poor dyno numbers from 408 :(

[rwhite65]

Well, I figured you were all nice enough to shoot me ideas, and even though I am waiting for the parts, I am fairly confident that the problem is the timing.

Took the cap and rotor off, and no springs or bushings, it is all removed. The shaft is "locked" out as the stuff on MSD's website shows, so I called them up and they are sending me all the different springs and bushings...for free!!! Got to say MSD is gonna be my next ignition.....if I ever quit being a chep @#$.

The only reason I can figure they have it locked out is because maybe this distributor was bought for or once used on a fuel injected car...any other ideas why they would have done this?

Last problem is the dang thing hot starts pretty bad after driving it, then stopping for a few minutes, then starting it back up. I have the timing backed down pretty far, but I am thinking maybe it needs a ignition retarding box. Any one have this problem or experience with these?
Ryan

[andy669]

I didnt even look at the dyno sheets til just now. I wish I had a scanner so I could show you what the A/F on a carb car is supposed to look like.

I use no ignition advance at all, but the 7AL3 has an optional 25 degree start retard so I dont really get the 'hot start' symptoms.

What cam is in that thing? After looking at the graphs, I'd say that thing needs more valve spring pressure.

Andy

[rwhite65]

I am taking it back to his house now, where all the info on the specs of the engine is suppose to be sitting in the garage for me. He told me it was the 2nd from the biggest cam that Comp cams offers for that engine.

I have no idea on the series, I hope to be able to post that info in a few hours. I aslo talked with the carb guy's tech people. They said if we sent it back in, they would make sure it was jetted to the car's exact specs.
Ryan

[rwhite65]

Took the car back, found the paper work....with all the stuff to put the advanced timing back in it.......oh well. So here is what this bad boy contains:

First- a Chuck Nuytten Carb- 750 Holley double pumper, with a 72 Primary Jet, 80 Secondary Jet, 6.5 Priamry power valve and no scondary power valve. The nozzles are 35 and the following is special features done to this carb:
Blueprint
Milled air horn
Venturi work
Booster work
Air flow modified base plate
Internal circuitry modifications
Calibrated for gasoline

The engine is a 72 351w block, ARP Main and head studs, SVO Girdle. BRC racing pistons (9.5.1), Eagle H-beam Rods, and Edlebrock RPM heads with Felpro Wirelock gaskets.
The cam is Comp Cams http://www.compcams.com/Technical/Se...umber=35-250-4 I am attaching this in the paper work, may help those of you who are more up on ur cam specs then me. I am reading it to be that they degreed the Cam in.

The car breaths thru a set of shorties and 2.5 exhaust with an X pipe. No cats on the exhaust and a pair of flowmasters.

Andy669, it also has Comp roller rockers and I think the springs that came on the edelbrock heads. The engine is not falling flat on its face like it would if the valves floated, nor can I hear that horrific sound when the valves float. The engine has lots of brute force down low, but then just kinda falls off as it revs. Unlike how I would expect it to just keep coming in and rev hard.
Any details I left out?
Ryan

[andy669]

Being a HFT cam, I cant really recommend a good spring. Most of what I know relates to HR's. What happens if you dont have the right spring is the valves will bounce back off of the seats when they close. That can be worth lots of power.

In the next couple days I'm going to post one of my dyno graphs. I have the hard drive out of the computer that used to run the chassis dyno here locally, I just need to put it in a computer and transfer the info over.

Andy

[7DMACH1]

I looked at your build sheet. The xe284h cam is part number 31-250-4. Comp Cams site says any cam with a 31 prefix uses the old firing order 1-5-4-2-6-3-7-8. If you are useing 1-3-7-2-6-5-4-8 this is your problem. I've seen it before.

[rwhite65]

Andy669- I am thinking he would benefit most from a custom cam, which I think he will have no problems with purchasing. Even though it is a shelf cam, I really think this thing should be able to run decent with that cam. I also found the specs on the Edelbrock valve springs and can post them if they would help at all.


7DMach1- I checked the firing order and it was where "I" thought it should be. I looked all over Comp cams website and can not find where it talks about the proper firing order. Where did you find that? I can not remember what firing order I went with, so now I got to take a look at my notes if I can find them.

thanks,
Ryan

[Ieatcamaros]

Originally Posted by 7DMACH1

I looked at your build sheet. The xe284h cam is part number 31-250-4. Comp Cams site says any cam with a 31 prefix uses the old firing order 1-5-4-2-6-3-7-8. If you are useing 1-3-7-2-6-5-4-8 this is your problem. I've seen it before.

I'll second that. A representative at Comp cams told me this very thing. Prefix 31 is the old 302 firing order and Prefix 35 is the 351W and HO 302 firing order.