4AGE small port --> making the ports smaller again

[92-GTI]

Hi People,

I was hoping that there are some people out there that have have made there small port heads even smaller in the quest for more power. Reducing the ports can be done with devcon or some resin based material.
I have been thinking about reducing the ports on my own small port. Small ports (not too small though) are the way to go. It was good to see in the fast fours issue before last that the word velocity was used and they didn't say much about making them bigger etc. Port Velocity has more to do with power out put than port flow and that is not just my opinion.

Anyway i don't really want an argument. i am just wanting to know the results if someone has done it.

Thanks

[roadsailing]

I haven't done it, but it is worth looking into.

have a look at this site for some info

http://mototuneusa.com/

it looks like popup galore and the guy went a bit overboard with colors etc, but he looks like he knows his stuff, has built many motorbike race engines.

you will have to sign up to view the tech bits, but well worth it, and you wont get any spam from him.

[YelloRolla]

This is a really good subject. I have not reduced the port size on an engine, but there are some really good articles around on the net about it.

Deciding the port to valve area ratio (the thing that you are really talking about here) is dependant on how hard you want to rev the engine. Also port to bowl area needs to be considered. 1 way to change the port to valve ratio is to increase the valve size (another way of thinking/looking at it). Cams are also there for altering the port velocity.

I rep you +1 for talking about something sensible. Some around here would have you believe that BIG port is the way to go.

Sorry that I have no more to offer, but it is good to subscribe to this thread so that I can read other people's experiences.

[92-GTI]

HI,

Thanks for the reply's. I have been looking at the mototune USA site for a while now. I think that he is good and the things he says are logical. He has made me think about some of the mods i have done over the years which have been good and bad.

My delema's are that my engine has 300k on it and if i take the head off to reduce the ports then i may as well put new rings and bearings etc, which would then introduce variables that would cloud the result of how much gain actually came from the porting v's the rest of the engine freshen up. I may just have to pay for 2 head gaskets because i want to be able to say port reduction and nothing but that mod resulted in + or - power.

Thanks again for the interest.

[ira11y]

Some around here would have you believe that BIG port is the way to go.

Jas i think a lot of references to the bigports are based on questions regarding turbo applications for which they are more suitable.

I was hoping that there are some people out there that have have made there small port heads even smaller

Bill Sherwood played around with his port sizes a few years back, i think he got positive results but youll have to ask him directly as i am not sure that he put anything up on his site about it. Basically he welded an inner ring at the entry to the port to create a greater initial velocity, then added the quad throttles to try and create better midrange if my memory serves me correctly.

[oldcorollas]

i would love to see this done.. and then compared with different boost pressures also.. if only we all had backyard dynos...

one thing i noticed from the mototune site is that he wasn't fully filling in the ports... what he seemed to be doing was to create a venturi starting from a large port, closing up, and then opening up just before the valve bowl. i find it interesting that he is claiming fairly substantial gains against the factory teams too... perhaps the factory tems go to higher rpm than he was or? dunno... he seems to start rambling a lot in his later issues

this is something similar to what "theoldone" discussed along with his squish heads...

[Dimitri]

ive mentioned this in other threads. i get to spend a bit of time around a bloke who does this type of work (porting, engine reconditioning ect). his name is geoff, he works at PLR engine reconditioning here on the north side of brisbane, but does his port work from home.

he refers to the substance he uses simply as "epoxy".

what he will do is start by cleaning up the ports in the usual ways (and the ways be has found to work in the past) he will then add plasticine in the base of the port and continue to increase the amount untill he begins to loose flow. one he has determined the right amount he will then replicate his work using the epoxy.

the shape he basically always creates is flat at the bottom and radiused back to the standard shape at the entry or bottom "lip" of the port. his ports will typically end up wider and much less tall than standard. he has mentioned this helps flow around the valve stems.

his engines seem to be VERY torquey. as much as some of his motocross customers are able to holshot starting in 3rd gear, where as previously this was impossible (they would bog down).

like ive mentioned in other threads too he has been working with some 4ag heads lately. once he has finnished i will post up some of his flow figures and maybe some pictures too.

[oldcorollas]

by many reports (from US etc), JBweld seems to last ok, but there must be other metal filler epoxies around that you could use....

[YelloRolla]

Jas i think a lot of references to the bigports are based on questions regarding turbo applications for which they are more suitable.

Hi Michael,
Actually I was referring to the turbo applications.

Do you care explain how a big port (all else being equal), will benefit a turbo application? Turbo engines are particularly bad for flow reversion, high port speed is a good way to combat this. One thing that I like about blown applications is that the air is now compressed and requires less pipe cross sectional area to flow through.

I have tried various manifold runners on my engine(s) and I can tell you where there were losses and gains in torque.

I will bet with a turbo application, all else equal, the small port will out-perform the big port. And by outperform I mean it's ability to accelerate a car through it's useful rev-range NOT the peak number it can produce on a dyno.

[Dimitri]

i agree with YelloRolla, its a common misconception that bigger ports are better for turbo.

slightly O/T but on the big port v's small port theme. apart from the big port ports being overly large, another one of their short comings and why they dont perform as well as a small port is the short turn radius. on a big port it is very shallow, where as the small port has a nice close to constant radius turn down into the valve seat.

this can actually be corrected on the big port with the use of epoxy, and if so, the big port head might then offer a superior shape port with its extra width, maybe. like i said above ill try to let you know once its all done.

[Darren]

one thing i noticed from the mototune site is that he wasn't fully filling in the ports... what he seemed to be doing was to create a venturi starting from a large port, closing up, and then opening up just before the valve bowl.

Thats Interesting. I've got a small port 4AG in a Corolla IP car with 320deg TRD cams, shim under buckets, TRD pistons, quad throttles etc. When we had it on the dyno it started making good power surprisingly early (considering the cams). But right in the mid range it suffered severe reversion that caused the power curve to flatten right off before going ballistic and making good top end.

We had some smaller diameter unfinished bellmouths laying around so we slipped them into the existing trumpets and wrapped some electrical tape around the lip to hold them in, essentially creating a venturi in the inlet trumpet. Very agricultural engineering, but it reduced the mid range power loss by more than half and increased the top end by 10%. "Hopefully" i'll have some nice cnc machined trumpets with an internal venturi tomorrow afternoon. Now i'm wondering if it would be more effective on the other side of the throttle....

You really need a flow bench to try these things on. Making the same changes to 4 ports, reassembling the engine then spending time on the dyno over and over again to find what works will do your head in and cost you a bomb. If you're serious, there are plans on the net for home made flow benches that might be worth considering. Mock up changes with plasticine to find what works on the bench before permanantly replicating it with epoxy.

Sorry if that sounds like a ramble, i'm trying to work at the same time.

Darren.

[myne]

I wonder what'd happen if someone turned the bigport into a distinct 8 port?
There's obviously enough room to spare for a divider, allowing seperate management per port.
I theorise that you could adapt each port, possibly with it's own cam grind for different ranges allowing for a broader power band.

"TheOldOne" Oldcorollas mentioned, I remember has an article about a top fuel engine they built. Each bank of the v8 engine was treated as a unique 4 cylinder motor, and each had a different target rpm range. They ran a different bore size, different rod:stroke ratio and different heads with different cam profiles.
The result, from memory, was an engine that out-performed a traditionally built engine and had a much broader torque curve.

It's certainly an interesting article. I wonder if atleast some of the principles could be applied to a 4 cylinder?
I'd love to know what'd happen - I just dont have the funding to find out.

Found it : http://www.theoldone.com/archive/pro...ing-engine.htm

[Starfire]

I believe he also experimented with running a V8 as 4 V twin engines with different bore and stroke on each pair.

There are certainly some interesting reads on his site.

[YelloRolla]

Referring to T.O.O - That was a pro stock engine, 2 x Vee 4 engines joined. You cannot do 2 x banks with a different stroke on a common crank.

Darren, you're telling us that the engine made more mid range and top end? I think that you told me this story in person once before. Just the way it is written "reduced the power loss" which I am sure that is a gain, and that is what you meant. Fuck it, I am work too, I just want it ot be clear to others reading your results.

Jase

[myne]

You can easily do 2 banks with different strokes on an 8 with a little creative journal machining. Remember how much $$ they threw at this.
I dont see where it states that it's a pair of v4's. And I'd say that'd be against the rules. Also at one point he clearly states "Nasty numbers for a Detroit relic!"