(s), cam timing etc) or tuned (not enough fuel, spark or timing), but the potential is there.

 

[57fairlane]

its way off . . . a stock 302 can make that.

the cam is small, I don't like the carb selection, and the intake would be small.

But even with an auto the thing should be on the other side of 300rwhp and probably 370rwtq.

 

[10secgoal]

Needs to be richer than 14-1. Just did one where it was almost 15-1 on a 378 cu in motor. It left making 472rwhp when corrected as upposed to 380 rwhp when it showed up. A/F is important, and you can get more timing out it when it's not really lean

 

[jasonn]

Well let's see.

1. Way too small of a cam.
2. WAY too small of headers. Get rid of the shorties.
3. Way wrong intake and carb. Get a vic jr (or at least a perf rpm or similar if you have hood clearance issues) and call pro systems for a good holley based carb.
4. Heads are way too small.
5. Exhaust is way too small. Mine with the 408 in my mach with 2.5 pipes lost 3-4 tenths in the quarter mile. Now with the motor in the pro streeter and 3", it doesn't loose any.

No, you don't have junk parts, just not the correctly matched parts for that big of c.i. These parts should stay on a street 302 or 351 c.i.

 

[stonecoldtx]

I'll say I have to disagree with those who say the cam is too small--while it's not the largest cam out there, it's plenty big enough to cause a rough idle in that engine, and when you have that, you have the potential for higher RPM power simply because of the behavior of airflow.

I have an XE258HR in my 5.0L that has 208 intake and 216 exhaust duration at .050" with .533 and .544 lift, and it makes good power all the way up through 5500RPM--with a smooth as glass idle. Once you start getting into the 220 degrees and above duration camshafts, especially with tighter lobe centers, you start seeing the rough idle characteristics.

I've had a bit of experience in choosing camshafts, and the best choice isn't always the biggest one out there. The cam you have with the engine size you have should make great power through 5500 and should be producing GREAT torque figures througout the RPM range, with a pretty broad, flat curve and a torque peak probably at around 4000-4500RPM

The heads you have are not the best available for that engine combination, but they're still not bad and should at least make some pretty impressive torque numbers.

The intake also isn't the best available, but it should be within 10-15 peak HP from a true Edelbrock, so that isn't the problem

I agree that the exhaust primaries should be larger--with an engine that size, 1-3/4" would be a good size, and long tubes would be preferrable

I don't see anything wrong with the Edelbrock series of carburetors . . . LOTS of Mopars over the years have made GREAT power with the AFB-type carbs, but there are others out there that generally make better power, like the Demon series from Barry Grant.

Having said all that . . . even with restrictive headers and exhaust, you STILL should be making FAR MORE than 210HP and 270 lbs-ft of torque.

I agree with those who stated that it's probably fuel delivery . . . you need an adequate supply in order to realize the full potential of the engine, and I don't mean just the fuel pump, either--you need lines from the tank to the pump and from the pump to the carb that are 1/2" (or a couple 3/8" lines in parallel) to deliver adequate fuel to this engine.

Timing is also a major concern--if you have the curve set right and adequate fuel to the engine, you should be making close to your goal with this combination of parts--I've seen it before.

One other thing that was mentioned is to make sure that the carburetor is completely opening up--if you are only getting part throttle out of it, you're only going to get part throttle numbers! Check your linkage!! Have someone put the pedal to the floor (with the engine turned off of course!! Had to say that!! LOL!!) and then look down the barrels of the carburetor!!

Just my two cents . . .

 

[BlackVert]

i suspect the summit intake is an air flow restriction. is it a single or dual plane? has it been ported or cleaned up?

also, are you sure the headers can keep up with the exhaust flow?

fwiw, i have an eddy rpm air-gap i bought when was going to convert mine to carb. then i decided to stay FI, so it is sitting in my basement

 

[mustangbrad]

I do agree with most of the previous posts, but instead of suggesting what parts you need I'm going to give you the best advice I can. Go to s b f tech.com (remove the spaces) and do some research. Get your post count up to 10 to open some other forums. Pay special attention to what Jay Allen and "Woody" have to say, they are sbf guru's. Or just call Jay at Camshaft Innovations or Woody at Fordstrokers.com, either one will get your motor making the numbers it should be making. Both of these guys have customer service that is top notch. Good luck with your engine.

 

[rc4mike]

408 HP

I just had a 94 roller bored and stroked to 408. Used twisted wedge heads, lunati cam. Had it dynoed by the builder with his stock headers and edlebrock intake and carb....i was switching to efi after installing in the car. Engine pulled 460hp and 470 torque at the flywheel. You should easily get to 400, so something must be wrong. Not smart enough to know exactly what's wrong.

mike

 

[C0V3R]

Order of stuff to fix/check
- Throttle linkage - i suspect along with the others youre not getting full throttle opening.
- Fuel - needs to go richer - should be closer to 12.5:1 @ WOT instead of 14
- Compression
- Spark


That carb should easily do 300-400+ hp, probably a heck of a lot more too. My 600 vac sec does. Even with a dodgy intake/exhaust you should be making way more than 250hp.