Thanks Howard.

I'm a little confused by your comments and conversation with SB. If there is not enough compression travel for a given ride height and spring rate, increasing spring rate is an option (or band-aid) to prevent bottoming out the shock. If a damper is bottoming out into the bump stop too early and more compression travel is needed, a shorter shock body is needed to increase this compression travel, usually at the expense of droop travel.

The off-the-shelf Ohlins DFV damper does not have helper springs and has ride height adjustments at the lower damper body and with a traditional spring perch. From what I can tell, the Sakebomb FPSpec Ohlins DFV "Long Stroke" coilover kit does not use helper springs on their "Grand Touring" or "Performance Street/Track" kits but they DO offer helper springs for the "Track Deicated" and "Tailored" damper options.

Sakebomb is a little vague on exactly what they did differently to increase the stroke of the damper, or by how much. Usually these types of coilovers with separate lower shock body ride height and spring perch height adjustments have limited droop travel (and limited stroke) because the main spring needs to have some tension in full droop; however, the SB FPSpec "Long Stroke" only uses helper springs for their track-dedicated models.

Given the confusion of your comments and the lack of information on what SB did, it's difficult to comment on these.

In regards to the JRi coilovers by Ultimate Performance Speed Shop, the stroke is maximized in these dampers to use all of the available travel of the FD RX-7's suspension geometry. The suspension arms cannot droop much more without binding than the overall length of the damper bodies allow. The bumpstops engage just before the tire bottoms out in the wheel well. The JRi coilovers have more overall travel and stroke than the off-the-shelf Ohlins DFV coilovers for the RX-7 and the use (and need) of the helper springs are an indicator of that usable travel.

Ultimate Performance Speed Shop currently lists this double-adjustable JRi coilover at $5,199.99
https://upspeedshop.com/product/ulti...ilover-shocks/

For comparison:
Fortune Auto Dreadnought Pro - 3 Way - $9,632
JRZ 12 Series - 3 Way - $9,030
JRZ 11 Series - 3 Way - $7,070
JRZ RS Pro - 3 Way - $6,650
MCS Suspension - 3 Way - $6,530
JRZ RS Pro - 2 way - $6,030
Feal 443 - 1 way - $5,939
JRZ 11 Series - 2 way - $5,800
JRi by Ultimate Performance - 2 way - $5,199.99
Fortune Auto Dreadnought Pro - 2 way - $5,031 to $5,431
MCS Suspension - 2 way - $4,870
Penske 7500 - Double Adjustable - $4,400 + $400 in springs = $4,800
Sakebomb FPSpec Ohlins DFV "Long Stroke" - 1 way- $3,895

*For motorsports dampers, sometimes there are hidden costs like various components such as main & helper springs, top hats, etc.. being additional charges so take the numbers above as the 'starting' price, which may be higher.

0.02

 

Something I find interesting (read: confusing) about double-adjustable coilovers is the debate between whether you should adjust ride height / corner weight with the spring perches or with the shock body.

You and I seem to subscribe to the opinion that preload should largely be left alone with these shocks (just dial enough in that the springs don't rattle), and ride height should be adjusted with the shock body.

The people who run High Performance Academy and at least one tuning shop I have spoken two swear that this is the wrong way to do it, and ride height should be adjusted entirely with the spring perches (preload adjustment be damned).

Of course, double adjustability is often a selling point for cheaper coilovers, but it's really just a manufacturing trick used to save money. High-end suspensions are almost exclusively single adjustable (spring perch only).

On another note, what benefit does reducing friction with roller bearings actually provide? I didn't quite grok that part.

 

I think the adjustable body is just a cost effective way to make one (short) damper size fit all by adjusting the body length. That's not really the way you should do it. Any high end shock, like the JRI pictured, use shorter main springs with a helper, so you're never pre-loading the spring, and still have contact at full droop.

I went with Penske 8300's precisely because they were easy to order at custom lengths for my car. I took a lot of measurements and came up with some ways to measure as they'd sit on the road to be sure I maximized the droop, stroke, and clearance at ride height, The JRZs they replaced (I got used years ago) were a little too long in the body, especially at the rear, and were probably made for a more conservatively lowered car.

JRI's look like a nice option. Do they have a versions with remote reservoirs?

 

The term 'double adjustable' typically refers to separate adjustability of compression damping and rebound damping.

For ride height:

A traditional coilover has a fixed body length and a single spring perch. Raising the height of the perch raises the ride height, increases compression travel, and reduces rebound travel. Lowering the spring perch lowers the ride height, reduces compression travel, and increases rebound travel.

Coilovers with adjustable lower threaded bodies/shafts. These coilovers have a spring perch as well as either a threaded lower body (like many entry-level coilovers and some mid-range coilovers) or a threaded rod and jam nuts between the lower damper body and lower mount (like many high-end motorsport coilovers). Ride height can be adjusted with the spring perch with the resulting effects as listed above, or ride height can be adjusted with the lower threaded body (or shaft) which will not affect compression or rebound travel.

There are so many misconceptions on how to set these dampers up, misconceptions on 'preload', and (IMO) people screw up their handling and ride quality significantly more (and worse) with these types of dampers than they would with 'double-adjustable' dampers with separate compression and rebound adjustments. Which is ironic that many people are afraid or timid of 'double-adjustable'/2-way dampers.

If you have access to HP Academy, their "Initial Setup and Ride Height Procedures" is pretty good and I agree with it. To properly set up these coilovers with two ride height adjusters, you need to set the bumpstop position first - by removing the spring, installing the shock, putting the tire on, compressing it until it bottoms out or the tire hits the wheel well; then remove the tire, adjust the lower threaded body accordingly until the bump stop prevents the tire from contacting the wheel well. Once the bump stop travel is set, then you *should* only adjust ride height from the spring perch since the compression and rebound travels are maximized. However, without a helper spring and depending on the spring rate and droop travel of the shock dimensions, it is possible to lower the ride height to the point of the spring being loose and rattling around under full droop, potentially causing damage or jamming when compressing from full droop.

-Needless to say this is A LOT of work that most people would not do.

Seating the spring perch against the spring so it does not move maximizes the rebound/droop travel without causing damage or problems. If there is excessive compression travel that allows the tire to contact the wheel well, packers (or spacers) can be quickly and easily inserted to limit compression travel, which is a reactionary adjustment to unwanted contact rather than a pro-active and time consuming one as listed above. Unfortunately, without helper springs, maximum droop travel usually cannot be properly optimized in a coilover with a lower mount threaded ride height adjustment.

Reducing friction with roller thrust bearings increase grip and spring predictability. Realistically, short of pro-racing, this benefit will not be fully realized. You're probably not going to feel a difference after installing them in your coilovers. However, they make it SIGNIFICANTLY easier to adjust the spring perch height and to me, I don't like adjusting suspension that do not have them.

As stated above, a lot of high-end motorsport dampers technically have the same thing, but often use a threaded rod and jam nuts between the lower damper and the lower mount of the damper (like a toe-link). But these high-end dampers on race cars have minimal damper stroke and travel to optimize the aero platforms of these cars, whereas on a street/track/ or 'showroom-stock' type of race car, its usually better to maximize stroke and rebound travel.

You essentially did what most shops do (or should do) when making a coilover kit for a given platform. You are a very rare minority when it comes to suspension customers. Are the 8300s for your FD? If so, post some pics!!

JRi do have remote reservoirs. Remote reservoirs often make damping adjustments easy, and they look cool, but unless they are absolutely needed from a capacity standpoint (due to packaging that requires a short damper body) it is much better to not have a remote reservoir in terms of response and cavitation.

Back in the day, it was all about monotube dampers and remote reservoirs. Today, the leading edge of damper technology is actually dual-tube dampers, solid pistons, 'spool valves', and NO remote reservoirs.

 

They're in my build thread, starting here. You can see some comparison to the JRZs they replaced: https://www.rx7club.com/build-thread.../#post12586924

 

The next installment is live!

Project FD RX7 Restomod: Part 28 – BJR Radiator, GC Cooling Fans, Hayden Auto Power Steering Cooler

Keeping a rotary engine cool is one of the keys for making them reliable. We designed one of the largest radiators ever made for an FD RX-7, keep it cool with GC Cooling Fans, and worked with Hayden Automotive to cool the cars’ power steering.

After spending years looking at the cooling systems of FD RX-7s from around the world, ranging from street cars to track cars, wheel-to-wheel race cars, hill-climb cars, and time-attack cars, it became apparent that most RX-7 owners/builders do not have a strong understanding of the importance of ducting or cooling system design. We also came to the conclusion that the off-the-shelf radiator and oil cooling solutions would not cut it for our build. This is somewhat ironic because of the challenge and importance of keeping the temps of a rotary engine under control. Because of this, we decided to reach out to our motorsport contacts to design and manufacture a much larger and more efficient radiator for the FD RX-7.


In the article:
-The Billy Johnson Racing (BJR) 56mm dual-core, dual-pass, crossflow radiator.
-Intercooler configurations: SMIC, FMIC, V-Mount
-GC Cooling Radiator Fans
-Hayden Automotive "HD Cool" Oil Cooler for power steering.
-Raceonly Billet AST Delete vs stock
-Fabricating coolant hard lines


https://motoiq.com/project-fd-rx7-re...eering-cooler/



Enjoy and stay tuned!

 

Incredible build @Billj747 You've more than demonstrated the value of this thread time and again imo.

A plethora of tuning and mechanical knowledge presented here and I couldn't have been more wrong about the direction of the project. I always look forward to updates. #keepitup

 

Very, VERY, nicely done!

One suggestion - switch out those worm style hose clamps for some constant torque hose clamps. The worm style clamps always loosened up on me after a few heat cycles when I used them with silicon hoses on my v-mount setup.
https://www.breezehoseclamps.com/bre...nstant-torque/

What are you using for an intercooler?

 

I like the thoughtfulness of locating the power steering cooler behind the coolest part of the multi-pass radiator, and using side-flow so the end tanks line up with the drier on the RX8 air conditioning condenser. I've heard side-flow radiators can be problematic in terms of air pockets, but I hope it works because the packaging does look very good. Replacing the factory power steering 'cooler' lines sure cleans up the radiator and intercooler ducting, too.

 

That setup looks pretty nice. Are you planning on a vented hood to help remove the heat from the intercooler and engine bay? Will the intercooler also be something that we could buy like the radiator? That would give us a both the intercooler and radiator for the v-mount setup to purchase, and would be a better option than the Greddy setup.

Also, are you doing a big brake upgrade in a future article? I'm trying to decide what to do with my brakes since I have a feeling they won't work well on track without ducting and an aggressive track pad. I have big spreadsheet with various options from other vehicles, but so far haven't found an OEM front and rear caliper setup with the right balance.

 

Thank you for the kind words. I'm glad to hear you are enjoying the build.

Thank you! Thanks for the suggestion. I will keep an eye on the clamps and consider those if I have an issue.

Crossflow/horizontal flow/side flow radiators typically have a -3AN bleed line that is run to the coolant reservoir to self-bleed the system. In most cars, the top of the radiator is higher than the water pump outlet of the engine and the coolant tank is higher than that as the highest part of the cooling system.

For the RX-7, the Thermostat Cover (replaced by the Raceonly Billet AST Delete) is the highest point in the cooling system, and the radiator is lower than even the outlet of the water pump. I had a 1/8NPT bung fitted to the radiator to run a -3AN line to self-bleed the system to the AST Delete (which has two -6AN ORB fittings conveniently on the side of it) but after thinking about it, the radiator will self-bleed when not running, and the likelihood of air being forced down and into the radiator is very low. So far I have not had any issues with air in the system and I have the ability to run a bleed line if I need to test and troubleshoot a potential air pocket issue.

A vented hood will be in the future. The factory SMIC is able to vent the intercooler into the engine bay without issue. I am going to do some testing on the intercooler's effectiveness at 400hp+ with a stock and vented hood to quantify the cooling benefit of the hood (which for sure is better no matter what).

The intercooler was a 1-off. It would be pretty expensive to make a low production run of them and the inlet/outlet plumbing requirements would differ depending on turbo placement and other modifications in the engine bay.

I will be upgrading the brakes as well. Now that the car is running, that is coming up on my to do list. I have many spreadsheets and brake bias calculations for a few different car platforms that I've consulted on and made brake systems for. I have a few different ideas and options depending on cost and complexity.

 

I second this. Worm drives have tended to just cause more wear on the hoses over time, especially with the heat cycles. And stay away from the HPS brand constant clamps. Breeze are really awesome and worth the money for the piece of mind they provide.

 

ive been thinking of my power steering & saw a FD electric power steering kit. is there a reason u chose hydraulic?

 

Steering feel

 

even found out some went electro-hydraulic

 

Electro-hydraulic retains the steering feel of hydraulic, but you need to mount the pump somewhere and it puts more load on the electrical system and alternator. If there is not a reason to remove the factory PS pump, the packaging of the OEM pump is much better.

 

Do you have stock gauge cluster? Did you get the speedometer to work with the cd00a swap?

 

The next installment is live!

Project FD RX7 Restomod: Part 30 – Finishing the V-Mount with a CSF Intercooler and Vibrant Performance

We finish our high efficient V-mount intercooler setup for the FD RX-7 using a CSF intercooler core, custom fabricated the end tanks, and charge pipes fastened with Vibrant Performance HD Clamps.

As we discussed in Part 29, a V-mounted radiator and intercooler is the best cooling system layout for track cars, street cars, and the majority of modified RX-7s. However, almost all V-mount setups have pretty poor ducting that allow air to escape around the radiator and intercooler rather than trapping that air and creating a pressure differential across the coolers, which makes a massive difference in heat transfer and cooling ability.


In the article:
-CSF Intercooler core vs Garrett Intercooler Core
-Fabricating the End Tanks
-Modifying the EFR 8374 and 9180 Compressor Housings
-Fabricating the Charge Pipes and using Vibrant Performance HD Clamps


https://motoiq.com/project-fd-rx7-re...t-performance/



Enjoy and stay tuned!

 

Honest question, love talking shop. How come you didn't aim to have soft angle straight shooters in your plumbing like the rhd v-mount?

My lay understanding tends to believe airflow prefers straight angles and direct paths and to my eye the hot/cold plumbing on the rhd low mount single turbo v-mount (purple coupler/hoses) appears to be better. This is mainly because your hot side is super short with a twist and the cold side seems unnecessarily long while also having quite a few bends in it. I understand this isn't apples to apples but in general I think shorter and straighter piping could've been achieved.

 

Reducing the amount of angles in the plumbing improves efficiency and reduces pressure drop. The biggest problem of the RHD v-mount with purple couplers (pic #3 in the article), is that the turbo sucks in hot air that is not dense that exits the intercooler and radiator. Our turbo layout prioritizes cold, dense air to feed the turbo.

As far as bends go:

RHD Low Mount (Pic #3 in article - purple coupler):
Hot Side: 180* bends into inter cooler then air needs to travel another 90-180* into the IC fins. = 270* to 360* of bends
Cold Side: 90-180* out of the IC, 45* then 45* then 90* Greddy elbow = 270* to 360* of bends

Billy Johnson Racing V-Mount:
Hot Side: 90* out of the turbo, 30* and 30* into IC, then air needs to travel 90* into the IC fins = 240* (30* to 120* less than the RHD).
Cold Side: 90-180* out of IC, 60*, then 45* then 45* then 120* = 360 to 450* (60* more than RHD).

So the BJR V-mount ended up having somewhere between 30* less to 60* more bends in the charge piping than the RHD Low Mount (Pic #3 in the article) while feeding the turbo far cooler and more dense air.

As far as length goes, the BJR setup has a significantly shorter hot side charge piping while the cold side is marginally longer due to the IC outlet being about 3" further towards the left-front headlight (where the factory A/C dryer sits).

 

That 3D printed intake elbow is some out of the box thinking.
How did you design it?

When you get around to dynoing the car, I'd like to here how much pressure loss the intercooler has.

 

Very valid point about intake placement on the rhd. From the one image, the rhd looks to be an older build imo and the intake could certainly be improved with something like an intake pipe elbow extended somewhere that sees fresh air. Not sure why the builder of that car did that. Some might find it a little cleaner aesthetically but as you pointed out less than ideal for performance.

And it looks like the rhd moved their A/C over slightly to accommodate the IC. Seems like a simple enough solution in concept.

 

Awesome build! Love seeing a properly fixtured V Mount setup. The 3D intake makes me want to stop being lazy and do something similar.

A vented hood whether ducted or not would be the cherry on top

 

I use Fusion 360; offset the plane and adjusted the angle and positioning of where I wanted the air filter, made circles on both planes, and lofted the two together with 2 guiding rails. I did this 3 times to get the air filter exactly where I wanted. There's a lot that can be improved with the shape and design that I will play around with later on. I printed it out of ABS temporarily but it's holding up quite well.

I have a library of pretty much an V-mount that I could find posted online. The vast majority of them mount the turbo inlet behind the intercooler & radiator because it's easier to package and most people don't understand the importance of feeding the turbo ambient air.

Thank you! A vented hood is in future plans.

 

In general, I agree that the "old school" of jdm tuning didn't produce a properly vented, ducted, sealed etc system. For modern jdm build, I came across Rock Suzuki's FD (Under's younger brother) and his 3-rotor setup seems quite efficient. Cold air for charge pipe, large IC core, pretty straight plumbing, etc. The inlet / outlet orientation on the end tanks looks really nice as well imo. Of course there are limitations to any build (typically talent, resources and / or support) but you don't seem to lack any of those. My personal taste prefers to see short piping with minimal bends, etc. Just curious why you didn't go for something closer to what Rock did?