Thread: Flow numbers Stainless PLOG and ported front exhaust manifold

Since I couldn't find any of this info anywhere I decided to have it tested myself. I have yet to have the rear manifold and a stock front manifold tested. This should be getting done soon though, just for comparison reasons. I originally wanted to start a "how fast on stock parts" thread but for the sake of me tearing into the engine, it would probably never happen thus never being close to full potential. What I will be doing is posting some scan numbers before and after each modification. Unfortunately I will not have track times, and probably never will in the future. This thread is for those of us that don't mind doing work ourselves to save a few bucks and keeping the car as reliable as possible for daily driver needs in all conditions. I live in Iowa. Weather can be unpredictable, along with street and highway conditions and the car needs to be up to the task at all times.

THese numbers will be as the manifold is in front of you, left to right

Plog- 186-200-182

Ported front manifold- 164-170-151



I have a half an hour into the ported manifold. I would have done a little bit more smoothing and polishing but the cheapo stone I had broke. I will be trying to do a little more with the low # port and probably leave it alone after that.

Did 3 back to back pulls yesterday. Was around 25*f outside. Pulls were in 3rd gear with car at 180*

All 3 pulls were consistant. 02 was 880, timing at top of 3rd was 10-11* IAT was around 38*f

the sewer. Didn't have a head to bolt them to. But at least there is some info to go by now. I bolted the manifold up after I did a bit more cleanup on it, nothing crazy. I will try to get scan numbers sometime before I do anything else to the car and see if there is any more timing added.

Took the car for a short ride today. I noticed no change in exhaust note but it must have opened a cork up somewhere because now I can hear the sc whine just pulling away from idle. I haven't gotten a chance to do a wot but part throttle feels much more responsive. I plan on getting a scanguage 2 whenever I get extra cash.

That's all I got for now. Maybe I just haven't driven the car enough to notice the intake louder since I gut the box and put a filter in it. I'm not going to get into a big debate about what I'm using for scan numbers. I have yet to see any threads that have any actual info on any modifications besides what vendors throw out there. So far I have 40 bucks in everything I've done.

Are you actually on the dyno or doing butt dyno pulls?

Who said anything about a dyno? If you want this stuff dyno'd I'd be more than happy to have someone else pay for it.

When you say you ported the manifold. Was this opening up the opening where the manifold meets the head only? If so, I'd think your flow numbers won't change much. Like you I went ported manis etc years ago. Although there was material added to my manifolds in the gooseneck area and supposedly they were ported further. Although I always wondered how anyone could get something into that area to port further. The gooseneck is likely the restrictive area on the manifold. Although I am not a flow expert.

That's kind of the reason for getting the manifolds flow tested. I took the one off my 15k car and the casting on the manifold looked much better than the one I ported. There may not be much of a difference. Won't know until they get put on the bench. Like I said in the opening post, this is more just to post some type of real info. If opening up the ports and smoothing them is a waste of time, then so be it. I'm not trying to prove anyone wrong here. More of an experiment I decided to spend my own money and time doing. It's winter time, I'm bored. The flange on the stock manifold looks more restrictive than the curves in the ports on the manifold. Besides, most of these cars aren't running that fast on blowers anyway. I doubt it's the front manifold that holds back the true potential of the 3800.

I don't see the point of flowchecking the manifolds if you're not bolting it to a head.

Bring me a head. I'll gladly test it the way you want done.

I have many. You are welcome to come get one.

If you look at the port on the head vs the manifold, I believe they match up pretty well. Never measured it though.

actually it will.

if your test conditions are the same, and your testing the manifolds in the same manner, then you want to see the % gained.

same thing with flow numbers on Cylinder heads. the CFM of a cyl head means nothing if you dont have anything to compare it to.....Every flow bench in the universe will give different readings. Ideally you have a stock head, and a modified head. Flow them under the same conditions, on the same flow bench and you will see the % gained.

You should only worried about the % gained over what you have currently have to show you the gains

How is what I am doing any different than comparing two different heads? If those of you that think I'm doing it wrong maybe YOU should spend your time and money doing this and share the results. All these tests are for is for manifold flow numbers and if a ported manifold is worth doing in terms of flow. I'm not hardcore into these cars. If this was for my grand national I probably wouldn't even bother getting flow numbers. I'd get dyno or track numbers. If it's only a 5hp gain in the end, so be it. I'll open my toolbox before I open my wallet.

And what's it matter if I use a head? Every single person on here thinks the downpipe and the front manifold is the major cork and what do all you guys think you have to do? Buy headers. All I ever read on this forum is that headers are the first mod that should ever be done because GM deliberately built these cars to explode if you put a cold air intake on them.

I'm sure those cheap ass speed daddy headers were built with head flow numbers in mind