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Index > @ the Pickup Bed (General Topics) > Thread: Forced Induction
Thread: Forced Induction [' This thread is 2 pages long: (1) 2 ']
rotarynews


Moderator
Too Many Rotary Websites
Posts: 206
posted January 28, 2002 09:37 AM

Forced Induction

Alrighty, let's keep this thread on topic, and th 4x4 thread on topic ;)

Forced induction: Turbo or Superchargers... Which is better for a repu?

My first guess would be the supercharger, since you get near full boost at any rpm... Which would be great.

My 3rd gen has its max HP range from 4.5k - 6.5k with max torque aroung 5k, and hp at 6k. (302ft lbs, and 313 rwhp).

As for my repu, I haven't driven it enough to get a good grasp on what it needs.

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repuguru


Redlining
Posts: 319
posted January 28, 2002 01:05 PM

Thats easy

It needs the motor out of your 3rd Gen....

       
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Klaus43


Rotorhead
Posts: 1259
posted January 29, 2002 11:20 AM

Yeah, minus the expense of the turbo(s) leaking and needing rebuilt/replaced every how often... or so I've read, anyway. Apparently the main culprit is residual heat after motion ceases...you'd think the factory boys would,ve worked that one out...
300-odd HP would be about right, tho... now if we can have that w/out the durability issues of bridgeporting, without the streetability issues of peripheral porting, and without the expense of a 20B or super/turbo motor...THAT'd be nice! And I won't wait for the rx-evolv to start showing up in wrecking yards, either! Life's too short . Time to live the dream for $5 to $10 k total resto-build cost...
(Five's more realistic, but I'm daring to dream)...
Back to work--must make glass into $$$ -K.

       
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repuguru


Redlining
Posts: 319
posted January 29, 2002 06:42 PM

Does the 3rd Gen car not come with a Turbo timer?
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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mazda-rotary


Newbie
Posts: 4
posted January 29, 2002 09:42 PM

quote:
Does the 3rd Gen car not come with a Turbo timer?


Not from the factory.

Is there any car that comes stock with a turbo timer?

       
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Jeff20B


Moderator
Posts: 661
posted January 30, 2002 08:37 AM

quote:
Is there any car that comes stock with a turbo timer?
I have no idea, but the 3rd gen should've come with one.

I'm with Dan. Torque in the low end, like when you're towing something, is very important. Go with a supercharger in an REPU.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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risc


1st Gear
Posts: 23
posted January 31, 2002 05:16 PM

I had a supercharger on my REPU(camden 7" @ 10psi), but I sold it. Partial to fund other projects and partialy because it wasn't right for a daily driver. Eventually I will be going turbo, maybe :-)

Supercharger pro:
Boost right off idle
More than enough power, yea right

Supercharger con:
Idle @1500
8mpg city
12-14mpg highway
very inefecient 40-50%
high intake temps
can't intercool

Turbo con:
Boost lag, with 4.6 gears I don't think this is an issue. Also if you need power for towing the load will be high and boost will build regardless of RPM

Turbo pro:
Idle @ 800 rpm
14mpg city
20-25 mpg highway
60-75% effeciency
powerstroke intercooler should fit nicely in front of the radiator


       
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repuguru


Redlining
Posts: 319
posted January 31, 2002 09:36 PM

Thats why I consider a Turbo ideal for ME. That supercharger is nice but its hooked to the crank. How much power would that thing produce if it didn't have to be hooked to the crank? And the 1500rpm idle? I wasn't aware of that. I guess the motor has to spin a little extra to turn the big air pump?
The type of turbo I would like to find is a small one, that spools quickly, with a limited amount of boost. 10-12 psi tops.
I only see the big Garretts and other well know turbos on most of the forums. With a few stock units thrown in the mix.. I realize most people are looking for all motor.
I'll keep looking till I find what I like. Which is never what I can afford.
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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Jeff20B


Moderator
Posts: 661
posted January 31, 2002 10:10 PM

The idle on my friend's street ported SC 13B isn't at 1500. It fluctuates between 800 and 1100, but only hits 1500 when the auto choke is on. Something on yours may not have been set up correctly.

The turbo idea with 4.6 gears does sound like a cool thing though.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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Klaus43


Rotorhead
Posts: 1259
posted January 31, 2002 11:13 PM

Even a high idle wouldn't bug me, but 8 mpg??? Is that with yer foot firmly planted thru 2nd gear as much as possible? The cost of building a Camden outfitted, fresh, ported, restored REPU demands better!
Curiously enough I recieved a phonecall today from Hayes rotary, in response to my catalogue/price/info request per email off their site... they claim to install a good number of Camdens, so I asked some questions...
For somewhere around $6K a beefed-up, street-ported SC 4-port motor could be had. Claimed HP: "around 300", at 10 psi boost. "We just put one in an rx3 that's being shipped out to Japan"..."...one guy who got one in his (REPU) would spin his wheels in 3rd gear at 65 on the freeway..."
Reality? ??? Also claimed "no problem" when I asked about high intake temps...
Conclusion: Time for more serious research, and a highly specific cost-benefit analysis. We've all, no doubt, heard our share of BS about what's REALLY the case w./ this or that motor, setup, or specific REPU... I'm not diving in before I explore the entire swimming hole with my scuba gear and underwater microscope.
--K.

       
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repuguru


Redlining
Posts: 319
posted February 01, 2002 08:57 AM

I like your thinking Klaus. I have been know to do a little cave diving myself.. I to am going to turn every rock I come to see if there is anything else to consider. Did you talk to Don Hayes? They are nice guys who I have used for numerous engine jobs. But"no problem" on intake temps sorta does throw up a red flag. I know there is a problem and if you can chose to ignore it and hope for the best you'll be stranded with a cooked motor.
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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Klaus43


Rotorhead
Posts: 1259
posted February 01, 2002 10:29 AM

So why does Hayes advocate 10 psi on a Camden, while Atkins, who builds 'em, is more conservative--recommending 6 psi boost? Could be the level of prep internal to the motor; could be different beliefs/understanding/experiences...
Yep, it was Don w./ whom I spoke... Good to know you've had good results w./ them! Without long-term durability, no major performance investment is worthwhile to me... I work too hard for my $$$ for it to burn up on me too quick.
Negative reports are few on the net, it seems... only've read one about a Hayes customer who said his motor was torqued together so tight, he was unable to turn over the motor until loosening/retorqueing the bolts...he opined that Atkins paid more attention to torque specs, since they built motors for aircraft app's. also...
So who else is good? Builders in my area (NW Oregon) all seem to have something neg. to say about some of their peers... and none of 'em appear to do as much business as Hayes or Atkins... we'll get to the top of this, eventually.
--K.

       
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repuguru


Redlining
Posts: 319
posted February 01, 2002 04:47 PM

I guess its just a matter of engine prep or opinion. Depends on who you talk to as whether they feel a high comp motor will take 7psi or 10psi. Mazda pushed 10 thru the 89-91 motor that has 9:0:1 rotors. I think that you could do it to the old 74-78 13b rotors with 9:2:1. Which I have.
I've been dealing with Hayes for about 10yrs. Had a bump or two along the way, but I still deal with them. They always seem to try and make you happy. Its easy to pick up the phone and say "this is what I want, send me a crate for the core". I have built up rotors and stacked a few motors, but I had to borrow the right tools and place to do it. It easier to go this route now.
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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Jeff20B


Moderator
Posts: 661
posted February 01, 2002 05:18 PM

If I were you guys, I'd trust Dave Atkins' opinions over Hayes. And that's my humble opinion :)

Actually, you're right about the fact that Dave is the guy who builds 'em. That's why I recommend Atkins for any sort of SC stuff. Hayes, on the other hand, are good in their own way.

Here's another two cents to add to the pile: I think 10psi with 9.2:1 rotors will probably be ok. But if it was my engine, I'd start with 6psi first and maybe move up to 10. Dave was saying that only the 7 inch SC has easily swappable pullies. Or maybe I remembered that wrong. Well, if you can afford the 7 inch, go with it because it can handle higher RPMs than the 5 inch.

Just a note about the extra length of a 7 inch: Dave had to cut his heater core pipe where it curves from longitudenal to transverse (against the firewall) on his Cosmo. He went to a 5 inch and now there is lots of space in that corner. It makes me think twice about whether to get a 5 or 7 for my Cosmo. At least I know there is an axtra step if using a 7 inch. As to how that relates to the REPU, Hmm... I could visually eyeball that section in my Cosmo and try to carry it over to my REPU. Fortunatly the REPU has a curve that hugs the fender/firewall where it takes a 90 bend. The Cosmo didn't need such a sharp bend because its engine bay is plenty large. I can't check it today though. The darn weather around here.
____________
'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7

       
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repuguru


Redlining
Posts: 319
posted February 01, 2002 09:35 PM

Tomato Potato

       
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Klaus43


Rotorhead
Posts: 1259
posted February 02, 2002 10:24 AM

Deadly nightshades?

Hmmn...both are New World fruits...associations mediterranian and irish, respectively... 'tomato/tomatoe//potato/potatoe'... Apples & Oranges by any other name? All looks the same after digestion thru a wankel.

       
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Klaus43


Rotorhead
Posts: 1259
posted February 04, 2002 10:42 AM

back to topic:

So now I'm waiting for a reply to my email request for more info. from Atkins... I asked about the latest developments for H2O injection, or any other method for cooling the charge, options for regulating boost psi beyond changing out pulleys, the consistency of boost over the rpm range, and any REPU-specific info/recommendations assuming a purpose-built 4-port 13-B w./ a Camden 7"... Mentioned I was looking for good bang/buck with excellent durability, and asked about the relative inefficiency percentage/ heat increase/psi on such a motor(W./ street porting)...
We'll see what they say!
When I get that response, I'll be more prepared to try to bend Paul Yaw's ear for a minute or two about fuel/flow options for such a beast. His website rocks! I wonder what he could acheive with the Camden, and what his choice of carb.'s would be to re-work for that setup. His increased-flow-over -racing beat's header design is an impressive item as well...
Rob Golden's opinion (pineappleracing.com) is also noteworthy: you can run up to 20 psi boost, with 2mm apex seals even, but it becomes a matter of flawless tuning and no mistakes, or the motor won't live...
I think I'd stick with 3mm seals and 10 psi tops...

       
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repuguru


Redlining
Posts: 319
posted February 04, 2002 12:37 PM

I know what Paul says, I asked him about 2 months ago the very same question. Quote.."Its a neat setup, it would be better if you could run an intercooler".
We talked about setting up one of his Nikki's on a blow thru turbo. He says he hasn't done one, but with the right mods it may work.ie..milling the throttle shafts to accept o-rings plus sealing other areas to keep fuel from being pushed out. Also says that if you could make a sealed pressure box for the carb to sit in the mods may be limited to getting a regulator that increases fuel pressure with increased boost. With that said it doesn't matter if you supercharge or turbocharge you can run an intercooler..
You know I am not knocking the supercharged system in anyway. Right now it seems like one of the few resonable options that a non-injected engine has.
I just think a small suck thru turbo with H2O inj is another option I must investigate. Because it may yeild the results I am actually looking for.
____________
77' REPU plus a few spare parts
for it.
85' GSL-SE
83' GSL

       
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risc


1st Gear
Posts: 23
posted February 07, 2002 05:06 PM

quote:

Rob Golden's opinion (pineappleracing.com) is also noteworthy: you can run up to 20 psi boost, with 2mm apex seals even, but it becomes a matter of flawless tuning and no mistakes, or the motor won't live...
I think I'd stick with 3mm seals and 10 psi tops...



That would be 20 psi of boost intercooled, not from a roots blower. But Rob is always conservitive, people have run 25-30 psi on stock mazda remans. Granted that is drag race only and they don't last too long.

As for the camden supercharger, he said 6psi for the street with 9.2:1 rotors. We talked about several ways to make it more streetable but in the end, I decided it wasn't for me.

Anyone thinking about a new motor should give him a call before you hand you $$$ to atkins or hayes.

       
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repuguru


Redlining
Posts: 319
posted February 08, 2002 03:57 PM

There is a thread going over at the RX7Club.com site talking about H2O injection. It is under the rotary performance catagory. I sorta had an idea of what needed to happen. They confirmed most of it.

       
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