Thumper 401?

[shimniok]

On the 360, planning to get a cheap FSJ without motor and swap in and sell the whole shebang to try and recoup cost.

I think the cam is hurting me. I am usu foot planted to hold 50-55 up to the tunnel. Motor is new. I've played with mix/timing for some time and improved power, but not lots. Ignition is already about as hot as it gets.

May install O2 sensor and tune carb more. Headers too. And may even try another cam. Hate to build a 401 without knowing what went wrong with the 360.

Higher CR is a must have as far as I can discern.

On the 80mph J-truck, what gearing, tire size, and cam? Thx.

Michael

[shimniok]

PS: Rig's barely visible on p15, Feb 03. Don't think there are other pics of it in its present state? My old 85 made cover in 01. Hoping to make Spring with an article about the St. Elmo area so rig may show up there. We'll see...

Michael

[Goose]

Well on the J-10 the tire size was 33's the gears are 3:73 (I'm pretty sure)
and the cam was the edelbrock performer cam.. There is kind of a mismatch on the cam and intake as the intake is a torker (2500-7000) and the cam is off idle to 5500 if I remember right. but I think I would look into your setup something has to be out of line to be as doggy that.
I would really wonder about the cam. It seems if youre making power above say 2500 this is about where youre holding the grade, Kicked down climbing like that if it's holding 50-55 and if it shifts it doesn't have the torque to mantain it without kicking down and bringing the RPM back up into the power band,
Mine (since it is a 4 speed) would continue to pull in 4th if you let it until it got ahead of the cooling system at low rpm and start to get hot, then down into third and cooled right down. that stretch from georgetown to silverplume is the toughest pull on the hill.
If I remember right I was turning about 2700 at 70 mph
The one caution I have to add in here is Fuel mileage from Denver to silverthorne was about 4 mpg. 16-17 under normal conditions

[shimniok]

Thx. Sounds like our gearing is identical. I get 8-10 mpg depending on number of hills, hwy vs city etc.

Here's graphs of D.D. tq/hp for Edel Perf, CC260H and Pontiac 9779066.





But sure, maybe it isn't tuned right, still. Would a degree of timing or being 1 stage lean or rich completely throw performance out the window?

...what is a sure fire way to set timing perfectly?
...what is a sure fire approach for dialing in carb?
...anything else I can do?
...how do I verify my 7 year hi flow old cat.conv. is not plugged?
...what else could rob lots of power?

Apologies if this is OT.

Michael

[Goose]

Well as for dialing in the timing, I use the "ping method"..Unscientific and If you don't pay attention and let it detonate a long time your going to break something but it goes like this. Set your timing about 5 -7 degrees advance from stock for altitude then go try it.. Keep advancing it till you start to ping at mid Low rpm full throttle acceleration. then back it off a little. as for the carb I dont have a good way, I usually judge by performance and driveability, you would have to be fairly rich to dump performance to the level you are seeing. If you were a little lean it would run better the higher you go. But you might save yourself some grief and pull that cat and put a "Test pipe" in it and see . even a partially plugged converter will degrade performance a lot. or you could find a station that has a old tail pipe sniffer exhaust analyzer (like they used to use for em tests before envirotest.)
Don't lose hope if that 360 is fresh it should drag that wag around in style.
What Carb are you running?

[shimniok]

thanx for the tips.

Running an old AFB. REALLY sick of the choke on it, can't get it dialed in. It does pull off fully, just too quickly (no heat riser). Maybe time for the EFI after all... (GM TBI) ... or a Qjet...

Will check out the exhaust issue, who knows...

Michael

[shimniok]

In case anyone's curious, I swapped on a Qjet, did some quick calibration, passed emissions, and improved performance (below 50mph). It drives like it has EFI at least below 50 and gas mileage went up quite a bit. It still is lacking on the highway. I haven't checked for the plugged cat yet.

Michael

[MrFurious]

Don't put a whole lot of faith in the DeskTop Dyno software, as it isn't very accurate in terms of real world numbers. When I worked down at Jeg's in the Tech Support Center, we actually plugged several crate engines into the software and none of them were even close on the HP and torque figures we got off the engine dyno. Typically, DD would show 50-75 more horsepower than was actually pulled off the dyno.

However, the power curves were usually pretty close in regards to peek power at such and such rpm, so using it to build an engine up for power in a specific range is possible. Just don't rely on the power numbers it gives you unless you want to be disappointed.

[shimniok]

Thanks for the info, that is good to know.

I noticed DD2k is significantly more optimistic than the original DOS-based version was (which claimed 95% accuracy and was closer to the original creator's vision I suspect).

I will keep that in mind and use it (and talk to some engine builders) to figure out what the best -curve- is for the setup I'm running. That's really the biggest question I've had all along, anyway.

Michael

[shimniok]

Thought I'd post again. I haven't done squat with the 401 yet. I am probably a jet size or two rich on the Qjet. I do have an EFI setup in the garage but that is a lot of wires to add and I'd hate to break down on the trail. That's why I never put it in. One of the guys on the CFSJA list runs an MPFI Edelbrock on his 360 and reports 90+ at the tunnel, but he also runs real low gears and stock tires and lift (so he must be spinning 4000 at hwy speeds?)

All the desktop dyno stuff I've played with says I can get 20hp and 70+ ft-lbs across the ENTIRE 2000-4000 range with a 401 and either an edelbrock performer or a custom grind like the Pontiac *066 (the latter is for big heavy Pontiacs with autos, the former is for small motors so puts the power lower in the bigger motor I guess). I haven't looked at all the possible cam grinds or called anyone yet. Have done a few searches here for cam advice.

I finally put together some money for the 401 so we'll see what work needs done to it and go from there. I'm also contemplating simply putting in a new bumpstick in the 360 along with headers. I hate seeing a $2800 motor go to waste or blowing a lot of money on the 401; I'm banking on it not needing any major machine work. Aside from lack of power the 360 runs fine.

If I do the 401 I am taking the advice here to heart: 9.0:1 or 9.5:1 CR pistons (or do I need to deck the block to improve squench?) headers if I can possibly afford it, and will keep the Edelbrock intake and Qjet carb, then do some kind of cam grind with 114* LCA and duration to support peak torque around 2800-3000, peak hp around 4000-4200.

Also to doublecheck I plan to take it to a muffler shop to see if the catalytic converter is bad after 8 yrs. (How else would I diagnose this?)

Michael