Blue Thunder intake manifold porting

You have no experience with the Shelby manifold, yet you are convinced it requires "straightening out"? What if "straightening-out" the manifold involves cutting down the plenum divider, softening low rpm power, and reducing manifold vacuum? Will that be an acceptable trade-off for you? What if the same improvement in horsepower could be achieved by merely blocking the manifold's exhaust heat passage? Blocking the exhaust heat passage would not soften low rpm power or reduce manifold vacuum. The manifold is 40 years old, surely if there's a problem its would have been documented in a publication somewhere. Have you read the advice recommending this modification from more than one source? If the manifold were such a dog why would it be so well liked by old farts like me? Wouldn't it be wise to use the manifold as-is before you have it modified, so you can compare the performance before and after?

If you must have the manifold modified, I can recommend somebody who is a professional at doing that work. He's a guy pro-engine mechanics send their work to. The guy you're looking for isn't him.

I agree with George. Leave it alone and run it as is.

If you are looking for more power out of it, and I don't know if there really is anything much to be gained, other than entirely ruining the manifold, get the Blue Thunder Pantera version and send that out for modification.

As a matter of fact I am quite sure the BT is already available from them with the plenum divided modified. It's just a matter of the size of the "balance port" (notch).

I think if you want to try something different, look for the Dominator version and use the newer Holley 750cfm Dominator on it.

In all these years, still haven't seen one Pantera running that set up.

If for no other reason, that monster carb would definitely draw some attention and is plenty big enough for a single carb induction.

For some strange reason, Pantera people aren't impressed by Shelby logos on their cars. They seem to be more in sympathy with the Commodere's perspective of American-Italian relationships? Best not go there at all.

I do have personal first hand knowledge of that manifold. I ran it on a Boss 351 with a Shelby solid lifter cam and a Holley 4779 750 dp carb.

It is impressive to look at but I personally found that the Edelbrock Torker way out performed it.

Now that's an interesting observation since all current dyno testing has shown the opposite in results and that the Torker is one of the worst manifolds built for the Cleveland.

I tell you this since you might want to qualify my info and I seem to be a contradiction to whatever seems to be documented scientifically?

I too am also an old fart, with lots of grey hair...but I got hair, lots of it! So take any advice here with a grain of salt, and don't forget to throw it over your left shoulder too?

Also remember that there is usually one in every group that seems to be the burr under the horse's saddle or maybe the hand up the Mona Lisa's skirt? Hey...why is everyone looking at me...and why do think she was smiling anyway?

Check for Dan Jones postings on his tests for 351C products.

Here's a good link.

http://www.network54.com/Forum...+Blue+Thunder+Intake

quote:

Originally posted by George P:
You have no experience with the Shelby manifold, yet you are convinced it requires "straightening out"? What if "straightening-out" the manifold involves cutting down the plenum divider, softening low rpm power, and reducing manifold vacuum? Will that be an acceptable trade-off for you? What if the same improvement in horsepower could be achieved by merely blocking the manifold's exhaust heat passage? Blocking the exhaust heat passage would not soften low rpm power or reduce manifold vacuum. The manifold is 40 years old, surely if there's a problem its would have been documented in a publication somewhere. Have you read the advice recommending this modification from more than one source? If the manifold were such a dog why would it be so well liked by old farts like me? Wouldn't it be wise to use the manifold as-is before you have it modified, so you can compare the performance before and after?

If you must have the manifold modified, I can recommend somebody who is a professional at doing that work. He's a guy pro-engine mechanics send their work to. The guy you're looking for isn't him.

That's quite an assumption George, considering you don't know me, or my experience with this intake or anything else!

quote:

Originally posted by Rob F:

... That's quite an assumption George ...

Yes its an assumption. I didn't think the statement was inconsiderate, unkind or insulting. I didn't mean for it to be. It has been my experience over the last 40 years that anybody who has ever used the manifold has never felt the need to modify it, most people are quite pleased with the performance. Hence my assumption. I offered my comments & questions just in case you were willing to ponder another way to go about doing things. Its the same advice I'd offer my son, a neighbor, or my best friend. But I never expect everyone to agree with me.

Seriously? You make a rude opening statement like that based solely on your perceived idea of my lack of experience with the item in question, and you feel it was NOT inconsiderate or insulting? WOW! Different kind of schools on your block I guess. I'm almost 70, and yes, I do have a bit of knowledge under my belt from MANY years of schooling, training, and experience! I've also been building motors and hot rods for better than 55 years, but I'm still willing to learn if someone has something worthwhile to say! I appreciate any input, advice, or ideas based on scientific evidence and real life experience. I do NOT however appreciate being insulted, especially by someone who seems to believe they have all the answers! I know I don't.

I honestly don't see the rudeness in the comment, perhaps you're right about the schools on my side of the block. If you feel you've been publicly insulted by my comment, then please accept my public apology.

Reflecting upon how I expressed myself I see another way I believe I could have expressed the same thought. I will try to do better in the future. Like you, I'm willing to learn.

HaHa George is pretty passionate about bastardizing the center divider of a dual plane intake. the cut down divider modification goes back at least to Holman Moody, they specified lowering the divider by 1". more recently Edelbrock Performer RPM & Airgap intakes feature a lowered center divider, i'm not sure how much has been removed as I have not handled any?

it's fair to say that the mod does improve top end capability, but at what cost to low end & midrange? with a manual trans you'll have less of a chance to notice what a stock auto trans car might experience in off the line /low throttle angle driveability

basically the mod creates a hybrid 1.5 plane manifold. remember that the more 'crosstalk' you have in the plenum, the larger the carb will act. instead of each side of the plenum accessing only 1/2 of the carb's rated CFM capacity each bank will be pulling from more near the total plenum & full CFM capacity

I am also not keen on cutting down dividers, they are at a certain height from the plenum base to the carb flange and who knows what strange internal turbulence could be created between upper and lower plenum surfaces with a reduction in the divider height. You'd need a dyno, lots of manifolds and lots of money.


Something i have done that seemed to work quite well at increasing a dual plane manifold's upper rev range without effecting the manifolds performance otherwise was adding a 2" open spacer below the carb.

With this set up you leave the manifold's divider as is (maybe just round off the sharp edges) and each plane of the manifold can draw air from both sides of the carb.

The best thing is if you don't like it you can just remove it and you are back to as it was.

I did this with a stock 2v cast iron manifold that had a 4barrel carb flange (these strange things exist in Aus) and the result was very noticeable and i left the spacer in place.

Yes the spacers can be used to a degree to tune the manifold.

The biggest reason to use the Blue Thunder manifold on the Pantera is that it is very close in height to the stock iron manifold.

That means that the entire assembly of manifold, carb and air cleaner will fit under the rear engine cover that the Pantera has.

A 2" high spacer would push them well past the top of that cover.

If one decided on that route than there are a bunch of much better manifolds to pick than the Blue Thunder.

The car does definitely look cleaner, i.e., better from the rear with the original cover over the engine.

Of course I'm partial to a gaggle of Weber carbs hanging out the back.

Some would akin this to a poor woman that has to bear the burden of a DD top with her cups constantly running over and find that very tacky?

Not me.

quote:

Originally posted by PanteraDoug:

If one decided on that route than there are a bunch of much better manifolds to pick than the Blue Thunder.

Doug, you have quoted the intake manifold comparison article published in the October 1993 issue of Super Ford magazine several times lately. I would like to point out that in that same article an unmodified version of the Blue Thunder manifold came in a close second place in terms of peak horsepower. It was only 8 BHP down to the Holley Strip Dominator. And it was 10 BHP ahead of the Torker. A modified version of the Blue Thunder manifold was also tested, the plenum divider was milled down by 1 inch, that manifold was 19 BHP down compared to the unmodified version, those results have been the reason behind my trepidation about cutting down the plenum divider of that manifold.

I wouldn't mill it down either. Think it might have potential to play with the size a little though but the problem is once you went to far, how do you put it back?

Why do you think I went through three of them?

I know it is definitely better off of idle than the single planes, very stock like, so that would be a better selection for an everyday car like when you had your Mach 1 and had to take it to work everyday?

These days though how many of us are worried about having to drive the Pantera in 5 oclock traffic everyday?

The Torker was a PITA that way. Lots of slipping of the clutch to move the car, then at 3500 the tires come off the ground like it's a big block.

I'm not trying to talk anyone out of anything Big Guy. I think sharing experiences helps people make their decisions about which way to go?

The much-discussed 'poor distribution' of corner cylinders vs center cylinders in V-8s is the subject of a current Hot Rod magazine article. They dyno-tested Comp Cam's new 4-lobe camshaft grind with 2-3 more degrees of intake lobe separation on the corner lobes relative to centers, ala NASCAR cams. The intake flow balance was substantially corrected; on a 500-horse dyno-mule, they got 9 more horses- for the cost of a hydraulic roller cam, short-travel roller lifters and beehive springs. They also got 7700 rpms out of the special hydraulic roller cam. To my way of thinking, the extra 2% power is hardly worth the trouble unless you're racing for money in a restrictive class. The extra rpms probably came as much from the short travel roller lifters and beehive springs as anything, but I could be wrong.

If you still want to see if it's worth the trouble, another cheaper, simpler way NASCAR tuners use to balance intake flow is with 1.80:1 ratio roller rockers on only the corner cylinder intake valves. This gives the same extra 2+ degrees of lobe sep plus a tiny bit of extra lift, without changing cams. Harland Sharp makes both 1.73:1 and 1.80:1 street roller rockers for a 351-C. Single rockers are about $25 each and if you already have a set, you only need 4 more to do this experiment. Let us know how it all works out, please.

There have always been dynos around, just not as prolific as today?

The first flow bench I saw was in 1976 or so. First dyno was in the mid 80s. Shelby was dynoing his race engines in '67 in the race shop in LA. I'm sure that was a present from Ford?


This debate over which manifold is better because one makes 8 hp more than the other, on the dyno, to me needs to be put into perspective. I am having difficulty with the concept.

I always thought I couldn't even tell 10hp. After all what that comes down to is a little crisper engine with new plugs, points and air filter.

My dyno was seat of the pants and if I was lucky enough to have the car running well enough on the drag strip and consistent enough with driving it to see the difference in 1/4 mile time.

Those were the days that if you had a 428cj Mustang, if you took off the air cleaner assembly, you could pick up 2/10ths in the 1/4. I may be mistaken but that equates to something like 80hp on the NHRA hp chart doesn't it?



I can only talk about my experiences. The difference between the Torker and the Shelby manifold, and ok, throw the factory manifold in there too, were really big. The Torker was better than 2/10ths over the Shelby manifold in the !/4.

The dyno now says the differences couldn't have been 10 or 15hp? The differences were like you had three other people in the car vs. just you. I don't believe the dyno now. I believe the time slips. 10hp doesn't act like that and give you 2/10ths better time.

On the track, the differences are substantial, AND the Torker in particular has never shown it is the top of the heap. Not so for the Holley Track Dominator.

I never ran the Holley Track Dominator personally but everyone I talk to that has and even dynoed them, the Holley manifold has always shown more and 1 to 2/10ths in the 1/4 is not uncommon.

Equate that absolutely any way that you want to. To me the dyno is just verifying what I thought was happening, that one manifold is better than the other BUT there seems to be a translation problem between dyno horsepower and results on the track? They don't come close to agreeing.



Exactly what the fascination now with the Shelby/Blue Thunder is, is beyond me at this point?

To me the value of it is it is a little better than the stock 4v manifold and it fits under the engine screen of the Pantera. It didn't come close to the Torker. It had NO top end by comparison, but was decent off of idle but much too much stock like. It would probably be a good manifold for an automatic transmission.

There have been a plethora of manifolds made for the Cleveland since those days. Granted most now don't want to deal with the iron 4v heads since the same has happened with new heads being offered but some manifolds can be applied to the iron 4v's with some work.

There is enough "recent" dyno data already by Dan Jones, like it or not, that should indicate some of the good, the bad, and the ugly.

If someone wants to spend time and money on trying to take a mediocre manifold by todays standards and make it run with the best available now, who's to stop them? Good luck pal.

The state of technology 35 or 40 years ago left room to find a lot of little tricks to be discovered by clever people like Smokey Yunick. Computer technology has really minimized that possibility now. Not eliminated it, just minimized it.

Tricks are now filed as models, updated and incorporated into new designs.



I'd guess that if someone Extrude Honed a Blue Thunder intake, there would be something more than just a few horse power to be gained? The practical question is how much cost per horse power is the number at now?

I saw the bill from Extrude Hone for a set of 289HP iron exhaust manifolds. It was $700. Somehow I suspect that the cost on that one was close to $700 per horse power. Others may think differently, but that's not even close to a good deal to me. It could be that I'm just very difficult to satisfy?