Opinions on poor dyno performance...388, 6 in. rods, 10.3 cr., Edelbrock race heads, BG race demon 850, Edelbrock Super Victor intake, Aeromotive 140 g.p.h. pump thru 1/2 in. line, 2.5 in. duals with flowmasters, Hooker Supercomp. headers, Richmond 5 speed, Crane hi-6 ignition, 36 deg. total in by 2500rpm. I am expecting 400+hp, 400+lb/ft.


http://photobucket.com/albums/b156/b...t=scan0001.jpg

 

You're pig rich at about 3400 and over. There's quite a few ponies there.

Brett

 

12.5 to 13 on the high side for best power. Did the dyno operator offer any suggestions (or the chance to do a bit of tuning) to you or was he just pushin' the button?

 

Besides being rich I'm not quite getting this combo. You have a very large cam and intake but not the compression to support it. Also not sure on the heads. What are "race edelbrocks"? What do they flow? A Victor JR would have been enough for high rpm and would pick up torque.

Your cam & intake choice is for a high rpm screamer but I would have expected more compression if that was your goal.

Signed,
Confused

 

I know the fuel mix is fat, but the power drops off at 5200 or so, and the torque is low even where the fuel mix is good, that is what throws me. The cam is a solid roller, good for 7,500rpm. I will change the secondary jetting before the second dyno run....best e.t=12.46, 60 ft. times..1.6+

 

Might play with the timing a bit also, newer heads sometimes like slightly less adv because of their design.

 

Yes, I tried 32 to 36 degrees, with no real power changes. the Edelbrock 23 deg. race heads have a fast-burn chamber.

 

to much fuel and to much timing.

 

zwede, the Edelbrock heads have 215 cc intale runners, 2.08 in. intake valves, Edelbrock/Jegs pn.77629. I, along with Crower, spec'ed the cam for this motor based on 388ci. with 7000 rpm. redline. Internally balanced rotating assy., 4340 steel crank w/ drilled journal throws. We spec'ed the cam with 112 deg lsa to help with torque. The fact that it is a 388 ci. engine makes all bolt-ons look a little smaller....BTW, the Super Victor intake is almost the same as a Victor Jr. with a 1 in. spacer, but it has larger runners....thanks for y'all advice..I need to find my missing ponies!http://www.edelbrock.com/automotive_...ictor_jr.shtml

 

I'm looking at your fuel trim in relation to your torque curve and see it dropping off right at the point where you go below 12.5 A/F ratio.

That cam does sound good for the intake and heads since a wider LSA will favor a deep breather on the top. But the wider LSA also depletes torque in the midrange. I don't see an issue in the cam other than what you may have been expecting in the torque curve at lower rpm. Wide LSA cams are the ones that "turn on" at higher rpm even in the lower lift and durations for relatively mild street/strip cams.

 

Always thought wide lobe sep was better for low/mid power since it built more cyl pressure while narrow lobe sep was better for upper rpm's since it allowed for better intake charge scavaging at higher rpm's.

 

Well, no, it doesn't work that way -at least not that you can say with absolutes. But please don't take my word for it. But don't take anyone else's word for it either. Do research on the issue from reputable sources, like cam manufacturer sites.

One very important timing event that most folks overlook is the intake closing point. This, more than anything, will tell you for a given engine how far it's going to rev and what the torque is going to look like everywhere else.

Wider LSAs will give you a smoother idle and clean emissions since you have less overlap but don't make nearly the off-idle and midrange power as a cam with a tight LSA. Most factory cams use wide LSAs for that smooth idle and good emissions, not because they make better low end power -because they don't. Narrow LSA gives you that lumpy idle and the reason you get that lumpy idle is that the cylinder charge is insufficient for combustion (charge contamination and VE) or complete combustion. This charge insufficiency is the same thing that makes two-strokes pop. This makes the exhaust very dirty. Lots of unburned fuel going straight out the pipe. But the narrow LSA is great for VE once you hit the gas. Obviously, you can't take LSA unto itself since, again, it's all the specs including airflow and what "fits" the theory on one engine is defied by another.

This is why Comp Cams is so successful in the street market. They have this issue down.

 

Ya, ya, but why does the torque fall off at 5200 when the a/f ratio is consistent?...If I can keep the torque up, the horsepower will follow.....

 

Thanks for the head info. They would seem OK for your application although flow # would be nice.

Next time you're on the dyno try uncorking the exhaust. Some people have found flowmasters to be very restrictive. Restrictive exhaust would make it run rich btw.

I'm still not sold on the compression. Is the 10.2 calculated or measured? When you calculate a 10.2 it could easily be 9.5 in reality. Was the block zero decked, chambers measured etc? I would like to see atleast 11:1 real CR in this motor. You probably would have to run more than 93 octane but it would really wake it up.

Uncorked, tuned and with 11:1 I'd expect 400 rwhp.

 

What are the specs on the valvesprings?

 

C/R was calculated, but 388ci., 70 cc head, flat-tops with composition gasket s/b about 10-10.5:1... the additional .5-.7 won't make that much difference...IMO...and the Flowmasters are 2 chamber...not 3, so not too much restriction there. Valve springs were as Edelbrock set them up. See above posted link.

 

Still... chambers are likely to measure more than 70cc... piston could be down in the block (will be unless zero decked)... compression could be down in the 9.5 range and that's just not enough for this combo.

Also, please clarify about the springs. The PN you gave says "set up for solid roller" on edelbrocks site, yet the cam card looks like a flat tappet solid... Are you running a flat tappet on roller springs?

 

The block is zero decked, the cam is a 288R..the "R" is for roller

 

Dem is sum BIG AZZED size intake ports you have on your motor there! I wouldn't run those on a street/strip 406 let alone a 383. You should put a RPM air-gap intake on to compensate for going too large on your intake ports in my opinion. Then again what do I know, my 170cc intake runner 355 LT-1 only runs 12.28@117MPH with 371 RWHP on a Dyno-Jet.

 

If those are chassis dyno numbers (330 hp), you're getting 400 net horsepower, in spite of your rich mixture. 400 net is about 450 - 460 gross. I don't think you're doing too bad.