I can see that the "real" Indy Pace Car had a throttle body on an Edelbrock intake but could never find details. Has anyone else found anything on what they used??
I can see that the "real" Indy Pace Car had a throttle body on an Edelbrock intake but could never find details. Has anyone else found anything on what they used??
The indy pace car, doesn't matter.. WHY because it didn't need to drive on the street,, it needed to run at 85-110mph The intake and head ports are to big for low to mid rpm..street driving, the signal is lazy.. it's no different than my 355v8 with brodix heads it is lazy until 3300 rpm and then it's like you flipped a switch.. and the rpm gets the air moving fast enough in the ports,, and why EFI multiport set up's help intake tracks that are designed for mid to high rpm as the intake tract doesn't have to carry the fuel, and why sequential even does better than multiport set up in bank or batch. Your intake and head ports volume, causes the "pull" on the intake tract to be weak, so that TBI pressurizes the fuel toward the intake floor, and the air not moving fast enough to keep the fuel off the floor.. any wet intake tract will have this issue.. The large ports are only part of the problem.. The intake plenum volume, that is as big as many v8's with 4 cylinders sucking on it, at low rpm (under 3000rpm) makes it lazy, now add the ports that are big by huge . only hurts it more at street rpm use.. If you were able to turn the TBI unit 90* so the injectors sprayed toward the ports instead of the intake plenum floor, it help a tiny tiny bit.. TBI sprays the fuel in a fine mist, it doesn't atomize it, it uses air velocity in the ports to do that, something the SD4 doesn't have at low/mid rpm.. A vacuum 2nd carb would have less fuel delivery issues than a TBI will .. And why with that Pontiac motorsports, edelbrook cast intake, I'd drill the injector ports and run the intake as a dry intake tract..
[This message has been edited by E.Furgal (edited 02-11-2015).]
According to April 1984 High Performance Pontiac Magazine:
"During development, the test car was fitted with a Holley 2-barrel carb, but this was repelaced on the finalized version of the pace car with a special throttle body injection system using a 21/4 inch bore air valve. The injector itself is rated at 115 lbs/hour compared to the stock inector which squirts at a rate of 51 lbs./hour.Pontiac programmed a special computer chip for the pace car's computer."
I don't have any details on how well the car drove at low RPM, but I did see the specs for the Pace Car cam, and confirmed it was for an RPM range of something like 4,000 to 8,000 RPMs.
[This message has been edited by edfiero (edited 02-11-2015).]
Found it, it was in the tote labeled 'Fiero Intakes'
The capacity is relatively large. I got to 10 cups before the tape sprung a leak. At this point it was up to the 0.5in or so below the carb mounting surface. That volume would be about
(3.75" X 3.75" X 0.5") = 7.03125 in^3
Subtract the filletted edges that have a radius of 0.75in
0.5in(3.1415in * (0.75in^2)) = 0.88355in^3
= 6.1477 in^3
Add the ~10 cup capacity (144.375in^3) = total volume of roughly 151 cubic inches. Now THAT's funny.
In liters, that would be about 2.5 liters.
Took the picture just after it started leaking, that's why the level is lower.
The capacity is relatively large. I got to 10 cups before the tape sprung a leak. At this point it was up to the 0.5in or so below the carb mounting surface. That volume would be about
(3.75" X 3.75" X 0.5") = 7.03125 in^3
Subtract the filletted edges that have a radius of 0.75in
0.5in(3.1415in * (0.75in^2)) = 0.88355in^3
= 6.1477 in^3
Add the ~10 cup capacity (144.375in^3) = total volume of roughly 151 cubic inches. Now THAT's funny.
In liters, that would be about 2.5 liters.
Thank you for that - very much.
With the displacement of my engine at about 3.4L - now I'm wondering if the manifold is UNDERsized (not that I could do anything about it - no room for carb spacers).
[This message has been edited by fierosound (edited 03-11-2015).]
With the displacement of my engine at about 3.4L - now I'm wondering if the manifold is UNDERsized (not that I could do anything about it - no room for carb spacers).
Ya that's it, it's under sized.. maybe at 10000rpm
"...the volume of an intake plenum generally matches the displacement of an engine. This means if an engine displaces 500 cubic inches, then the volume inside the plenum is typically going to also have a volume of around 500 cubic inches. Under this type of design, ideally no cylinder is starved for air because the volume inside the plenum is enough to fill all the cylinders simultaneously.
If the volume of the intake plenum is not properly matched and is too small for the application, an engine could develop a stall or sluggish response from an engine at the starting line or after each shift, as combustion events literally draw all the available air from the manifold faster than it can be filled by incoming air. Engines with too small of a plenum may perform well at lower RPM but suffer as RPM increases."
"A plenum that is too large for the application could also cause too great a loss of velocity as the incoming air is slowed too much when it enters the plenum. This again results in a lack of power as the intake ports and cylinders won’t fill as fast as possible. A lack of velocity can also result in sluggish engine response – especially in the lower RPM range – and an improper air/fuel ratio."
[This message has been edited by fierosound (edited 03-11-2015).]
"...the volume of an intake plenum generally matches the displacement of an engine. This means if an engine displaces 500 cubic inches, then the volume inside the plenum is typically going to also have a volume of around 500 cubic inches. Under this type of design, ideally no cylinder is starved for air because the volume inside the plenum is enough to fill all the cylinders simultaneously.
If the volume of the intake plenum is not properly matched and is too small for the application, an engine could develop a stall or sluggish response from an engine at the starting line or after each shift, as combustion events literally draw all the available air from the manifold faster than it can be filled by incoming air. Engines with too small of a plenum may perform well at lower RPM but suffer as RPM increases."
"A plenum that is too large for the application could also cause too great a loss of velocity as the incoming air is slowed too much when it enters the plenum. This again results in a lack of power as the intake ports and cylinders won’t fill as fast as possible. A lack of velocity can also result in sluggish engine response – especially in the lower RPM range – and an improper air/fuel ratio."
Think about this for a minute.. using that 500cid exp. you have any idea how huge the intake would have to be plenum is the shared part.. not the whole intake.. nevermind that the signal to the fuel would be so weak., and air velocity would be junk. an intake like this, would do nothing but puddle fuel on the floor and have an a/f ratio all over the place..
your problem is the intake plenum and runners, the intake ports in the head are to big.. even with your 3.3ltr fuel is heavier than air, when the mix moves slow the fuel drops out of the air. The air doesn't get rocking in that intake till 2500-3000 rpm , the tbi doesn't help matters, as it's aiming at the intake floor.. This is the same reasons v8's with big intake port heads and big intake most times single plane, are dogs till the rpm's get to 3000+ , ya the tbi helps a little over a carb that requires a signal to pull the fuel.. the tbi just dumps it into the intake, if the velocity of the air is weak the fuel still falls out of the air.. and the engine is still a dog.. multi port injection takes the need of the fuel to stay in suspension from baseplate to valve to only injector to valve.. That is huge in an oversized intake tract at lower rpm, as it keeps the a/f% steady.. unlike the wet intakes that the a/f% are all over the place..at rpm below it's designed usage . That intake and head are fine if you are going to drive on the street at 3000rpm and up all the time, it was designed to "work" at over 3000rpm, not under it.. and why big intake,big head,big cams need loose converters and tall gears to get the engine into the useable power band.. A real exp.. my 357 cid v8 huge ports, huge intake 87hp at1500 133 at 2000 167 at 2500 245 at 3000 310 at 3500 420 at 4000 780 at 7800 800+ at 8700 and that is a v8 the torque curve is even worse making spit until after 3000 rpm.. between 3000 and 3500 it jumps 200+ft lb.. great for a stock car or sprint dirt car that never need to be in the under 2500 rpm at all. driving on the street was a pain, it load up, fart, cough, but go like a raped ape once you got it to 3000rpm. your head/intake fall into the same problem.. great for high rpm use, but to big for low rpm use as a wet intake.. put the injector right outside the head port and some of that goes away, it won't help the lazy air movement of the big port, but at least the a/f% will be stable..
Don't know where you are getting that intake sizing math.. but the edel. rpm dual plane intake has a small plenum compared to even the smallest single plane, yet it makes the most power and gives up almost nothing at the top.. on street engines.. even beating many tunnelrams.. the 80's thinking of big ports, big intakes,etc is long since died.. for the street.. racing bigger is better if matched to the rpm band.. Sadly I think your engine with a ported duke head will make more power from idle to 4000 rpm , I don't know about you but that sounds more like the rpm it'll see on the street most of the time.. not the 3000-9000+ rpm that package sitting on your short block is made for..
I'm following this thread with interest since I'll be running the same intake on my SD4. I'll admit that I know nothing on the subject of intake volumes and what is best, but I have also come across multiple sources that state that the intake volume should be the same as the engine displacement on naturally aspirated engines, and larger on turbo applications. So I am open to learning more on this subject and finding out what is going to lead to the best running car at Street RPM levels.
I would be curious to know what is the volume of the STOCK Duke intake. What is the volume of the intake on an engine which might be making equal power to the SD4 from the TBI era like a 4.3 V6 or a 5.0 V8. Obvoiusly more displayment than the SD, but with output in the same ballpark it might be an interesting point of reference.
Also I'd like thoughts on the following. If we assume the SD4 intake is too big, what size should it be? AND, what about filling the manifold with something like epoxy which would flow evenly over the manifold and reduce the volume to get the desired number. If this is do-able it would be far easier than having a custom intake fabricated. Something like this http://www.pcepoxy.com/our-...ste-epoxies/pc-7.php could be used to fill the intake and reduce its volume. This particular item may be too thick to pour since it mentions spreading, but there should be a similar product which is resistant to fuel which could be used to displace the necessary volume in the intake as needed.
[This message has been edited by edfiero (edited 03-12-2015).]
