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redblockpowered converts from 240 to 940

Stiff front springs arrived in the mail today! Well, stiff in a relative sense. They're OE Volvo p/n 1329826, with 14.8 mm wire and ~370 mm free length. Looking forward to the chassis improvements I have planned for springtime, anchored by the springs, IPD front bar I already have installed, and 960 front braces.....

Were those OE Diesel springs? I wasn't aware the 7/9 had a HD spring upfront with a redblock...... so just guessing at the source.
Were those OE Diesel springs? I wasn't aware the 7/9 had a HD spring upfront with a redblock...... so just guessing at the source.

They're listed for 85-87 760 Turbo, Diesel, V6 with certain chassis codes on the build plate. I sourced them on eBay and had pretty much no luck finding them new. With the thicker wire and slightly shorter free length (the OE ones in my car are listed at 13.8 mm x 385 mm) I'm wondering if they were a part of a factory sports handling kit of some sort, or maybe European market equipment. I found them digging through all the front springs listed in the 740/940 parts catalogs on gcp.se.
We'll see how it does during tomorrow's drive to school. Maybe I'll get up early and take the back roads (or as back-roads as this side of Massachusetts gets).

I'm running the IPD rear bar too. Pretty significant dynamic difference, really wakes the car up a lot. Maybe too much, if I didn't already know I was planning on adding front spring. One of the 960 front crossmember braces is in but the other one's on backorder so those will have to wait for now. To complete the handling improvement suite(?) I'll be picking up a set of Firestone Firehawk Indy 500s to put on the set of Hydras I got off a parts car.
Initial thoughts?

I'm pretty sure this thing is magic. The powertrain flexibility the V15 affords me is absurd. At the cost of a marginally rougher idle (only obvious on cold starts) I get a palpable increase in torque from ~3700 to redline. It's finally happy running past 5000 rpm and I can still lug it down around 1500-2000 at cruise without any weird vibrations or general nastiness. It has a "factory special" kind of feel to it now, like a 940R or something.
Both 960 crossmember braces are finally here, not the one that goes between the radius rods but the front pair. Not sure if I'm a believer yet but we'll see after I install them. They were pretty affordable, some $18/ea from Volvo although one side was on backorder.

Fuel economy with the V15 seems to be nearly identical to the T. Cool.
Did you install those HD front "diesel fit her" springs? Curious if you did, and the before/after ride height and apparent stiffness. It would be interesting to know the wire diameter difference between the stockers and those springs.

Good news about the V15 cam...... I've run the IPD Turbo cam for years, and also long suspected that it wasn't as good as the TB lore led us to believe. While the IPD cam is surely better than the T, I've had a K cam for years that I've always threatened to run IF I had any reason to go back into the 8V head on my DD. Fortunately, it pulls great with the 19t, so I don't see that happening right now.

Keep those updates coming.......
The springs are not in there yet, but I've measured them at 14.8 mm wire diameter vs the 14 mm of stock. Free length is 370 (or 375, just checked with my tape measure so nothing too scientific) vs the parts catalog's claimed 385 mm for the ones that are in there. I suspect the shorter free length and stiffer rate likely cancel out with regard to ride height especially when considering my front springs are probably at least mildly sagged. We'll see. Too cold to do anything outside today.
Braces are in. Handling dynamics feel the same but steering seems a lot more precise. No more small mid-corner corrections. 940s can't use the middle bolt hole without modification but I think this is known. Car is starting to feel pretty good. Certainly can't complain about a palpable handling upgrade for some $40 from the dealer.

Careful not to dump the big pile of engine dirt from the crossmember jacking point on your face when you put them in.
Just got back from the dyno. T cam, 13C, stock exhaust, boost controller set to 14 lbs, car made 184 whp and 253 wtq on tuned LH 2.4.


or https://imgur.com/gallery/IDfh4Bh if you want to look closer
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Nice! You could cross post this in Kenny's BPU thread for fun(Linuxman). I thought you already had the V15T cam in? But, didn't you want to measure it first?

How do you make the picture bigger on imgur? It's still small on the computer for me.

What RPM were the peaks at and what rpm did you start the pull at? Someone posted a comment on Imgur.
Clicking on the gallery version of the image should enlarge it, at least it does on my computer. Pulls started around 2500. Peak torque is at 2800 and peak power at 4800.
Alright, since I was curious about the stock front spring options on this car and confused about where my new springs come from, I did some research.

On the 1329826 front spring I (still) have yet to fit, the catalog on GCP.se says as follows:
14.8mm wire, for chassis code 161, 278, 279

This number only appears in the 85-87 740/760 catalog. Perhaps it was superseded but the following information tells me it likely wasn't and is a three year only part.

If you look up p/n 1329826 on the Volvo Parts US Web Store no results are returned. What gives? A quick look at GCP's 85-87 catalog reveals that it is specifically *NOT* for US/Canada market cars. So, it's a RoW only front spring, for 760 with any of the available engines (D24/B280/B230FT). At least, originally. It seems like the Kilen/Lesjofors equivalent was probably available everywhere seeing as I was able to pick up a set with basically no issue. Maybe I'm just lucky.

Looking at my build plate, the car has front spring code AC which cross references to 1329824, the fabled "diesel" front spring. If you take the Kilen applications list as law my car should have the 14 mm x 385 mm 1329823 front spring, instead of the 14 mm x 435 mm spring the Volvo catalog claims the car has. So who's right? I guess we'll find out when I take the front suspension apart. It seems to ride high in the front and is definitely soft. Does anyone around here have an 85-87 760 with one of these chassis codes?



At least the rear springs are simple. Sedan or wagon? It sure looks like 240 rears will fit if you really wanted to get weird.

Next up, some fun with stock spring rates.

I figured I'd start with something RWD of comparable weight to figure out a wheel rate target, and found this forum thread on the similarly-weighted BMW E36 M3.

So to compare, I need to know the ride frequency front and rear, and to know that I need to find my corner weights and motion ratios front and rear. First, the corner weights as measured by TB user Magnum TE in a thread started by... Me, age 13!


1992 940T Sedan
Total: 3220

Front : 1780
Rear : 1460
FL: 900 - FR: 860
RL: 740 - RR: 740

One model year off but it'll do.

For the sake of simplifying things I averaged out the front axle as 880 lbs on both sides. I won't be staggering spring rates so this will do. I estimated my unsprung weights as follows:
Wheel and tire 40 lbs
Rear axle 131 lbs
Half lower control arm 3 lbs
Half the shock 3 lbs
Half tie rod negligible
Front brake 20 lbs
Spindle/hub 6 lbs
Rear brake 16 lbs

And that gives me sprung corner weights of:
Front: 808 lbs
Rear: 612.5 lbs

Now we move on to the motion ratios. With a McPherson strut setup the motion ratio is simple, equal to the cosine of the strut angle. I put an angle finder on both struts compressed to ride height and averaged it out since I didn't trust that the car was on level ground. This returned a measurement of 12.45 degrees. Cosine of 12.45 degrees is (almost, I hope I'm not getting graded on this) 0.976.

In the rear, I measured from the center of the trailing arm bolt to the center of the wheel, and to the center of the rear spring.

Trailing arm to wheel 665 mm
Trailing arm to spring 810 mm

810/665 = 1.218 motion ratio in the rear.

Wheel rate = spring rate * motion ratio^2

I calculated the following wheel rates based on the various wire diameters I found in the parts catalog, assuming (oops) they would all work out to have the same number of active coils as I measured on my car, that being 7.5 rear and 4.25 front.

Front springs:
1329822 13.6 mm wire, 126 lb/in spring, 120 lb/in wheel rate
1329823 13.7 mm wire, 130 lb/in spring, 124 lb/in wheel rate
1329824 13.8 mm wire, 134 lb/in spring, 128 lb/in wheel rate
1329825 14.4 mm wire, 161 lb/in spring, 153 lb/in wheel rate
1329826 14.8 mm wire, 181 lb/in spring, 173 lb/in wheel rate
IPD front spring measured by mikep 145 lb/in, 138 lb/in wheel rate

A company called Rallyboutique sells a 16.1mm front spring for rally use, that works out to a 261 lb/in rate at the spring and 249 lb/in at the wheel.

Rear springs:
1273759 9.8 mm wire, 51 lb/in spring, 76 lb/in wheel rate
(???) 10.2 mm wire, 60 lb/in spring, 89 lb/in wheel rate
1273977 11.3 mm wire, 93 lb/in spring, 138 lb/in wheel rate
1359710 11.9 mm wire, 117 lb/in spring, 174 lb/in wheel rate
1273978 12.1 mm wire, 125 lb/in spring, 185 lb/in wheel rate
IPD rear spring measured by mikep, 95-140 lb/in spring, 141-208 lb/in wheel rate

If you have more spring information please let me know!

The formula for ride frequency in Hertz is (1/2pi)*(sqrt(K/M) where K is the spring rate in N/m and M is the sprung mass in kg. Plugging in previously mentioned values provides the following results:

1329822 13.6 mm wire, 1.206 Hz
1329823 13.7 mm wire, 1.235 Hz
1329824 13.8 mm wire, 1.254 Hz
1329825 14.4 mm wire, 1.374 Hz
1329826 14.8 mm wire, 1.457 Hz
Rallyboutique 16.1 mm wire, 1.747 Hz
IPD ??? wire, 1.306 Hz

1273759 9.8 mm wire, 1.095 Hz
(???) 10.2 mm wire, 1.192 Hz
1273977 11.3 mm wire, 1.485 Hz
1359710 11.9 mm wire, 1.661 Hz
1273978 12.1 mm wire, 1.722 Hz
IPD ??? wire, 1.499-1.848 Hz

For comparison's sake, the BMW stock regular springs measure in at 1.02/1.12 F/R and their factory "Sport" springs measure in at 1.47/1.41 F/R. Conventional wisdom says you want a 10% higher rear ride frequency. My car stock comes in at 1.25/1.48 and with the RoW 760 front/wagon rear setup results in ride frequencies of 1.46/1.66.

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make like the kool kids our age and just cut the damn sprangs

JK, but seriously I wonder how my 300 and 150 lb/in springs do in regard to ride frequency. Probably not remotely close to 10% higher in the rear, ahah