poor dyno numbers from 408 :(

[rwhite65]

Here is the combo of a 93 a buddy of mine just bought. Of course I am the one now that is gonna do the wrenching on it since he is still new to the scene as far as hands on.

93 LX, 408, t-5, 3.73 gears. The 408 has edelbrock rpm heads, a Weiand Stealth intake, msd dist, msd 6AL ignition, shorty headers, decent exhaust....but not sure what yet, and a 750 Holley that has been custom tuned by some guy, but I have never heard of him. It also has a mechanical fuel pump....may be stock, I got to get the car over the pit so I can take a look at it and the car may still have the stock fuel line on it. Has a comp cams, but all I know right now is it is the second from the biggest they offer...I hope to get the specs soon.

my buddy dynoed it today and brought me the sheets, and I must say they were not very good. Best horse power pull was 309, if u need the rpm I will go look at the sheets again. Best torque was around 370, but that fell off quickly after 4,000 rpm's. the part that scares me is the air/fuel ratio was around 17.

my first thoughts on this is to check the timing, firing order, but I suspect the car is running out of fuel, so I am really looking at that fuel pump and fuel line. He is gone for the next week and I am going to try and push more horses out of it for him, any advice or help is always appreciated.

One last thing, with the fuel system being so lean, am I gonna hurt this thing by doing runs with it, as I try to diagnose the problem? my buddy (the owner) feels it is just not right in the upper rpm's, and he also said some of the people at the dyno run thought the timing on the thing sounded funny. To be honsest, I think the thing is starting hard for the 70 degree weather.

Ryan

[Dark_5.0]

AFR of 17 is dangerously lean. The guy probably jetted the carb way down in an effort to get better gas mileage. Maybe the back barrels are not opening??????????

I wouldnt even drive the car anymore till the seriously lean condition is figured out.

That motor should break the 400RWHP mark pretty easily.

[rwhite65]

well, I do not want to drive it a lot, but need to drive it a few miles to my buddies house to work on it in the morning. I know the timing is a problem, it is too far advanced from the way it is starting warm, but until I can get a light on it I will not be sure.
Ryan

[rwhite65]

ok, here is an update. The thing was hot starting pretty bad, so I backed it off by ear a little, then threw the timing light on it. It is around 10-12 degrees initial timing. So then I have my buddy start to slowly rev the motor, nothing. Now on my mustang (65) with a vacuum advance, if I rev the engine while timing it the timing mark advances rather quickly. This thing, doesnt budge...slowly reving it or giving it a little quick blip. So, who is running an MSD distributer or 6AL. There is no vacuum advance on this thing, so what of those two parts does it? I do not think this thing is advancing at all. I have never ran either one of these products...so I am kinda at a stand still right now.

I am attaching the dyno sheets this time. From the sheets, I am leaning towards the power valves. Am I way off here? Anyone runnig a 408 or close to that? Can you give me a baseline for what the jets should be in this thing.

thanks guys,
Ryan

[Fat0eknee]

Originally Posted by Dark_5.0

Maybe the back barrels are not opening??????????

I think he is on to something about the secondaries not kickin in... seems like a pretty reasonable explanation

[rwhite65]

I originally thought that, but after some drive time, the thing feels like to me it only pulls strong when the four barrels (pedal mashed) are kicking in. I am not exactly sure on this, but I am gonna play with it tomorrow, and see if I can see the barrels squirting or not. At this point, I think something is wrong with the mechanical advance in the distributer.
Ryan

[~The Jester~]

All that's in there is weights, and pins. Does he have the sheet with that came with the distributor? It explains it all in there. If not, head over to www.msdignition.com and hit their message boards, tech guys over there are AWESOME.

If the stock fuel line is still on that car, take it off and beat him with it. Find out what pump he's running. Stock ain't gonna cut it there either. That's just silly. Check the jets in the carb, I'd START with about a 70 up front, and an 80 in the back. Make sure that the accelerator pumps are working, make sure the levers didn't get messed up when the guy put the bowls back on. Check the secondaries as well.

It's definitely a fuel problem IMHO. Timing will make the car lazy, but it won't give you an AFR of 17! Think fuel, think fuel, think fuel.

[rwhite65]

Well, the fuel line has been updated, a real nice large new piece with a mechanical Carter high volume..although I have my doubts about the mechanical pump.

I have not taken the carb off, actually need to take the distributer apart tomorrow and take a look inside it too. Now that you have given me a reference point on what jets to look for, I will look for those as well.
Thanx Jester!!!
Ryan

[andy669]

Its possible that the distributor has had the weights removed and they were just running total timing. Its kinda hard to guess on jet sizes without knowing whats been done to the emulsion circuit. You said someone had worked on it, thats usually the first thing carb guys do. A bigger emulsion circuit will want a bigger jet size.

Get rid of that mechanical pump and put a good electric one on it. Try to get the A/F down to around 13.5.

Andy

[rwhite65]

http://www.chucknuytten.com/ Any of you guys deal with this guys carbs... this is what is on the car. I am gonna call him today hopefully.
Ryan

[red82gt]

The A/f from the dyno graph doesn't look too bad to me, the 17 is just when they started the run and wasn't at full throttle, the rest of the run is low 13 to high 13's which isn't too bad. It seems to rev smoothly up to just over 4000 and then things just aren't right. If the timing isn't advancing, that will be your first problem as the mixture is firing way too late, especially as the rpms go up. I think that is 99% of the problem, the A/F looks fine to me.

[~The Jester~]

My Chuck Nuytten 850 actually flows around 920! Awesome carb. IF it actually came from Chuck (and some gearhead hasn't played with it since then) you should be good to go on that piece. Timing still might be an issue, but it's not gonna make the car way lean like that.

One mistake we've made in the past was swapping intakes. Went from a single plane (flat carb mount) back to a dual plane (slanted carb mount). What that did to us was made the rear float level WAY too low. Maybe check on that too.

Get an answer from MSD yet? I think they even have the diagrams on there too, hold on I go looky for ya.

[~The Jester~]

I think this might be what you're lookin for:

http://www.msdignition.com/pdf/8350_...4_frm23728.pdf

[rwhite65]

Well, this carb is really one of his, a beautifull carb...has his labels on it and all. I called them today, and they were very helpfull, although I need to get more numbers off of the houseing tom.

I am hoping they tell me that the carb was built for another motor, and can help me as to what jets I need. As red82gt pointed out from the numbers, it just kinda falls out after 4,000. Still pulls, but nothing like I would expect.
I will keep ya posted,
and thanks for the link to MSD Jester!!
Ryan

[rwhite65]

After reading that Jester, I suspect they may have the mechanical advance locked out.
Ryan

[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