Headers or iron manifolds?

[Supercharged111]

That sounds like a great build idea! One of the things that really turned me on to TPI was drivability, which is one of the nebulous qualities people boast about when their setups don't make power, but it does really have a lot of low speed responsiveness because of just how early that manifold builds torque. My IROC-Z when fully warm will drop into overdrive going up a hill at 1200rpm and it's totally fine. Stab into the throttle at any time in any gear and the rpms come right up with a big smooth wave of torque. Which is sorta replaced by noise and disappointment by 5500rpm, but hey in a truck that's redline. It cruises awesome, basically, and the data supports it:

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TPI makes a lot of power below 3000 rpm on a stockish 350, and you can feel that efficiency all the time.

That chart really doesn't woo me into wanting a TPI intake. Torque production at torque peak is great. True low end torque isn't really all that much better, and it all comes at a significant punch in the balls at the top end. That mini ram really is the best of both worlds on the stock engine.

 

[L31MaxExpress]

I ran a TBI with a dual plane, TBI with a single plane and the TPI on the same engine in the same vehicle. The TPI did not make more torque than the dual plane with the GM TBI until it was at 2,800 rpm and it only exceeded the dual plane until about 3,800 rpm. It was a very narrow torque spike on the TPI compared to the TBI on a dual plane. Above 1,500 rpm a single plane manifold was equally torquey with the TBI on top, very flat torque curve similar to a LT1. The single plane gave up about ~10 ft/lbs at true peak torque but carried power on another 800 rpm. No real peak, just a big flat plateau.


The manifold that still surprises me in its torque production is the L31 truck or L31 Marine manifolds. The curve is very flat until it drops off a cliff at 5,200-5,500 rpm. At any point under that except a little hole in the torque curve around ~2,000 rpm it is extremely flat. For some reason there is a dip in the airflow at a ~2,000 rpm at WOT. The dip can be seen on the GM Powertrain marine dyno chart as well.

A few screenshots of what the PCM sees running the 383 under the marine manifold. The predicted torque values while they may not be 100% accurate give a very good representation of the shape of the actual torque curve. The VE numbers are accurate to the way that GM calculates them, using ideal gas law, rpm and displacement.

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[CNRED]

Motor Trend Engine Masters did some testing on a small block Hooker cast iron headers. The performance was good while noise and maintenance was reduced. You might investigate the correct product for your 88.

 

[GoToGuy]

I ran a TBI with a dual plane, TBI with a single plane and the TPI on the same engine in the same vehicle. The TPI did not make more torque than the dual plane with the GM TBI until it was at 2,800 rpm and it only exceeded the dual plane until about 3,800 rpm. It was a very narrow torque spike on the TPI compared to the TBI on a dual plane. Above 1,500 rpm a single plane manifold was equally torquey with the TBI on top, very flat torque curve similar to a LT1. The single plane gave up about ~10 ft/lbs at true peak torque but carried power on another 800 rpm. No real peak, just a big flat plateau.


The manifold that still surprises me in its torque production is the L31 truck or L31 Marine manifolds. The curve is very flat until it drops off a cliff at 5,200-5,500 rpm. At any point under that except a little hole in the torque curve around ~2,000 rpm it is extremely flat. For some reason there is a dip in the airflow at a ~2,000 rpm at WOT. The dip can be seen on the GM Powertrain marine dyno chart as well.

A few screenshots of what the PCM sees running the 383 under the marine manifold. The predicted torque values while they may not be 100% accurate give a very good representation of the shape of the actual torque curve. The VE numbers are accurate to the way that GM calculates them, using ideal gas law, rpm and displacement.

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What tools or software are using for this display? This looks like something I could wrap my brain around.

 

[df2x4]

What tools or software are using for this display? This looks like something I could wrap my brain around.

L31Max can surely provide more info, but that appears to be the datalogging portion of the HPTuners software.

 

[Martin Evans]

Hello.
I am working on an 88, 4wd, 3/4 ton pickup.
It will be street driven and I plan on doing some towing and hauling.
Stock 350 is getting a mild cam, early 70's heads (1.94 x 1.50), 600 cfm carb, edelbrock performer intake, hei dist.
I am not looking to squeeze every ounce of power, but I don't want to cork this thing up, either...
I contemplated shorty headers, but it looks like I would never see my spark plugs again.
Are they that bad?
Are there cast iron manifolds that would do me better than the factory TBI units, power-wise?
I would like to run dual exhaust if possible, unless an aftermarket y-pipe could give similar results.

Thanks.

Shortys should give you a little more torque and power than stock manifold, but not as much as long tube headers. One advantage to shortys is that most of them are designed to bolt up to the stock exhaust. Dual exhaust with 2 1/2" pipes will give you about 40% more and faster flow than a 3" single y-pipe. An X crossover pipe will yield more torque than an H crossover and either one will yield more torque than no crossover pipe on a dual exhaust setup.

 

[Martin Evans]

The general consensus has been that shorty headers are not worth the hassle. However, some swear by them. If you are already replacing cracked/warped manifolds then maybe it makes sense.

A properly sized and plumbed single exhaust will always make more power and torque than a similar dual exhaust, no matter the engine.

Most have reported a greater gain with a less restrictive y pipe than by switching to shorty headers.

*Edit* my original statement of any vehicle will make more power with a single exhaust was wrong since many vehicles may not support the space or required to plumb a single exhaust properly.

Single exhaust is used by the manufacturer because it costs less, not because it's more efficient. If what you were saying was true, then the manufacturers of the Corvette and ZL-1 Camaro or Dodge Hellcat or Ford Mustang or Ferrari or Lamborghini or BMW or Mercedes Benz or Lexus or any other performance vehicle wouldn't be putting dual exhaust on their highest performance vehicles.

 

[Martin Evans]

if you do not want shortys get ram horn manifolds way better then logs.

headers like this may be an option but I do not think you will gain any thing from them other than sound

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He might gain a little. But if he is going to use that style, he may as well go with long tube headers since he is going to have to do exhaust work anyway. Personally, if decided to use shortys, I would only choose ones that mount to the stock exhaust flanges.

 

[Martin Evans]

I think the theory is there's less surface area of gas touching metal which slows it down, so the single of equivalent flow capacity has an edge, on paper. I think it would be tough to really prove that either way because each setup is going to make power a bit differently.

There is also a junction at the y-pipe which more than offsets any gains from reduced surface area.

 

[Martin Evans]

I do not know my 454 tbi has the o2 in the y pipe. did all 305 and 350 tbi engines (87-95) have the o2 in the manifold or did some get put in the y pipe like on my 454?

I'm not sure and my truck isn't at my house for me to check right now but I think the O2 sensor is in the downpipe in my 89 5.7 K1500