trochoid

iTrader: (6)

I am in the process doing my first rebuild and port job and have several questions/clarifications.


1. I bought the Mazdatrix bridgeprt template. They have 2 different ones and this one is not the racing template. I made a plexiglass copy of the template to check the track of the seals and that seems all well and good. However, it looks like I will need to notch the rotor housing because the bridge cut in the end iron goes past where the housing will mate up.

I'm pretty sure I will need to make this notch in the housings and I don't have a problem with that other than it was not explained on thier website. Do most bridgeports require this notch and will I need to notch the rotors also? If I notch the rotors, will the need them rebalanced? If they do I will probably forego notching them.

I've enclosed a pic of the area to be notched in the housings.

2. I bought a pair of housings off eBay awhile back, and now that I am finally getting around to using them, I find that the exhaust has been ported. This was never mentioned in the ad of course.

I would like an opinion of the ports, keeping in mind this is for a half bridge (end irons only) that the engine has a very good chance of being turbocharged soon. The ports seem to go up quite a bit and not down and I am concerned with too much overlap

Pic enclosed of stock and the ported housings for comparission. The edges of the ported housings do need the factory bevel added.

3. I am currently running a mikuni 44pph jetted for a stock 12a with headers. I had hoped to run this carb with the turbo, but it sounds like it may not support the bridgeport, let alone the turbo. If it will I would like jetting suggestions.

If the mikuni is not useable, I also have 3 holleys, 465,600,650 at my disposal. Suggestions for jetting and set up for those would be appreciated also.

Now the friendly rules for relies:

Please don't tell me to search, unless you have a very big smile with it. I have done countless hours searching on several forums for all of the above mentioned items.

If you tell me that this or that can't be done or won't work, back it up from your experience, not from what youve heard.

If you have questions, please ask, as I would like to get a usefull discussion going on about 12a turbos.

I have a TII and 2 TII engines that need rebuilt. I concidered the swap. I even have nearly all of the parts to do it. That part of the discussion is closed. There are only so many TII's out there, and there are less and less of them all of the time. Eventually we will need other options, this is one of them that I am pursuing.

The first person that says you can't turbocharge an N/A should be forever banned from logging on without first using the search button . (humor) (I still don't know how to insert smiley faces in the text.)

Enough of the rules, let the discussion begin.

I knowt his is long and for that I apologise. If you've gotten this far, then maybe you can help or are interested in the project, and for that I thank you.

Scott.

kenn_chan

sounda ot me like you got the racing version of the template, but having never used there templaste i am not sure, nrmall on a partial bridge (small bridge) whatever you want to call it there is no grinding to be done on the rotor houseing. when doing a jport bridge you would grind on it.

no you do not grind on the rotor in any way shape or fashion less you want to use them as paperweights!

go to racing beats web page, they used to have a detailed desription of how to do the porting for a bridge, if not then PM me and i will get back with you about this.

cheers, ken

trochoid

iTrader: (6)

Kenn,

Thanks for you reply, you're the first.

I had already decided not to notch the rotors, mostly because of the balance issue, but I have seen pictures of it done before.

When I first laid out the template and discovered I needed to notch the housings, I went back to the Mazdatrix website and confirmed that I did have the right template. They are # and color coded and both matched. Their race bridge is quite a bit wider. The Racing Beat site also shows the housing notched, however they insist on new housings for the notch.

Now for the new problem. I roughed out the main secondary port last night and started drilling for the bridge. If I follow their directions on drilling and using the 15-20 degree angle, the to 1/4 of the bridge will go straight into the water jacket.

I'll post pics of this later tonite.

Scott.

rotarygod

iTrader: (1)

There are 2 bridgeport templates as you have stated. Both of them require notching of the rotor housing. Just make sure you do not go as far as the water seal with the notch on yours.

trochoid

iTrader: (6)

It looks like I will be cutting about 2 1/2 mm towards the seal. So I should be good.

From what I've been reading, the suggested cut is at a 45 degree angle. I need to put the plate and housing together to get a visual reference, but my mind is asking why not round the cut, (convex) for better laminar flow.

REVHED

This isn't exactly true. Any decent bridge-port will require notching of the rotor housing but it usually stops short of the inner o-ring. A j-port is when it breaches the water jacket.

Nope. It is actually possible to notch the rotor to gain some extra port timing but it's not very common. I've seen it done before though.

REVHED

I'm not sure how big these templates are but, often the top part of a bridge-port will blend down into the rest of the port on an angle so it doesn't hit the water jacket.

trochoid

iTrader: (6)

REVHED,

That's exactly what I'm thinking I need to, angle the port down to miss the water jacket.

I've also concidered dropping the entire port down alittle, but I will need to look at the plexiglass template to see how this will affect port opening timing and tracking of the seals.

My other option is to just simply shorten the bridge at the top and not get as much flow. that may defeat the pupose of the bridge though.

Thanks, Scott.

trochoid

iTrader: (6)

Here are the first picks of the bridge. They are rough, I don't have the right stones or any sanding rolls yet. I think I may have gotten a little too far into to the coolant seal land with the nicks that you see.

The second pic is the same template laid over the intermediate plate. The green masking tape shows the difference in size of the ports. I'm thinking of porting the intermediate plate this big, without the bridge.

Opinions welcomed.

Thanks, Scott.

karism

Torchoid:The ports shown in the pics dont look bad at all,well done!

You will have quite a rough bridge with the size that the exhaust port was made,but it will provide a very nice powerband up top.

My 2cents : The combination of the intake,and the wild exhaust might cause a Turbo to take forever to start spooling.It IS possible though,but you will have to be patient.

How wide is your bridge?

Dont worry about notching the housings.It doesnt hamper how long the engine will live at all.Your is still quite a distance away from the water seal.

Karis

trochoid

iTrader: (6)

Karism,

Thanks for the input, and the compliment.

I posted pics of the exhaust ports because I have another set of housings I can use. Those I would take down as opposed to so far up as the ported ones are.

The bridge is just wide enough to get my 1/8" burr in, plus a little extra room from chattering. Looking at where the pitting is in the iron, was my cause for concern about porting going too far.

I just ordered some sanding rolls, tapers and smaller burrs fom McMaste-Carr. Seems there are some places I can't get to with the burrs I have.

Scott.

numan2

that exhaust port looks a bit too high and not matched well to the sleeve and that will hurt your exhaust flow by causing some reversion and turbulance I think you might be better doing your own ports there but your intakes look good for a rough cut.

trochoid

iTrader: (6)

numan2,

Thanks for the compliment, and I tend to agree about the exhaust port. I've enclosed a pic shot from the manifold fold side for better reference.

I'm afraid with the late closing that there would be way too much overlap if I do the turbo later on. First step will be to get the engine running peoperly in NA form. If that is succsessul, then the turbo.

trochoid

iTrader: (6)

I decided to port the primaries the same size as the secondaries, without the bridge. I've enclosed a pic of the first port roughed out, along with a stock port for reference.

The port has had some smoothing with a stone, but no sanding. Ordered some smaller burrs, seems I don't have any small enough for the tight places. Sanding rolls and tapers on their way also.

rotarygod

iTrader: (1)

The exhaust port is fine for a bridgeport. Have a read at this and look at the pictures of the 12A exhaust port. It's a good article.

http://www.yawpower.com/Flow%20Testing.html

trochoid

iTrader: (6)

rotarygod,

Great link. I hadn't seen that one. Looks like I may be widening the exhaust port a little. Still not decided about the overlap concerns when the turbo comes into play.

All said and done, this engine will probably be in and out of the car more than once to get porting to where it needs to be. It's a learning and growing experience.

Thanks, Scott.

rotarygod

iTrader: (1)

Look at the size of your exhaust ports and then look at the size of the ones in the article. Yours aren't even close to that big. They removed the exhaust sleeves altogether. A bridgeport relies on high overlap. This is why you need to have a very good intake and exhaust system.

SS124A

I have my 12A bridgey taken apart right now.
it is a similar setup to what you are planning.. the original 12A was HUGE street port. then a bridge was added.

The engine is being reassembled using a GSL-SE center housing that will be given the same HUGE street port. then with my 74/75 12A bridgey housings... I'll take some pics later if you want to see them..

THe only note i have for what I have seen is:
it is hard to explain the rotor housing bridge notches... it is easier if you see a pic. looking at your pic,i would go a bit deeper towards the water jacket. but not close. i usually just grind away the steel inner trocoid sleeve. I guess i will have to post pics...

On the exhaust port, you need to go over that, bring the top up and make sure it is beveled or the engine will not last due to seal chatter.
If you do stick with the Turbo idea, then don't go up much, and maybe channel port the exhaust, or turn the port shape into a "V" shape.

Along time ago when the first 10A and 12A were released they had 3 small exhaust ports. mainly the australians found... but if you combined all 3 ports into on larger port mantaining the radius at the bottom by the single bottom port hole it is beneficial to turbo use... on our traditional 12A housings porting a shape like that isn't that great for N/A applications.

BTW,
Racing beat has 12A racing rotors on clearance... for only ~$230 which is dirt cheap.

I have a Mikuni 44Phh on my 13B now.. I also fear that this will be too small for the 12A bridge. I'd like to try a side inlet manifold. with larger venturi. IF not a 51IDA may be in my future.

kenn_chan

Thats interesting, around here i don't think any of the private (shade tree, etc.) tuners due this, I never have (hell I never even thought of trying) mostly cause balancing around here is non existent (balancing a drivshaft costs about 1000.00 around tokyo, and thats if you cut, alligned, and welded it yourself. wouldn't want to think of what it would cost for a rotor.
Thanks for the info, you learn more stuff every day.

ken

kenn_chan

God must have PM'd St Mikey on that one. Thats an excellent article, and very informative. with that said, time to start a thread about flowtesting!

Ken

trochoid

iTrader: (6)

Well the ports are done. Been done for a week, just haven't been posting.

Any critique will be appreciated.

The bridges are a little narrow and slightly uneven and the bridge ports are a little too wide. That's what happens when the slot is supposed to be about 1/4" wide and the narrowest bits I had were 1/4". I bought some 1/16" burrs and the first one lasted 5 minutes before it snapped. Porting, in general, doesn't seem to be that hard, but the bridgeports are very tricky to get right.

Since this is my first port work, I won't complain. I'll be happy just to get my first rebuild running halfway decent.

Thanks, Scott.

karism

Good port work there Sir!
For a first attempt :I would say great!
Think you will have good results from the ports.

What carb/injection are you going to run? (Sorry if you said it before..)

karis

trochoid

iTrader: (6)

karism,

Thanks for the compliments.

I have a mikuni 44 phh on the car now and it's still stock. I read on the Aussie forum that it won't be big enough, no matter how I jet it. I also have a holley 600 with the RB intake. that is probably what I will start with.

If I end turbocharging this motor, I would really like to run the mikuni. I would be easier to plumb for an intercooler and has an added bling factor.

I have a holley blue fuel pump and regulator ready to go in, along with a refurbished GSL-SE fuel tank and lines.

Any suggestions would be appreciated.

Thanks, Scott.

trochoid

iTrader: (6)

Well, I decided not to paint the housings and powdercoated them instead.

Anodized silver and black chrome.

The engine is not assembled, just stacked for the pics.

waysrx7

I'm bumping this up so I can ask trochoid how he likes his half bridge port.
would you rather have done a street port or full bridge?
From reading your posts it seems like the half bp is truly a happy medium.
You've made me reconsider just doing a street port and going for the half bp, but I was wondering how it would work with a stock nikki.