6-71 Blower Surge

[GT63]

Well now I have a temperature weirdness happening. Once it warms up it jumps up 210 degrees and stays there about a 5 minutes or so, then when the 180 degree thermostat opens, it drops to 160 ans stays there. Every now and then it will burp up about 8oz of water.

 

[OldredT]

Grant, you may want to richen it up a bit , my big block chev /671 blower started heating up strangely to 210 and then back down to 180, the surge was there also . I fattened up the jets and bumped the timing up a touch, and it cured the surge and it cooled down some also. I am running 2 750 demons side by side , I have not heard much about the inlines. 1st I would make sure you are using both carbs on the idle circut that will make it surge big time . The new blower looks great !!
Chad

 

[GT63]

Thanks,

I contacted Barry Grant about the carbs and they told me these carbs come with a boost reference power valve and I need to run a vacuum line from the manifold to the port on the front of each carb.

I asked why they didn't include this information in their instructions, since all they do is ship them with the manual for the standard carb. Still waiting on that reply. LOL

 

[wixomhead]

Hi Guys:

I'm in a similar boat... Mind if I share some info/maybe we can help each other out?

My app is 460 Ford with BDS 8-71 and two 750 CFM Barrry Grant Mighty Demons, "blower calibrated' carbs. I'll spare you all the details, but running 8:1 compression, 22 Deg initial mech adv timing, good alum radiator. strong flowkooler water pump, 2500 CFM elec fan, Xtreme Energy Comp Cam, CD ignition...

I've got it so my motor idles like glass at 900RPM, but I'm experiencing 2 problems:

1. All eight idle mix screws are turned out only 1/2 turn all around. This seems excessive. Any more turns out - even 1/4 turn more on any of the eight - and the motor imm begins to surge (600RPM -1200RPM) over and over. Any turns in and it dies.

2. The motor is idling very, very hot. I've got a 195 thermostat in there right now, and the thing will slowly climb to 225 deg before I shut it down.

Plugs look clean/light brown. BG tech also told me to hook up boost reference pwr valves and I then should then be able to turn screws back out some, but when I did this - it didn't have any effect at all.

I'm going to call BG again today and also install 180 degree thermostat, but apprec any help if you see any glaring probs with my setup. Thanks.

 

[blownt]

How do you know you have a "good alum radiator"? Is this a new build? Did you have that radiator with the 460 without the blower? I'm thinking that radiator is not big enough to handle a 460 with a blower. I had the same problem with a shorty brass radiator. With a mildly warmed over smallblock it would drive around town at 210. Get into rush hour traffic and it would run 225. Put the blower on it and it would run 225 and in traffic get to 245 and start poppin seams.

I tried everything with no help. Finally bought a Walker Cobra Z radiator and have no problems, Runs 185-205. I have no themostat. I run the middle size restrictor.

Also you might try an oil cooler. Get the oil temp down some and the engine will run cooler.

 

[GT63]

Hi Guys:

I'm in a similar boat... Mind if I share some info/maybe we can help each other out?

My app is 460 Ford with BDS 8-71 and two 750 CFM Barrry Grant Mighty Demons, "blower calibrated' carbs. I'll spare you all the details, but running 8:1 compression, 22 Deg initial mech adv timing, good alum radiator. strong flowkooler water pump, 2500 CFM elec fan, Xtreme Energy Comp Cam, CD ignition...

I've got it so my motor idles like glass at 900RPM, but I'm experiencing 2 problems:

1. All eight idle mix screws are turned out only 1/2 turn all around. This seems excessive. Any more turns out - even 1/4 turn more on any of the eight - and the motor imm begins to surge (600RPM -1200RPM) over and over. Any turns in and it dies.

2. The motor is idling very, very hot. I've got a 195 thermostat in there right now, and the thing will slowly climb to 225 deg before I shut it down.

Plugs look clean/light brown. BG tech also told me to hook up boost reference pwr valves and I then should then be able to turn screws back out some, but when I did this - it didn't have any effect at all.

I'm going to call BG again today and also install 180 degree thermostat, but apprec any help if you see any glaring probs with my setup. Thanks.

Wix, I solved my problem by replacing the BG Demon carbs with Edelbrock 1405s. I followed their instructions for tuning them for a blower application and they work real good. I also changed my blower pulley ratio from 18% under to 10% under. That made a big difference in tuning.

If you don't have one, I'd reccomend getting the book "Street Supercharging: DIY Guide to Street Supercharging, How to Install and Tune Blowers " and since you have Demon Carbs try this book "Demon Carburation"


Do you have a shroud around your fan?

How much vacuum do you have at idle?

Is your temp sender in the front or back of the manifold, or is it in the head?

Are you running straight distilled water, straight AF, or a mixture?

What is your pulley ratio on the blower?

What is your cam lobe separation?

The recommended total timing is 36 degrees for a blower motor(from book listed above). I have my SBC set at 18 initial, 18 advanced all in by 2800, and it seems to like there. So far my plugs are still light brown and it curises real nice. It pulls like a monster when I get on it too.

 

[wixomhead]

:razz:Thanks gents:razz: for the feedback and ?s.

Blownt: I say this is a good alum radiator b/c I bought it new and put very few miles on it. Its a Griffin universal fit, 31x19 overall, 2 x 1 inch rows. Oil cooler is great idea, don't have this...

Update, I let it idle today for 30 minutes ea with 180 and then 160 thermostats; temp seemed to climb and hold at 210 steady with both of them in 80 degree climate here. This is down from 225+ yest with 195. I cleaned all plugs before both tests this am and pulled a few out after...they were clean as a whistle, no carbon fouling.

GT: YES, I do have Pat Ganahl's Street Supercharging book. UGH. I paid $600 ea for the BG carbs, I did this to reduce trial and error tuning...how ironic. I'd like to avoid swapping them out. To address your ?s:

Do you have a shroud around your fan?
NO. I have 2500 CFM Elec Fan mounted 1" in front of radiator (clearance is very tight w/ belt) acting as a pusher. Blows strong (maybe not strong enough?).

How much vacuum do you have at idle?
15 inches steady.

Is your temp sender in the front or back of the manifold, or is it in the head?
In top front of manifold, 'below' thermostat.

Are you running straight distilled water, straight AF, or a mixture?
50/50 tap and anti freeze with rust inhib.

What is your pulley ratio on the blower?
1:1 for 10lbs boost at 6000RPM WOT

What is your cam lobe separation?
110

The recommended total timing...
I set it up with 22 initial with 18 more by 3500 RPM, I think...I followed procedure laid out in the book for this.

 

[blownt]

if you are just idling in the driveway you cannot really tell. Once you get it out on the street and cruising then you will really tell how it does. Mine runs hot it just idle. Once you get out with air going thru it you will know for sure,

I run straight water (demineralized), no antifreeze. Just a rust inhibitor and waterpump lubricant. This is what Stewart Components recommends for the best cooling.

I use a timing light with the knob on the back. Turn the knob to 34, rev motor to 3000 and set mark at ZERO.

 

[sstock]

I've tuned my share of positive displacement blowers, centrifugal blowers and turbos granted mostly by EFI, however same holds true for carb'd applications. Usually when you get a surge it is because of improper air fuel mixtures caused by a whole host of different reasons. It is always helpful to have a bung on the header pipe so you can plug a wideband to confirm this and aid in nailing a good tune.

 

[wixomhead]

OK guys, great info thanks. Hope this data helps others.

My motor idles very well now and under cruise seems to be running around 190; need more miles/road time to be sure. What I want is the security of not getting stuck / overheated in hot stop and go traffic for an hour.

What I really find amazing is...I've got all idle mix screws at 1/2 turn out. if I move even one of them OUT only 1/4 turn more, the motor begins to surge up and down. If I screw only one screw only 1/4 turn IN, the motor starts to die.

I didn't expect the margin here to be so damn close on a blower motor; I expected lots of fudge room with the idle mix screws...

 

[brenshar]

hello gt63 have read about your blower surge i am considering same carbs for mine did you solve issue if so what did you end up doing Brent

 

[RPM]

He replaced those DEMONS ( a good name for them) with some 1405 Edelbrocks. We run a pair of 1405s on our blown 350 Chebbie.

 

[GT63]

hello gt63 have read about your blower surge i am considering same carbs for mine did you solve issue if so what did you end up doing Brent

Exactly what RPM said. I replaced those crappy Demons with a pair of Edelbrock 1405's and then re-jetted them according to the instructions Edelbrock provided for blown engines. I haven't had a problem since. I've even been able to change my pulley ratio closer to 1:1.

 

[Screaming Metal]

Blower surge is blower surge.....richen it up on the idle circuit.....its hard on the engine when it does that.............

 

[Screaming Metal]

Hi Guys:

I'm in a similar boat... Mind if I share some info/maybe we can help each other out?

My app is 460 Ford with BDS 8-71 and two 750 CFM Barrry Grant Mighty Demons, "blower calibrated' carbs. I'll spare you all the details, but running 8:1 compression, 22 Deg initial mech adv timing, good alum radiator. strong flowkooler water pump, 2500 CFM elec fan, Xtreme Energy Comp Cam, CD ignition...

I've got it so my motor idles like glass at 900RPM, but I'm experiencing 2 problems:

1. All eight idle mix screws are turned out only 1/2 turn all around. This seems excessive. Any more turns out - even 1/4 turn more on any of the eight - and the motor imm begins to surge (600RPM -1200RPM) over and over. Any turns in and it dies.

2. The motor is idling very, very hot. I've got a 195 thermostat in there right now, and the thing will slowly climb to 225 deg before I shut it down.

Plugs look clean/light brown. BG tech also told me to hook up boost reference pwr valves and I then should then be able to turn screws back out some, but when I did this - it didn't have any effect at all.

I'm going to call BG again today and also install 180 degree thermostat, but apprec any help if you see any glaring probs with my setup. Thanks.

Get your advance Straightened out.........get it all in as early as you can, run a 160 Degree thermostat.....or even take your themostat out and see how it does........on a blown engine.....you want to run slightly rich.....

 

[1924 c cab]

In my 24 C Cab I have a 385 sbc with BDS 6-71 running with 8 lbs boost.Msd 6al ignition with boost time master. 18 degrees inital advance and 36 total at 2800 rpms.Dart iron eagle heads,76cc 215cc runners,2.08 and 1.60 valves. Crane solid roller blower cam,Jesel shaft mounted rockers.Jesel belt drive. Custom made pistons,7.9 to 1 compression. Forged crank, H beam rods.Holley black fuel pump.Bypassing fuel pressure regulator.etc. I have dual holley 750 hp4150s with modified power valves for blower operation. on mine. it used to surge badly. I found that the carbs were out of sync slightly. It was a bitch to get them to open at the same time. the linkage had to be modified as the geometry was not the same. it opened one at a different rate than the other. Fixed that. The surge was lessened but not gone.. I end up drilling the idle circut passages in the metering block to a larger size to allow enough flow. Now the surge is very slight almost unnoticable. My wifes car has a 350 with a Weiand 142 and it also surged at idle. It has a Edelbrock 750. I had to also open the idle passages on it to eliminate the surge, Hope this helps.Steve

 

[brenshar]

thanks for all the responses i sure like the looks of the twin demon jrs but am going to re think this and take a good look at the edelbrocks thanks again

 

[GT63]

thanks for all the responses i sure like the looks of the twin demon jrs but am going to re think this and take a good look at the edelbrocks thanks again

Here's a few pictures of the Demons installed on my blower. You can see that the fuel inlet is on the drivers side and makes it difficult to route the fuel line with out interfering with the throttle linkage. That plus the inability to eliminate the blower surge is why I switched to the Edelbrock 1405's. It's a monster now.


Picasa Web Albums - Grant - blower_installed

 

[donsrods]

Some people pay big money to get that sound. :wstupid: I love hearing one idle like that.

Don

http://www.summitracing.com/search/?keyword=ford crate engine&dds=1

[ame="[media=youtube]3QldWWo7n7o[/media]"]YouTube - P8240276[/ame]

 

[blownt]

mine does and I ain't changing it. Makes for alotta head turning when you drive into a parking lot. Tends to load up regular plugs but I have no problem with Bosch Platinum Plus 4's. Take them out once a year just for a general clean-up.