BC

How dislexic John?

bd0nalds0n

I like my Autorotor twin screw setup. I chose TS over centrifugal because I wanted the lower end grunt with an automatic transmission with the 2.20 rear end--since it wants to spend so much time between 2k and 3k RPM, I mostly let it. After the doubly-thick-compared-to-stock Cometic head gaskets were installed, I haven't heard any knock/detonation associated with tip-in leanness, which was always pretty easy to control for anyway--for some reason, I never have people wanting to drag race at the stop lights anymore. What led me to SC the car in the first place was due to being humiliated by a some ugly broad in a Camaro in a stoplight to stoplight race shortly after I purchased the car.

I like that the oil supply for the autorotor is self-contained. Plus I got the kit from a fellow rennlister for a couple thousand $ discount compared to the centrifugal kit price. I've had the SC and the manifold off several times, and it really wouldn't be that big a deal to switch back and forth with the stock intake. FWIW, if I go easy on the gas pedal, my mileage is better on the highway than it was stock. I was actually more intimidated about needing to move the radiator fans to the front and running an oil supply line for the CS than I was about swapping the intake, although this may not be in any way based on the difficulty in reality

I think the twin screw with a 5 speed and the 2.54 or whatever it is would've led to 1st and maybe 2nd gear traction issues. If I had a 5 speed, I would've been more inclined to consider going with the centrifugal, as I'd likely be revving the engine higher even under "normal" driving conditions. I would definitely want the helical-cut rather than straight gears that I heard on Blown Beast's car last year, but that's just a matter of personal taste. No point in giving away the surprise...

My biggest reservations about the twinscrew were regarding the belt routing (the need to remove one of the PS pump bolts while somebody pulls up on the pump to clear the AC ear) and intake/air filter routing, both of which have been addressed by DR's kit. It's a solution that has really come into its own regarding completeness, although I think if they would've just used a few more idlers (in the spirit of timing gears rather than chains/belts), they could've eliminated the need for belts completely.

In all seriousness, I don't know how much fear one needs to have relating to loading the main bearings due to the tightness of the SC belt, but the additional peace of mind by having everything loaded as per the original design is quite noteworthy, and desirable.

Lastly, I was under the impression that the twin screw produced the lowest temperature charge, but this was disputed by Tim some time ago in which he posted a page from one of the Bell's supercharging books that indicated that centrifugals were the most temperature efficient.

My 2 cents.

BC

There is a difference in TS to CS in output charge temp. There is not a large on in the lower boost range, but it does increase, with what I have resrached, when you get into 11psi (relative to engine size - boost pressure is just that - pressure and not actual CFM) and beyond. CS is lower buy a larger margin in those higher areas.

Vlocity

For what it's worth I am attaching a few pictures from last weekend at Beaverun Sports Complex which is located north of Pittsburg.

I have run my twinsrew in two autocross events this year and it has performed without any glitches. The true test I figured would be flogging it on a road course for two days as part of a PCA DE event. While I may have started out a little easy as we all know that doesn't last very long.

The acceration is just amazing. I used about a quart of oil over the two day period which is pretty close to what the consumption was prior to the install. It was a cool weekend in the mid 50s. No heating issues and in the morning sessions the fan wouldn't even turn on until I was almost back to my trailer in the paddock area.

Since it was a DE I really didn't have many people to compare times with and this was my first time there but ran consistent times in the 1:11 range when the track was clear of run group traffic.

I am running a 5 speed and 2.73 LSD. I haven't had any traction issues, but then again I am running 11 inch rims on the back. So YMMV.

If I have any regrets its that I didn't or couldn't forsee DR putting together such a sweet package. I'm sure my set up works 95% as well since I made my own cold air intake set up...but DR's it's just tidy.

Either way you guys decide to go...you will never be able to go back to a normally aspirated car.

Regards,

Ken

MarkRobinson

The FMU is not a bad idea as it's one of the best ways to quickly match incoming air with fuel, not relying on a 20-year old system to meet your fuel concerns when you go from 200hp to 450hp in a couple of seconds. When you power comes on fast, it's good to know you have more then enough fuel to match if that's how you prefer to tune. Yes, a completely mapped system is safer, but time is money & the fuel-speed needed for an increase in power needs to be overkilled to a small/medium degree.

Jim_H

I think traction issues are way overstated. I believe my 90 GT has the lowest gearing? I ran 10" Toyo T1S's on it and had no issues. No doubt I could smoke the tires to shreds in 3 gears if I wanted to. But as everyone knows these cars are well balanced and they handle the hp fine. With a heavy foot you can smoke the tires on a Pinto. In fact watch this

Fastest928

how about we gather some data:

It would be very intersting to see a chart of the following

rwhp
rpm for peak rwhp
rwtq
repm for peak rwtq
octane for run
boost level for run
ambiant air temperature


And include "Type of boost". A nice matrix with three cols and the above as rows ...

SharkSkin

That would be a handy way to layout a single dataset(one per boost type) but I would think the items you mention ought to be columns, with additional columns for boost type, AT/MT, MY, US/ROW. Then you would have a table not limited to a particular set of samples or to a particular quantity of samples... you could then sort on FI type, RWHP, MY, etc.

Warren928

This has always been a fun topic. Each kit can be better than the other depending on the stage of it, at least in most cases. But what about cost effectiveness?
I found in my case that Andy's Eaton supermodel with IC is a very cost effective solution. For around $5,000 you can get 8.8 psi model that will add around 20 hp per psi, or 175 hp. Most people seem to agree that pushing past 9 si will result in a head gasket failure at some point.
So that puts my car from 288 hp to 463 hp, then add a dual 3" stainless magnaflow exhaust (25 hp) with x-pipe and high flow cats (25hp) at my local custom exhaust shop and once its tuned properly I should be at 513 hp. Not bad considering nothing will be done with headers, internal engine work or a more expensive SC setup.
I do wonder how much more psi the Eaton could take if I changed the head gasket to a Cometic double thick unit. Anybody know how much CFM or HP they are good for?

bfellows

There always seems to be a lot of discussion regarding 0 - 60 times and ultimate horsepower comparisons between the various kits, IMO neither of which have much importance during everyday driving here in the UK due to the amount of traffic! I'm more interested in the overtaking capabilities of the cars in everyday situations - 50 - 70mph, mid range power. Any thoughts?

Imo000

My guesstimation would be 25 hp for the complete exhaust system. 50hp minght be a bit too optimistic.

Jim R.

I guess I'll be the lone Murf SC owner to chime in here. I have had mine since last december, and have had way too much fun with it. Easily driveable with light throttle-I take my 2 and 3 year old kids and my wife out in the car without any second thoughts. Drop the hammer, and all hell breaks loose.

As far as useable power, I tend to not lug the engine, so the lesser low end torque was not an issue with the CS supercharger for me. I have gotten below 4 sec's 0-60, and on a dastech dyno have put down 551 rwhp. I will try to get a dynojet done when I get around to it, but another SC'd 928 ran 404 rwhp on the same dyno for comparison. I still have not used the g-tech for a 1/4 mile run, but will get around to it hopefully this fall. Right now, family, work, and my recent move with much renovation being done be me come first.

Both systems have there own advantages and disadvantages. Do your research, try to get a ride in each, and spend your $$$$ where you are happy. Anyone up by me who wants a test ride (not drive!), let me know. It is nice to have the options for boost, once you have it, NA is just not the same (unless you spend big bucks on a killer stroker motor). If you have any specific questions, let me know.

Jim R.

BC

551 at what boost Jim?

Jim R.

Brendan,

8-9 psi, stock cats, RMB with wheelspin in 4th on the dyno. It seems high, and I want to get a dynojet reading done to get a better handle on the power levels. I don't know how dastech compares to dynojet for power readings. I hope to add a WBO2 sensor and do some tuning of the fuel curves first, possibly add a x-pipe and get rid of the original cats. It was pretty funny to come off the dyno, then get the NY emissions on the rolling road/dyno and pass.

Jimg

BC

While i would love to see 551 at 9, I'm concerned that that is high or totally off. I was hoping to get 550 at like 11 with all my changes, but Tim was at 13 I think to get 556. Not sure.