Sure, the weakest link theory has much merit. Naturally, if you have heads that flow 300CFM at XX lift but an intake that can only muster 100CFM at a given engine RPM and mainfold pressure, then the intake will restrict the flow. Similarly, if you add headers and keep the stock cats and muffler, you will certainly realize more gains with a high flow muffler and no/high flow cats. In some ways, the system is only as good as the weakest part, which is the way I like to look at it.
Picture a pipe system with water, say it's a 3" pipe and then it necks down to 1" and back to 3" agan. Does it affect the flow? Yes. Does it restrict the flow? Yes. Energy is lost by the fluid at that intersection that will not be recovered after expansion back into the 3" region.

Alas, I've been out of the academic world for too long to think about it, although I can recall thinking about things from your standpoint when I was there. Just drink more Pabst and you'll be OK .

 

First off, you are obviously nuts. You ever see that movie 'real genius' with val kilmer and the laser. You're that milo dude, when you winnin the frito lay prize, lol.

Anyhow, i'm not gonna get nuts with equations and such, thats why i got my degree, lol. Important concepts to consider may be like this though, kind of brain storming...
Conveniently, 305s and 350s share the same stroke and rod length, so that stuff actually is constant so at least piston acceleration is constant, eh? Let's say identical cams too so the valve is open the same amount of time for both, and that this goes down inversely with engine speed (less time at higher rpms.)
Now, what determines how much air gets into the cylinders. If it were simply total airflow then it would be easy to compute as FILL = AIRFLOW*TIME (airflow would be screwed up b/c of valve lift but oh well), but we know thats not true since VE is not a straight line down.
Other factors such as velocity. Aceeleration of the charge, then it's continued inertia as the valve closes. Inertia is directly proportional to mass so a long intake runner has more mass, so more velocity than a short runner intake. Good cylinder filling. As velocity increases, laminar flow effects against the walls impose frictional losses on the intake air charge, so a short runner has less surface area, so less friction. Also with velocity, turbulence throughout the intake becomes an issue, and if you've ever seen the inside of a TPI plenum, it was designed by cocaine users of the 80s looking for something cool. Here's my heavily modded plenum, including semi siameseing the stock runners through the flange. http://rain.prohosting.com/imwhom/junk/inj
And thats not even talking about the effects of ram-tuning and other acoustic effects. And the simple frictional losses of having so many bends. Any turn will always impose a flow/pressure loss. Now take a look at all the turns air takes in a TPI set up.

So in conclusion, i'm just a computer engineer, thats just a cursory overview of the way i see it. Seems much more logical to just test and observe. Don't get me wrong, some basic calculations come in handy. Such as total airflow numbers as you mentioned. Airflow and port size determines hp potential and velocity which you can make generalizations from with experience. You match these with intake design and cam (and engine/size) obviously and the total picture comes more into focus, again, expereience and generalizations can get you a lot of places. You just can't break it down to every equation and factor. Thats what scientists waste their time with. I mean, big bang, big crunch, who cares we'll never really get to utilize such a discovery, we can't even get engine paint that won't burn off headers in a arattle can.
If you're still reading....8675309

[This message has been edited by Ed Maher (edited October 22, 2001).]

 

D*mn laminar flow. I have no idea what that is, so I fold. However, next semester after I take the appropriate classes, expect to see this post again with numerous, even gratuitous, references to laminar flow. That was a pretty good response Ed. I can see why experimental data would be a bit more feasable.

Also, can anyone reccomend a few good books on the subject of fuel injection or just general engine mechanics. (If you say TPIS Insider hints you will be automatically disqualified.)

I would also like to draw attention to Ed's veiled, and seemingly unnecessary reference to Jenny, or 867-5309. What gives?

 

... WTF are you talking about Ed? You know all this chit and you can't find your boots? Come down and git your exhaust and driveshaft

Tim



------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

TPIGuy - Have you bought that book yet?

[This message has been edited by the roc (edited November 01, 2001).]

 

Dont worry, I will mail him a pair!!

 

Cool man, i'll owe you a pint. Next year at hot rod weekend?

 

Not to reply to my own post, but I got my 355 dyno'd last Friday. It has 11.1 compression (forged SpeedPro pistons), LT4 rods, studded 2-bolt mains, TF 23* heads, ported Edelbrock intake base, and stock runners, plenum, and TB, plus all the usual engine mods like headers, cat-back, K&N's, etc. I've also burned my own chips.

My best run was 257 hp at 5650 rpm and 347 lb-ft of torque at 3400 rpm. This is with only 28 degrees of total timing since any more gave me knock, even after richening up the PE quite a bit. I have 2 power peaks, the first one around 255 hp at 4400 rpm (see above) due to the stock runners, the second peak at 5650 rpm (other runs peaked between 5500 and 5700 rpm), with a dip in between centered at 4800 rpm and power dropping off after 6000 rpm. Once I finish porting out the SLP runners I just bought, I'll install them and go to the dyno again, maybe with the stock TB and a 58mm TB to compare them too. If you want to see a graph of the dyno run, go to:

http://www.mafb.org/mafb/registry/detail.cfm?id=21

and click on the dyno graphs in the Photos section. Quite a broad powerband for a stock-runnered TPI engine. I'm hoping to make some runs at the track on Friday so I can beat my crappy 13.5@100mph run by quite a bit. I had quite a few problems at the track that day, like a slipping/vibrating tranny, knock, and Drag Radials with too much air pressure in them...

------------------
Greg Westphal
'87 IROC 355TPI/A4

 

Wow, talk about a flat HP line. I think thats more a testament to the restriction of the stock runners than anything else. With the SLPs i'd bet that the dual peak effect will be gone and you'll see a *much* higher peak HP. Right now the runners are trying to make you peak low and early but your cam and heads just won't let it die.

 

Greg, that is probably the flatest HP line I have ever seen from about 3,500 rpm to 6,100 rpm. Based on your TQ line, I wonder what your engine was making below 3,500 rpm? I think that if you had measured below 3,500 rpm, that that TQ might even be higher.

I wonder what the HP/TQ would look like with a Miniram? Looks like your cam and heads want to go further.

 

You're right Ed, I'm figuring that the curve will improve from 4000 rpm on up with the SLP runners (with a nice port job to shorten them even further). It should look more like Mike Davis' recent dyno runs where the hp continues to climb up to the peak.

Glenn, the graph cuts off the torque peak at 3400 rpm because of the numbers at the top left/middle of the plot. All of my runs had the torque peaking at 3300-3400 rpm, with my runs starting around 2800-3000 rpm. To see what a Mini-Ram would look like, look at Mike's dyno runs posted by Traxion at the top of the page. Mike runs the same cam and very similar heads as me, we both have headers, and I have a little more compression (can't run as much timing, but more timing made a few less hp anyway).

------------------
Greg Westphal
'87 IROC 355TPI/A4

 

well in response to the original topic my tpi will rev until a rod flys out the bottom end or a piston pops out the through the head. hehehe

------------------
86',88',89' IROC-Z, 350 TPI, 700-R4

94' Formula, LT1, 6spd



[This message has been edited by mystikkal_69 (edited November 01, 2001).]

 

In reply to the main topic, my friend has the stock style TPI, and 3.23 gears. He is running 8.0's in the 1/8 @over 86 mph and is shifting @6500 from 1st to 2nd and 6200 from 2nd to 3rd. So yes, TPIs will turn and make decent power. That is one Tuned Port Terror

------------------
1986 305 TPI
8.0 @88 in the 1/8
**Soon to be 355