I have a 408 with 10.5 compression edlebrock alum heads decked and ported with a comp cam534 lift and 286 duration with 1.6ratio rockers which brings lift in the 570 range have a 750 edlelbrock carb. on the chasie dyno it has 325 horse and 344 ft lbs torgue at 4500 rpm.The motor is in a 68 dart gts 391 gear with 4500 stall converter. My 60 ft times are in 1.8 and best et is 12.20 at 108. Any help they tell me the car should bi in the mid elevens. Thanks

 

Loose weight.

 

4.56 gears will help a little but not if your motor isn't balanced well enough to get into the 6-7k+ rpm range.

 

A couple of questions?

What is the duration at .050?
What spring are you using? Installed height, open and closed pressures?
Cam installed center line? Or send cam number and I'll look it up.

IMO your buddies are correct. You are leaving a ton of power on the table somewhere. Those are decent HP/TQ for a 360 but your 408 should be much more. The 4500 stall scares me a little unless you are using a very light assembly and were shooting for hp peaks at +6000rpm / torque at 5000 rpm? HOWEVER, Im not an expert on selecting stall.

Sounds like a decent motor. Send some more info so we can point you in the right direction.

 

Cam timing? Let's see the dyno curve. Are you saying PEAK Hp was at 4500??????

 

at.50 its 242,250 duration comp springs comp cam crs5089/5438 h109+3

 

Sounds like you planned this build right and I wouldn't panic. Cam pick looks nice! Something is just a little off. I still cant figure out your springs or how you set up the valve train from those numbers but it has only been one cup of coffee so my memory may snap to

We need to make a couple assumptions and Im not trying to sound condescending but overlooking some basics can create the same issue. We've all done it.....

Make sure the spark and spark delivery is good. Then fuel flow / pressure and air at the intake and exhaust is appropriate.

That cam and head flow of 260 cfm plus you should take peaks in the ball park of HP peak of 5800rpm in my opinion and torque around 4700 rpm plus.

Can we assume the dyno operator shut it down because fuel started getting rich and power started dropping or bouncing on the graph? If so follow guide below. If not what did it do?

Couple of things i would do.

Get out the marker or dykem and make sure the valve train sweep is correct on the stem. In your post you said "decked". Are you using an LA or Magnum block? Or shaft or stud rockers? Which block?

If memory serves correctly your Eddies come w/installed height of 1.8 with a pocket of 1.46? (check you eddie specs).

You need spot on PR length and no flex. Roll some on glass and make sure you aren't bending them. And for that cam i would use a quality name brand rod, Smith Bros or Comps. Check stems for mushrooming from rockers bouncing.

Next: What rocker are you using. Comps stamped stuff and the stamped roller is rated for 350 pounds of spring and your needs have you over that.

And lastly: Pull a spring, measure your installed height by adding the retainer back to the valve stem and no matter what the spring says from the manufacturer have a shop test it for your heights / opened and closed pressures. I have had bad and wrong springs delivered as such.

Those are the freebies that need to be confirmed before you spend a nickle or change part.

If you know your heights / springs / etc.. post back.

 

comp valve springs pt no 978 installed at 1.85 height at the time was 127 lbs opening pressure using edlebrock 1.6 ratio roller rockers on studs magnum block milled 34 thousands off heads which were 56 cc. Crushed the original edlebrock springs due to the lift

 

Got it. The 978 is what is called for so good call on pressures.

I got more questions but we are getting close.

The Eddy Magnums springs have an installed height of 1.8. If you used the stock spring and killed them I think we have found some of our problem.

The Max Lift the Eddy's can handle is .58 or the retainer will smack the guide. You are .570 ish? And you floated the valves and toasted springs right?

Who swapped the springs? To get an installed height of 1.85 you had to machine the pockets to add that .05 or did you use an offset lock or special retainer? If so are you still hitting the retainer? Does it sound like a sewing machine?

I'll do some math tonight on the spring bind height using a .020 safety factor for tolerances for the head application.

Springs become a solid mass when compressed if you did that you need to check PR for straightness and make sure your studs are not bent.

I would pull a spring and measure installed height. And check for valve train damage.

Also keep in mind the Eddy 3/8 ARP stud need 1.5 turns to set lash for the magnum hyd roller lifter. That nets you .060 preload. Dont do a ( Chevy half Turn netting .020 preload.)

Last question? Are you using the Edlebrock 6.93 Pushrods for use with guide plates that they recommend? If so get them out. The base circle on that cam is small to net you .57 lift and you need to remeasure. Those PR are for stock cam base circle. Plus you cut the heads. Not much but measure. Did you use stock .040-.042 Head gasket or go thinner or thicker? That will play in the PR length too.