Re-tune after installing hooker header/sidepipes

**jims427400** · 02-12-13, 08:06 PM

I have a 68 427x400 that has been bored out a bit and is still running hydraulic lifters which was rebuilt last year. I'm running the original tripowers rejetted for pump gas and TI ignition. I'm going to install the hooker set up in the spring, my question is what adjustments am I going to have to make to compensate for the headers? For those of you who have done this what did you experience in performance changes.
Although I'm sure I won't care after I hear that sweet sound of side pipes.

Jim

**Hib Halverson** · 02-12-13, 11:07 PM

Originally Posted by jims427400

I have a 68 427x400 that has been bored out a bit and is still running hydraulic lifters which was rebuilt last year. I'm running the original tripowers rejetted for pump gas and TI ignition. I'm going to install the hooker set up in the spring, my question is what adjustments am I going to have to make to compensate for the headers? For those of you who have done this what did you experience in performance changes.
Although I'm sure I won't care after I hear that sweet sound of side pipes.

Jim

If these are the Hooker Headers and sidepipes which use slip-in glasspack mufflers, I'd do some testing before you change any jetting. The slip in mufflers are quite restrictive and may in fact be similar in restriction to a stock exhaust, so you may not need to make any changes.

Also, I'm curious...what jetting changes did you have to make to run pump gas and transistor ignition?

**jims427400** · 02-13-13, 08:54 AM

I sent the carbs out couple years ago to Craig Woodruff to get rebuilt and said he set them up for pump gas. May or may not have re-jetted. They are Hooker type w 4 inch slide ins. I'm going w the STS type very low restriction. I guess Hib with TI all I can change is timing? I have been thinking about taking it to someone when I'm done to get a professional tune.

Thanks

Originally Posted by Hib Halverson

If these are the Hooker Headers and sidepipes which use slip-in glasspack mufflers, I'd do some testing before you change any jetting. The slip in mufflers are quite restrictive and may in fact be similar in restriction to a stock exhaust, so you may not need to make any changes.

Also, I'm curious...what jetting changes did you have to make to run pump gas and transistor ignition?

**Crimson Thunder** · 02-13-13, 05:41 PM

You are going to love the sound with those STS Spiral Baffles. Do you plan to drill a hole in the end cap for more sound or leave them alone? I initially drilled a half inch hole when I first installed mine because Lars said he did. I thought at first it was a little to loud and plugged up the hole but now wish I would have left it open.

**Hib Halverson** · 02-13-13, 08:28 PM

If the guy who set the carbs up before, did a proper job, based on your statement that the mufflers are some kind of low restriction type, you may need to jet the end carbs a little bit more rich but, I wouldn't do anything until you can test on the chassis dyno with a widband.

As for the transistor ign. distributor, it uses the same weights/springs system as point-type distributors so you can recurve it, if you choose.

**jims427400** · 02-13-13, 09:28 PM

Shark,
I was thinking about drilling a hole, so 1/2 is all it'll take? Guess I won't open it up all the way.. I was even thinking of making my own. I was a pretty good welder back in the day..

Hib,
I learned something today, I assumed my TI didn't have the weights and springs, well I've never quite understood how to do that recurving bussiness, even after reading papers on it. I agree on waiting until I get them installed and see how they do.If it needs some tweeking then I'll find a tuner around here some where.
I'm sure you know the answer to my next question, is it possible to set my outer carbs to kick in sooner. I've heard there's different tensioned spring that can go inside the diaphragm.

Originally Posted by Hib Halverson

If the guy who set the carbs up before, did a proper job, based on your statement that the mufflers are some kind of low restriction type, you may need to jet the end carbs a little bit more rich but, I wouldn't do anything until you can test on the chassis dyno with a widband.

As for the transistor ign. distributor, it uses the same weights/springs system as point-type distributors so you can recurve it, if you choose.

**Hib Halverson** · 02-14-13, 09:34 AM

I'm not familiar with different diaphragm springs but that'd doesn't mean such a thing doesn't exist. The carb on my 71 is a 4bbl Holley with mech. secondaries so I'm not real familiar with the specifics of secondary diaphragms on 3x2 systems.

That said, I wouldn't fool with that unless you know the change would be worthwhile. Just opening the secondaries sooner doesn't necessarily mean that will enhance performance.

If there are different springs, I'd try some and test the car's acceleration to see if there was a difference.

**Crimson Thunder** · 02-14-13, 04:04 PM

[QUOTE=jims427400;1120826]Shark,
I was thinking about drilling a hole, so 1/2 is all it'll take? Guess I won't open it up all the way.. I was even thinking of making my own. I was a pretty good welder back in the day..

Go ahead and install the mufflers closed to see how it sounds at first, then you can take the side tubes back off and open them up if you wish. My friend's Vette with a 540 and STS baffles sounds totally different than my small block so you may want to play with it a little to get the perfect sound.

**jims427400** · 02-14-13, 06:47 PM

I like the way your thinking. It's easier to drill the hole bigger than try to make it smaller. Who did you order yours through?

[QUOTE=sharkcar71;1120878]

Originally Posted by jims427400

Shark,
I was thinking about drilling a hole, so 1/2 is all it'll take? Guess I won't open it up all the way.. I was even thinking of making my own. I was a pretty good welder back in the day..

Go ahead and install the mufflers closed to see how it sounds at first, then you can take the side tubes back off and open them up if you wish. My friend's Vette with a 540 and STS baffles sounds totally different than my small block so you may want to play with it a little to get the perfect sound.

**Crimson Thunder** · 02-16-13, 10:14 PM

I ordered mine directly from STS.

**TimAT** · 03-07-13, 11:52 PM

The nice thing about the STS Baffles is that if you do open the end cap more than you wanted, you can get a plain old freeze plug and have it tack welded on- presto- no more hole.
FWIW- I drilled mine 4 times each with a 1/2" drill bit. Made a cloverleaf shaped hole. Would have been easier to just grind the welds off.

**Crimson Thunder** · 03-10-13, 07:31 PM

I did mine the lazy way. I just ran a tap through the hole and stuck a screw in it.

**TimAT** · 04-05-13, 10:58 PM

Jim- I'm running the original TI ignition too- make sure you have the correct coil. All the weights and springs for the old style GM point type distributor work fine.

Disconnect the vacuum hose and plug it- see where the timing is at idle and at 3000 RPM (dial back timing light helps). Then swap weights and springs until you get 36* TOTAL at 3000 RPM. I use a fairly quick advance curve (light springs, heavier weights), but I'm running a 12 pound flywheel and want the quick RPM.
With the cam I'm currently running, idle advance is 12-14* and ends up about 38*. 12.5:1 compression and VP110 fuel too.

I didn't change anything as far as jets when the headers went on. Seems overall to be pretty happy with real gas so I'm ok with it.