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

[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

[7DMACH1]

Here's where I found it. Ray
http://www.compcams.com/Technical/Cu...HTML/62-65.asp

[rwhite65]

I appreciate the help, but the cam card I have has a 35 prefix, so as I understand the replies that would mean I need the late style firing order??
Ryan

[andy669]

If the firing order was wrong, you would hear it. Plus, if that thing made 300 horses on only 4 cylinders? Holy shit! That thing would be a monster. 1-2-6-8 will still fire correctly either way. Good thought, but I dont think thats the problem.

It could very well be something timing related. 15 degrees of timing was worth exactly 100 horsepower in my car.

Andy

[rwhite65]

I really think it is going to be the timing. I have just gotten busy with work here (begining of my work week) and have not had time to put the advancement pieces back in.

I am hoping tomorrow to put it together correctly, which should give me atleast 20 more degrees total advancement (give or take a few). Will post when we do it.
Ryan

[andy669]

Heres a couple of my dyno pulls.

Andy