formula to determine plenum size

[bill jones]

-I think there is a couple of things here that we need to know.
-#1 is Dave talking about part throttle or wide open throttle?
-#2 is what altitude are you at?
-It sounds like the issue here is one of drivability, being gutless at part throttle.
-like my wife says, why don't you put lower gears in it or get a different car that does runs like you want.
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-I don't think too many people ever seriously dyno test at part throttle to see what sort of power and accelerative power you can get with 14-12-10-8 or 6 inches of vacuum and do that at different rpm's and still not go to wide open when they test for acceleration.
-Maybe Dave should run it on a chassis dyno and get some numbers at part throttle and try to figure out a dyno testing method so that he can later on try to prove that any of his changes are indeed recognizable and valid.
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-According to Billy's formula (the way I read it) if you take 84,000 and divide that by 5600 the total intake runner lengths should be 15" long now and at 4000 they would need to be 21" long for wide open throttle ram tuning.
-I'd be curious as to what the hot cranking compression is.

[sc2dave]

no racing at all, i thought it would be easy to make one for daily driving that is driven under 4500.

[BillyShope]

Great story! I recall hearing that a long time ago.

Here's another old story you'll enjoy. (Perhaps we should start our own thread and simply swap stories.)

In '54, Ford introduced their OHV V8 and a lot of kids were running around with 2 door posts equipped with V8 and Fordomatic. A characteristic of these cars was a significant tire chirp as they upshifted to second. Quite impressive for the time! Unfortunately, what many didn't realize was that, in many cases, this chirp was due to a transmission malfunction and not due to torque that the tires couldn't handle. A valve body timing problem resulted in the engagement of both first and second gears during the shift. In other words, the tires were momentarily locking up and skidding.

I remember that throttle linkage trick. I had assumed that was done "in-house" at Chrysler, but perhaps your outfit designed it.

The common trick, to improve both performance and fuel economy, was to fiddle with the odometer and speedometer. I remember my '57 Plymouth would record a full 1.1 miles between the mile roads there in Detroit. That's a 10% improvement in fuel economy right there! I had access to the odometer gearing and speedometer error information for Chrysler, Ford, and GM. I can't remember whether GM or Chrysler was closer to "reality," (I think GM was slightly better) but I do remember that Ford was waaay off! Same with speedometers. I remember a "Motor Trend" test of one of the early Thunderbirds where the speedometer was registering 143 and the actual speed was 112. Cadillac, for some reason, was almost "right on." A portion of the speedometer error is to avoid litigation problems, of course, but there's no excuse...that I can see...to justify the odometer errors other than to improve calculated fuel economy.

[OldSStroker]

The common trick, to improve both performance and fuel economy, was to fiddle with the odometer and speedometer. I remember my '57 Plymouth would record a full 1.1 miles between the mile roads there in Detroit. That's a 10% improvement in fuel economy right there! I had access to the odometer gearing and speedometer error information for Chrysler, Ford, and GM. I can't remember whether GM or Chrysler was closer to "reality," (I think GM was slightly better) but I do remember that Ford was waaay off! Same with speedometers. I remember a "Motor Trend" test of one of the early Thunderbirds where the speedometer was registering 143 and the actual speed was 112. Cadillac, for some reason, was almost "right on." A portion of the speedometer error is to avoid litigation problems, of course, but there's no excuse...that I can see...to justify the odometer errors other than to improve calculated fuel economy.

GM speedos couldn't read low, but they could read up to 10% fast @ 60. Normal production was about 3-5% fast. Of course we sometimes "calibrated" speedos as well as tachs for magazine testers. Non-linear tach readings were subtle. 2500 was 2500, but 5000 could be 5500-6000 depending on who the mag was.

Odometers usually were the same % off as the speedo.

Back on topic: sc2dave, you aren't going to get much improvement in torque under 4000 (or is it 4500?) without a lot of intake manifold, valve timing and exhaust manifold tuning. Search for a torque curve for that SC2. The peak is at 4800 but it's not a very peaky engine.

As I said before, it already does very well in torque/L. That was part of the design criteria. Sorry, but there's no magic bullet or simple bolt on which is going to help that.

If you want to accelerate faster, shift it about 6000 or higher (WOT of course). If it's not accelerating hard enough at low rpm bill jones' wife has some excellent advice:

"-like my wife says, why don't you put lower gears in it or get a different car that does runs like you want.

[sc2dave]

this is mainly to "experiment" with.I know it won't make a big difference,even might not help at all. I don't know anyone that soups up engines anymore and i don't know anyone that owns any type of shop or service.That's why i ask these questions.

[1989GTATransAm]

Gee Dave, that was a quick reply.

[sc2dave]

I know,i tried to post but it kept telling me no more than 1 every 60 seconds.

[ian_12]

Sorry to revive an old topic, but I am in the same situation with a different direction. I have same type of car, 1.9l dohc saturn, and I am trying to come up with an intake manifold to make the most out of it naturally aspirated. The engine has good flat torque curve (I have dynoed one steadily above 105 lbs/ft from 2200 RPMs up to redline when it made 112 lbs/ft). I am looking to make power from mid range, 3500 RPMs, to redline which I may eventually increase to 8000 RPMs when I build the new engine.

As of now, it will run stock cams at stock timing. If I can, I might pick up some mild cams later (the car will be still a daily driver!) but my intentions are to remain with stock cams with the exception to use the intake cam on the exhaust side also. It has to be flipped 180 degrees and advanced 1 tooth which I think is close to 10 degrees.

Why am I doing this? I want to see what kind of power I can squeeze naturally aspirated from it. The intake side of the engine seems a bit lacking for power. I am guessing thats why the engine doesn't benefit much from pre-plenum modifications. I hope to not hurt the low end as it is good to get around everyday. Of course, looking for the WOT power without sacrificing part throttle and low end.

So my idea was to run a very small plenum with a vertical mounted throttle body utilize oval runners to match head and bend them up vertically slightly (short runners). I thought of making them equal length, and scavenge but wasn't sure if that is a benefit to the intake. I thought plenum size still mattered to fuel injected engines. So this is why I am asking how to design one for what I am looking for. So if you need more information, let me know. I can give just about anything needed.


EDIT: just to let some know who might not know about the engine. I saw someone ask original poster about the intake design. It is a single runner per cylinder and doesn't have a secondary runner control.

[tt_skylark]

After looking around I am still in need of some formula advice.
The motor I am working with is a late 60's Buick 350 V8, I fabricated some header/turbo manifolds.
9-1 comp
Iron heads
forged rods
forged pistons, coated as well
6 speed manual trans
in a heavy 65 skylark

I am on to fabricating the MPFI intake, I have come to land on 5.20 length 5 degree tapered runners. The plenum size is where I am at now, it is currently at approximately 365 cubic inches but I am unsure if I should include the runner volume in that total and what the plenum volume should be?
Any help would be great, or point me in the right direction!!!!
Thanks!
P.S. I cant figure how to shrink the pics to fit the size limit or I would show you

[Batto]

I use a few different ways. For instance because in one rotation only 1/2 the capacity of the engine is on intake gives 350 cu/2 = 175cu at say 100% VE. Most European street engines used this on mpfi. But of course when ever would you be driving at 100%? So I've noticed over the years street engines are using about 3/4 of 1/2 capacity of a street engine as a plenum. In fact I was checking little Peugeot 306 2l twin cam. The inlet didn't really have a plenum. It was like a set of exhaust headers in reverse. Lots of torque out of a little engine too.
And they are keeping the inlet manifold very hot.

[mag2555]

In regards to volume Keep this in mind on this type of non flat crank 16 valve V8, that being that at any moment in time that the motor is running you have 5 of the 8 Intake valves closed.
If you have a common Plenum then only 3 valve are drawing on it !

[pdq67]

About the 1.9L Saturn engine with the 200 duration cam in it.

You want more low end grunt then either blow her or install a 185 to a 190 duration cam in it. Or whatever the cam guy says to install to drop your grunt RPM.

Example here.

One of the best grunt cams that Chevy ever made is the old -929 hy-cam. at if memory serves me right(?), 195/202!

It's been installed in everything from a 195hp/283, 300hp/327, 295hp/350, and finally the 265hp/400... And as the engines got larger as time passed, grunt came in at a lower RPM..

I forget of it was Crane or Crower that made the "Baja Beast" line of cams that started off way small and got bigger as the engines got bigger. Might look into them? Or the old, "Compu-cam", line of cams. CC's, top of the page, "Pure Energy", cam falls in here too!

And remember that a little-bitty engine will GENERALLY take the SAME type cam as a BIG engine, ONLY ratio-wise SMALLER due to cubic inches!

pdq67

[RDY4WAR]

This thread is from 2005.

It was recently linked on facebook so that's probably why it got bumped. Someone didn't see the date.

I have wondered about this myself though. I'm putting together a 393w for a towing application in an F250. I've been debating building my own port injection EFI manifold. I've wondered how much of a difference the runner size and length and plenum size makes under 3000 rpm where there's no appreciable wave tuning to be had.