Carb Spacer

[SPF2245]

What's the largest carb spacer I can put in a newer SPF with a roush 427 and not hit the hood. I've got some fuel boiling problems. Also, would this also cause fuel starvation issues, I've had two cases of the motor shutting down during hard acceleration and one during cornering when the motor/carb was hot.

Thanks,
Dan

[SPF1061]

Depends on your intake, air cleaner and type of motor mounts. Put a piece of modeling clay on the top edge of your air cleaner and close the hood. There's your clearance with your present set-up.

[wtm442]

Your first question is answered above. Your other questions have a "YES" answer. Fuel can boil in either bowl and/or the gas line and make the engine run super rough and/or stall at any time.

[SPF2245]

Thanks, I'm guessing I've got about a 1.5 to 1.75 of an inch to play with. Would a small spacer help and if so, which is the best material/type to filter out the heat.

[Bill Wells]

not necessarily apples and oranges with your R and my Ford 392 crate stroker . IF you have the space, go with a 1" spacer if you can . I added one to my engine , Pro Sytstems custom 780 Holley , single plane high rise manifold , replacing the 1/4" spacer that was there ....and on a Mustang brand chassis dyno it added almost 20 rwhp as well as 20 more in torque . NO fuel boiling issues either . i have just a hair room left of space under the hood/scoop, but it does not touch . It is some type of synthetic material, plastic like .

Also, if limited space, Holley offers a very thin aluminum heat deflector that has worked well on some cars , but not sure it cures all the ills on all engines . Mine is the size of the base of the carb, the Holley aluminum one is larger than the base and helps dissipate the heat as well as its size deflecting alot of the heat .

Bill

[SPF1061]

Dan,
Like Bill said, a 1" spacer would almost surely solve the fuel boiling problem. I don't know how much effort you want to put into this, but if
you want to try to get the most horsepower out of the hood clearance you have available, another approach would be to put in the lowest height riser that will sove the problem - I use a 1/2" wooden spacer purchased from AED
(they only show 1" on the web site, but they do have 1/2"-call them)

http://www.aedperformance.com/Accessories.htm

Now add 1/2" height to your air filter. K&N will custom cut their filters in 1/2" increments to any height you want. The spacer will add hp/torque at the low end and the increased air flow will from the larger filter will let the engine breathe better at higher rpms and add hp up top. HAVE FUN!

[RedBarchetta]

It also depends on car build #, too. The newer cars have slightly more crown in them to accommodate more vertical space.

On #747, I'm running a dual plane Edelbrock Performer RPM with 1" spacer and a tall 2" K&N filter. Used clay on the back end and still had about 1/8-1/4" of clearance. If I ever go to an Air Gap intake, I would have to reduce the spacer to 1/2".

-Dean

[efrost]

What about Wilson tapered spacers? Has anyone used on of these? I read where they alluded to a 27hp and 110cfm gains with their tapered spacers. Not certain of the test engine specifics but an increase nonetheless.

In addition to heat and vibration isolation the pickup of a few horsepower got my attention.

http://wilsonmanifolds.com/

http://store.summitracing.com/egnsea...s=false&N=+115

I plan to check my hood clearance for the 1-inch version.

Ed

[Bill Wells]

yep , 2 good points mentioned :

1. i keep forgetting about the raised cowl and higher scoop on later spf's vs my older 156 , thus allowing more clearance.

2. also, my 1" spacer was also tapered - i forgot about that til i read a later reply . my chassis dyno figures of about 20 hp and 20 trq at rear wheels increase would theoretically put the crank in the high 20s range . also, my dyno was on a mustang dyno which typically understates the rwhp vs a dyno jet chassis dyno .

Bill.

[hkelley]

Originally Posted by SPF2245

What's the largest carb spacer I can put in a newer SPF with a roush 427 and not hit the hood. I've got some fuel boiling problems.

Dan

I just had this problem two weeks ago. The spacer is a good place to start but if the heat is being picked in your lines it won't help. It didn't for me...I had to do some rerouting and added a bypass fuel regulator.

Joe

[niles]

I think your assumption that boiling fuel is the problem might be suspect.
My experience with air coming directly onto the carb via the scoop results is a realitively cool carb. I have never seen a problem with or without spacers.

I would start an logical elimination process; 1st thing to eliminate is to insure your float hights are correct with engine hot and running. 2nd trace your fuel line route and make sure that anywhere its "sees" the headers, that you have the line insulated and a heat shielded, so that any line (gas or brake) can not get direct radiation heating from the very hot headers

gn

[wtm442]

If the heat is affecting the fuel bowl, use a spacer

http://store.summitracing.com/egnsea...=KeywordSearch


If the problem is too much heat in the fuel line, you will have to install a return line to keep the fuel moving.

[scootter]

Holley makes a nice aluminum heat shield with the spacer. I had to use a smaller spacer that I got form 4 seconds flat since I have the 514. Since I put in a smaller spacer, I had to cut holes for the accelerator pumps. You can see in the picture.
How much gas did you have in your car when it died under hard acceleration? I had this problem. I went through everything on the car. I found that with a 1/3 of a tank of gas or less( about 3 1/2" of gas in a 7 1/2" deep tank), the fuel pump would suck air under hard acceleration. With the shape of the tank, all the gas rushes up the back and leaves the suction line sucking air. It happened to me on the freeway again the other day. So I let the car coast while the electric fuel pump fills the bowls and fire it back up. Some day I will change the tank pickup.
Scott

[greg schroeder]

I've been in your same situation searching for solutions to stumbles and stops. I hope this isn't too wordy, but it may help.

For your stall out on hard acceleration I'd check your rev limit to make sure you're not hitting that. I changed mine to 7000 rpm. For my engine a little below is a nice place to shift for maximum acceleration good for 1/4 mile 130+ trap speeds on a nice day in the 70Fs or colder with 29.8 or higher on the baro. I'd also check your jet size. If you're lean it will stumble and fall off particularly in top gears with a taller tire.

When your car stumbles stopping and cornering you may have fuel slosh. You might even get fuel up over the vent tubes from the float bowls to dump fuel down the carb.

I have a similar set up to yours, Superformance 2040 with Roush 427R-095 Single plane manifold. I have no spacer, but usually run my Pro-Systems 1000 cfm double pumper set up for in line acceleration. Theeee best mod for the money I've had so far, but it's not a cornering and stopping carb.

This carb from Pro-Systems was built for track racing. I've never used it, but thought I'd share the image as it's suppose to be able to get tossed around hard with no ill effect as well as having improved mileage.


I've never had a problem with starting or fuel boil here in Arizona summers, maybe that's because of the single plane intake. One pump on the gas when engine is cold and immediate woof varoom start. Once warmed up if I'm at long multi direction stop lights I'll shut the car off while I wait. To start there is no pump on the gas and it starts immediately. If the car is warm and has been sitting in the parking lot for several minutes I hold the throttle down half way. It takes a few turns to start there, but always starts. I run the Pro-Systems 1000 cfm carb set up for drag racing most of the time.

I did throw away the Superformance supplied fuel filter and replaced it with a pop can size Aeromotive 100 micron filter. I no longer use the 3/8 inch fuel line that came with the car either. I have 8AN line and quality fittings from tank pick up to carb now. I have a mechanical self regulating Carter fuel pump. While the old line was a quality install I believed it was restrictive with some of the 90 degree bends that flattened out as well as there were cast elbows in and out of the mechanical fuel pump that were drilled suspiciously restrictive.

[CHI-TOWN TOM]

I too am having a fuel boiling problem with my Speed Demon 750, but not when running. After the car is shut down hot, the bowls absorb manifold and other underhood heat. I am going to install a spacer, but for now I run the fans manually for a few minutes to remove underhood heat. This makes a huge difference when the car is restarted. Your problem sounds like float level and/or heated fuel from the line. Immediately after a drive, my carb float bowls are cool which indicates plenty of underhood air flow. Check yours, if hot then fuel is picking up heat elsewhere. Good luck in your efforts.

[SPF2245]

Thanks for all the replys...when the motor is shut down, I can hear the fuel boiling in the carb after a slow ride. I have considered other carb related problems and will adress those with a quality dyno check and tune.

Greg,
Thanks for the info on the pro-systems carbs...I've about had it with the Holley supplied by Roush...it's been nothing but a PITA, I knew I should have gone to FI, oh well live and learn.

[greg schroeder]

Originally Posted by SPF2245

Thanks for all the replys...when the motor is shut down, I can hear the fuel boiling in the carb after a slow ride. I have considered other carb related problems and will adress those with a quality dyno check and tune.

Greg,
Thanks for the info on the pro-systems carbs...I've about had it with the Holley supplied by Roush...it's been nothing but a PITA, I knew I should have gone to FI, oh well live and learn.

First I'd like to say I'm not an expert, but have gone through a useful learning curve from using the forum here and while searching the net and picking minds of assorted individuals.

My car was delivered with a Holley 750 double pumper. It's a very good carb if it's jetted and set up properly. Mine wasn't due to the engine installer's selection of tuning options. He did a beautiful job putting the engine in, but it ran lacking. Looking for the easy street and not knowing how to tune a carb myself at the time I went out and purchased a Holley 870 Avenger vacuum secondary from a local performance shop. I actually bought it thinking it might be a good idea for around town because I saw it was landing on top of other Roush 427Rs that were coming out of the location were my car came from. Granted I do have a single plane manifold with less low rpm vacuum than that of a dual plane intake at low RPM, but I'm 99.9% certain the Cobra is too light for that vacuum secondary. Holley seems to think so as well. I tried every secondary adjusting spring option all along with a combination of jet options. I used an actual car in motion testing device to graph power and G values and acceleration. I had lag invariably when I nailed it from a roll. The top power isn't bad once you're banging off gears, but that lag sure does suck if you want to go from a roll.

When I ordered my first Pro-Systems carb I told Patrick I want to go fast in a straight line. He pretty much knew what was up with the set up for the Roush 427R and asked what's your zip code. He tuned the carb to the actual density altitude at that time in my location. Mine was tuned dead on. I got the carb, put it on and it absolutely hammered with lightning throttle response, was smooth always and works beautifully on my single plane intake manifold at low RPM. If you can't get a 2500 lb ride rolling from 2000 rpm with 350 wheel ft lbs of torque at that rpm you need to release the emergency break.

Here's my dyno sheet with the Pro-Systems carb and a couple changes including exhaust options I changed. Note the punch at a bit over 2000 rpm and how the torque comes on. That's at the wheels and a zero smoothing on the graph with no games for representation of having smooth power.

[CHANMADD]

If you are experiencing perculation the best spacer is a phenolic type available from Summit,these do not transmit the heat like all metal (Aluminum included) and as said elsewhere the spacer does improve torgue.