944Hybrids: 924/944/968 and 928 V8 Conversions
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Mon Jul 08, 2013 3:56 pm by Admin

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Post  Jim7 on Thu Jul 11, 2013 4:18 pm

It's not possible to do that with the 968, and I tried and tried.  I trimmed the hood brace, cut the nose on the intake TB end, tilted it down, cut the oil pan to the max and still needed to put in 1/2" spacers.  I suppose if I'd kept the car high up on the suspension then bump steer wouldn't be a problem.


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Tubular cross member update - Page 2 Empty Many thanks

Post  Gutterboy on Thu Jul 11, 2013 11:17 pm

Appreciate the collection of opinions on this bump steer matter. Eric I meant no dig on the crossmember progress your efforts and work are sincerely appreciated I just truly didn't know where that venture ended up and if it was truly related.

I had seen the bump steer top hat kit from xschop but I have no idea if the 1/2" is all I need for my c5 ls1 in my 88 944s conversion. Not to mention I don't know how much that ride height would change the feel of the car. I ain't knowledgeable enough to know the difference most likely it's just the OCD in me that wonders if I could get a hole in one by filing clearances on the hood and throttle body and not touch a thing to upset the natural balance of the car.

Also since I am a newb mechanic for all intense purposes being an electrical engineer who loves cars, I fear inadvertently maiming myself by unbolted the coils while trying to put xschop bump steer top hats on.

Thousand thanks to the recent follow ups on latest bump steer thoughts all in the same thread.


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Post  money pit 951 on Fri Jul 12, 2013 11:00 am

Sorry, didn't mean to throw the grenade and then leave.

So some basics so we're all talking the same thing:
Bump steer is caused by the difference in the arc of the suspension travel and the steering tie rod. As the suspension moves the two members have to move together or the wheel angle will change. From the factory, the 944 has a great design with very little bump steer -you can see it by watching how the A-arm and tie rod are almost always parallel.

So, what happens when we throw the V8's into it? Really, nothing changes. The subframe contains the A arm mounting points and the steering rack mounts so as it's shimmed down, the whole system moves as one. The centers of the arcs that they tie rod and A arm make are still in the same position as are the attachment points on the upright.

So why all this talk then? When the subframe is dropped and ride height lowered, as many of us have done, the angle of the A arm goes from something pointing down to something pointing up. All this affects the car's/suspension's roll center which people feel when driving. People have tried to correct this by redrilling the inner A arm mounting holes on the subframe which would then angle the A arm back to more a preferred angle and returning the roll center to where it should be. It's a great solution for fixing the roll centers and even compensating for a dropped car.
So, pulling it all together if the inner A-arm mounting points are moved on the subframe and the steering rack stays where it is, those nice parallel arcs that Porsche worked so hard to design are gone. The A arm will swing in one arc and the tie rod in another. As the suspension moves through it's arcs, the steering angle will change - hence the bump steer!

How do we fix it all? Well, easy way is to keep everything as it left the factory at the factory ride height... but that's not why any of us are on this forum! To fix the roll center, the inner mount for the A arm has to be moved up. A redrill of the subframe is the easiest fix for that. Then how to fix the introduced bump steer? Well, we could move the steering rack up on the subframe, but those mounts are harder to move and everyone's favorite oil pan is in the way. So we could move the mounting point on the upright. If you look up the elephant racing bump steer kit you'll see that's what this does.

So I'm not trying to poke at anyone, but I hope this explains why changing what the tie rod looks like doesn't change the arc in which it sweeps. The sweep is determined by the points it's connected to, not what the center section in the middle looks like (hence the figure 8 comment)
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Tubular cross member update - Page 2 Empty last point of clarification, i think...

Post  Gutterboy on Fri Jul 12, 2013 2:07 pm

1. so if i just use the normal deluxe conversion kit with my ls1, i will have dropped the crossmember with spacers for the engine to fit right?
2. but i haven't changed my ride height, correct?
3. so i shouldn't have a bump steer issue???
4. or would i still have it cause the a arm angle is not parallel with tie rods now as you had explained?

if i have points 2 and 3 wrong than aside from the elephant bump steer kit to solve the issue, does xschop's coil top hat kit acheive the same thing if you all did was use up to 1/2" spacers on the crossmember?

excuse my newbiness here.

thanks in advance,


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Post  Arthropraxis on Fri Jul 12, 2013 7:03 pm

There are a lot of people running these cars with 1/4 to 1/2 inch spacer. I have yet to hear anyone complain of the steering. You don't have anything to worry about, just put in the thinnest spacer that will serve the need.

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Post  Rich L. on Fri Jul 12, 2013 7:23 pm

To everyone doing a budget conversion, don't worry about bump steer. The accepted method is using crossmember spacers without drilling to move the a-arm mounting location. You do have to do some trimming for the oil pan to fit nicely. The rack is lowered along with everything else so the factory steering geometry is maintained. The front roll center is affected but few find that an issue.

What others are discussing is trying to compensate for the lower crossmember by moving the a-arm mounting location and then correcting the steering. Personally, I avoided all the trouble by not spacing the crossmember off the frame. This created more inference with the hood and the brake master cylinder but was preferable because my car is a racer.

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Tubular cross member update - Page 2 Empty few more clarifications

Post  Gutterboy on Fri Jul 12, 2013 7:57 pm

thanks for the insight on the budget conversion since that is what i would classify my street car conversion; budget but the right parts and drivetrain to put a smile on my face.

my last questions are in regards to Rich L.'s sentence as follows: "The accepted method is using crossmember spacers without drilling to move the a-arm mounting location."

the crossmember spacers ended up moving the a-arm location right. you don't add spacers to the a-arm mounting location right? sorry, having trouble envisioning this since i have yet to even start step one. Right now i am in the procure all parts and read everything under the sun before i rip everything half apart leave it for a couple of weeks and then return to a bunch of unlabelled parts of which i don't know what to keep and what to toss.

secondly, the oil pan in the kit is not directly bolt on after you get the right crossmember spacers? i was not aware that trimming of the crossmember was required to get an ls1 with conversion kit in the engine bay. i thought spacers and eric's oil pan made it totally bolt on and no mods necessary?

curious, with no spacers i can understand the throttle body height issue to which some have commented with pictures that a bit of filing does the trick with a notch in the underbracing of the hood but how does the master cylinder interfere on height? even if you kept the cereal bowl and deleted the booster and threw on the classic wilwood wouldn't you still be well below the height? or are you running some crazy hydroboost that needs way more room for your racer?

after all the invaluable input here, i am steering (pardon the pun given the thread topic) towards minimizing spacers as much as possible maybe even zero to maintain geometry out of perfectionist sake, notching the hood for throttle body and done assuming wilwood with sloan plate and 10 degree angle shim block and x mm long pushrod to get to the brake pedal 3/4" inch up will fit under hood. (still not decided on whether to just throw the porsche booster away since it won't fit and reuse cereal bowl to maintain the necessary 10 degree angle or do the shim on the sloan plate).


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Post  Admin on Fri Jul 12, 2013 8:46 pm

Throw the cereal bowl away. Don't think of it as a usable part with the conversion. It will cause you tons of headaches and it has to be heavily modded.
As far as the spacers go. They have only to do with hood clearances. They have nothing to do with the oil pan fitting. The pans that we are selling now only require the hard lines of the power steering to be moved a little. You can run without spaces but you will need a bump in the hood, grinding and cutting isn't going to make it happen except on some 968's. Even with 1/4" slavers you will have clearance issues that ginding may or may not fix. If you're building a street car, you will probably never notice the spacers being in place except when you close your hood,..........


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Post  Gutterboy on Fri Jul 12, 2013 10:54 pm

I will definitely take your word on pitching the cereal bowl as well as the spacers and thanks for the heads up on steering lines.

Guess I'll make the Sloan plate and do the 10 degree shim to prevent sideloading on the wilwood pushrod piston. 944-lt1 gave me some big pointers on the pushrod dimensions after I missed the boat on his angled shim part. Seems easy to fab but could mess with the typical custom dimensions people normally fabricate the pushrod to with the added shim width in between the Sloan plate and the wilwood. Was hoping there would be just enough thread for it to reach 3/4" up pedal with the shim if I made the Sloan plate half thickness to make up for the angle shim. Could be a bad gamble without just measuring through the firewall to be sure.

Should be buying my kit in august and hopefully any other stuff outside the conversion kit that makes sense.

Thanks again.


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