Offenhauser 360 vs Edelbrock Performer 180

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Allan Robinson
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Offenhauser 360 vs Edelbrock Performer 180

Post by Allan Robinson »

I have a Dax Rush and soon to take delivery of a 4.6 RV8 to replace my existing 3.9. At present I am using an Offenhauser 360 intake manifold which fits everything very nicely under the bonnet. I have been told that the Edelbrock 180 is a much better manifold; however, being taller would probably require quite a lot of disruption to the bonnet.

Two main questions come to mind.

1. Is the Edelbrock that much better and therefore worth the change?

2. How much higher is the thermostat housing vs the Offenhauser? My concern is that I already struggle to achieve a header tank water level above the coolant highest point. i.e.. the T/stat housing.

Any views would be greatly appreciated.



sidecar
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Post by sidecar »

If the Offy is a dual port (not the same as dual plain ) then personally I don't think they are all that good, I understand what the idea of the dual plane is port the web across the port reduces the port area too much in my humble. They are low rise which means that the inlet charge has to turn sharply to get into the head. The Eddy manifold is a 180 degree manifold which should help bump up the mid range but having said that it 'could' restrict the flow at high RPM. The real issue with the 4.6 engine is that the standard head restrict the flow anyway so as standard the 4.6 does not want the rev very high. I have a stage III 4.6 with an Eddy manifold, peak power is around 5.5k RPM and the engine will rev to 6k RPM. I had the same heads on a 3.5 engine and I think that it would have revved to over 7 k RPM if I let it. It was not all that nice though because I knew these sorts of revs were too high for many of the components in that engine so I had to watch the rev counter like a hawk!

Its worth doing the 'drilling' mod to the Eddy manifold, is involves drilling two 7mm holes into the coolant channels just behind the thermostat.
Last edited by sidecar on Sun Oct 22, 2017 9:14 pm, edited 1 time in total.

Allan Robinson
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Post by Allan Robinson »

Thanks Sidecar. I should have previously mentioned that my chosen 4.6 has stage iii heads and a Stealth cam. I don't race this car; however, it would be pointless spending extra on these performance items only to have it compromised by the inlet manifold. I believe mine is an Offenhauser 360 dual plain manifold? (central divider) resulting in left bank fed from L side of carb and right bank fed from right side of carb.

My existing Offy is nice and low; however, does result in a 90 change of direction just below the Edy carb which I would have thought was not ideal. Also I guess that engine pulse / firing order effect will have some weird flow characteristic.

I did ask a very knowledgeable person who just txt " No brainer - Edelbrock Performer" unfortunately he did not state a reason.

I just wonder if the difference between the Offy 360 and the Edy 180 performer is significant enough to warrant making the change? I have the rev limiter set to 6000 Rpm and when driving enthusiastically will accelerate hard up to 5500 Rpm.

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Post by sidecar »

Your Offy may have a split under the carb but I think that the split will run from left to right, not front to back, the front of the carb (both venturies) feed all 8 cylinders via the lower section of the manifold, the secondaries do the same via the upper section of the manifold, basically the manifold is 2 360 manifolds sat one on top of the other, this is a dual port manifold. A dual plane manifold differs from this, the right side of the carb feed the two centre cylinders on the left side of the engine and the front and rear cylinders on the right side of the engine, the left side of the carb feeds the other cylinders.

A 'normal' true 360 manifold has no divider at all under the carb.

I was building a stage II 3.9 a few years ago, I spoke to V8 Developments as the owner of the engine already had a dual port manifold, V8 Dev would only sell me a very mild cam because of manifold, in the end we junked the manifold and fitted an Eddy 180 which meant we could use a decent cam!

I think that these low rise manifolds are only any good when you have absolutely no choice due to bonnet clearance, I reckon you would notice a big difference between the two manifolds on a 4.6 as the engine really needs to be able to breath. I would port match the manifold to the heads which is not too hard to do.

Allan Robinson
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Post by Allan Robinson »

Thanks again Sidecar. It is actually a V8 Developments 'Warrior' long engine I have ordered. The Txt re the Edy manifold also came from them so for now lets just assume that Edy performer manifold would be the better option in terms of performance.

The Edy is obviously taller which for me creates and issue with regards to the T/stat exit pipe in relation to the water level in the header tank which I cannot raise. I may have to consider making a straight or 90 degree horizontal outlet while retaining the pump bi-pass pipe.

In order to evaluate I really need to know the height from the valley gasket to the top of Edy T/stat manifold. Can I be cheeky and ask you to measure yours if you still have that setup?

Many Thanks
Allan

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Post by sidecar »

Allan Robinson wrote:
In order to evaluate I really need to know the height from the valley gasket to the top of Edy T/stat manifold. Can I be cheeky and ask you to measure yours if you still have that setup?

Many Thanks
Allan
LOL, I'll measure it when I get home. Don't forget to do the drilling mod if you go for this manifold. I've seen two engines that would overheat very quickly before the thermostat opened but after the mod they were fine.

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Post by sidecar »

The height of the casting where the thermostat sits is 110mm from the valley gasket. My thermostat housing which bolts to the manifold points foward and up at about 45 degrees, it is higher than 110mm but you can get other covers which may not be higher than 110mm. Hope that helps.

Allan Robinson
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Post by Allan Robinson »

Excellent. I have just sold my engine so can't absolutely confirm the height of my Offy valley to top of T/stat flange; however, measuring the Offy T/stat flange to a spare valley gasket I make it 100mm. So if the Edy T/stat is only 10mm higher this puts it well within the scope of modifying my existing T/stat housing by cutting and cranking over the rad hose tube to horizontal.

So it look like the Edy manifold install is a potential goer. I now need to wait until the new engine arrives (6-8 weeks) and in the car so I can fully evaluate all implication. I can also look out for a used Edy manifold before splashing out on new.

In the mean time I am in the midst of installing the T5 gearbox which I am enjoying but has resulted in almost every aspect of the car being modified in some way.

Many thanks for taking the time to provide the Edy measurements.

Allan

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Post by sidecar »

Allan Robinson wrote:
In the mean time I am in the midst of installing the T5 gearbox which I am enjoying but has resulted in almost every aspect of the car being modified in some way.



Allan
T5 gearbox....yep I remember fitting one to my 4.6, you need to measure the spline engagement and the spigot bearing engagement carefully! All of this depend on the bellhousing and flywheel that you are using, my bellhousing was from a well know 'V8 tuner' (But not the one called V8 tuner!), if I had not checked then I would have had hardly any engagement and I reckon that the splines would have stripped in no time at all. It took a lot of machining to sort out the bellhousing. The tuner in question does not like hearing feedback on his products and work so I gave up trying to tell him in the end. :?

Allan Robinson
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Post by Allan Robinson »

Yes, we have previously corresponded on this subject. I did manage to buy what I believe to be a TVR bell housing but due to the shorter T5 mustang input shaft I recon I need to remove circa 6mm from the housing for clutch and spigot bearing engagement. I can't progress this as waiting for the clutch plate (and engine) to arrive so that I can confirm measurements. I seam to be constantly waiting for bits which is holding up progress.

Re the V8 supplier you eluded to, I know who you mean. I too was annoyed by his arrogance.

Allan

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