2003cobra#2's 3.4 Whipple Build

03cobra#2

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I wanted to post to bring this back for a quick update. Car has been running well except for a small drivability issue. I stumbled across this post


And I believe this is my exact problem.
A part throttle hiccup when the boost bypass shuts as I transition into boost. This week I'll be pulling the blower off and doing a fresh set of intake gaskets, and modifying the hose from the blower plate to the boost bypass solenoid to accept a nitrous jet. I have a few different size jets ordered so I can fine tune how quickly the bypass shuts to get into boost. Apparently this is a known issue with some whipple setups. Newer cars that have this problem are drive by wire and it can mostly be tuned out, not so with our cars.

Other then this hiccup the car runs nice with the cams and 3.4. I'll keep you posted.
 
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Blackedout

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I was having the issue where we couldn’t get the car to stay running going into gear (auto car) it would drop to about 3 inches of vac and die... with the blower belt off it’s perfect..... I wound up trying the low boost actuator L&M offers (it has no spring in it) on the Dyno it was great but street driving was a huge issue... I wound up installing a spring to keep the bypass valve open until about 3 psi and so far street driving is way better....
this is a pic of the Whipple Low Vac bypass spring that closes the valve ...
 

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03cobra#2

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I was having the issue where we couldn’t get the car to stay running going into gear (auto car) it would drop to about 3 inches of vac and die... with the blower belt off it’s perfect..... I wound up trying the low boost actuator L&M offers (it has no spring in it) on the Dyno it was great but street driving was a huge issue... I wound up installing a spring to keep the bypass valve open until about 3 psi and so far street driving is way better....
this is a pic of the Whipple Low Vac bypass spring that closes the valve ...

Interesting I was thinking of possibly doing something like that but was not sure if it would make the problem worse or better. Whipple puts a light spring in them now for the last few years so they work with aggressive cams but it's a total light switch cruising around. I have the blower off the car and am heading to the parts store to scrounge up some vac fittings. Holiday weekend so I won't have all my parts right away but I hope to report back with results in a few days.
 

Blackedout

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1st Pic...The bottom spring is the Whipple Low Vac spring (keeps valve closed)
I used the top spring to keep the valve open
2nd pic is how I Installed it ...
 

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03cobra#2

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So when the engine is off the bypass remains open. Then using boost to close the valve correct? So you said it takes about 3lbs to close it. How is drivability? Also where did you get the spring? Thanks!

Edit: Also did you remove the factory spring in it and if so how did you do it. Also how did you keep the spring in place in the second pic?
 
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Blackedout

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So when the engine is off the bypass remains open. Then using boost to close the valve correct? So you said it takes about 3lbs to close it. How is drivability? Also where did you get the spring? Thanks!

Edit: Also did you remove the factory spring in it and if so how did you do it. Also how did you keep the spring in place in the second pic?
Yes the spring keeps the valve open to about 3 psi... so far street driving is way better than no spring at all.. I work on medical equipment so that’s what I tried... I wrapped 1 end around a 14mm socket to enlarge the end so it couldn’t come out of the hole where the rod is... the actuator that I’m using is the L&M which has NO spring in it... looks like they whole sawed a 3/4” hole to remove the spring and epoxied a plug in it... PM me an address and I’ll send you a couple springs if you want to try it..
 

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03cobra#2

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Yes the spring keeps the valve open to about 3 psi... so far street driving is way better than no spring at all.. I work on medical equipment so that’s what I tried... I wrapped 1 end around a 14mm socket to enlarge the end so it couldn’t come out of the hole where the rod is... the actuator that I’m using is the L&M which has NO spring in it... looks like they whole sawed a 3/4” hole to remove the spring and epoxied a plug in it... PM me an address and I’ll send you a couple springs if you want to try it..

Thanks for the offer but I'll hold of on chopping the actuator up for now. I'll try this restrictor method and see how the results are. Appreciate the Info
 

03cobra#2

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Update: Part throttle drivability is fixed (for the most part).

Just to recap, I have done a lot of reading on this over the last year or so and it is definitely a problem that comes up on Whipple cars. Cars that have drive by wire can be tuned around this, not on our cars. So I pulled the blower off, and extended the vac line from the blower plate to the boost actuator so that I could access the line in the engine bay with the blower bolted to the engine. A little testing with the blower off the car shows the bypass closed nice and slow when you take the vacuum away using a .020 jet. Once I got everything buttoned back up I took her for a spin this morning. No more light switch effect in transitions from vac to boost.... nice and smooth now. In fact it's pretty remarkable how smooth the car starts, idles, and drives with stage 3 cams and a larger blower.

Couple things I noticed after putting the restrictor in. When I quick stab the throttle say in neutral the rpm's feel a bit lazy at first, probably due to the bypass valve being slower to close now. Also I can definitely tell boost comes on a bit slower, not instant. This is perfectly fine for street driving, and I suppose if I ever take it to the track I can take the restrictor out. I also ordered a few jets that are a bit larger that will speed up the closing transition, so I can play around with it and fine tune from here. Overall very pleased now.
 

4sdvenom

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One more thing. Do you have any pictures of what you did to the vacuum line to be able to insert a nitrous jet inline? I realize you lengthened it to make it accessable, but wanted to see how you were putting the nitrous jet in the mix.
Thanks
Ken
 

03cobra#2

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One more thing. Do you have any pictures of what you did to the vacuum line to be able to insert a nitrous jet inline? I realize you lengthened it to make it accessable, but wanted to see how you were putting the nitrous jet in the mix.
Thanks
Ken

Sure, I'll upload a pic when I get home.
 

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