Gun Jam

I was running my new trick flow heads and comp cam (218 intake, 224 exhaust, .513 gross valve lift ) with a performer 289 intake and carter afb 600.

I was told that switching the intake to a Performer RPM Air-Gap would provide quite a bit more top end power without hurting drive-ability...a slight probably un-noticable reduction in low end torque due to the larger runner size.

Also a Holley 670 carb to go with it.

I installed the air gap and put my carter 600 ontop and it seem to run well I only drove it a few miles this way to make sure intake was okay and it seemed to drive quite a bit like the old intake driving it easy around town..I also made one hard accel with it and it seemed to make good power! felt better than before.



I then placed the Holley ontop and set the idle and float level. It idles amazing and during idle pulls between 14 and 13" of Hg and produces an indicated A/F ratio of about 12.9 (at peak vac 13,14")

It would also curise smooth with indicated A/F of about 14.8 but any applied power would cause it lean way out into the 17s for moment and it would stumble badly. I switched main jet for 65 to 70 and that solved the stumble issue but caused the car to run pig rich at cruise (low 12s) and bog during accel (into the 10s) switched the 70s for 68s and now it cruises at about 14.0, from a stop it accelerates smooth and the A/F ratio does not dip below 12.5 during normal accel from stop.


Issues:

in 5th gear (maybe any other gear as well) I can be going 70mph back off the gas for 0% power then apply 20% power and it run dead lean and will backfire, stumble and then start to make power.

In any gear above 1500 rpm I can back off the power for 0% and let the car coast all is normal but when I put in the clutch and let the engine rev down to idle rpm it will momentarily run rich (low 13s) and then rapidly lean to an extreme 19.9 (max displayed) drop rpm and proceed to die which it will always do if not all the way warmed up. If it does not die it richens back up and runs normal idle mix of about 12.5 A/F

Fuel millage seems to really suck. was getting 20 to 23 with old intake and carb with new cam and heads now its noticeably worse

it currently has a 6.5 power valve...

I think its making pretty good top end power and seems to maintain 12s during WOT....Im also running the heavy spring in the 2nds probably should switch but im more concerned about whats going on the low end side.

Idle rpm is 750
Timing initial is about 9.5 deg adv.

Thanks

-Gun

kenash

Hi,
I'm amazed at your low initial timing. There many differences in details,but, I run a 16 deg initial. Have you tuned timing?

Gun Jam

Timing very well could be the issue before all of this I ran 12 after the head swap AND as well after the intake and carb swap. I noticed that after 9 deg I would get an odd exhaust note some what sounded like a piece of loose metal inside the muffler what I think was a popping through exhaust.

It seems to me that adv timing would reduce this tendency due to a more complete fuel burn.

16 initial sounds pretty awesome but im not sure how to go about safely advancing timing that far.

kenash

Hi,
My mention of 16 deg. was not an implication you should try it. It works for me , but only, after a lot of testing. I would bump it to at least 12 though. Are running a distributor vac?

Gun Jam

im running a mechanical advance and it reaches max timing at about 2700 rpm its running the medium springs. total timing is about 28deg with initial of 9

gjz30075

Subscribing.. I want to listen to this one.

kenash

,


OK, when you state "total timing is about 28deg with initial of 9", so you're distributor only has 21 deg built in? Is there a reason you're hesitant about increasing the timing? I see your running TFS heads, 170s? or bigger? Your cam is no too crazy. What cubes? have you stroked this motor?

Gun Jam

Yes that is correct about the timing. (9+19 for 28).

In the past I always ran 12 initial then I changed only the heads and cam (roller cam) and I did put miles on the motor at 12 deg but found two issues.

1) during normal light accel the engine would momentarily lean if power wasn't smoothly and continuously applied. It was this way BEFORE the head changed too and I just tried to roll power on smooth to keep accelerator pump pissing. Reducing the timing to about 10 reduced this issue)

2) AFTER the head swap running 12 deg sometimes made it sound like there was a piece of loose metal in the muffler at idle (Which I thought was actually the case since they got banged around a bit during the swap) when I reduced the timing the sound became a single pop say around 10 deg adv. Reducing the timing further made that go away and produced a clean note like it was before the head swap so I left it there at 9 deg because I have not yet determined if: A) thats a normal sound for that style of combustion chamber and high(ish) lift cam. Or B) could produced damage to something overtime.

The intake runners are 170cc
the motor is 302

Thanks

-Gun

kenash

Hi,
OK, so your distributor only has 19 degrees built in? Just so you know, the reference to "total timing" is distributor mechanical "plus" initial. Most all performance based engines run 34-38 degs. "total" ...and this "total" is all-in between 2500 and 2800, maybe a little lower.
Again, it depends on various mods etc. But, we generally agree, "all-in" early and with a total as mentioned. I'm not trying to beat this up, just trying to make sure we are on the same page.

Gun Jam

Yes

9 initial, 19 advance (9+19=28 total) Mech adv is all in by 2800

Its starting to sound like timing is probably one of my issues... although I suspected that some time ago it appears however it is retarded by an amount larger than I thought.

-Gun