Hey guys, I know in some racing series where a stock unmodified exhaust manifold is required they will make a cap to seal off one end of the manifold and fill it full of battery acid to basically port the manifold without making it look any different.

Since the upper manifolds on these things are impossable to fully port does anybody know what type of acid I should use on aluminum? Will sulferic work or do I need something more like myratic (sp?) acid?

 

Uh...don't cheat. Work on your driving skills, instead.

 

uhh yea..stripping material off cast iron is probably a bit different than aluminum, you just may wind up with a molten ball of toxic lava by the time it begins to do it's thing.

 

lol, this won't be for a race spec car.

I'm sure there is an acid out there that can be usable for this. NAPA used to make an aluminum brightener about 7 years back that had an acid in it that basically etched the surface. Left it there a little too long and it would start taking material off. I'll just have to do a little research I guess.

 

What do you plan to do with the acid when your done with it? The better thing to do is send out your upper and lower intakes and have them extrude honed. This is a process that uses an abrasive putty that is forced back and forth inside some thing and removes material. The process is acurate enough to balance air flow rates in ports as well as increase air flow. The finished product looks great and performs better.

 

why would you want to port the stock manifold anyway?
it's a big box as is and aren't the ports themselves large enough to fully fit around the exhaust on the motor?

 

Wait, isn't the stock exhaust manifold cast iron? Cause I've never seen aluminum that weighed as much or rusted as bad as my old exhaust manifold.

 

Well from what i know from chemistry.. You would want to use a concentrated Strong Acid eg. H2SO4, HCL, HBr, HI, HNO3, or HCLO4. Probabaly 2-3 Molar. Its not too hard to get strong acids(HCL is probably the best bet), but i would suggest that you know the fundamentals of chemistry and how to work with chemicals before messing around with them. Keep in mind not all areas of the manifold will be the same density, hence some areas will dissolve faster than others and you will get an uneven flow surface. Also this is the subsequent unbalanced reaction..

HA(l)+Al(s)---> AlA(l)+H(gas)

NOTE!!: H2 gas, very flammable, very reactive. H2 is given off when an acid reacts with any metal. Because of the high concentration of the acid, H2 will be producted at a significant rate.

You would not want to seal off the manifold with plugs on both ends becuase the seals would likely blow off and send concentrated acid everywere.... In fact, for your own safety and the safety of others.. dont try this.. haha now that i think about it. Cheers

 

There are bigger bottlenecks to be concerned with. I really wouldn't waste my time with this.

 

read the post again./


He is talking abotu the UIM, not the exhaust mani. He just referenced the exhaust mani.


BC

 

Oh, gotcha. I guess I missed that. And yea, I dont see any way you could do this reliably. You would likely end up with it flowing worse that stock. Just get a dremel and follow the "intake porting" thing in the archives.

 

I agree that, with the acid roughening the surface, you could actually end up with a worse flowing part.

--Alex

 

ExtrudeHone. Search for Icemark's experience with the product.

Or just use the long flexible attachment on your Dremel tool.

Honestly though there are minimal gains.

 

+137428, especially if its a turbo'd engine

 

The rest of the engine will be pretty stout for a N/A I'm pretty sure the UIM will be a restriction. I don't see how there is any way to get all the way up inside with a flex shaft, there is a straight section about 6" long with a tight bend at either end.

If I'm going to spend the money on extrude honing I'll just fab the materials to make a better one and pay one of the guys at work to tig weld it for me.

I've played with some pretty strong acids before and feel comfortable handling them. We have plenty of ventilated areas I could use to keep the hydrogen ventilated. We also have a sonic tester that I can use to check the density and thickness of the metal in the ports We use that on some of our aluminum parts.

I really didn't want this car to turn into the project it's becomming. I just wanted to do a medium performance engine build as one to learn on for a turbo build later on.

I already have 1k into the engine with a HUGE amount of work done myself and I need a minimum of another 1k in parts to do the actual rebuild, lol. At the moment I probably have another $700 or so in the rest of the drivetrain and suspension with another couple hundred to go before I'll be satisfied with it, lol.

By the way does anybody want to see my CMM reports I've been doing on the engine parts?

 

^ Sure let's see.

Even if you were to try this acid etch idea, how would you prevent parts like the flanges from being eaten away? Regardless I really think you'd be better off spending your efforts elsewhere. eg. having your friends at work weld something up would probably gain you the 2 hp you are looking for.

Do you have a 13B in a REPU or a B2200 (or similar)?

 

I have a 87 RX-7 and a 87 B2200.

So your saying the stock S4 manifolds will support 180-200 hp?

 

Nope. The air flow meter is the main restriction. The intake manifold flows MUCH more than it does. The S5 manifolds make more power but from a flow standpoint they flow a little bit less. This is because there's more to power than just flow. There's also tuning but we won't get into that. Flow is important but you need to understand how and when you need to address it. More is not always better. This is the biggest misconception there is when it comes to modding engines. Just as an example, what if your intake manifold does get hogged out a bit and flows more? What if it flows more than your intake ports? Do you think your power will increase or decrease? Think about that one for a while. Then what if you enlarge your intake ports and runners to match the manifold flow? What will happen to your powerband? Will it gain top end at the severe expense of power everywhere else? There is a lot to think about. If you are really concerned with getting the most out of an n/a engine, get a standalone ecu and an entirely different intake manifold. You'll get it with tuning.

 

Here's some potent n/a engines from the dyno section:
S4 n/a with exhaust/intake https://www.rx7club.com/time-slips-dyno-128/s4-na-putting-down-147-4-a-496362/
"Ported" intake: https://www.rx7club.com/time-slips-dyno-128/s4-n-6-port-puts-down-172rwhp-488387/
T2 intake: https://www.rx7club.com/time-slips-dyno-128/na-streetport-6-port-dynoed-182whp-details-inside-416012/
S5 intake: https://www.rx7club.com/time-slips-dyno-128/na-%3D-193-9-hp-141-tq-498774/

Not that I've personally built a 200rwhp n/a, but I don't think that the AFM is the main restriction in intake. Take the TII, people have made a LOT of extra power with the AFM intact. On my webpage www.geocities.com/jeffguilfoil/afm.html I've quoted this:

 

The inlet of a stock turbo is MUCH smaller than the afm. A naturally apirated car responds very differently as there is nothing there to add pressure to the system. A turbo can compensate for many things. You can mess up pretty bad in turbo engine design and still get good numbers. You can't do that with an n/a.