RCR GT40 THROTTLE ISSUES...

Hello,
I have recently completed my RCR GT40 and I'm trying to improve it's driveability. I have the RCR pedal box which has a Lokar throttle cable connected to a Borla 8 stack injection. Two issues:
1) The Borla intake operates fine when first started but when things warm up to operating temp it tends to hang up when returning to idle, causing the idle to stay around 1800 rpm and then will slowly back down close to normal after a long wait. If I "blip" the pedal it will return to normal idle immediately. I have checked all of the linkage for binding and have loosened all the throttle plates to re-center them but the problem persists. I'm pretty certain it isnt a hang up in the cable. I have also rerouted the cable to make sure all curves in the cable are larger than the cable specs. Does anyone have any experience with this issue...a possible hidden gremlin in the Borla intake?
2) The throttle is hard to press, giving it poor "feel" when using the clutch. The Borla intake has the stock springs at each throttle body and has no additional return springs. I'm thinking the geometry of the RCR throttle pedal doesn't have the adequate leverage needed to easily operate this intake. Again, I have inspected and lubricated the cable and it operates without friction. Has anyone had a similar issue? Maybe a mod to the throttle pedal to give it more leverage?

Thanks for throwing in!

Kim
 

Ian Clark

Supporter
Hi Kim,

It would be helpful if you posted a few pics of the throttle hook up at the pedal box and the induction system to get a handle on possible causes and make suggestions. The three RCR pedal boxes I've set up all worked very well once properly adjusted. The same care is required with brake bias and clutch master cylinder throws. Pics please, happy to assist if I can.

Cheers
Ian
 
Thanks for your reply Ian. I was able to get a couple of photos of the areas you requested. Although I'm fairly certain there is no binding or misalignment in these areas. I have spent many hours trouble shooting these problems. I've had the cable disconnected from the intake and the pedal and cable run friction free. It seems like the leverage geometry of the pedal and the size of the bellcrank and the return springs on the intake are making for the stiffness in the pedal action. I have set the pedal position to be on the same plane as the brake pedal when it is engaged. The car is driveable but an easier action at the pedal would make it much better to work the clutch.

Ian, when you set up the 3 RCR pedal boxes were any of them connected to a Borla 8 stack intake?

Kim

IMG_0324.jpg
IMG_0323.jpg
IMG_0322.jpg
 

Bill Kearley

Supporter
I had the same issues with the Borla 8 stack. You will have a heavy throttle with Borla, after all you have 4 shafts to open and close. All you can do is lube the cable and pivots then find a balance between pedal travel and effort. The high idle when hot was only resolved after I bought a syncro gauge and set up the throttle bodys myself as it was never set up properly by the people that tuned and dyno'd my engine. A sugestion was made to remove some return springs and or find lighter ones, I didn't go that route.
 
Bill, thanks for your input. It confirms what I was thinking. I might add some length to the arm of the pedal, get more leverage there. I don't want to change the spring action at the intake for fear of adding to the problem I already have with the slow return to idle when hot.
 
I had this problem on my race car. What i did was warm the engine to reflect the problem and then disconnected the cable at the carbs linkage and checked to see if it would return to idle. It did...repeatedly. I lubber the system and made adjustments and still had the problem. I replaced the cable (it was old) and that ended the problem. A couple of things though. Carbs were. Multiple webber’s and my cable was the type that has a solid wire. I don’t know the makeup of a Lokar cable. Mine was a solid wire and replaced with a stranded wire. My approach was to isolate the two in operational conditions and determine which was causing the issue.

Gale
 
I had this problem on my race car. What i did was warm the engine to reflect the problem and then disconnected the cable at the carbs linkage and checked to see if it would return to idle. It did...repeatedly. I lubber the system and made adjustments and still had the problem. I replaced the cable (it was old) and that ended the problem. A couple of things though. Carbs were. Multiple webber’s and my cable was the type that has a solid wire. I don’t know the makeup of a Lokar cable. Mine was a solid wire and replaced with a stranded wire. My approach was to isolate the two in operational conditions and determine which was causing the issue.

Gale
Thanks Gale, My photo is mis-leading. The cable goes almost 360 degrees around the bell crank circle where it attaches so I think we are on the same page setup wise.

Kim
 
I had this problem on my race car. What i did was warm the engine to reflect the problem and then disconnected the cable at the carbs linkage and checked to see if it would return to idle. It did...repeatedly. I lubber the system and made adjustments and still had the problem. I replaced the cable (it was old) and that ended the problem. A couple of things though. Carbs were. Multiple webber’s and my cable was the type that has a solid wire. I don’t know the makeup of a Lokar cable. Mine was a solid wire and replaced with a stranded wire. My approach was to isolate the two in operational conditions and determine which was causing the issue.

Gale
Sorry Gale, my last post was a reply to George's post. I did all the things you did to isolate the problem. I still got the hang up of the idle with the cable disconnected so its definitely an issue with the intake. The Lokar cable has a stainless braided housing with a teflon insert..stranded cable.

Kim
 
I have the same Borla Setup and don’t have any issues. My throttle has the cable attached differently compared to your setup from what I can see in the pictures. The throttle wheel has two cable settings and your setup looks different from mine. I used the furthest position on the wheel. Hope this helps.
George,
My photo is mis-leading. The cable goes almost 360 degrees around the bell crank circle to where it attaches so I think we are on the same page setup wise.

Kim
 
I don't have one of these, so take this idea with a grain of salt. If you have isolated the stiction to the intake/TBs, try isolating one TB from the rest of the linkage to see if one in particular is sticking. If they are daisy-chained, start by removing last in the chain, and work towards the middle
 

Dwight

RCR GT 40 Gulf Livery 347 Eight Stack injection
Supporter
I had to make a bracket for a return spring.
IMG_E9098.JPG
 
I don't have one of these, so take this idea with a grain of salt. If you have isolated the stiction to the intake/TBs, try isolating one TB from the rest of the linkage to see if one in particular is sticking. If they are daisy-chained, start by removing last in the chain, and work towards the middle
Thanks for the reply, Tom. I tried that but got inconclusive results. When any of the throttle bodies were disconnected I couldn't bring the rpm up to duplicate the problem. The "stiction" as you called it, is only noticeable with the engine running. Can't see where its hanging up visually.
 
is the spring a clock wound one, or standard coil spring? If coil, maybe adjust the anchor location, both distance from the bell crank, and angle, to increase the closing force at idle, and perhaps lighten the spring force further into the bell crank rotation.
 
is the spring a clock wound one, or standard coil spring? If coil, maybe adjust the anchor location, both distance from the bell crank, and angle, to increase the closing force at idle, and perhaps lighten the spring force further into the bell crank rotation.
Tom,
The added spring was a coil. Is that physically possible...to pull the throttle closed and at a certain point open? It sure would be the answer but I'd have to see a diagram on the placement to understand how that could work.

Kim
 
I have the Borla 8 throttle body system on a 302 block. The springs make the force to open very hard. If you look closely, there is one spring that is a duplicate per side. I removed it. That left me with one spring per throttle pair. I think it is still too hard to push the pedal. Be sure that you have enough lever ratio on the throttle pedal and that you are pulling your cable at a 90 degree angle. Moving the cable location DOWN on the pedal will allow more stroke and less force by the foot. First figure out how much foot throw you can use, and then change the lever ratio until the throttles are almost fully open at maximum stroke of the foot. Be very careful that you don't have more pedal throw when the throttles are fully open since you might break the cable. There will be almost zero difference in power at 95% throttle as opposed to 100% throttle open.

I asked Borla about softer springs or less preload, and they thought what they had was appropriate. At one time, I sent out a post suggesting that we make a group buy on lighter springs. However, the other day I did an autocross run and forgot to open up the rear deck to cool the engine. On the way home, the throttle would stick at a small throttle angle. I had to blip the throttle to get it back to idle. I presume this was from more friction in my cable, but the strong springs were probably helping me then, so I'll stick with the springs and look at a better throttle cable.

If you disconnect the throttles and actuate the cable, it might indeed move freely with no force; however, when there is a force on the cable, it will pull the cable into the side of cable housing and create friction and hence more force. Never use a solid cable if you have any bends in the routing.

Although your delay in getting to idle might be a function of the throttle not closing all the way quickly, it could also be from a bypass source of air. For example, an idle speed control valve, or possibly a bad check valve on the vacuum booster of your brakes, or it could be from a vacuum leak on your intake gaskets. Maybe not too probable, but good for a quick consideration if the engine doesn't go quickly to idle when actuating the throttles without the cable.

-Bob Woods
Tornado GT40 in Texas
 

Ian Clark

Supporter
Hi Kim, a lot of good suggestions concerning the throttle linkage, levers and springs thus far.

I'd really like to see a pic or two of your linkage hooking up to the throttle pedal as this is not clear in the photo posted.

On the RCR pedal boxes we've set up a clock spring is installed on the throttle pedal to help with throttle cable return. This in addition to a return spring as shown in Dwights' setup is really for safety sake rather than compensating for cable or lever setup issues.

There's also the question of the change in lever ratio of the bell crank on the manifold opening the throttle bodies. I imagine the throttle pedal starts off heavy then lightens up as the throttles open. There appears to be some bell crank / linkage / throttle arm geometry issues at play here too.

These are all quality parts and should provide a smooth, progressive throttle application. It's going to need to be gone through front to back with everything disconnected and checked individually for bind, then collectively at the manifold, then at the throttle cable to the throttle pedal (after determining there's no bind in or between them).

Primarily, I'm suspicious of linkage geometry, throttle bodies synchronization and cable routing/mounting as the culprits. Any one of those items can cause the problem you're having, put two together and you're definitely going to have a unhappy throttle pedal.

Cheers
Ian
 
re my point on helper spring, it should be
1) tangent to the bell crank at idle ie 90 degrees so that it is at maximum efficiency
2) a "light" spring rate relatively speaking
3) anchor point stretched pretty far, so that there is significant preload at idle. As bell crank sweeps through range of motion, increase in spring force will be fairly minimal, but it will lose efficiency, in effect providing little additional spring force late in the sweep. Just be certain the closing force doesn't go "over the top", as stuck throttle is a disaster.

All this said, Ian provided a great check list to go through before you reinvent the wheel.
 
Thanks everyone for your valuable input, tons of good info, much appreciated! I spoke with Ed who is the Borla tech adviser for the 8 stake intakes and he acknowledged the heavy spring issue with the intake. So I decided that better pedal geometry is what will improve the heavy pedal issue. One thing I didn't mention, but I just realized, is I have the older version of the RCR pedal box. My car was an u-built kit from 2008 and looking at the current pedal box on the RCR website there is quite a bit of adjustability of the pedal ratio. My pedal has zero adjustability unless I fabricate different mounting points.

I will re-check my bell crank linkage but feel I set it up to optimize its operation in respect to bell crank leverage but it wouldn't be the first time I got my thinking backwards. Suffice to say, it's a definite challenge attaching and adjusting things on this intake, what with things being buried down under the fuel rails. Add a hot motor to try to duplicate the sticking issue...calling the job unpleasant is a kindness it doesn't deserve. I'll report back with what I find.

Kim
Hi Kim, a lot of good suggestions concerning the throttle linkage, levers and springs thus far.

I'd really like to see a pic or two of your linkage hooking up to the throttle pedal as this is not clear in the photo posted.

On the RCR pedal boxes we've set up a clock spring is installed on the throttle pedal to help with throttle cable return. This in addition to a return spring as shown in Dwights' setup is really for safety sake rather than compensating for cable or lever setup issues.

There's also the question of the change in lever ratio of the bell crank on the manifold opening the throttle bodies. I imagine the throttle pedal starts off heavy then lightens up as the throttles open. There appears to be some bell crank / linkage / throttle arm geometry issues at play here too.

These are all quality parts and should provide a smooth, progressive throttle application. It's going to need to be gone through front to back with everything disconnected and checked individually for bind, then collectively at the manifold, then at the throttle cable to the throttle pedal (after determining there's no bind in or between them).

Primarily, I'm suspicious of linkage geometry, throttle bodies synchronization and cable routing/mounting as the culprits. Any one of those items can cause the problem you're having, put two together and you're definitely going to have a unhappy throttle pedal.

Cheers
Ian
Thanks for this Ian. I found it difficult to get pics of the pedal hook up. I'll try to get better photos this weekend.
 
Top