BUILD THREAD 86 GP 2+2~Blown 6.0

[81cutlass]

Swapped the 275's from my 8.5" wide vectors onto the 10" wide rallys.

The vectors stuck the tire a little far out for my liking but they cleared, I could roll the quarter and they'd be good. The rallys put the extra 1.5" wheel width on the frame side (which the vectors had a ton of room) so fingers crossed they will clear.

The rallys pull the outside of the tire in maybe 1/4" and I gained a about 0.5" of tire width at the sidewall.

 

[Supercharged111]

Swapped the 275's from my 8.5" wide vectors onto the 10" wide rallys.

The vectors stuck the tire a little far out for my liking but they cleared, I could roll the quarter and they'd be good. The rallys put the extra 1.5" wheel width on the frame side (which the vectors had a ton of room) so fingers crossed they will clear.

The rallys pull the outside of the tire in maybe 1/4" and I gained a about 0.5" of tire width at the sidewall.

View attachment 179069
View attachment 179070

I observed a similar phenomena eons ago by mounting 275/40/17 tires on SS wheels (left) and Z06 wheels (right). At first I figured the treaded RA1s ran narrow, but after a few people mentioned rim width maybe that's what it was. SS is 9" wide, Z06 is 9.5".

 

[81cutlass]

I planned to do some test pulls to check that my fuel pressure holds yesterday but it was raining (which I am NOT complaining since it's been so dry)

So I test fit my 15x10's. They fit well. The only semi complaint is that they are close to the frame rail. 1/8-1/4". Closer than I want but they do clear on the outer side to the quarter nicely.

I had 295/50/50's on the car for two years and they were also really close. They lightly rubbed but that was with stock upper rubber bushings and the rear is centered much better.

I MIGHT semi notch the frame if I have issues with rubbing. Probably a half notch if I go that far to the weld seam. TBD.

I decided the clearance is probably fine, but didn't want to go to the track and then have issues so I popped on the fleabay and decided to buy a pair of 1/4" spacers. Problem is they are not expected until middle of next week and I need them for Friday. I had some 2" spacers for the front when I ran C5 wheels on this car so I decided why not just cut them down.

As our friendly neighbor from up north said recently "I have a GD lathe", I might as well use it.

Dewalt brand parting blade

Bam!

I don't plan on running the spacer unless I have issues. They will just be tool box items in case I have issues.


I need to clean up the other spacer, swap the front shocks to the old 90/10's I have, and do some quick tuning. Pack the tool box and should be ready for the track this Saturday.

 

[motorheadmike]

That looks amazing. Also, just notch it. Weekend job at best for you.

 

[liquidh8]

Looks awesome with those wheels

 

[81cutlass]

That looks amazing. Also, just notch it. Weekend job at best for you.

I probably will. I need to decide what bracing I am going to put in. I am going to put a shock brace in similar to what you did but I want one in the front too.

Trick chassis sells this rear crossmember bar but I don't think I have the room with the full exhaust out the back. I don't think I am going to go as beefy on the LCA brace but I do like the tie-in.

 

[motorheadmike]

I probably will. I need to decide what bracing I am going to put in. I am going to put a shock brace in similar to what you did but I want one in the front too.

Trick chassis sells this rear crossmember bar but I don't think I have the room with the full exhaust out the back. I don't think I am going to go as beefy on the LCA brace but I do like the tie-in.
View attachment 179403

That brace is going to monkey with your brake lines (hydraulic and emergency) too. You can also see how thin the frame gets at the front without the inner boxing. Yikes.

PS. Stop stealing my ideas! 😉

 

[64nailhead]

That looks like a great idea - but…..some extreme overkill. 1000-1500hp upgrade there imho

WHP that is.

 

[81cutlass]

That brace is going to monkey with your brake lines (hydraulic and emergency) too. You can also see how thin the frame gets at the front without the inner boxing. Yikes.

PS. Stop stealing my ideas! 😉

Lol, I don't see a patent on anything 🙂


I laid under the car and can confirm. That brace is square in the brake lines and e brake cables. Jim is right, it's overkill and more for a full on race setup where you are 1000hp+

I think a design like this that I sketched in red would work on my car. It could bolt or light weld to the LCA's brackets. It is going to take a small pipe and something that has a tight radius to clear the drive shaft.

However I agree most of the strength lost is from the super thin part of the chassis. Adding some bracing there is likely the biggest area to improve. My red tube sketch part would probably help the frame from pulling in and might be a good place to triangulate off (blue bars? but yeah, bracing that inner part is very clear improvement.

 

[81cutlass]

And data analysis since I think stuff through the best by typing it out.

I pressure tapped a bunch of places with the 2 pumps running.

With 58 rail pressure I see 60 at the tank with the -8 feed. That's pretty dang good! I need to re run my calculations and see if my coefficient of friction value matches the single pump -6 case.

The bad part? The pressure on the return is a LOT. I am using the stock carb steel feed line from the firewall back to the tank.

32 psi at the regulator. Ish.

And to narrow down, is it the section of line between the regulator and the line near the tank, is it between the tank and there, I tapped right where there is a rubber junction on the stock steel feed line to the tank return


22 psi.

So I have 10psi of restriction through the first 80% of the line and the flex fuel sensor
and 22 psi of restriction in the last 20% of the return. I think a lot of that probably lies in the return tube that is soldered into the fuel pump hanger. I can't really go any larger because the hat runs out of room for another (or one bigger) return.

I could replace the section of line between the flex content sensor and the tank with 3/8" AN and loose maybe 8 psi restriction which would be helpful, but not as much as I want.

The other dilemma is the FPR is not lowering fuel pressure at idle. Potentially overloading the regulator with flow, possibly there is too much backpressure on the system. Probably the later.

So the solution (as mentioned) is to switch the second pump on with boost. I don't have a switch on hand and since I need to leave home to race Friday, I don't have time to set it up. I think I am going to just pull the fuse on the second pump to drive the 3 hours back to Dad's and when we head to the track I will pop the second fuse back in at the track.

I (slightly) don't like the idea of switching the pump on because if the switch fails I can lean out and kaboom, but all that additional fuel load is a lot of amps, I'm sure added heat to the fuel, and going to cause issues with getting the fuel system return line sized correctly.


But enough of so-so news, the good news, the dual pumps supply the fuel flow the engine demands.

Base pressure is 57/58ish and I am getting 65 psi under 10psi of boost, so 7-8 psi of pressure rise for 10 psi is close enough.

I also am 5-10% rich in the boost range so I need to pull fuel out. That makes sense because the injectors are seeing 65 psi instead of 45 psi.

I need to pack my tools tomorrow and do a pull with some fuel pulled. If everything looks good fingers crossed it runs good Saturday and everything stays together. Rain looks like a non issue.