dhirocz

I am looking for some info on primary tuning online, and cant find too much of what I'm looking for. I'm using an LT1 with a tuned port intake tuned to 3900 RPM on a 383, which will be running duals (3" collectors and extensions to a 2 1/2 pipe). I will be fabbing up some headers to fit my application, so I have some flexibility here.

Can anyone steer me to some info on this subject?

96capricemgr

What is perfect for the engine and what fits in the car are unlikely to be the same thing. Which makes finding practical information on this difficult.

jasonface

Try this, lots of info here
http://www.superchevy.com/technical/...exh/index.html

Joe Urban

If this were a high-end "get the last hp" engine, you might choose to use headers which boosted the output in an rpm range that your intake doesn't. For that kind of calculation, a program called "Pipemax" is excellent. It is available from Maxracesoftware. I found it easily on Google. It's only $40, so you might give it a whirl. It does a lot more than exhaust, by the way.

From what you described for your engine, Mr Vizard's information seems pretty good. From everything I have heard from some very successful engine guys, choose your primary diameter based on maximum horsepower and build headers that fit in the car and then choose your mufflers wisely. Magnaflow makes some very efficient ones.

Question for you: You said you were using a tuned port intake on a 383 LT1. If this is the GM TPI, isn't it kind of small for a 383, and doesn't it take some modification to make it work on an LT1? Maybe I'm just confused.


Joe Urban

dhirocz

You heard right. It is an Accel LT1/TPI intake base that was used for the superram on the LT1. They no longer make it. Alot of people think that TPI intakes are chokers...maybe at 6000 RPM. They are tuned...and have to have runner length and cross sectional area sized according to the peak torque that you are shooting for. Meaning, the same people who dont understand this and try to make them work outside of their RPM range are usually the same ones who complain they dont work well Normally, you have a little room to work with, since the powerbands are not very broad, but you can tune for both up to about 3900 RPM with long tube runners...and a little more with siamesed runners ported to the correct size and length.

Correctly built and modified, they make for great street engines with good economy. They dont make very good race engines though

Another great thing is that there is no coolant flowing through this particular intake and tuned port intakes are very sensitive to temperature.

It's actually been a very fun motor!

I'll have to check that out. I am looking to tune the exhaust to 3900 RPM as well, meaning I need a 51.9" primary tube, 1 5/8 ID. Wow. I would use larger primaries and call it a day, but that would mess up the tuning effect... off to do more research

Joe Urban

dhirocz,

I am curious about the use of this engine. If you are tuning for 3900 torque peak what are your flywheel torque goals? 500? 550? More?

Is the engine going to run pretty much at a constant speed around 3900? It seems to me that if you get much above that you will have a big dip in the torque curve and not much power.

Is the primary pipe ID or length more critical for tuning? Again I'm confused.


Joe Urban

dhirocz

It's just set up for a street engine.

The intake/exhaust flow bias, and airflow dynamics of these parts will produce a drop in peak torque at about 4000 RPM. The cross sectional area and runner length dictate peak torque with a tuned intake, and I am trying to tune the exhaust to match, to maximize scavenging. The rules are a little different for a toruqe motor than a HP motor.

It's a low RPM street motor. I am trying for 500 ft. lbs at the wheels, which is why I'm going to this extent with the exhaust.

Joe Urban

I didn't know there were "rules". Oh well, every day is a learning experience.

It seems to me that this engine will have a fairly short usable rpm range when running at full throttle for best acceleration. Doesn't that mean that you will be shifting a lot to keep the engine in the high torque area? Wouldn't that be just about the opposite of what makes a quick and easy driving street car?

I looked up some stuff on how much torque a 383 can make at 3900. If you use a 14% driveline loss for a stick tranny, 500 wheel torque is about 580 at the flywheel. That's about 1.52 ft-pounds per cubic inch which is pretty high.

I'm interested in the rest of the engine breathing needed to do this. What are you using for heads and cam?

Joe Urban

unstable bob

What kinda car is this engine going in, broh?

dhirocz

This is going into a iroc Camaro.

The rules I was referring to are the ones you follow to properly set up an intake tuned for maximum torque production at a given RPM. There are tuned and non tuned intake manifolds...the rules can be more strict with an engine with a tuned intake, since it is more vital that the engine components work together with themselves as a unit because of the characteristics of the intake. With an intake like an LT1, which is not tuned, they offer a good usable powerband, but since they are tuned to any one particular RPM range, they work well with a wider variety of components.

Tuned ports make far more torque than they do HP. I am not even paying any attention to HP at all...I will get what I get as a product of torque. Too many build engines with parts designed for torque, and they try to get horsepower...which to me seems foolish and counterproductive.

The ram charge effect in the intake at peak torque RPM with a tuned intake fills the cylinder to the point where it can be actually considered an 'artificial supercharging' effect by some, though I wouldnt go that far. I'm just trying to optimize this and see what I get out of it.

Is it alot of torque? yeah. But I'm trying some new things, just trying to get some more out of it. Call me the guinea pig

1989TransAm

Do a Google search for PipeMax and Larry Meaux. He has a program you can buy that will tell what size headers and collectors to use. From that you can design your headers. I'm using PipeMax to design the best shorty headers I can build.

Joe Urban

I appreciate your point of view, but from what I have learned studying people like Professor Gordon Blair, Philip Smith, and listening to some very smart engine builders, I can't agree with everything you are saying.

I really agree that the engine components have to work together no matter what kind of an engine you are building. In my opinion, that is where most people go wrong.

Every intake manifold is tuned if it has any runner length at all. Some tune for different harmonics than others. Generally the shorter runner intakes like the LT1 tune at higher harmonics than longer runner manifolds like the TPI or LS series. The lower the harmonic the stronger the ramming effect, so that might be why you said the LT1 manifold is not tuned. Of course it is.

A correctly sized and length manifold and the correct cam events really can produce a "supercharging" effect at the point of intake valve closing. Over 5 psi of "supercharging" is not uncommon. It happens all the time is very powerful engines. I think that is how some NA engines get well over 100% VE.

Professor Blair has written extensively on this. It took me a number of times reading his stuff to get much of a grasp of it, but it was worth the many, many hours required.

Horsepower is just torque produced at some rpm, so isn't the real goal of engine builders to produce the most torque in the rpm range they want the engine to run in? Maybe that is too simple an idea, but that's what I have come to believe. It is not an original idea with me. I have heard other people who I look up to say about the same thing. The first time I saw it written it was from a quote by Warren Johnson. I actually had the chance to listen to him discuss some technical stuff with one of his suppliers a few years ago. He is a very smart man, but shorter than I expected him to be. I think he deserves his title of The Professor.

I'm not telling you that you are wrong. I really think you should do what you want to do but I also think you should be aware of different ideas. Some of your ideas are not shared by the "experts" I have read and listened to.

I hope you succeed in your quest.

Joe Urban

dhirocz

I cant argue with that.

I suppose the reason they are not considered tuned is because with a 3" long runner, that makes for a very high tuned RPM. Not to mention, the CSA of that runner is too small at that point to be a good match. But yes, everything is tuned to a certain RPM. Guess it depends on how you look at it.

This intake has been tuned for torque by both CSA and runner length. 520ft/lbs isnt uncommon with a well built TPI stroker (engine dyno), though the HP sucks. I dont care about that though. There should be around a 1200 RPM split between peak TQ and peak HP, and after I get it tuned and dyno'ed, I will use that data to determine optimal shift points. They will be rather low, but again, it's a street engine. Throttle response, mileage and torque are my primary concerns. This comes at a cost though, since it required welding on the floor and on top of the intake, port matching, extrude honing to desired size, etc...lots of prep work here.

Since the exhaust lacks tuning for a TPI intake, and that is one of my biggest problems now, I figured by tuning the primaries and collectors for scavenging I could possibly aid the incoming air at peak torque. Even though reversion into the intake isnt a significant factor anymore, I want to evacuate it as much as I can to help bring in the fresh intake charge. This is going to make for a very long set of primaries and collectors though. Custom city there. I'll post some pictures of my 'monstrosities' when I get done with fabbing them up. I'm going to start next week.

Interesting thing to note, is that from what I gathered on here, at peak torque, a 350 TPI has 93% VE. Pretty good considering the flaws in the castings. I should be able to get a little ways over 100% at peak torque, and the exhaust is going to help here significantly. With 383ci, this will make the engine run like its over 400ci. Should be interesting. I cant wait to see what it does.

Regardless it I hit my target, it's fun, and it'll be a little different. I enjoy doing crazy junk like this appreciate the feedback!