[JohnyR17]

I put together a 400 small block chevy for my '79 pickup. It runs well, but Im no master of tuning and Ive got a few questions.

The truck is a half ton 2wd with a TH350 and 3.08 open rear end. I plan to replace the rear end with a 3.73 setup in the future.

The bottom end of the 400 isnt fancy. Stock crank, stock 5.565" rods, speed pro hyper flat tops with 4 valve reliefs. The heads are 70cc Edelbrock Performer RPMs. Compression on paper is 10.25:1 or so. I did not cc the chambers so that figure is rough. The cam is a Comp 270H, .480 lift, 224 duration @50. Edelbrock performer RPM Q-Jet intake and a Jegs remanufactured Quadrajet on top. Ignition is a factory HEI. The truck has headers and dual 2 1/2" exhaust.

The truck is sluggish down low. The rear end gear doesnt help any. It really wakes up at 4000rpms but the bottom end isnt stout so I keep the revs below 5500. Ive got the initial timing set at 6 degrees. Is this too slow? Can a factory HEI be recurved or should I invest in an aftermarket distributor? Any advice or suggestions are welcomed.

[KNanthrup]

Not that you want to take the engine apart again... but you could have advanced the cam timing say 3-4* to have it start the powerband a little earlier. Did you check your cam timing at all when it went in? That cam I would think should start making power earlier than 4k rpms.

[blown67SS]

do you know what your total timing is at??

try setting your initial timing at 8 degrees..see if that wakes it up

[Steve karch]

My initial timing on my 406 is 18 deg with 34 total at 2500 rpm or so. That is with iron Sportsman ll heads. Your set up should support 14-16 degrees and 34 total. Your compression is on the high side but aluminum heads will support that compression ratio. Make sure to back off the idle after setting the timing. This will also allow a lower base idle setting on the carb and will allow it to stay in the idle circut when cruising at lower rpm. Your engine set up, even with 3.08's should really wake up at lower rpm's. Play around with the timing. Hook your vacuum advance to a manifold source so that it will advance your timing at no load situtations and retard it under high load situtations. This will also help with smoothing your idle out and creating better throttle response and better driveability. Your engine set up is good. You just need to work the kinks out. Have fun.

[NAIRB]

Originally Posted by JohnyR17

I put together a 400 small block chevy for my '79 pickup. It runs well, but Im no master of tuning and Ive got a few questions.

The truck is a half ton 2wd with a TH350 and 3.08 open rear end. I plan to replace the rear end with a 3.73 setup in the future.

The bottom end of the 400 isnt fancy. Stock crank, stock 5.565" rods, speed pro hyper flat tops with 4 valve reliefs. The heads are 70cc Edelbrock Performer RPMs. Compression on paper is 10.25:1 or so. I did not cc the chambers so that figure is rough. The cam is a Comp 270H, .480 lift, 224 duration @50. Edelbrock performer RPM Q-Jet intake and a Jegs remanufactured Quadrajet on top. Ignition is a factory HEI. The truck has headers and dual 2 1/2" exhaust.

The truck is sluggish down low. The rear end gear doesnt help any. It really wakes up at 4000rpms but the bottom end isnt stout so I keep the revs below 5500. Ive got the initial timing set at 6 degrees. Is this too slow? Can a factory HEI be recurved or should I invest in an aftermarket distributor? Any advice or suggestions are welcomed.

You've got too much cam for a truck with 3.08 gears and an automatic.

You need to get those gears changed, and use a little more stall speed in the converter. Otherwise, you need to go to a camshaft with about 205 degrees intake duration@.050.

[hotrodf1]

Originally Posted by Steve karch

My initial timing on my 406 is 18 deg with 34 total at 2500 rpm or so. That is with iron Sportsman ll heads. Your set up should support 14-16 degrees and 34 total. Your compression is on the high side but aluminum heads will support that compression ratio. Make sure to back off the idle after setting the timing. This will also allow a lower base idle setting on the carb and will allow it to stay in the idle circut when cruising at lower rpm. Your engine set up, even with 3.08's should really wake up at lower rpm's. Play around with the timing. Hook your vacuum advance to a manifold source so that it will advance your timing at no load situtations and retard it under high load situtations. This will also help with smoothing your idle out and creating better throttle response and better driveability. Your engine set up is good. You just need to work the kinks out. Have fun.

What he said! right on

need more timing

[Big Mouse]

Did you say a factory stock HEI from 1979?

If so, check when your timing comes all the way in. My '80 HEI came all-in at 4600 RPM's

I bought a timing curve kit (about $10) and put one light and one medium spring on the mechanical advance. That really woke up my old 400. Once I hit the 3000 RPM mark the motor pulled nicely. Worked for me... I could clearly tell the difference. On my motor, I was then all-in by 2400 RPM's (but I had much lower compression). You should be good if you are all in by 3000 RPM (if you ping, back it off a little).

+1 on better gears.

Just my $.02...

[JohnyR17]

Yes the HEI is a factory stock 1979 model.

Will a summit 'HEI advance curve kit' (pn SUM-G5212) include the necessary items to correctly recurve the distributor? Does another manufacturer make a more complete kit?

Would it be smart to also buy an adjustable vacuum advance canister?

[Big Mouse]

I used a kit very similar to this example:
http://store.summitracing.com/partde...0&autoview=sku

I simply cleaned up my mechancial advance mechanism (they get gummy over time) and I only used the springs from the kit.

The vacuum advance depends on your engine. How many degrees does your vacuum advance move your timing right now? Check your timing at idle with vacuum advance plugged. Then recheck your timing with the vacuum advance hooked up.

I have not had to mess with my vacuum advance; however, many people here have. Do a quick search here to see how many degrees is recommended. Then, compare that to what yours is doing. You'll then be able to determine if you need the adjustable VA or not.

[JohnyR17]

Finally got some time to play with the timing this afternoon.

I got a HEI recurve kit, installed the weights and used one light sping and one medium spring.

Set the initial at 15 degrees (vac adance unplugged). Checked the total timing and at 3000 rpms, where the advance should be all in, and it is only 25 degrees.

So if I understand correctly, the mechanical advance in the distributor adds only 10 degrees?? Does a recurve kit limit the amount of mechanical advance?

I neglected to check the total timing before I switched the springs and weights in the distributor. The initial advance was set at 6 degrees and the engine ran better before I installed the recurve kit.

The distributor is a factory '79 model and the recommended initial setting is 4 degrees which would lead me to believe that there was originally much more than 10 degrees of mechanical advance in the distributor. Any advice is appreciated.

[Blazin72]

Nevermind...

[squeeezer]

first the basics
run as much base timming as you can (hot) .....your starter will let you know if too much

make sure all of your timming is in @ the rpm you are in when you are going cruize speed (whatever your speed limit is in your state)

this way all your timming is in @ lets say 70mph and 2500rpm you dont have overheat problem on freeway=extended engine life as well as performance

[Rick WI]

It sounds like your weights are sticking and not allowing the full advance. Is everything clean inside and appear to be rotating smoothly?

Having run cams in that range with truck with your rear ratio it's not the cam. That's not a big cam for a 400 with your compression.

If the distributor is old and the internals look shot it would be worth it to get a small cap MSD with an external coil and retrofit your truck. You are going to want to bush the new distributor to give you around 36 to 38 degrees of timing with some reasonable base timing, 14 max. You dial in too much base and in combination with the high compression you'll detonate the piss out of it.

[JohnyR17]

The recurve kit came with 3 sets of plastic bushings that the supplied weights ride on.

It is possible that the set of bushings I used are too snug and do not allow the weights to swing out properly. Ill pull the distributor back out and inspect it.

[hotrodf1]

Just a dumb question: did you try running the motor up to 3500, 4000 RPM to see if the dist. was still adding timing? Perhaps it would add more past 3K, which means you need to use lighter springs yet.

FYI: I have had decent luck using the factory weights and then using the springs from the recurve kit. I always think the recurve weights fit like crap and just dont generally seem very well designed. I just lighten the springs up, and watch what happens to the curve with my dial back light. Course, factory weights are different for different motors, so your "mileage" may vary.

But, the recurve kits I think do limit the amount of mechanical timing, by how much I'm not sure. The bottom line is, unless you get a nice MSD or other brand distributor that is made to be more easily adjustable (like the advance stop bushings that were spoke of earlier), you will have to trial and error your HEI until it does what you want. It's sometimes not easy to get them to cooperate!