Benjamin4456

Ok, I know that there have been countless threads on the subject but being that I'm about to tackle my first engine/port job, I'm looking for some opions and info on porting 'fundamentals' and such. That said, the motor is a 12a and will be fed by a modded Nikki (NA for now), free flowing exhaust, cleaned up intake manifold, DLIDFIS, etc.

As for porting, I've seen some various opinions on how the bowl/cup shape of the port affects performance as well as other various factors. I'll be using templates (most likely the Pineapple Racing large streetport for both the intake and exhaust), so I'm more so curious about the design and execution of the interior shaping and how to best profile that. I'm open to all opinions and theories, and I realize that a fair number of people prefer to keep specifics under wraps.

Now I know this is a brief post so I'll gladly provide any other info requested.

Jeff20B

iTrader: (13)

I prefer 74 spec size ports. They are a better port for the street than RB's streetable ports which were more meant for racing. Pineapple is the same way as RB in that it is a racing port that is still streetable, but it hurts low end. Low end is something that is good to have on a street driven car. Yours will be driven on the street from time to time, right?

Qingdao

iTrader: (3)

I think this is what you are looking for.

You want the intaking air to blow into the chamber. So port like the first image if you are looking down into the iron from the top.

Benjamin4456

Jeff:
Haha, your 74 spec port opinion has been very well documented on the forum - probably every other thread I read contained a rendition of your "74 spec" response . Now the car is street driven, as in it's essentially a daily, so street manners are of course of relative importance to me so thank you for bringing that up. However, I'm willing to lose some low end to push the power figure up a bit, although that's where I really don't have any context. With larger streetports (like Pineapple's for example) what sort of side-effects can be expected - low rpm bucking, around town driving difficulties (of what variety), etc? 'Real-world' examples would be appreciated so I can get a better grasp on what I'm dealing with - essentially I'm trying to weigh the alternatives here as I am willing to sacrifice some driveability for power.

Qingdao:
Yes, thank you, that is most definitely one of the things I was looking for. One bit I'm curious about though is the outer edge (along the water jacket): should the roof of the runner/port, if looking at the iron on its face, be trimmed much at all to increase the angle (as in making it a more gradual transition) or should it be left like a rounded 90 as depicted in the first photo? I feel like you meant the first sketch to be entirely correct, I simply want to make certain. Also consider that I don't have the engine apart yet - it's on the stand and ready to open, I just haven't had the time.

Jeff20B

iTrader: (13)

Well Ok, I'll up the ante and tell you my current 12A has pineapple porting on the end plates and slightly smaller ports on the primaries which are still bigger than 74 spec. The exhaust ports are true pineapple ported (huge). I also have an extremely hogged out 79 intake manifold also done by pineapple and run a hogged out Nikki (well several as I assemble and test them and have tried all the sizes that are possible in the Nikki form factor). I also have an S5 turbo and a full" exhaust. DLIDFIS, Mallory 40309 fpr, MSD 2225 pump and lots of other stuff I probably forgot about lol.

This engine lacks grunt below 2k which is understandable considering the porting and manifold etc. I also have an RB light steel flywheel and one of their classic red painted street strip pressure plates (softer than an Exedy stage 1 but stronger than an Exedy OEM duty stock replacement pressure plate). The disc is from the Exedy OEM replacement kit and holds all the power the turbo is making so far at an indicated 15psi or so. 225mm. The previous ACT performance copper woven disc would slip so that's interesting that the stock duty Exedy is superior.

How much power does this thing make you ask? I dunno. 200-ish maybe? Others here have said if stock is 100 and 300 is crazy, then 200 is the perfect right amount. I'd have to agree. It only has 155 miles on the fresh rebuild and I took it up to 7k today in boost. Shhh, don't tell anyone.

tim.

iTrader: (1)

I used the pineapple racing large Street Port template when I built my 12a. It is a 79 with R5 irons.
For the exhaust I just copied the size and timing of GSL-SE housings, which were way bigger than my stock ports. I also run a hogged Nikki, and I find the car to be very well behaved.
My opinion for porting a NA engine is to keep in mind that the engine is pulling the air into the combustion chamber, and that air generally wants to travel in a straight line.
I set the rotor on the housing and moved it through the intake path and watched the pathway for the air.
I don't have dyno numbers, but I took it to my local dragstrip, and it runs 15.0 at 88 or 89 mph.
The next engine I build will be the same, but I am going to add a semi-peripheral intake port as well.

KansasCityREPU

iTrader: (9)

Jeff - when using the 1979 intake, what do you do, if anything, about the open exhaust port in the center iron on the intake?

j9fd3s

iTrader: (3)

it is possible to port too big, and there is plenty to gain in the exhaust/intake/ignition area still.

its the real fine tuning where it take a lot of time, where you're getting all the parts to work together

Benjamin4456

My engine originally had an entire SA set up minus the engine (it's an 83-85) and I discovered that the center exhaust port had just been thoroughly, and I mean thoroughly, filled with something similar to JB weld. Not certain what it was, but it worked like a charm and was a pain to remove when I was attempting to track down my extreme smog issues.

Jeff, what all was done to the intake? Were the runners hogged or what? I'm not planning on doing anything else to mine for the time being (I have an FB manifold that I cut the channels into and then cleaned them up - top of my intake and Nikki modding thread). What is actually different between the early and later intakes besides the different ACV set up and the missing channel/shutter valve that was added to the FB's?

Jeff20B

iTrader: (13)

KansasCityREPU, the rotor housings are 79 so they don't communicate through the ACV port at all. But I still filled it with quicksteel.

Benjamin4456, the mani runners were very hogged out.

It turns out you might not need to cut a channel in the 81-85 manifolds after all. There is already a hole connecting primary to secondary, and there is a nice anti-reversion lip under the machined circular area where the shutter valve is located. I'd still clean up the runners just a bit though, at the top under the spacer.

The difference going from SA to FB manifolds is the primary runners of the 79 are better but the secondaries runners are worse than the FB. If you study them both you will see the differences. The 79 can be trimmed in the ACV area to allow an S5 turbo to fit closer than the FB manifolds, which has a large water jacket area that would need to be cut into.

Benjamin4456

Very interesting. While I'm not planning more intake mods in the near future, that's definitely some intriguing info. I know that hole you're referring to and I actually plugged it (along with all the other remaining divets from the shutter valve to reduce turbulence - or at least that's the thought that went through my head at the time) when I cut the new channel to make both sides more similar. After completing it there was a noticeable increase in the smoothness of power delivery and even the exhaust note was different. I do have a couple SA manifolds so perhaps I'll mess around with them sometime.

Back to the subject of porting, what is the philosophy behind the shape of the exhaust ports? Straight closing and/or opening vs curved, timing, interior profile etc. and how do those change based on NA vs turbo applications. Now as I said before, I plan on using templates, I'm simply curious about the pros and cons of different shapes and when (in general) they should be used. Also, it sounds like the pineapple streetports - intake and exhaust - will be fine regarding street manners in my mind (a loss of torque under 2k isn't much of a concern for me as I don't often try to accelerate significantly around there as it is). It would also seem that with my stock(ish) runner manifold, the higher velocity would help offset some of the torque loss you're noting - then again you're turbo and I'll be NA (for now at least) so that's a hit on my side. Sort of similar to that, to what extent is cruising affected by porting?

Any additional general thoughts about porting or more specifics about intake port design are still welcome of course.

Qingdao

iTrader: (3)

I have a set of professionally ported irons that I have used in the past. They are amazing much more power than my 6 port hack job I have in my car now. I attest most of the power of my 4 port "pro" engine to the fact that the primaries open (or close cant recall atm) at the exact same time as the secondaires. I believe that one of the latter RX7's did this and picked up some substantial gains in power.

So whatever you do don't just go big. Do what the templates show or mimic a Mazda port job.

chuyler1

iTrader: (1)

I can basically confirm most of what has been discussed here about port size. Lately I have been jumping from two vehicles set up as follows...

a) '75 REPU with stock '74-'75 (not sure which or if they are different) ports but a large quad 42mm ITB throttle body setup. 4.10 rear end.
b) '85 RX7 with large street port on all 4 ports running twin 45mm ITB throttle body setup. 3.90 rear end.

The REPU has no dead zone. You can putz around town at 1,800 RPM if you want. You can rev it out to around 8,000 RPM and it makes power smooth. Dyno says it's making 160 to the wheels. It feels dangerously quick for such an old vehicle. I thought I was going to eventually port the motor, but now I think it's just fine as is.

The RX7 is anemic below 6,000RPM. It's all noise and no go. It will not accelerate below 2,000RPM in higher gears so you can't putz around town lazy shifting and keeping it in high gear when other drivers are pulling in and out of side streets. Just won't do it, you have to downshift to get back up to cruising speed. On steep hills like those found around Deals Gap, I had to remain above 4,000 at all times. It feels tragically slow until you reach that power band centered around 7,000. The gearing is currently too tall to keep it in the power band at the track so overall it doesn't feel any faster than the stock 12a porting. Dyno says it's making 152 to the wheels...but area under the curve is drastically less than the truck and I can feel it even though the Rx7 weighs 300-400 lbs less.

Jeff20B

iTrader: (13)

Perfect example of how so called "street ports" really are not good on the street, but can be driven there if necessary (just not enjoyably so). I'd request that we stop calling streetable racing ports "street ports" but it ain't gonna happen. Just go with 74 spec on the street and smile with every mile.

Kenku

Or drive it like you stole it, and go bridge or peripheral port.

j9fd3s

iTrader: (3)

:thumbs: no dead zone on the P port!

Kenku

In all seriousness, we're once again at the "people have different tolerances" thing.

I've some RX-8 irons I want to try brazing material into the exhaust port to plug it - I'd really like to try the entire Renesis induction side with a peripheral exhaust. Other than that maybe, I can't see dealing with side ports any more on anything where I'm not required to by rules, but I'm targeting weekend style stuff rather than attempts at being civilized.

j9fd3s

iTrader: (3)

true, but you can get it to idle at ~750rpm without brapping.
two, if you're accelerating, it makes power, there is no waiting. in fact this immediacy is why it is so good to drive.

if you're just going a constant speed, its not happy, too much overlap

Mr Fujita, from FEED made some plugs for the exhaust port, would not be hard to do that. and then run GSL-SE rotor housings, and you have instant 280ps engine

Kenku

I couldn't get mine to idle happily at 750rpm without brapping, but that was on a Weber at the time. Thinking hard about doing a simple manifold to snowmobile TBs though and throwing it in an FB shell.

Yeah; my RX-8 is in need of a rebuild at this point so it's a really tempting route. In between everything else...

Benjamin4456

Ok, so I guess at this point I'm a little mixed up. For obvious reasons everyone will always have a preference and I get that, but it seems like this thread has come full circle by this point concerning the opinions on porting . I've finally gotten the engine apart and everything seems fine, although the corner seal springs were extremely flat and there's quite a large amount of blow-by. There's also evidence to suggest that this engine suffered an inner coolant jacket failure. Thankfully, though, there is no chrome flaking to be seen, the bearings are all in fine condition, and the only notable step wear is on the outside edge near the spark plugs, which according to what I've found is pretty common. If anyone has any brief tips or tricks for engine rebuilding feel free to share.


Back to porting though, I'm having a bit of a mental dilemma here. From what y'all have said I'm a little concerned that pineapple's large street ports are going to be too large, though I'm also worried that if I go too small I might regret that as well. I plan on shooting pineapple racing an email before monday to see if they can provide any ideas on how drastically their various street ports will change driving characteristics, but other than that I'm at a bit of a loss for the time being. Jeff, your setup sounds quite similar to what my goals are, although I'll be running NA for at least a good time. Perhaps you give some more insight here? I've also discovered that the pineapple large template combination has enough overlap to give a fairly brappy idle (assuming the videos I've found are true about their porting templates), which I don't mind, although I've never heard one in person. Just to reiterate, my car is currently running a modified Nikki (no choke, no smog equipment, trimmed boosters, AP mods etc. and soon to receive hogged out venturis), an RB short primary header to a custom (and in need of replacement) 2.5" free flowing exhaust, DLIDFIS (GM modules), and soon a fuel pump upgrade (which will happen the same time as, or before the engine swap most likely). So given that, what do y'all think my best route(s) for porting would be? Also consider that I don't spend much, if any, time below 2k unless I'm in neighborhoods - my car is rather loud...


Thank you to everyone who has contributed so far.

Jeff20B

iTrader: (13)

More insight? Um... Mine can have a brappy idle or a smooth idle. It depends on the carb and the tune. I kinda prefer a smooth idle. Does that help at all?

Benjamin4456

Yeah, I guess that helped a little. I mean heck, I've gotten my stock port to brap when the secondaries were stuck open a hair lol... Anyway, you mentioned that your porting (at least secondary and exhaust) is pineapple porting - do you have an idea about which template they are most similar to?

lwrobins

The fact that this tread has come full circle should tell you something, 74 ports rule for a street driven car. There will be trade offs on a NA car. You cant have it all! Just turbo it...

diabolical1

iTrader: (3)

i'm old enough to remember that the '74 and '75 13B housings/engines were what you wanted when building back in the '80s. however, i am now seasoned enough to have tried a few different ports since i started building engines, so i know there is such a thing as too big. i never actually got my hands on any of those old 13B housings, so i never actually built a full engine to that spec, but i do know what they look like having handled turbo engines now. i can imagine 4 ports of that size would be nice on the street. i'm saying that to say taking Jeff's advice is probably the "safe" bet.

So now you're left with the dilemma of how do you obtain or make a template for that ...

i don't own a Pineapple template for an old school engine, so i simply don't know how large they are. if i were to guess based on their '86+ templates, it is probably fairly large (pretty much as far as you probably should go and still make power). nevertheless, it's still conjecture on my part, so from your standpoint it should be neither here nor there. i have used RB's template for old school engines though, and i like it. it's conservative (maybe moderate might be a better term) in my opinion, which is why i think it works well.

j9fd3s

iTrader: (3)

i'd go 74 spec for a street car. you have to think about the whole engine system as a package. everything needs to work together. the 74 spec ports gain a little flow, and still work with the nikki/RB exhaust. going bigger with the port you loose some low end, and the nikki/rb exhaust will keep you from gaining on the top end.

if you switched to a IDA Weber, for example, and spent some time optimizing the exhaust, you could make more power with the larger port.