Hi there im thinking of buildin a new engine for my rallycar. I have to use carbirators. I want something not to expensive to build and it needs to last. I would like to be able to go 8000 rpm without having to worry. I my current engine is 13b 4 port with 12a centeriron and 48mm carb. I getting close to 180 hp but its build from old scrap parts.
What would be the best engine to use. Ive been thinking about a 89 6 port with a street port and my old 48 ida. Will that bring me closer to 200 hp ore could bridge giv me closer to 220?. What about reliability 6port vs old 4 port? Please share your thougts and ideas

Best regards Rasmus Andersen Denmark

 

i don't know what you consider to be "not too expensive", but i would say since this is a race car then you should bridgeport your 4 port engine. of course the 48 IDA will need to be modified to suit, but you can address that once the engine is broken in and you start tuning it.

 

By exspensive i mean balancing and new gears ceramic apex ect. i know thats n not that expensive in USA ore Austrailia but in denmark it would cost me a fortune.
i currently have the 3 progressionhole 42 mm chokes and the carb diaeled in, my new exhaust has given me alot more power and i have dlidfiss working great. so all of that should be covered.
Becaus my current engine is buld from scrap parts i would like to put that in storage in case of mid season failures some races are only 2 weeks apart and parts for theese cars a allmost not excisting and very expensix here in denmark.
Could you explain why the 4 port is a better engine for my application.
I my head the 6 port would be better because of the higher compression? could i put high comp rotors in a 4 port without any machining..


Best Regards Rasmus

 

If money wasn't an object, s5 rotors and counterweights with 4 port rotor housings would be almost perfect for you, will help you in the low and high end once you get it tuned right, be able to hit 8k

 

and S5 means what exactly

 

S5 means Series 5 (basically 1989-92) cars. check out the 2nd Gen section and you can gain a whole wealth of information.

S4 rotors = 9.4:1
S5 rotors = 9.7:1

they can be used in the older engines.

i can definitely understand the desire to keep your current engine available for an emergency situation. ceramics wouldn't be necessary, but depending on what you end up with in terms of powerband (mainly your usable terminal RPM) you may want to balance, clearance and go with carbons.

the 6 port is not a bad engine. it's just going to be a rough road getting to the power levels you mentioned above (if you're talking about power at the wheels) - and you're planning to do it with a carburetor. you should probably check out some of the threads where guys have built cars with the 6 port and see if it will be a good fit for what you want.

 

Thank you i have never understud the terms s4 and so on. I read about the s5 rotors on racingbeat but they say that it dosnt fit. I may actually have easy access to s5 rotors and counterwheigt.
I dont have any demand for high level hp im not that good a driver yet.
I just wonna build a new engine correctly and as powerfull as i can afford. The main thing is reliability

 

i have a bit of experience with both setups with weber

.. the 4 port extend port will have a fatter mid range but be flatter off the line and up top
the hi comp 6 port will be sharper away from the line, less peaky in the middle but will rev to 8500 and not taper off so abruptly

the 6 port is easier to drive with tall gears and faster on the street with them

the 4 port is faster on the track when consideration is given to the final gearing to keep that fat mid range at the shift points

 

oh.. PS.. it is earlier rotors in late housings that clash at hi rpm , the rotors need to be face clearanced

putting late rotors in earlier housings has no fatal consequence for NA engines
asided that the side loading of the apex seal when not perpendicular... has been reduced

ie.. the housings post 85 are "thicker" with the chrome material
and this is to account for the fact that a 2mm seal when laying at its most horizontal angles to the housing surface is only 1mm off the centre point of the apex slot

and a 3mm earlier seal is 1.5mm off the centre of the apex slot

 

Does that mean that i should take 0.5 mm off the tip of the rotor?.
So can use a old 4 port and s5 rotors with counter wheigt to gain some torque

 

A good 13b bridge port motor 4 port with PTS apex seals will be reliable and make around 240 hp at 85 to 9000 rpm with 48mm webber

 

I am pretty certain just the non turbo rotors are 9.7:1, and no, no machining is needed to put them into a 4 port block

 

What kind of matching and would it be worth the trouble

 

no offense, but were you tired when posting or are you restating the already stated just for kicks?

i never made any reference to the turbo rotors since Sa22rally only mentioned 6 port engines to replace his old school 4 port. so yes, the ones i posted were for 6 port (or N/A) engines.

your other comment about not needing machining to use the rotors was already covered by Bumpstart.

 

according to what Bumpstart posted, you will be fine. you would be putting later rotors into your older engine (which would have the slightly larger peritrochoid), so you'd be good to go assuming all the counterweights and such transfer in with the rotors.

as for the type/location of the machining that would be needed for putting earlier rotors in a newer engine, i have a picture in my head, but it's probably best waiting for Bumpstart to detail it. i am just as much a student here as i am a teacher.

 

haha thanks guys theres a lack of experience with theese cars in denmark. ..
Will i get more torque by using 9,7:1 rotors? ore am i spending to much time on something not worth the wile.

Could i just make a couple of more questions while i have your attention.
1. How do i tell the difference between different rotors and wheigts.. the place i can get them is pretty messed up but i bet they are in there somewhere
2: what is the different betwen the old 4 port 13 b engines ive noticed that some of the housings have different exhaust sleeves. what are the different engines and what about pro/cons. i gues the housings with different sleeves cant be mixed..

 

here is one extreme rotaries half prepared earlier

note this is to fit the pre 1986 rotors into post 85 engine housings ( FC upwards ) and avoiding a clash at hi rpm

most commonly this comes about when people build "12c" or "12d" engines using 12a rotors and crank in machined down FC/FD 13b housings with FC or FD engine plates

 

1/
i have a post somewhere where it allows you to find the ID for front and for rear masses using measurements and not weights
( metric )

mazdatrix have something similar ( US imperial ) but only for rear weights and also for stock flywheels

2/
whole world of pain answering that one as it is year and market depending question

generally s4 onwards housings have the big exhaust ports and "cali" engines generally the smallest

in the early years the exhaust ports move up and down depending on application,, and the markets with large exhaust ports seem to have a common port made from both positions milled into overlap with each other

in the old 13b stuff,, very early housings may only have a ring exhaust port insert to reduce the port exit diameter to that of the header

later they get a more involved formed and shaped insert and it may have air injectors routed through it
( early rx4, with hollow air injection banjo bolt accessed via sump )

or even into the skin underneath and thus around it ( cosmo )

or externally on the outside face of the housing and into the header directly
( mid run carb 13b through to FD )

some of these can all be cut to a common port
ie.. if you have one with a low port,, and one with a high port,, you can make both a "large" common port

or the exhaust port inserts can be taken out and deleted or swapped to match up

so that does give some scope to matching up what appear to be odd housings

caution must be taken with FC housings ( generally, US market not included )
as the s4 NA ( n326 )has different leading spark plug location to that of the turbo ( n318 ) ,, and either of the s5 ( n350 NA and n370 turbo ) and FD housings

in the US.. all s4 housings ( n332 turbo and n326 NA ) have the odd leading spark location , different to s5 and FD

 

different than what i thought, but looking at it, this makes total sense.

i love it. 12C and 12D ... cute .

 

Oh, hm. Know of anywhere in the US that does machining of the flanks to make a 12C or 12D? It would be nice to be able to do a 12A compatible motor with fresh housings.

 

Kenku ~
give Goopy a call. i know for a fact he can get the housings cut down to 12A size because i've seen it. we did not discuss the rotors that day, but i would imagine he can get them machined as well.

 

be aware that a 12c or 12d will require custom plate to adapt to avail inlet manifolds

but brings bonus in the oil pump and the tapping for the turbo oil systems and or EOMP
and has avail the use of middle or rear engine mounts ( if you remake the sump )
( a 12c or 12d can also use a 12a sump direct if fitted with 12a timing cover )

some places can grove the engine plates too for water seals
and in doing so you can bring a 12a tall port centre plate ( or even the end plates too )
into the bargain
and thus you can build the ultimate 12 engine from edge worn 13b housings

 

I keep hearing this, and I put a new and old 13B rotor housing against each other, locating by the dowels, and I could not detect any difference in size or shape.

Measuring rotor face clearance is always a good idea, of course.

8000rpm is easily done with original internals. 3mm iron seals will be hard on rotors and housings, though.

I feel that there is no reason to use 3mm iron seals nowadays, given that 2mm seal rotors are easier to find and better.

 

all right guys i feel like im loosing something in the translation. could you please tell me if it would be worth it to put s5 9,7;1 rotors in a pre 86 4 port 13b. and am i understanding correctly that this is easy durable.
one more question.. in my mind carbon apexseals would be the best thing to do also considering that im using old housings?. is that corerect i was thinking apex seals would adapt to the shape of the surface better.

 

yes 9.7 is good , better than the early 9.2 heavy 13b rotors that have less gear fixing pins

they weigh close to s3 12a rx7 rotor specs, so will spin like tops in comparison, and make better TQ down low
( despite 4 large ports being exactly what you dont need to make good low down TQ )


carbon apex seals just suck/// the housings are designed to take steal, and mazda went there with good reasons
carbon doesnt last long , and it may seal great now,, but dont expect 50 000 km

if you where building the ultimate NA rotor motor then you would be getting the housings lapped and purchasing the ultra lightweight ceramic seals

which give you the mass advantage of carbon
with the hardness advantage of steel