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Thread: street or bridge
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20b-3rotor
Newbie
Posts: 9
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posted January 04, 2004 01:08 PM |
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Street or bridge
I am rebuilding a s4 TII motor for the repu and I can't decide what to do Street or Half bridge. I am looking to run it with a t04s or something similar. What do you think is better for the repu?
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74 REPU
89 RX-7 20B
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kick
Hauling
Posts: 149
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posted January 04, 2004 04:20 PM |
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Could someone tell me whats the point with a Half bridge?
I have seen some people talk about it on Rx7club forum.
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1972 Rx2 - no enigne or trans
1974 Repu - runs and drives
1976 Rx4 - no engine or trans (klaus42 old 4)
1977 Repu - Parts
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Jeff20B
Moderator
Posts: 661
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posted January 14, 2004 10:12 PM |
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I am seriously considering a half bridgeport in my REPU.
Since I have two REPUs, one will be more of a tow truck. The other will be a cruiser. Do you think I should do a half bridgeport on the cruiser?
My future plans include an Atkins Camden supercharger on the mild ported tow truck engine. The cruiser will get a 20B. Or maybe I'll do it the other way around. Anyway, a supercharger shouldn't be installed on a half or full brdigeported engine according to Dave Atkins.
My theory is that since I have two trucks that need engines, I might as well do one mild port, and one half bridgeport.
What do you guys think?
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted January 15, 2004 09:40 AM |
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Why do anything halfway?
Since bridgeporting invariably compromises engine longevity--eventually the bridges give way--why not go 'all the way', one way or the other?
I would think any argument in favor of power gains beyond big streetporting, short of at least a full 'baby bridge' (non 'J'-bridge), would be eclipsed by a cost/benefit analysis...
Of course, if the 'brap brap' sound is your objective, and cost/longevity are not major issues...
What can I say, I'm not about to throw bucks after exhaust note/image over actual, practical performance increases.
Of course, if you've got time, money, and housings to spare, experimenting could be cool, too!
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Jeff20B
Moderator
Posts: 661
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posted January 15, 2004 02:14 PM |
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I guess I'll be the first on this forum to do a half BP in a REPU?
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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brad
Rotorhead
Posts: 1672
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posted January 15, 2004 08:54 PM |
 Edited By: brad on 15 Jan 2004 20:55 |
some peoples who want more top end hp than a streetport but still have good bottom end will bridgeport all four plates, but only cut the extra ports towards the top of the port.
picture a normal bridge but only cut the upper half of it. people call this an eyebrow port
that will reduce overlap overall, and not overlap until later in the intake cycle.
more top end, don't lose as much bottom end. but still not as much top end as my full j-bridge with ceramics :)
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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Jeff20B
Moderator
Posts: 661
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posted January 16, 2004 01:00 AM |
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Interesting. At this point, anything is possible. I'll be running up to 8 grand on occasion (with 8500 as a buffer zone). Not that that has anything to do with porting styles, but I'd still like to cut full port length bridges on the secondary plates. Hmm, the primaries with short length bridges located as high as possible may be a possibility.
A little brap at idle is possible with BP secondaries, so maybe I won't push my luck and BP the primaries. I'll be using a four barrel carb with fully seperate primaries and secondaries.
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted January 16, 2004 12:09 PM |
Edited By: klaus42 on 16 Jan 2004 12:12
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Ceramic Rotors, Brad?
...or ceramic Apex seals...? (Obviously, I'm waaay behind the technology curve...)
Wish I had the bucks to buy the rx-8, go SCCA racing, get on the Mazda racer parts program, and get another renesis motor that way to drop in a REPU...and call it my daily driver!
A set of one-piece Racing Beat carbon apex seals + springs just didn't get bid up high enough on ebay... the seller emailed me with an offer to buy for $65+shipping from PA... if you need 'em, email me and I'll hook you up. Just can't ever tell if maybe they were dropped, or something... if my understanding is correct... you just never know. But the price sure sounds right!
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brad
Rotorhead
Posts: 1672
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posted January 16, 2004 08:03 PM |
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ceramic apex seals
seal better than ALL other apex seals, even stock irons. light weight so they don't walk out in high rpms. traditionally used on 8600+rpm GT or EP motors. don't absorb moisture like carbons do. carbons also don't seal as well and have lower compression.
But you pay for it. $1002 per rotor and they are two or three piece. I don't know who started the idea that bridgeport = 1 piece apex seal mandatory. The motor in my rx7 is proof that 2 piece works.
ceramic rotors? nah.... gotta go stock rotors. they look like cast steel to me.
as for racing..... if you wanna go as cheap as possible see if PRO-7 is in your region. SCCA or NASA. SPEC-7 too.
racing a new car is never cheap or easy. i couldn't budget it but a renesis in a repu sounds like a truckload of fun!
quote:
...or ceramic Apex seals...? (Obviously, I'm waaay behind the technology curve...)
Wish I had the bucks to buy the rx-8, go SCCA racing, get on the Mazda racer parts program, and get another renesis motor that way to drop in a REPU...and call it my daily driver!
A set of one-piece Racing Beat carbon apex seals + springs just didn't get bid up high enough on ebay... the seller emailed me with an offer to buy for $65+shipping from PA... if you need 'em, email me and I'll hook you up. Just can't ever tell if maybe they were dropped, or something... if my understanding is correct... you just never know. But the price sure sounds right!
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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Klaus43
Rotorhead
Posts: 1259
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posted January 17, 2004 12:49 PM |
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Over two grand in apexes....(!)
THAT's insane! Must be nice... At that point, a whole lot more becomes possible, too, I'd think...
Far as the renesis goes, I just like the idea of updated oldschool daily drivers with cleaner, higher-tech reliable power... 238 to 250 HP would be just fine for everyday in a REPU.
Looking forward to when that dream becomes a cost-effective reality...
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brad
Rotorhead
Posts: 1672
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posted January 18, 2004 05:13 PM |
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yeah, ceramics cost a lot
but they last a loooooong time. and can be reused. the wear on them is not even measureable. carbon apex seals, when revved to 9600rpms all season long, are generally the first thing to break in a race motor. lots of guys with carbons rebuild their motor after every 11 hours of use (a typical race season).
i decided i didn't want to pull my motor once a year so bit the bullet. plus they make more power and can take more timing than carbon. the decision was easy to make.
mabye in 4-5 years we'll start seeing rx8 j-spec motors being shipped to usa at good prices.
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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rotormunky
Redlining
Orlando, Florida
Posts: 424
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posted January 19, 2004 05:55 AM |
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quote:
mabye in 4-5 years we'll start seeing rx8 j-spec motors being shipped to usa at good prices.
I got to wonder how easy its going to be to get the same performance out of the renesis as it gets in teh RX-8.
It makes me a little nervous that its impossible to get 'correct' HP figures on a dyno because the computers let the car make max power unless actually being driven on the street. Makes me wonder what you'd have to do to get one to work in an engine swap.
I'd be interested to see someone like Racing Beat take one down to the housings and build it back up with aftermarket stuff and forced induction to see what it can do. The simpler the better.
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-Martin
Orlando, Florida
http://www.themonkeyhouse.org/REPU
'77 REPU (Some assembly required :)
'91 Cabrio (Battered and bruised, but she's still my baby.)
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Klaus43
Rotorhead
Posts: 1259
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posted January 19, 2004 10:12 AM |
Edited By: klaus42 on 19 Jan 2004 10:14
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If simpler is better...
...forget the forced induction! On the other hand, why wouldn't it be as 'simple' as swapping every last bit of engine computer stuff right along with a stock engine? Understandably, even this could be a royal pain in the ass...
Given the peri. intake/ multiple side port exhaust configuration --not to mention that exhaust temp. had to be an issue-- I've gotta wonder about forced induction on a renesis not originally built/delivered as such...
BTW, there's some ceramic apexes on Ebaymotors right now for an opening bid of $775.00 ...(forget the item # at the moment; sorry!)
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Klaus43
Rotorhead
Posts: 1259
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posted January 19, 2004 10:29 AM |
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Item number...:
# 2454137957 for those ceramic apexes... :)
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rotormunky
Redlining
Orlando, Florida
Posts: 424
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posted January 19, 2004 10:38 AM |
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quote:
...forget the forced induction!
Unfortuantely I've gotten to thinking that this is the only way to get a high level of performance out of a twin rotor engine. You can probably push close to 275-300 out of an n/a 20b but I'd think ~220 is about all you're getting out of the 'traditional' twin rotor.
quote:
On the other hand, why wouldn't it be as 'simple' as swapping every last bit of engine computer stuff right along with a stock engine? Understandably, even this could be a royal pain in the ass...
I get the feeling that it would be pretty hard to get swapped over without a lot of labour.
The biggest problem I have is that 238HP isn't really all that great considering the lack of torque which is what I'm really after for the truck (assuming you could even GET that once configured in the truck).
quote:
I've gotta wonder about forced induction on a renesis not originally built/delivered as such...
THat's why I say take it right back down to the housings and start over seeing what you can do with the new exhaust port configuration. If you can knock the compression down that would be a good place to start. Also that's why I was hoping somebody like Racing Beat would be pursuing this. Doesn't really seem like a job for me and buddy in the backyard. I guess I'm just anxious to see how the new configuration responds to forced induction given that it starts with a bit better power.
One one side I pref a nice computer controlled setup like a Haltech to tune the power for maximum efficiency, but it seems like the Renesis setup is pretty complex.
I'll either go with a plain-jane streetported rebuild with exhaust or TII streetported setup with exauhst. The latter should yield a little better power and better efficiency but would cost more.
Going to depend on what my money looks like when I get to that point.
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-Martin
Orlando, Florida
http://www.themonkeyhouse.org/REPU
'77 REPU (Some assembly required :)
'91 Cabrio (Battered and bruised, but she's still my baby.)
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Klaus43
Rotorhead
Posts: 1259
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posted January 19, 2004 10:50 AM |
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I definitely hear ya...
...on the 'money' end of things! Betcha' Racing Beat's already quite a ways along in the R&D on the Renesis... Make no mistake, if I had the $$$$ I'd be all over the SC setup for the REPU as well!
I still like the idea of newer tech., including that variable-length intake system... and the greater overlap of the renesis would seem to be a plus for boost--even as the exhaust might be more of a challenge...
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brad
Rotorhead
Posts: 1672
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posted January 19, 2004 12:24 PM |
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those ceramics are not official MazdaCompetition parts
The real Ianetti Ceramics you have to buy thru MazdaComp or RAcingBeat.
I do not know of anyone who used the eBay ceramics and cannot comment on them except that I have heard from engine builders that two piece apex seals seal better laterally (left and right across the seal).
quote:
# 2454137957 for those ceramic apexes... :)
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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brad
Rotorhead
Posts: 1672
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posted January 19, 2004 12:27 PM |
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Yawpower is dynoing a supercharged Renesis
for SCCA Speedtv World Challenge GT racecar. We'll know this season how well it does in competetion and hopefully a dynochart will surface.
http://www.yawpower.com/renespic.html
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-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge
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Jeff20B
Moderator
Posts: 661
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posted January 19, 2004 12:31 PM |
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Klaus, the intake of the Renesis is not peripheral, if that's what you were thinking. Also, there is not overlap.
I think the Renesis would make a great REPU engine. It starts out with more power than a stock REPU engine, so I'm not concerned about a so-called lack of torque or whatever. It'll be way higher everywhere in the RPM range.
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'74 REPU
'76 Cosmo
'77 MG Midget 13B
'81 RX-7
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Klaus43
Rotorhead
Posts: 1259
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posted January 19, 2004 04:05 PM |
Edited By: klaus42 on 19 Jan 2004 16:10
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Oh yeah!
That looks like fun!
You caught me talking out of my ___ there on the renesis intake... and what I really meant about 'overlap': I was under the impression that there was an inherent bit of improvement in this new design, in terms of intake/exhaust timing with zero communication between them... or am I wrong there as well?
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