3.2 Intake Manifold Runners-FLOW

[Jakester1168]

I've heard the 3.2 intake manifold runners have some uneven flow. I was thinking of having the manifold "honed" for better flow. Is there any potential horsepower gain, if so, what may they be, if not, is it worth the money to have done? I am also uprgrading to Euro spec pistons , a B&B exhaust K&N Air Filter and DME upgrade.

Thanks

[Eagledriver]

I've heard that also but only from the people that sell the process of honing them. I suspect there is no flow difference when the engine is sucking the air through them. The restrictive part of the 3.2 intake is the airflow meter box. If you were to replace this with another MAF system you might be able to improve the performance of the engine, especially at high RPM. Euro spec pistons will give more power if you can use race gas so you can keep the timing advanced enough to take advantage of the higher compression.

-Andy

[Steve@Rennsport]

Andy:

I don't sell the process of honing these intake manifolds and have no vested interest in anyone doing such things, but we have done extensive flow testing of these since 1984 and there certainly are variations in airflow from branch to branch in many of these things.

We've seen up to a 30% difference in runner airflow that does affect cylinder power balance. Assuming for the moment that each cylinder receives the same amount of fuel, balancing airflow in each runner does improve HP and lessen crankshaft stresses.

Speaking only for myself, I would tell anyone that its worth having the intake manifolds flowed to see what kind of benefit one might gain from such a process.

JMHO, as I have no "dog in this hunt",... I simply have learned what works and what doesn't.

[Jakester1168]

Thanks Andy and Steve....Do you think I should NOT go with Euro pistons and stick with stock? I really would like to increase my horsepower...Will I need to upgrade my DME (CPU) as well?....Thanks again.

[Steve@Rennsport]

Without knowing where you live and your local fuel octanes, I could not offer any advice about whether you should raise the CR or not,...

If you do, be sure and get a custom chip (911chips) made for your car.

[Eagledriver]

I have no doubt if you put it on a flow bench you'll see different flow rates. There is more than enough flow through each one for the engine. It's kind of like the K and N air filter. It will flow much more air than the stock paper filter. But the engine only pulls the same amount of air though both. If the manifold will flow 300 CFM through one branch and 500 through another and the engine only flows 200 CFM per cylinder then the "imbalance" is fictitious. If there is a pressure drop accross some branches of the manifold then yes they should be machined to get rid of those differences. The flow inside the manifold is also much different on a running engine than it is on a flow bench. A big part of the performace is the use of resonance to increase pressure at the intake port. If the size of the runners is altered you change the fequency of this resonance and may actually imbalance the flow. Keep in mind my arguments are theoretical while Steve has actual experience with building these engines so maybe there are gains to be made there that he has found through trial and error.

-Andy

[Jakester1168]

I live in the Tampa, FL area....I think I'm "safer" going with stock pistons, a chip upgrade, K&N filter, hollowed out cat and a B&B exhaust. This way I do not need to worry about any "pinging".

Christian

[hcoles]

I would very much like to see dyno charts for..
as is with uneven flow then modified for even flow - I guess this would mean the lower flowing runners were reworked to come up to the highest flow runner... I call this "free" power.
and
with the only change being different MAF to see better flow at higher rpm's - this assumes the AF and advance would remain constant for both tests... this could also be called "free" power IMHO

[KTL]

Not trying to steer the topic in another direction, but the MAF is also a know restriction related to throttle response- another "free horsepower" gain. Get the MAF stopgap out of the way, and then flow the manifolds, no?

[hcoles]

Kevin, good point... I guess you mean waiting for the barn door to swing open restricts the flow

[Eagledriver]

It's not waiting the the door to open that is the problem. It's the size of the box the door is in. The area of the metering box is too small to flow all the air the 3.2 needs at high RPM.

-Andy

[hcoles]

Andy, ok got your point. Yes, when you look at the size of the opening with the door swung open, it is surprizingly small. This is why I asked for dyno or flow or some sort of comparison between using a stock MAF or one of the other more open styles e.g. hot wire. Steve Wong sells one and there are a few others... or are there other "bottle necks" of similar magnitude?

[JeremyD]

Originally Posted by Jakester1168

Thanks Andy and Steve....Do you think I should NOT go with Euro pistons and stick with stock? I really would like to increase my horsepower...Will I need to upgrade my DME (CPU) as well?....Thanks again.

Good gas in Tampa Florida -

With that in mind - I would not worry so much about euro p & c's in this area.

That said - I would definitely extrude hone the 3.2 (and early 3.6) intakes. #1 for piece of mind - you sure don;t want one of your clyinders to go lean on you.

I wish I could find my paperwork - but when I did mine = there was one that was out of whack - by over 15% -

Of course if you really want to increase - go with the 3.4 p&c's -

what are you planning on doing with the cam?

Before Extrude Honing



here's an after shot

[Jakester1168]

I appreciate the help...but boy...now I'm really up in the air as to what mods to make...I was planning on staying with the stock 3.2 p&c's, adding a 911Chips chip, K&N air filter, and a B&B one in two out exhaust...and gutted cat....Thanks

[JeremyD]

With the stock cams - even with a 964 type cam - you will probably find the engine breathes fine. I would not do much with the cam unless you plan on changing out the exhaust - and I mean - dual headers / ghl or b & b or georges european headers 1 - 5/8" or larger. I would not waste the money on SSI with a better breathing 3.2. Steve Weiner has a nice option system of ghl headers with 3.2 type heater boxes.

With the stock heat exchangers - I'd look at a euro premuffler and a sport muffler like dansk, MK or fabspeed. combine with a steve wong chip for a cost effective solution. I don;t know many people who go out and buy the B & B single in mufflers - they are expensive - they really don't sound that well - and they are prone to splitting - especially the older ones.

Check out the engine Jeff Alton is building - 3.4 with ITB's
3.4 build part 2!

or Ralph's 3.5 carrera
3.2 to 3.5 - Part II

For comparison, here's my 3.4, in blue, compared to Ralph's 3.5, in red, compared to a bone stock 88 3.2 with a euro premuffler and stock chip, in green. (courtesy of Steve Wong)

[/QUOTE]

Lots of options some more expensive than others - probably a better question would be what is your budget and what are you going to use the car for?

[Jakester1168]

Thanks for the chart and "links" Jeremy....I use my 911 as a weekend driver no track time....I think for now, I will stick with the "cost effective" option...although I have a feeling this will turn into much more than that!!

[Jakester1168]

I'm new to this BBS stuff....can someone guide me through the steps on posting pictures in the threads regarding my engine rebuild?

Thanks

[Jakester1168]