|01-07-2005 12:59 AM|
There is only one way to reasonably identify if the intake is a restriction to the heads, that's on a flow bench. Even then, you don't get a clear picture on a carburated appplication since in actual use you will be flowing both air and liquid not just air. But, even so on the flow bench with the carb bolted to the intake and the intake bolted to the head you can see trends. In some applications we see no difference. A couple of weeks ago on a Ford head with the new Edelbrock Victor EFI manifold we lost over 20 cfm from .500 lift up. So that intake is getting some work done to it. That's a ton to leave on the table. Worst case on a serious street application we like to see less than 2% change max.
Intake runner size and plenum volume play a huge role in making power, so it is something to think about in a stout build up. Stout being 450hp+ small blocks and maybe 550hp+ big blocks as some general guideline. In my intake I have about $1700 invested in both the bare Super Vic plus porting work in the runners and plenum plus the cost of the EFI parts. Since I run EFI the inside of my Super Vic looks nothing like the inside of a stock one. It's all setup to flow air only. Having 454 cubes also meant everything has to be much bigger to keep velocity down. So in answer to the question on EFI, your correct. The intake needs/can be optimized to flow air. What changes need to be made? You really need to work with a cylinder head person directly on that. They will want the heads and the intake. You do want to get those bung out of the runners though.
You want to minimize turbulence in the intake as it slows flow. That is the gripe a lot of racers have with the plenum design on the Super Vic. The wings induce too much turbulence making the turn out of the plenum and they flow like crap, as we found out again two weeks ago. A Victor Jr. or Victor E is a better intake choice in many applications.
Working the inside of the plenum is all based on the cubic inch and cylinder head flow of the engine and heads. Just opening up the intake plenum may not make a difference, and may really hurt you as cylinder distribution can be affected. We have a person with Edelbrock in their R&D department that we contact with specific application issues. I wish I could post his name but I'd be shot. What I would suggest is if you think you have an application out of the ordinary and need some advice on what to do, contact Edelbrock and see if they can guide you in the right direction. If you have the flow data prior to calling then you might have some luck getting with someone who deals with it every day.
When our guy is finished porting an intake for either EFI or carb it is basically similar to a CNC or sand rolled finish inside.
Extrude Hone is alive an kicking. Just saw them at PRI in Indy a month ago. Still whore house priced but sometimes it's the only option if you have to run stock stuff and can't get the porting tools in there. It does the same things as acid porting only leaves a very smooth finish on the surface.
Brezinski is about an hour from where I live. What they specialize in, and do a very good job at, is acid dipping. We do this all the time as well, in restricted iron cylinder head and intake circle track motors. Basically you use a much more potent muratic acid mixture and fill the intake runners or cylinder head ports and let sit for a period of time. The port openings are sealed with special rubber plugs you fabricate up to contain the acid. The result is the acid eats into the ports, runners, plenum and opens them up all while keeping all the original casting marks intact. Therefore it still looks stock, expect it's bigger. This is beneficial as on a lot of these restricted motors we spin them to 7000-7500 RPM. We need as much volume as possible.
As for matching an intake to a head. If the intake only has a slight mismatch into the head and the intake is smaller than the head there is very little if any change in power with this minor mod. If the intake is bigger than the head and the airflow hits the wall of the cylinder head that's not the best and should be fixed. Air doesn't like to hit a wall.
|01-06-2005 09:30 PM|
|01-06-2005 09:26 PM|
I think I somehow got confused from another post or from PM's. I have been talking EFI with another member and for some reason I thought that this engine was going to be MPEFI.
Carry on......I agree with the not polishing
|01-06-2005 07:28 PM|
Rough Ports (was in a few in the Navy)
What would probably do a better job would be one of those emery paddle wheel sanders with some 20-40 grit, run at a very low speed.
This would give you more of a cross-hetching pattern as you would see after you run a glaze buster down through a cylinder.
|01-06-2005 07:24 PM|
If I am in search of a rough surface after polishing an intake port in cylinder heads, I just lightly grind the surface with a rough stone so it looks like a roughly honed cylinder wall. I keep the scratches perpendicular to airflow to help with suspension.
Thanks for all the extra info on manifolds though, was not expecting a huge discussion on a simple question Nice to see lots of ideas.
|01-06-2005 07:09 PM|
As for the sandblasting runners and ports, That would probably leave the kind of finish I was talking about, a florentine, rather than mirror polishing them.
The process that I had seen articles on was that they were usingvery dense sand slurry (consistancy of mud) to actually enlargen the runners. The last time I saw an article on doing that was in the early 80's, and it was $600-1000 bucks to do a manifold, and about double for heads.
The last time I checked, an RPM Air Gap was a carbureted intake, not an FI unit.
Willys36, Im glad you are the aeronuatical engineer on this one. You did a lot better job of explaining the laminar air flow thing than I could.
|01-06-2005 06:54 PM|
Willys, the method was called extrude hone, and I think an abrasive clay like media was used.
I've done something similar to this before, which is kind of an extreme sand blasting operation. High air pressure and some fairly rough sand ran though a port for a period of time.
I've even finished hand port jobs with fine white silica sand, and it really smooths the work out.
The rougher sand does more "removal" , and the finer sand leaves a cleaner finish. I usually do this after hand porting, because the effectiveness works better on iron that has already had the factory porous cast removed.
It will surprise you how much you can change the port by doing this. Does it help? I think it does to a small degree. After all, if you are blasting sand suspended with air through a passage, the airflow through it is similar to air/fuel mixure passing through the port on a live engine.
I like the asthetics of my work after blasting it, but that's more fit and finsh than anything else.
Alot of racing rules prohibit this practice as well as acid porting
|01-06-2005 01:30 PM|
|johnsongrass1||Willy, Some circle trackers of old are stilll doing this to there exhaust manifolds or those bound by rules with stock two barral intakes, steel heads, No porting is often a rule to help keep cost's down. Everyone knows rules just drive up the prices of power, leaving the poor man to suffer against a team with money. I currently know no one who does, for I've never asked for it. But I do know its still around.|
|01-06-2005 12:51 PM|
|01-06-2005 12:46 PM|
Max and willys,
You are missing his point. On a MPEFI intake there is no fuel in the intake. Fuel is injected at the head entry point. So, intake port finish is not needed to keep fuel suspended. Only in the head is this an issue.
|01-06-2005 12:32 PM|
Re: polishing intakes
There are several ways to induce and sustain this turbulence. One is to have the gas go around a bend which induces turbulent flow. Most manifolds don't have sharp bends so the only other alternative is to add roughness to the passages. Envision the gas flowing in a conduit and the molecules in direct contact with the conduit wall are by definition not moving. The next molecule out is moving a little but due to friction with the stationary one, it is not as fast as the next molecule out. Speed of the molecules increases as they are spaced away from the wall. This virtually no-flow region is termed the boundary layer and the thicker this is, the worse it is for an intake manifold. Continue looking at the molecules as you go to the center of the flowing stream and you will find they get faster and faster until the very center ones are fastest of all.
There is a definite break-over point in any flowing stream which is a function of fluid viscosity, velocity, and conduit roughness where fluid goes from 'laminar flow' with a very large boundary layer where there is no turbulence to the desired full turbulent flow which nearly eliminates the boundary layer. In the former case, gasoline will tend to condense and drop out of the stream causing many problems so it is good practice to design the intake runners with significant roughness.
Incidentally, this is why golf balls are designed with the rough surface - by breaking up the boundary layer of air flowing over it's surface, the ball will fly significantly farther than a smooth ball. This drag or resistance to flow by very smooth surfaces can be overcome with aerodynamic design which is why airplanes and race cars can be smooth and go fast but for shapes that can't be designed that way like golf balls, rough surfaces are preferred.
|01-06-2005 12:19 PM|
|Big Blocks Rock||Thank you all for the extra advice.|
|01-06-2005 11:42 AM|
Right, it's not for the novice. I've see a lot of butchered intakes at swap meets. The norm for the street on a duel plane is one inch deep and two inches long in the center of the divider. other than that it would take a lot of flow testing.
|01-06-2005 11:10 AM|
I highly advise against polishing intake runners both in the intake and the head. The problem with polishing them is that it allows the fuel air mixture to become unsuspended, costing a lot of HP. What you want is a florentine finish. Something to do with laminar air flow, and since Im not an aeronautical engineer, I wont try to explain it. What I do understand is that you need a certain amount of roughness in the surface of the runners and ports to keep the fuel air mixture suspended.
Polishing on the exhaust port side, however, is an excellent idea.
besides not needing the rough surface to keep the fuel air mix together, polishing the exhaust side reduces the ability of carbon etc to cling to the runners causing restriction.
I heard a lot of hype about extrusion several years ago, but the cost was so prohibitive, compared to any benefits. I think it kind of died on the vine.
You dont want to just go in and start cutting down the divider in a dual plane, indiscriminately.
There is an outfit in Wisconsin called Brezinski that specializes in doing this with factory steel intakes for stock car racing, where stock intake manifolds are required. They also do a lot of other internal work in the intakes.
Ive talked to them a few times. It takes a lot of time and work to get that just right.
Take too much and you mess up a manifold, take too little and youve done nothing.
Plenum chambers are a very finnicky area to play around in.
|01-06-2005 08:40 AM|
On this subject, does anyone know if someone is still offering the 'extrusion' process where they force a paste loaded with carbide grit through a manifold, thus opening up the passages? It was hyped in the rod magazines for a time in the 90s and I have heard zero about it since.
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