Building Up A Blown Olds Motor for an "A/GS Gasser"

The Holley carbs had 73 jets front and back, left 'em for now, but had 10.5 PV's, cut em back to 6.5's in front and 4.5's in back. Started right up and seems to be running much better. Will hook up the Innovate and see what the A/F is running.

Just cruising around I sometimes see the vacuum down to 10 or 9, most of the time around 15, so don't need PV's opening up and dumping additional fuel when just cruising around. So far so good, I drove it home from the shop, about 15 miles of back road mostly, 2nd and 3rd gear stuff.
 
2Loose said:
As I can't get the tuning parts I want from Demon, those are going back on the shelf for now.

Can you be a little more detailed Willy? I'm considering buying a new Speed Demon for the TBucket, so your comment got my attention.



Forgot that my Demon fuel lines won't hook up directly to the Holleys, different threads, so now am chasing the right parts to do this hookup.

Is the only difference the threads or is the distance between bowls also different......any thing else ???



Willy
Click to expand...
 
i use a 0.0 powervalve in mine if i remember correctly, and i have one only in the primary(single carb).
 
The Holley jets and power valves work in the Demons, but the idle air restrictors and idle fuel bleeds are unobtainable, and the Holley parts don't fit. You can drill the ones that are in the carbs bigger, or solder them closed and redrill them smaller, requires the really small needle size drill bits and a hand held chuck to drill with them is what I was told, haven't tried it myself. The fuel lines require a connector with a different thread at the bowl for the demon carbs, don't remember what it is right off the bat. I used all AN braided fuel lines and was able to get both 6an and 8an fittings with the correct thread for the Demons from Summit. Went with the 6an at each bowl and then 8an back to the fuel pump. Had to change the fitting at the bowls when I put the Holleys on. Summit had them.

The broadband O2 sensor is telling me I'm running rich, around 10, with these carbs too, so need to do some tuning on these also.
 
Am jacking the rear end up to pull the 3rd member and change the gears from 3.50 to 3.00, and check out the Detroit Locker, as it seems to have a helluva lot of slack in it, more than I think it should, plus when I drained the oil (still the original oil from the first install with the new Currie 9+) there seemed to be a lot more metal in it than I thought there should be. So gonna check it out.

I had bought a used, bare Mosier 9" housing with 35 spline axles, narrowed the housing to fit the gasser with 12" rims in back (minitub job w/ coilovers, ladder bars, panhard), then added the new third member and narrowed/resplined the axles to fit. Used heavy duty 9" axle truck drum brakes.

More later....
Willy
 
mathd said:
i use a 0.0 powervalve in mine if i remember correctly, and i have one only in the primary(single carb).
Click to expand...

I reduced the primary side PV's in the Demon carbs to 4.5, and plugged the secondary sides, it ran better but still needed more leaning out. Had the main jets down to 72/74 and did not want to go any leaner on the mains. It was the idle/cruise circuits that were seemingly untunable for me, so I switched to the Holley HP 600's, also blower referenced carbs. They presently have 73 main jets, and had 10.5 PV's, I downsized the PV's to 4.5's, still way fat, might plug the secondary PV's. They have the 50cc pumps in them, so will have to get some different pump cams and play with that.

Where did you find the 0.0 PV's? For a blower setup running rich, that sounds like a better deal to me, but I would need to find them.

A buddy just bought a drum of race fuel, don't know which octane rating. He said he'd sell me some, like 5 gal., so I can put some in at the track next weekend. Am thinking up putting in my overdrive pulleys, a 38/34 combo instead of the 36/36's I'm running now, and with the race gas added, see how it likes it. Am thinking about one gal. to ten or even one to five for the 92 octane pump gas. Hope I don't blow it up! :shock:
Aloha,
Willy
 
Mine came with the 0.0 PV(so pv open only under boost), i also have both 50cc pump but i use a 30cc pump cam for the primary(green iirc) it has some nasty throttle response last time i drove it to put the car away for the winter, so much it was a challenge not to spin the tire in first gear.
With straight race fuel you can run more boost i dont know for ignition, probably more advance too if your going to run it all the time. But i see your going to mix it so id dont change the tuning for it also more octane is always better, dont think you will blow it up in fact i think its the other way around it will be more safe(detonation wise) so long it do not has alcohol in it because alcohol need much bigger jets.

Tuning the idle was a breeze with the holley, just tuned it for higest vacuum at idle, when i got my lm-2 it was dead on no adjustment was needed, just need to have all idle screw set to the same turn.
I dont remember what jet i have in but they are bigger then yours and are dead on, just need to tune the accelerator pump circuit very well(am really close to perfect tuning from the feel of the car and the logs)
 
The 3.30 low gear ratio in the Doug Nash trans seems to be well suited to the new 3.0 diff gear I just put in the 9", it feels good out on the road.

Went to the track yesterday, got in four pretty good runs at Test&Tune, but it's still not hooking up very good, lot of tire spin, and must not be making the horsepower I wanted, as only getting 12.6's out if it.

Did interior vids of each run, they are grouped together in the six minute Youtube vid below. It's an "unlisted" vid file, but you can access it with the url below.

The clutch was starting to slip on the second run on the shifts, you can see it in the vid, so didn't hit the shifts so hard with the throttle on the 3dr and 4th runs and it didn't slip as much if at all. But on the 5th run the clutch let go in the wet box during the burnout, so had to take it home!

Now I get to take it apart, one more time!!!
Aloha,
Willy

LINK to YouTube vid at the track...
 
Remember that in Oct. I did 2 runs at our local Maui track and broke a u-joint, then in Nov. I did 5 more runs, then the clutch let go. Nothing nasty about the runs, mid 12's, around 114 mph max, 12" wide cheater slicks, this clutch never should look have failed like it did.

Finally pulled the Centerforce DFX clutch apart and found these toasty parts inside:

Pressure Plate Side:
P1030911.jpg


Flywheel side:
P1030910.jpg


Closeup of the Centerforce DFX Ceramic Clutch Puck:
P1030923.jpg


The flywheel is scored and will need resurfacing or replacement:
P1030926.jpg


The pressure plate got really hot, blistered the paint:
P1030915.jpg

When the clutch surfaces let go, the pressure plate fingers
pushed the throwout bearing further back, and the clutch
arm outside of the pivot closer to the pressure plate shell.
That contact was relieved whenever I stepped on the clutch
pedal, but as the clutch engagement, what was left of it,
was now at the top of the pedal, the clutch arm had to
make contact with the pressure plate shell to engage the
clutch, resulting in the marks you can see here on the outer
edge of the shell. It probably also contributed to the heat
problem.

When I changed from the aluminum to the steel flywheel, I had
originally run into this problem, with the clutch arm hitting the
shell due to the thicker steel flywheel pushing the whole assembly
back. Shortening the pivot ball support 1/16" solved that problem!
(See post above somewhere in this thread....)

And scored the surface of the pressure plate, it will also
need resurfacing or replacement:
P1030913.jpg


I wrote to Centerforce about this failure, so far I have not heard back from them.
I will update you all as I get more info. My advice at the present is to stay way far away from the Centerforce DFX clutch setup. They market it as a street/strip setup. This one never should have failed like it did.

I get the feeling that Centerforce uses guys like us as their R&D department!

Aloha,
Willy
 
after the pressure plates been either replaced or totally rebuilt and the flywheels surface ground Id strongly suggest the flywheel or BOTH the resurfaced flywheel and rebuilt pressure plate,be magnetically tested for FLAWS/CRACKS that may not be obvious, the cost to do that testing varies a great deal, between machine shops , so if its not cost effective in your area you might want to skip the process and just replace the parts with new parts.
you might want to take the pressure plate to a local clutch re-builder, they usually have BILLET rather than cast pressure plate components and can set up the clutch with stronger spring clamp pressure, most street pressure plates have 2400lb-2600 lb clamp pressures, most performance clutches 2600lb-3000lb, but a good clutch shop can install stiffer springs or more springs depending on the application, I generally had my race cars set up with 3600 lb clamp load Borg and beck clutches, but be aware theres a very noticeable increase in petal pressure required so on a street car its not always a great option, I know my wife could not depress my race cars clutch.
clutch durability is mostly dependent the materials used and the clutches design for effectively applied clamp loads and surface area plus the ability to dissipate heat rapidly , the larger the area in the clutch design, to absorb and dissipate heat and the faster the clutch locks up the lower the heat generated


undetected cracks can cause problems
you can have stiffer springs installed in a clutch pressure plate that can significantly increase the clamp loads, this tends to increase petal effort but also increases clutch life in most cases
clutchpressureplated11.jpg


swapping to a dual disc clutch effectively more than doubles the clutch surface area and reduces heat build up, so thats an option on high torque applications, here you need to increase holding area, a correctly built dual disc clutch can hold over 700 hp/700ft lbs easily
clutch8.jpg

viewtopic.php?f=71&t=447

flyexp1.jpg



RELATED INFO
viewtopic.php?f=71&t=447&p=840#p840
 
whoa that suck, really bad luck :(. i think something must have been set wrong?. sure a blown big block with slick need a very good clutch, maby this one was just not good enough.
 
The clutch linkage was stock '55 Chevy that was reworked by me (ok, ok, don't say anything.....) and the linkage as I set it up put the clutch engagement movement right in the middle 1/3 of the pedal travel. It had about a 1/3 travel at the top of the pedal before starting to engage the diaphragm clutch fingers with the throw out bearing, the bearing was moving smoothly on the tranny nose, and had about 1/3 pedal travel at the bottom after the clutch was disengaged. I put adjustment on the link from the pedal to the Z-bar and from the Z-bar to the clutch arm so I could keep it all well centered.

When I changed from the aluminum to the steel flywheel, I found that the steel was slightly thicker and moved the whole clutch setup rearward, which I could not take out completely with linkage adjustment and get the pedal movement and feel I wanted, unless I shortened the pivot ball stand and moved the whole clutch arm rearward 1/16", which is what I did. After doing that and adjusting the linkage accordingly, then it was back where I wanted it when I initially set it up with the aluminum flywheel. It felt good out on the street, and the first couple of runs at the track felt good, then it started going down hill....

Have any of you worked with Southbend Clutch? They were recommended to me for my next try at getting this right!
http://southbendclutch.com/
Here's something from their website:

"Stage 2 Drag

Drag racing requires a Single Mass SFI approved Flywheel to be included with each kit when the original design is Dual Mass. This system features a Heavy Duty Pressure Plate modified for a puck style disc with no cushion between the linings to keep the clutch pedal travel short and quick. The puck design disc reduces rotational mass and total drive surface area while increasing pounds per square inch on the surface of the friction material. This combination minimizes inertia, accelerating the transfer of torque from the engine to the wheels. The friction material used for this race application is Graphite Impregnated Ceramic. This compound exceeded all other friction materials when testing for durability, reduced chatter, heat transfer and torque capacity.

Recommended uses are drag racing, drifting and limited street."

And:

"Stage 4 Extreme

This is a “build to order” clutch kit intended for cars with HP modifications exceeding the stage 3 parameters. The Race Engineered pressure plate is modified for maximum plate load. The discs are puck design with sprung and un-sprung options. Friction material options include Sintered Iron and Graphite Impregnated Ceramic. Engagement characteristics can be abrupt. Hydraulic systems may need enhancing for proper clutch separation. Single mass steel SFI approved flywheels are required for safety. Torque ratings are calculated at time of ordering."

Willy
 
Am also using a centerforce clutch, but am using the DualFriction type with Organic/Carbon composite material. Dont know wich of the 2 material is better and wich last longer(i know the organic/carbom composite is easier to drive on a daily basis and has a smoother engagement) but looking at the clutch design the dual friction type look better since it has more contact area?
I went with centerforce because i read on this forum about them and so far am really pleased, I have read no feedback about Southbend clutch.
 
Went with this as a replacement:

ACT GM6 HDSS, full face clutch disk, rated at 735 ft. lbs.

GM6-HDSS_2.jpg


Talked with them at length, decided this was the best choice for my application, mostly street with occasional runs at the track. Need to do a good "break in" of the clutch system when I install it. Will go back to my aluminum 12 lb flywheel, as it is essentially still new.
 

Can you compare this one to your old one.....such as the force rating of 735 lbs and price....etc ???

 
I hope your choice works out for you, but I will point out that my experience with racing big block engines with torque loads similar to what your super charged engine can potentially produce makes me extremely doubtful that the clamp loads that it can apply are nearly adequate.
now Ill fully admit its been a few years since I personally raced a big block manual transmission car, but I just found that a LONG or BORG &BECK style clutch set up with a 3200-3600 clamp pressure lasted much...MUCH longer than the disc and diaphragm designs
 
I hope your choice works out for you, but I will point out that my experience with racing big block engines with torque loads similar to what your super charged engine can potentially produce makes me extremely doubtful that the clamp loads that it can apply are nearly adequate.
diaphragm style clutch pressure plates by design are meant to provide smooth operation, over clamp loads
now Ill fully admit its been a few years since I personally raced a big block manual transmission car, but I just found that a LONG or BORG &BECK style clutch set up with a 3200-3600 clamp pressure lasted much...MUCH longer than the disc and diaphragm designs, a good local clutch rebuilder can custom spring a a LONG or BORG &BECK style clutch set up to have dual springs in each location and get a 3600 lb clamp load, thats resistant to slipping, but Id also point out the increased petal pressure required and it takes a different driving style as the clutch is basically in or out during a shift without much slipping

THIS THREAD MAY GIVE MORE INSITE
viewtopic.php?f=71&t=447
cltchinfo.jpg
 
Maby the first clutch needed some break in time? didnt think about it but now you say it, most clutch(including my centerforce) need some break in.
 
You must log in or register to reply here.
Back
Top