Those are great post Steve and Greg, good info.Good to see some real hands on ,can prove what they say engine builders.I think Gregs post about the ls1 intakes prove something most haven't thought about.If you have a good flowing head and stick a restrictive intake on it then it holds back the total flow thru the two.Its funny how such a restrictive intake(ls1 & ls6) can make the horsepower that they do.I think it shows that the way an engine pulls air in pulses as the intake opens and closes is not the same as a steady flow like on a flow bench,same as heads on an engine sometimes a bigger cc port will flow more on a flow bench but will make the same or less then a smaller cc lesser flowing head.
Also agee with you Steve that you should have a intake that can move the air that the head needs to flow what its capable of flowing,whats the point of a 350 cfm head and a 250 cfm intake???

 

I know Greg would like the intake that moves more air too although he can speak for himself quite well. The fact though is that better heads almost always seem to be worth something though whether the manifold is changed or not. The intake design and it's flow are very important however. The LS6 and the FAST are also the same basic design but flow much more and have bigger runners and a bigger plenum as well. They do make more power easily. Now put the great heads AND the great intake tuned for your app and you're even better off!

 

Yeah Eric, I do prefer that the manifold drop the head flow as little as possible. I just know from experience not to get all worked up over a flow gain on an LS1 type long runner manifold, and I know that I had better not reduce the port velocity too much while opening up any manifold in general.

It's easy for people to get lured into wanting maximum steady state flow numbers on an intake, but the problem with it is that once the manifold has been ported large enough in size that is does not drop the head, or drops it very little, it is then quite possibly too large to have the velocity necessary to run down the track. The engine won't pull up from a gear change as quickly on a drag car, nor will it come off a turn as hard on an oval track. Manifolds that are too large will trick you because they tend to dyno well on a water brake dyno, but don't accelerate well at the track.

The only way to know for sure is to go in reasonable increments, and try it at the track. When that R&D work is done, the map is made, and you can mass produce that port job for similar applications.

The flow/velocity requirements of an engine usually end up being a compromise on both sides. It's similar to a see-saw.

 

Hey Greg,I'm building a singleplane carburator intake for a drag race ls1 408,my intakes are 235cc"s measure 3.25 x 1.200 wide, making the runners on the intake the same size,how will this work?Powerband 5000 to 7500 plus.Short runners are about 6 inches, long runners about 8 inches.

 

Yep, I can still remember with Aaron's LS6 heads that everyone on the net thought we were fast because of that prototype aluminum manifold we had "that added over 50hp". We popped the plastic LS6 on after that and won the Pro-Stock class and then took out everyone in the King of the Hill shootout too with that black plastic baby! Everyone thought the stock plastic manifolds were down at least 50hp!

No one could say @(&* after that! Of course now with a better medium runner intake or a good sheet metal you can go faster.

 

On a single four intake, you DO want the thing to flow well in steady state. I assume this a sheet metal manifold you're building?

I would taper the port so that it's about 10% larger at the plenum.

 

That's the exact situation I was thinking about, but didn't want to add more to an already long post. Jud made a good call. He thought that if the car went fast with the LS6 manifold people would give credit to the manifold. It (LS6 manifold) wasn't worth all that much. I can't remember the exact numbers, but I wouldn't have wanted to live off the difference between the two.

 

Yes it aluminum,3\8flanges,1\4 bottom of runners and 3\16 intake runner sides.I haven" t put the top of the runners or plenuim on yet.Its tall.the runners are at a 45 degree angle from level and go into the intake inline with the intake port side walls(you can"t feel where the 2 ports come together,its port matched.It looks like a winston cup motor intake.

 

No, I took issue with:
but you later said:
which clarifies your statement so I no longer take issue

 

Greg,

If you had a LS6-style intake that could be opened up and ported, would you shorten the runner lengths? Not to increase steady-state flow of course, just to take advantage of the resonance at higher RPM. I believe the LS2 intake is 2 or 3 pieces epoxied together, so this may be a possibility without paying for a LSX.

I know the ideal runner length would depend on the cam and RPM range. Do you know the length of the intake valve from the edge of the port?

Thanks for any help.

 

Im still waiting on a decent answer on your first question too the head porters about trying to sell the guys with 5.3's and 4.8's the same heads as they sell for the 5.7 and 6.0. Maybe they really dont know wtf is going on. [/QUOTE]



we at tea try to make every set of heads the best possible product for the application as a head porter here at tea I have only seen two sets of heads for a 5.3 both of which where super charged engines they got FI chambers and 2.00 intake valves to better the low to mid lift flow on the small bore

to my knoledge we don't sell them the same heads as everyone else

and if we have in the past that is left up to sales people to explain, I think I speak for most actual "headporters" when I say I know what is going on.

 

we at tea try to make every set of heads the best possible product for the application as a head porter here at tea I have only seen two sets of heads for a 5.3 both of which where super charged engines they got FI chambers and 2.00 intake valves to better the low to mid lift flow on the small bore

to my knoledge we don't sell them the same heads as everyone else

and if we have in the past that is left up to sales people to explain, I think I speak for most actual "headporters" when I say I know what is going on.[/QUOTE]

Wanna bet?.Want receipts? Pictures? No supercharger here. I was sold a set of heads with a 3.90" bore for a 3.78" bore. I stressed also that I had a 3.78" bore. 2.00" intake and 1.55" exhaust valves. The intake valves shrouded the hell out of the chambers. I finally sold them and am having someone else do them. In fact Brian tooley told me that they have had many trucks with the same setup. The bottom line is that he lied to me, so did some of the other people I spoke to there. I guess it was more important to just sell a set of heads than to sell the right set of heads for my application.

 

Awesome thread, guys! I guess I'll bring it back from awhile ago -- I have a question about cyl. volume and how it related to intake port volume + runner volume. From reading this thread, I began to wonder if you might see power gains from making the port volume + runner volume = the cylinder volume so that air won't have to be pulled from the plenum during the intake stroke. I know the general knowledge is shorter runner is better for a higher RPM powerband, but what would be some benefits and downsides to making these volumes equal to each other, or maybe have the intake volume a little more than the cylinder volume. I'm running a forced induction setup on an engine that isn't an LS1, but I imagine the principles would be the same. In addition to my previous question, do you think that the results would be similar with a naturally aspirated engine and a turbocharged engine? Thanks for your input!
--Bryson

 

I have a question.

The stock 5.3 head when fitted on the stock 3.78 bore uses a 1.89 intake, 1.55 exhaust, valve. The valves are shrouded already.


The flow numbers @ .600 lift are 226in, 174ex,

The cfm requirement, has to be higher.

So working with a given bore size that is already shrouded by both valves, how do you get higher flow numbers that are needed?

Or possibly, do you leave it up to a larger camshaft to create some sort of balancing act?

Any opinions or guidance would be appreciated,

 

Before port matching an already good flowing 'D' port to a set of headers, I decided I should address the board for pros and cons...
Obvioulsy requiring attention to angles, but I have a feeling losing some of that big step from the end of the runner to the beginning of the header primaries may assist in getting rid of some of the turbulence in the beginning of the system. I'm more-so talking about the bellow (top and top-sides) part of the 'D'. I've done a LOT of induction fabrication, including a few sets of heads, but haven't yet touched on this idea. I could always make a 1/2" flange spacer and port-match the 'D' to the 1-3/4" header primaries if more recommended. Every ounce counts, right?...
Have any of you try-it-alls (that know what you're talking about...) experimented with this? Results?

Much appreciated.

 

Nose,
Contact Jere Stahl in PA.

Chris

 

Is Mr. Stahl a member here? I have only a day or so to make the decision, so quick info. from an experienced head porter will help get the ball rolling quick...Thanks again Chris

 

Nose, I read wrong, I thought you were talking about headers.

Chris

 

I actually spoke with a buddy of mine who is a mechanical engineer about this very topic.

He is amazed that we don't port match on the exhaust and make a smooth transition into the exhaust tube.

As we all know most headers leave a huge margin where they enter the tube. In mechanical engineering terms this boundary layer actually costs flow because it forms a hydraulic restriction. it also forms a are of turbulence in the dead spot where the port drops off into the tube.

Now, I was reading the other day and this is actually reported to be a benefit on a cylinder head. That step "allegedly" creates a boundary layer that reduces reversion into the exhaust port.

I have not checked to see which one makes power. But I know there are two perspectiv to it. I can't say which is correct as I have no data either way.

 

I was also woried about what removing that step would do for reversion. That's why It was asked before acted upon. I think it's going to be a hit or miss sort of thing. It'll be great information to contribute to this thread. I'll go the adapter route.

The one problem with testing this myself will be very much like tossing on a larger intake manifold w/o tuning for peak performance both before AND after. It wouldn't show the actual, or full benefitial difference. The cam design should have a lot to do with potential in such a case. If the flow bench shows noticeable improvements in exhaust flow, I will go with the spacer and have Chris design the cam per the specs with the spacer intact. I think he'd just have to cut back a tad more on exhaust duration. We all know the advantages of making the same or more pwr with less cam...

The exhaust system is a super high-flowing 3" dual X system with 1.75-1.88 stepped headers and firing sequence assist ('try-y') collectors, so maybe reversion without any backpressure in the picture will be less of a problem in this case. There should actually be somewhat of a vacuum in the system. Probably over-scavanging...The cam is going to be what some would consider fairly mild (probably around 236-240* intake @.05), so reversion because of that as well may not be much of a problem.

I don't believe only another half inch primary length (or any length after the runner) in itself will cause much of a performance conflict. If anyone objects, I can easily remove a 1/2" before I make the length perminant (welding). I have the collectors tacked to make the primaries between 30.5 and 31" (varies between cylinders). I guess I could leave out the weld and see what the dyno says during tuning...