Suspension Specs.

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ImpulseRocket89
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Suspension Specs.

Post by ImpulseRocket89 »

I translated this stuff from a Japanese website a couple of years ago. I posted it up on Isuzone, but there are so few first gen members on there that it was largely overlooked.

Some of the translations are quite literal.

This Info is specifically for the 88-89 Cars with the Lotus tuned suspension.


Coil Spring Rate [kg/mm]
Type Year system

IMPULSE 88+
Front: 4.3
Rear: 2.3 - 4.8
Remark: HBL

Coil Spring spec (HBL - Handling by Lotus)

HBL(MT) 88+

FRONT:

Free Length(mm) 400.0
Wire(mm) 14.5
Outside(mm) 116
Number of active coils:9.83
Total number of coils:11.58
Identification Color: no info

REAR:
Free Length(mm) 303.5
Wire(mm) 10.8
Outside(mm) 123.6
Number of active coils: 5.5
Total number of coils: 7.25
Identification Color: no info

Shock Absorber rate [ (0.3m/sec時)kg ]


HBL
Year 88+

Front
Extends: 82
Shrinks: 30

Rear
Extends: 63
Shrinks: 64

[kg/cm^2]
20.6(F,R)

sway bar. mm
23 front
20 rear

Suspension Stroke [ mm ]

type: HBL
Year: 88+
Front
Stroke- 143
Most expansion- 390
Most reduction length- 247
Rear
Stroke- 158
Maximum expansion- 748
Minimum length- 320

Front Alignment
Type: HBL
year: 88+
toe in: 1mm
caster: 4°30'
camber: 0°00'


Here are the specifications for the Irmscher suspension.

Coil Spring Rate [kg/mm]

IMPULSE
Front: 4.7
Rear: 1.4 - 7.2
Remark: Irmscher

Coil Spring other spec

FRONT:
Free Length(mm) 383.0
Wire(mm) 14.0
Outside(mm) 101.1
Number of active coils: 7.93
Total number of coils: 9.68
Identification Color: No info
REAR:
Free Length(mm) 339.5
Wire(mm) 9.2￾`12.5
Outside(mm) 106
Number of active coils: 7.63
Total number of coils: 9.13
Identification Color: No info

Shock Absorber rate [ (0.3m/sec時)kg ]

Form: Irmscher

Front
Extends: 87
Shrinks: 35

Rear
Extends: 130(92)
Shrinks: 38(38)

[kg/cm^2]
no data


sway bar. mm
25 front
17 rear

Suspension Stroke [ mm ]
type: HBL
Year: 88+
Front
Stroke- 152
Most expansion- 397
Most reduction length-245
Rear
Stroke- 197
Most expansion- 488
Most reduction length- 291


Front Alignment


Type: Irmscher
toe in: 1mm
caster: 4°30'
camber: 0°45'
1988 Isuzu Impulse Turbo.
2005 Ford Crown Victoria LX

RIP 1989 Impulse Turbo, aka "Rakete"
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Piazza_man
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Post by Piazza_man »

I can't tell from these specs alone which version is the better handler. Was there ever a comparison test published between the two tuners?
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archangel62
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Post by archangel62 »

After giving that a quick look, I reckon the HBL would have better turn-in at the cost of slightly more oversteer, based on the swaybar sizing. The HBL would also be slightly more linear in the back end, based on rear shock absorber valving and a slightly less progressive springrate, although it'd come down to driver preference as to if that's better or not. I'd prefer it, but the ride might be marginally less forgiving over bumps, albeit still not too bad.

The camber setting is interesting, however, with HBL at 0deg, which would be good for tyre wear and straight-line braking, but pose a notable loss to turn-in over a negative cambered setup. The Irmischer notes camber, but I can't figure out if they mean negative (good) or positive (bad). At the end of the day, though, that's easy to adjust yourself.
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Piazza_man
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Post by Piazza_man »

Thanks mate. I notice the HBL springs are softer all round, especially in the rear, compared to Irmscher, but they've gone for the stiffer rear bar setting, which kind of negates the stiffer front bar. Would that translate to less body roll for HBL? As far as spring rates are concerned I would probably prefer the HBL softer rate and let the Konis control the rebound better, and then use the Irmscher stab bar specs to dial out the understeer. It's hard to work out precisely what the tuners wanted to achieve, but I'm more surprised there doesn't seem to be any head-to-head comparisons published. I'll have to keep a closer eye on any Japanese articles.
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Post by IZU069 »

Pity none of the ICCA guys are here (Isuzu owners Car Club of Aus - nee Bellett-Gemini CC of NSW), some of them race(d?) Piazzas.

My Guru once gave me a run down of the variations (& GMH stuff ups) but any memory of brief notes taken are well hidden now. And Guru has since left the Marque as well as any sites (the latter as I have too LOL).

Not that I was that interested in Piazzas at the time, it was more the G200W overlap (since I didn't consider the 4ZC1-t 135HP nor 180HP worthwhile).
And I can't recall who was racing Piazzas so I don't know whether they are inies or outies. (Coincidentally, parallels with female front bums may be applicable.)
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Re: Suspension Specs.

Post by twocan »

I know this is super old but this information helped me a heap when i was trying to get some springs for my HBL car to go a little bit lower.

I made some measurements with the suspension disassembled and basic calculations (using the formula MR = (lower arm length / spring distance) * sin(spring angle) and it looks like the motion ratio based on the measured dimensions for
- the front is 0.536
- the rear is 0.80.

I.e. 100mm of travel at the wheel = 53mm of spring compression etc. the dimensions measured are as per below.

front
Image

Rear
Image

I then used an excel sheet to calculate and compare the motion ratio's and the measure corner weights of the car to see if the measuremnts and calulation came up with the same spring rates and lengths to what i measured which they did. Also Faulkners in the UK measured the actual spring rate of the HBL spprings in my car and this is the response

Results

Fronts
390 mm free length
245 lbs/” average (4.375202kg/mm)
Random fitted of 300 mm load 874 lbs aprox
c/g x 1 86.4 i.d.
nearly closed not ground 87.3 mm i.d.

Rears
312 mm free length
125 lbs/” average (2.232246)
Random fitted of 200 mm load 508 lbs aprox
c/g x 1 99.8 i.d.
nearly closed not ground 100.2 mm i.d.

fronts
Image
Image

rears
dont have photo's

and this i the calculation sheet with notes etc that i used. hopefully this is of use to someone else in the future.
piazza suspension and spring calculator.zip
(9.92 KiB) Downloaded 193 times
I will post more information about the custom springs made in the custom springs post.
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Re: Suspension Specs.

Post by Piazza_man »

Thanks for the detailed write-up twocan. Brilliant stuff. Although my car is lowered I’ve been thinking about redoing the rears as they are loose and kind of want to fall out when jacked up. Maybe slightly thicker rubber/nolathane pads to close the gap, but haven’t found anything yet.
twocan
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Re: Suspension Specs.

Post by twocan »

Yeah I did get a set of escort lowering springs for the rear from one of the other piazza guys but they weren't captive with the spax shock I have. They ended up getting custom made shorter shocs from Gaz in the UK to solve the issue.

I struggled to find shims of the correct dimensions as I was thinking of try to get the corner weight correct ish, best I found on ebay was 3mm thick rubber washers for 1000l bulk bins. I think there are 2 inch lift spacers for 4wd's that might fit though havent had one physically measured.
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Re: Suspension Specs.

Post by Piazza_man »

:tonqe: funny you mentioned the escort lowering springs and my rears are off Escort MK2 front lowered springs (variable rate). My shocks though are Koni. Because the springs are slightly different diameter to factory ones the rubber seats aren’t sitting properly in the springs. Ideally want this fixed with new seats and if the rear height was increased 5-10mm I’d be happy.
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Re: Suspension Specs.

Post by Piazza_man »

:tonqe: funny you mentioned the escort lowering springs and my rears are off Escort MK2 front lowered springs (variable rate). My shocks though are Koni. The springs are slightly different diameter to factory ones which aren’t sitting properly in the factory seats. Ideally want this fixed with new seats and if the rear height was increased 5-10mm I’d be happy.
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Re: Suspension Specs.

Post by Piazza_man »

:tonqe: funny you mentioned the escort lowering springs and my rears are off Escort MK2 front lowered springs (variable rate). My shocks are Koni though. The springs are slightly different diameter to factory ones which aren’t sitting properly in the factory seats. Ideally want this fixed with new seats and if the rear height was increased 5-10mm I’d be happy. I know the Koni shocks can be custom shortened so that could also come into play
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