Looking for suspension setup for Drag racing on N/A Diff

[Geoturbo]

Hi guys, 

I'm new to the forum and I'm looking to see what is working for Drag setups on an IRS FC TII diff.

Right now I have weld front runners up front and Weld rears on 26-8.5 M/T. Suspension is stock shocks, but not too sure on the springs as they are the same ones (yellow in color) that were on the body when I bought it.

Here is my setup.

1988 RX7 (gutted-with rollcage installed)
355 SBC Twin Turbo set at 8psi
TH350 3800 Stall.
Welded TII diff

Problem is the car will not hook at all.

The 60' is at 1.88 with a best of 1.60 (I was low on the converter that time and just feathered out the lights).

The car sqauts as soon as I preload the suspension, but all through the run it seems as though I am driving on ice. 

It's a fun ride but I just cant manage to get any type of traction. And I cant even raise the boost untill I can actually start putting it to good use on the track.

I am going to order new slicks, to get a fresh pair on there and I also want to see about rolling the fender to possibly install some 28 M/T. But before I start spending money I want to see what is working out there.

All info is greatly appreciated and will be taken into account.

Thanks

[stangslayer]

what does the rest of your time slip look like?

do you have the rear sway bar hooked up still? Its not very strong but it will help some to keep the weight distributed evenly between the rear tires.

When I was still on stock rear suspension (bone stock) with a pinion snubber,  I would nearly sit on the bump stops all the way down the track which increases the amount of camber for the rear tires and reduces grip further. My 60' on motor was 1.67-.72 and then my fist pass with the DIY 8.8 still with the same 4.10 gear and 26x9" ET street was a 1.58 and I was spinning!

[PapioGXL]

Video would help to see how the car sits and hits the tires.

I'm curious on the matter myself, but I have a much slower clutch car. 

[Geoturbo]

Rear sway bar is still hooked up. Shocks are stock.

Only ran the 1/8 mile this time around and I've only been able to take it down the 1/4 mile once and it spun through the traps.

1/4 mile
60ft-1.933
12.538 @ 111mph

1/8 mile
60ft-1.845
7.936 @93.05

1/8 mile
60ft-1.880
7.882 @90.79

1/8 mile
1.690
7.766 @79.06 (I hit the brakes before the 1/8)

I got to go through the videos I have to see if there is a good one where it gets the rear on the start..I do have one mounted on the rollcage and all you see is the shift light on regardless of what gear I'm in since I'm spinning the slicks. I literally spin from start to finish.

[Geoturbo]

Here is the car on a previous set-up. It still sqauts the same on pre-load though except now I have minimal traction when boost comes on.

[zbrown]

the front end rising is good, transferring weight to the rear axle


the rear squatting is bad for two reasons

it is unloading the rear tires, and you are loosing tire contact patch from the camber change

you dont have antisquat with the irs like you do a live rearend



really firming up the rear compression valving will help, as will adding camber at your static ride height, so that when the suspension compresses it will mantain the full patch on the tire

[Geoturbo]

Should I install some stiff shocks in the back?

I've been reading up on the KYB AGX adjustables for the the rear, is this the path I should take?

[Geoturbo]

Ok so I am thinking of adding some KYB AGX shocks. Should i mess with the springs or leave them as is?

I am also going to order some new slicks. Has anyone had any luck fitting some 28 by just rolling the fenders?

I have 26 inch slicks on right now and they are rubbing on the outer sides.

Also I feel like the car needs less gear but I have not found any gears for the diff any ideas where to get some?

Thanks

[andrewb70]

Should I install some stiff shocks in the back?

...

Yes! I used to run 175 lb/in springs in the rear and I probably should have run something even stiffer. I ran Tokico struts and they were too soft even at the firmest setting. The KYBs are definitely stiffer.

The FC swing arm rear suspension has no anti-squat geometry. This is not bad for an underpowered car made for handling, but for drag racing it's terrible. So the only way to stop the rear from squatting is doing it with spring rate and shock valving.

Andrew

[zbrown]

yup

[Geoturbo]

Perfect!

I appreciate everyone's input on this.

I'm going to order new slicks...First I am going to see about rolling my fenders and either purchasing some MT Et drags 27 or maybe some 28 slicks.

Order for the KYB's will be put in this Monday and I'm going to see what else I can do to stiffen up the rear suspension. Really excited to see this car actually hook....Then I have to worry about gears...later.... as the th350 and TII diff are too much gearing for my engine combo..

[zbrown]

28x9 mickey et drags will fit the feneder just rolled, i dont know if they will clear the trailing arm since i dont have that anymore, but i think it should

this is with a 8" wheel with 5.5" backspace

[N2v8fcs]

I run KYB AGXs set on either 6 or 8 and I also have 120 Lb springs..I would go stiffer but this is my DD . I pulled 1.61 60'  foot on 26x8 MT slicks launching @ 5K . I think fresh slicks,and the KYBs will get you where you want To be.
BTW for more ideas check the Drag racing section "50 fastest RX7s" and look at what those guys are running. Zac and Andrew are both on the list. These guys know there stuff.

[Geoturbo]

I was really hoping to get some new 28 x 8 slicks on the car but I just checked the backspacing on weld rims and it's 4". Not what I wanted to see...i was hoping it was 5.5
 I guess I'm going to have to order 26 x8 slicks again.

anyone running rims with 4 inch backspace and a bigger slick than a 26?

I think even the 27 inch slicks will rub on these weld rims..The 26 inch slicks were rubbing about 1/4 " of the slick on the fender on launch..

[Geoturbo]

Another question i forgot to ask is what brand of spring is everyone running on the rear?