This post is related to the ugly internal weld post:
https://www.thirdgen.org/forums/exha...pipe-ugly.html

There was a request at the end to see the results of the modified y-pipe. I'm not very happy with these results yet but they do show a difference between the original y-pipe and the modified version. I have decent flowing heads but still have the stock lower intake and stock plenum, stock air flow sensor, and stock intake ducts. I do have SLP intake runners and a 58 mm BBK throttle body.

This summer I replaced the headers and exhaust. The car had some 1.5 inch headers with 2.5 inch collectors that were on it when I bought it. It also had a true dual exhaust with 2.25 inch pipe but the bends were not done very well (not mandrel bent) and had some rattles. I wasn't crazy about the sound either. I knew the headers were too small for the 383 when I put it in but didn't have the money at the time to upgrade them.

So this summer I went with the hooker 2460's and the 16767 y-pipe with a Borla 3.0 inch cat back. The graph shows measured air flow with the original headers and exhaust (dark blue trace), the new headers, y-pipe, and cat back (red trace), and the modified y-pipe (light blue trace) which now has 3.0 inch mandrel bent pipe from the modified y-pipe all the way back.



So you can see that the new headers with the unmodified y-pipe reduced the flow past ~ 3500. With the modifed y-pipe to 3.0 inch outlet the air flow is better across most of the RPM range. I was a little surprised that the increase wasn't larger after fixing that choked off cross section.

Probably should have made it more clear that the "stock" condition here is referring to the hooker y-pipe as delivered (red) vs the modified version with 3.0 inch outlet (light blue).

 

I'm curious, how did you measure airflow vs RPM? Was this done with the car running?

TA

 

measurements made using autoprom in second gear

 

The problem with that is that the exhaust is almost certainly not be the limiting factor anymore. For example, if the intake is restricting the engine (and we know it is), the exhaust cannot flow more air out of the engine than the intake can supply in. You are not measuring the flow increase of the exhaust, you're measuring the increase in flow of the entire engine system. Take heart, if you get a good base/runners and do the siamesing mods, after proper tuning you will think you were launched off of a aircraft carrier catapult.

TA

 

The stock lower manifold is the bottleneck now.You have a big ole TB,larger runners going into a stock base.Really gonna choke a 383.

 

So what kind of flow can the stock lower intake support? When you say a good base, how much flow would that be and which one do you think is best? Are there any that can be purchased as a stand alone, as I already have the SLP intake runners and a ported plenum. Looking at some of the threads on this it's not at all clear.

 

If you havent already do some searching about the before mentioned porting to the SLP runners.Have you ported the (upper manifold)plenum?I`m sure you have if you have those runners and a 58 mm TB.Look at the edelbrock or TPIS manifold base.They are the same casting I`ve heard but the TPIS might be cleaned uip a little bit more and a lil more expensive.I dont think the accel/SupperRam base is made anymore but you may be able to find it on ebay or something.Check out the FIRST system.I cant remember if the base is compatible withother TPI components but its supposed to flow the best IIRC.It has a monoblade TB and is pretty expensive.For your 383 have you considered any of the higher flowing type intakes HSR,SR,MR.I just saw a complete HSR sell on ebay for about 450 or 500 bucks last week.Any of the LTR setups will PROBABLY be a restriction on a 383.As for airflow I dont have any numbers but I know you can find them in the archives if you look a little.Someone may post up with some.

 

Check out this thread:
https://www.thirdgen.org/forums/alte...fications.html
I know it's for a superram, but pay attention to how the base is welded up around the injector holes and opened up at that pinch point, it seems to make a big difference even on aftermarket bases, as 383s are very air hungry.

TA

 

very cool, thanks

Looks like this is where I need to focus my efforts next. What kinds of mods are required for the intake ducting then? Is it pretty much home built cold air intake or ram air hood?