Does anybody use this Offy manifold?

[Argess]

I use this Offy 2x4 intake:

http://www.offyparts.com/product_inf...roducts_id/195

There's a pic in the link page that can be enlarged. It's actually a pic of the low version. Carb pads are a bit higher on mine.

I was virtually given this manifold when I was buying some used engine parts, and thought the dual system would be a nice touch for my car. It seems to work well, however I don't have an abundance of low end torque. I was thinking of advancing the cam a few degrees to make up for it, but have been advised a manifold change would be a better idea.

There is a few things wrong with this manifold other than low rpm response. To run Holley's, there are adapters required that move the carbs back to make room for the distributor. I have those, but even then, there is not enough room for a large diameter distributor, so I wound up using a Mallory YL (with a few modifications for other reasons), so crossfire potential is higher than with a large dia cap. Ports are tall and narrow compared to most Ford FE cyl heads, so there's a bad mismatch to deal with. So, I may try to find a good dual plane 2x4, if not original, then a good quality copy.

But before I do that, I was wondering if anyone else used this manifold and how they like their low-end response. All comments are appreciated. Thank-you.

ps: actually, the power comes on nicely between 2000 and 2500, and the idle is smooth and good transition off-idle, just not a lot of grunt under 2000 rpm. Makes the car docile down low and no "lurching" or anything difficult to deal with. Runs like a scalded cat once over 2000 rpm or so.

[lovehamr]

Might want to look on this forum for more info as well.
http://www.network54.com/Forum/74182...ffy+2x4+intake

Steve

[Argess]

Not the most encouraging info, is it? LOL.

Thanks for the link though. The more info I cna get, the better decision I can make.

ps: I used to use 6.5 PVs in mine, then bought a pair of new carbs from a known carb modifier that had 5.5s in it. I recently had to re-build those carbs and put the 65s that came with the kits in as the 5.5s measured around 3 in Hg. I think I have about 15 in Hg, maybe 16....can't remember at the moment. At 17, and you have 85s, I wouldn't worry about it unless you get a rich spot during acceleration. I suspect if you hook up a vacuum gauge and drive around under cruise to moderate acceleration, and make sure you select PVs below your min vacuum under those conditions, you'll be fine.

[rustyBob]

the bad port matching is probably your problem with low end torque and i think that manifold should be used with highriser heads only anyway.

[Excaliber]

I was wondering about that myself rustyBob, with the desciption being "tall" ports, High Riser was the first thing that popped into my head!

I'm running a High Riser and the difference between MR and HR ports is quite remarkable. Different intake gaskets are required due to the size difference.

My setup is a matched set, 1964 heads and 1964 dual four intake. NO HEAT RISER exhaust ports for exhaust flow through the intake on the High Riser's. What about this Offy intake, got heat riser ports?

[Argess]

Yes, the manifold has an exhaust cross-over passage. I have it blocked off using gaskets without those ports.

And yes again, I thought it was probably for tall port heads which I assume are the high riser ones.

I would have thought the mismatch would have affected high rpm performance more than low. It's only between idle and 2000 rpm where I think there is power yet to be unleashed.

I've tried researching this manifold and there's not much on it. Most people pooh-pooh it, but in reality have never tried it. I did find 2 posts on other forums where the contributor used it and both of them liked it. If the manifold really is the problem, I suspect both of those guys had it in an automatic tranny vehicle where the engine could get up a bit in revs before the torque convertor started to load up.

I've also read two posts in another forum where guys with the Fireball cam (like I have) both said that their engines "came alive" with the cam advanced 4 degrees, but wern't specific about "how it came alive".

Despite the fact a new manifold might be pricey and advancing the cam costs nothing but elbow grease and some new gaskets, I'd much rather change the manifold.....a lot easier. But as I mentioned before, I was hoping someone else who had tried the manifold could confirm or deny they had similiar problems as after all, it would be disspointing to change the manifold and not find a significant improvement.

Then there's the fact I have a very driveable car with more power than I can get to the pavement from 2500 rpm up. Right now, if I get it just over 2000 rpm in 2nd, I can only give it 1/3 to 1/2 throttle (depending how hot it is ooutside) before I worry about losing traction.

But it would be nice to let out a little tire squeal without much effort.....

[Excaliber]

The issue might have more to do with cam profile than the intake manifold. That and make sure you got enough base timing.

[Argess]

Yes, I sort of think it's more the cam, but it can't be denied the intake isn't the best design, so it's a hard one to argue.

When I selected the cam, I spoke with Crane's technical support and the cam I wanted was the last cam up that would give me a decent idle. Crane did a computer profile of my engine and got 480 peak Hp. Next cam up would have been 540 HP. Personaly, I don't believe either figure as the software probably assumes perfect fuel delivery and perfect igntion timing. I figure I'd be lucky to get in the 425 hp range.

Now, looking at manifold comparison tests I've seen over the years, people get real excited when a manifold shows a 10-15 hp increase. Well, on a 400+ hp engine, this isn't a significant change for street driving, but it is for 1/4 mile times. And I've never really noticed much HP/torque difference in the low rpm range on any of these manifold comparison tests.

On ignition timing, I am working on that. Currently at 20 deg intial and 38 degrees max. At 28 intial, I have a problem, but I may be able to squeak 24 or 26 out of it. The 38 max will probably remain at 38 as the higher rpm range is fine. If this darned manifold would let me install a larger dist, I'd go for a vacuum advance unit. That could make a huge difference seeing how these cars demand part throttle (and hence part vacuum) in low gears to maintain control. Right now, I don't want to spend the money on another small dist with vacuum advance only to subsequently change manifolds and then go to a large diameter dist. Not that I'm cheap, but there's no reason to waste money either.

Sidenote: Building the car was fun. Driving it is OK, but tinkering is the most fun. If I ever get this car perfect, I probably won't drive it much. But that probably won't ever happen....in my mind, a kit car is "always a work in progress"

2nd sidenote: Public roads are horrible for doing test runs. Too much traffic around.......

[Anthony]

If the intake was for high-riser heads, then the intake wouldn't match up right with MR heads, such that the valve cover rail would have a step up at the intake head interface.

High riser heads and intakes, are taller at the intake-head interfacce.

[Argess]

Originally Posted by Anthony

"After jumping into an early lead, Miles pitted for no reason. He let the entire field go by before re-entering the race. The crowd was jumping up and down as he stunned the Chevrolet drivers by easily passing the entire field to finish second behind MacDonald's other team Cobra. The Corvette people were completely demoralized."

Is that true? It's a great story......my favourite of sig's !!!

[Excaliber]

True story, and indeed one of the BEST of the Cobra legend(s).

I understand the Vette team filed a protest, something about you can't pitt for a drink of water, that's GOTTA be against the rules, right? Apparently not, protest denied!

Demoralized, humilated, buried, man that must have been one glorius day for Shelby.

[rustyBob]

I just can't see Offy makeing a manifold that didn't come close to port matching a set of heads it was made to fit.........I have an Offy intake that is a port-a-sonic dual port single 4bbl intake from back in the 70's that is basically 2 single plane manifolds in one there is a set of runners for the primaries and a set for the secondaries, its hard to explaine this thing but there is a devider in the runners that seperates the primaries from the secondaries its the only manifold that i have ever seen like it and man does this thing look odd it's very short in height kind of like a stock 4bbl manifold but the ports matched up rather well i only had to do a little work to get it to match the ports on the heads. Maybe some body at Offy can give you some info on your manifold that will help.