SC Kit for reliability (Jackson vs HKS)

[mrg666]

Originally Posted by toast

Purple trace is boost. Log file from an Edelbrock kit (mine).



In your world using only wikipedia as a source that purple line would be flat. Surely you've done a WOT log for someone, look at your manifold pressure vs rpm.

This was discussed before. Did you read my post, last sentence?

[Yoshoobaroo]

Originally Posted by mrg666

Oh no, we are going through the same stupid arguments again. There is Honda and Koenigsegg that used Rotrex before. Search and find, I will not post links again. But you are right. Market, people like you, want instant power, muscle car response. That is why OEMs prefer positive displacement although it is less efficient, bulky, and heavy. But, I agree with one thing, positive displacement can be more dependable. I guess we are done.

Fair enough. I didn’t know some OEMs used them, albeit in niche applications.

[mrg666]

Originally Posted by toast

Apparently it is only a stupid argument because you keep making it and are wrong.

No one said anything about muscle car response, Honda or Koenigsegg other than you. You are advising someone on a purchase and you made an incorrect statement on how a system on your own car works.

The OP should understand what the end product will feel like. I drove an ACE header 86 and then a JSRC 86 back to back and until you wind it out the JSRC feels slower under normal driving conditions. He should understand that.

Yeah, right! Good luck.

[CSG Mike]

Originally Posted by Yoshoobaroo

It has to spin that fast because it will only build boost at crazy RPM’s. A side effect of the fact that a centrifugal compressor builds pressure at the square of the input rpm, this also means that in order to not overboost at redline you are forced to cut boost significantly at low rpms. Centrifugal compressors work much better in turbos, where the shaft speed isn’t linearly tied to the crank speed.

Positive displacement systems have a linear pressure vs rpm curve, which suits an ICE much better. They don’t need a 97% efficient gearbox cause they need ~5 times less shaft speed to get to the same boost. This means they can use a traditional geared setup that is much more robust and doesn’t rely on proprietary fluid that is designed to wear down the contact faces in the transmission.

Sounds like youre describing a turbocharger!

[CSG Mike]

Originally Posted by toast

You do not get linearly increasing boost with rpm in a centrifugal blower, it is simple physics. You get linearly increasing torque with rpm because as the torque curve would normally start to fall in an NA engine the boost grows as the square of engine rpm.

If one wants linearly increasing boost they should get a Harrop/Cosworth/Edelbrock.

boost or mass?

[Yoshoobaroo]

Originally Posted by CSG Mike

Sounds like youre describing a turbocharger!

I mean, the front half of one...

[CSG Mike]

Originally Posted by Yoshoobaroo

It's simple enough, that's how the compressors/pumps work in a vacuum (not literally). The flow rate of the engine is the other half of the equation.

Used as a supercharger on and ICE the behavior of the system results in linear pressure increase with RPM for the PD blowers, and Quadratic increase of pressure vs RPM for the centrifugal compressors.

There's a reason no OEM uses centrifugal compressors unless they're bolted to a turbine. No consumer wants that kind of power curve.

Koenigsegg?

[weederr33]

Originally Posted by CSG Mike

Koenigsegg?

Now son, don't pull that card out. The majority of OE manufactures, both affordable and premium, use positive displacement units. How many people are driving around in a Koenigsegg? Let alone, driving it enough to know or care if it uses a centrifugal unit.

[GrabTheWheel]

Originally Posted by mrg666

All those arguments you mentioned are why I chose Rotrex. Those are the desirable qualities for me.
- Low boost at low rpm for high engine reliability given that FA20D was not designed for FI
- Linearly increasing boost with rpm to get power at high-rev of FA20D. FA20D was designed as a high-rev engine. Still drives like the same sports car not a drag car. I like shifting gears instead of just smashing the gas pedal. The whole rpm range is useful with rapidly increasing power level. Acceleration is so much different than a muscle car and exactly the sensation I want.
- Efficient, no wasted gas at low rpm, driving around town.
- Light, whole kit is just ~30 lbs additional weight. I have already offset it with a lighter battery and lighter wheels. There is zero change in weight balance of my car.

So, Rotrex works much better than any other FI for my car since it does not change anything that made this car desirable for me. If I buy another twin, I would choose Rotrex again.

For reference my Jackson kit with a C38 weighed 66lbs ready to ship and my Edelbrock kit weighed 99lbs. It's hard for me to believe either box had more than 10 pounds or so of packing material.

Back when I had no mid range torque I use to believe this too. Who wouldn't want to shift more and enjoy the peak of the powerband? Torque is for lazy drivers who just want to mash the pedal. There is a certain satisfaction to the way a centrifugal mimics the stock powerband without the torque dip.

When I was looking for a SC kit the Edelbrock had just been released. I made sure to test drive both the 1320TVS and the Jackson kit. I recommend everyone take the time do this if possible!

I was immediately enamored by the sounds and response of the Rotrex. The TVS on pump gas felt a little flat, with no extra sounds from the blower. My thought process back in 2015 was if I was going to spend the money on boost I wanted to feel and hear the boost. I was so use to driving the stock car for 2 years at that point that I was always keeping the revs above 4K rpm anyway and always had it on boil.

Much like any mod you will get use to the extra power and I feel all the SC kits really need ethanol to come to life. If you are concerned with numbers or straight line acceleration and only have access to pump gas I'd definitley opt for a turbo.

After having time to look back on the ownership experience of both kits. I think the Jackson wins in a few categories. It has the sound, it mimics the awesome character of the stock engine, it will put the least amount of stress (torque) on the factory internals. It still feels like a momentum car (sort of) which makes it so enjoyable to drive on tight 2nd and 3rd gear canyon roads. Which is what the car was designed for. But unlike the stock engine when you're slicing up a canyon and upshift to 3rd you are met with a delightful amount of power with the rotrex as opposed to an adequate amount of power in stock form.

So although the Rotrex or NA wins in terms of canyon driving (my opinion) the TVS shines just about everywhere else unless your main concern is fuel economy which will be marginally lower.

I do not have a dislike for centrifugals in general. I found it was well suited for my AP1 S2k and it made nice power from 4K rpm all the way to the 9K redline. They do serve a certain crowd and character of engine. In general I think if a car "needs boost" it is suffering from 1 of 3 problems A) the car is too heavy B) the engine is too small or C) Both

A C38 car on ethanol with a 4.55 final drive is a very quick car even if it doesn't put up huge numbers to brag about. I found the shorter final drive to make the car even more fun in the canyons and more lively for daily driving. For AutoX the gearing became less than ideal and I wouldn't recommend it with boost. Going down to a 3.9 would probably be better.

As much as I've preached how much better all the SC kits are with E85, at that point you are starting to push the limits on reliability. My recommendation is normally E85 and header for track guys and CARB legal SC for a street car.

As much fun as it is to drive momentum cars and push them hard on the street; as I got older and started to do more track driving the less I started enjoying canyons. I still like them and am lucky enough to drive excellent empty roads daily but hardly ever push it past 5/10 's or 6/10's on public roads. It's just not safe or responsible even with only 200hp and prius tires.

I'll take torque and lots of it in just about any other driving situation aside from the tight canyons. Everyday driving, freeway, autox, track, you name it I think it's more fun with ample torque. I find I shift way more on the street (not track) with gobs of torque. I'm constantly going up to 6th gear and back down to 3rd. I shift more with a V8 I think than I did with the Rotrex. The only difference being the downshift is optional. The car pulls great in every gear. So yes you can be lazy and not downshift but I don't find myself driving that way.

To test this theory I'll be back in a momentum car this Friday at Buttonwillow. I have rented a 2300lbs, 135hp, track prepped, gen1 RX7 for the day. I will report back how it compares to a 2900lbs 500hp NA BRZ.

Sorry for the long ramble, just thought I'd share my take having spent a decent amount of time with both kits.

[CSG Mike]

Originally Posted by weederr33

Now son, don't pull that card out. The majority of OE manufactures, both affordable and premium, use positive displacement units. How many people are driving around in a Koenigsegg? Let alone, driving it enough to know or care if it uses a centrifugal unit.

irrelevant, as absolute statements get absolute answers!

[weederr33]

Originally Posted by CSG Mike

irrelevant, as absolute statements get absolute answers!

Only a Sith deals in absolutes

[GrabTheWheel]

Originally Posted by toast

Apparently it is only a stupid argument because you keep making it and are wrong.

No one said anything about muscle car response, Honda or Koenigsegg other than you. You are advising someone on a purchase and you made an incorrect statement on how a system on your own car works.

The OP should understand what the end product will feel like. I drove an ACE header 86 and then a JSRC 86 back to back and until you wind it out the JSRC feels slower under normal driving conditions. He should understand that.

Was the Jackson kit on the CARB tune? That's how mine felt with the C30. Below about 2800rpm it felt like it was lagging. After a retune that pretty much went away. Only time I felt a little delay was tipping into the throttle in 1st gear.

I have a dirt driveway and use to do a little 1st gear slide in the dirt every time I came home. With the Jackson kit I felt like there was a little delay on throttle tip in compared to stock, it was much less noticeable after the retune but still there.

I'd also think if you're doing a back to back comparison the louder car would "feel" faster. Not sure if they had similar exhaust setups? Although like I said I think the difference between a stock CARB SC'd car and a header E85 car isn't huge.

[Calum]

Originally Posted by GrabTheWheel

500hp NA BRZ.

Engine swap?

[GrabTheWheel]

Originally Posted by Calum

Engine swap?

Yes. 6.8L