Help Re Inlet Manifold height on V8s

[Cinnobar]

The TR7 V8 Engine rebuild is progressing nicely and I now need a manifold for the Weber 500. I sent a mail to RPI and they came back suggesting the Offenhauser. Fine but I'd really prefer an Edelbrock as its the more modern manifold (guy at Real Steel said same as well).

I asked about clearance and Jane at RPI came back with the following:-

 

Edelbrock And "Offenhauser" Manifold Heights From Centre Of Rocker Cover To Top Of Air Filter Housing

Weber carb on Offenhauser manifold with 2" air cleaner is 4.5 inches

Weber carb on Edelbrock manifold with 2" air cleaner is 6 inches

 

Help where is she measuring from as in whats the Centre of Rocker cover?

I have probably 1/2 inch 12mm with Defender type SUs does anyone know if the Performer is OK or where I measure from?

Does anyone here run an Edelbrock Performer?

I am running sub frame spacers.

 

Jim

[Guest JohnG]

Fit the Edelbrock, much better for a TR7 V8 .Offy OK for 4 X 4.

 

JohnG

[Guest stagmann]

on the same-ish subject, Im running a Holley and Offy at the mo. Should there be an insulating spacer between the carb and Manifold?

[martynharrison]

If this question remains unanswered, I could go out and measure my 360.

 

From the POV of which, the 360 isn't dual plane, although this is how it is often described. The difference is in fuel distribution, I've tried to describe how this works in these two pages, having become aware of it recently:

 

Dual Plane

Left / right

 

Note how the left / right split manifold has a double demand of airflow for an eighth of the cycle, and no demand at all on another eighth, while the dual plane manifold has a flat demand through the whole cycle. This is a consequence of the firing order and left / right demand.

 

A dual plane, like the Edelbrock, mixes the outer cylinders on one side, with the inner cylinders on the other, which means the airflow must "cross over" at some point and this means the manifold must be higher, or have narrow runners which will restrict airflow.

 

Restricting airflow isn't always bad, it raises gas speed and promotes good vaporisation but mostly limits revs and spoils throttle response, so you probably want something thirsty and grunty.

 

On the whole, the 360 is not too bad, but the Edelbrock is better if you can fit it all under. So I think anyway, expert opinion is welcome, as ever.

 

Stagmann - Holley and Offy, there is a plate on mine because the studs which hold the carb on, are differently spaced to the holes in the manifold, on account that it is designed for a Buick or something. The plate adds some extra holes in a different position. If you have studs which fit ok, you're lucky and don't feel you need to change it.

[Cinnobar]

Alec, the thing is I can't find either for sensible money S/H!

Chased a few on E Bay and they're going for near new money.

New they are the same price from RPI but I'm also on the V8 forum http://www.v-8.org.uk/forum/ which has a huge knowledge base on RV8s and consensus on their is although the Edel is better manifold run the Offy cos their won't be clearance for the Edel. even with a 2" air filter.

So the question still stands is anyone running an Edel on a 7V8 with the subframe spacer kit? Or those running Offy how much clearance have you got and are you running a spacer kit & a 2" filter?

 

Jim

[martynharrison]

Actually, I can be more specific without measuring. The height of the engine depends on the subframe. Bodged or "normal" subframes are quite high and leave you room for an Offenhauser 360 and thin pancake filter, like with Malcolm's car. Mine has an S&S subframe which is lowered, it means there isn't room for a power steering rack under the engine but does mean there is room for a full depth pancake filter and the 360.

 

The Edelbrock is an inch or two higher, so Malcolm's would have no room at all for a filter and mine would probably be reduced to using a thinner height one.

 

So, if you have the lower S&S subframe you might be able to fit an Edlebrock but you can't with anything higher and you might not manage with one anyway, meaning restricting the airflow through the filter and that probably takes off any advantage from the taller Edelbrock anyway.

 

The JWR dualport supposedly gives more fuel economy but I was disappointed by the performance. It does have plenty of clearance which means you can run a thick pancake even with the higher subframe.

 

So basically, use the Offenhauser, if you have a reasonably low slung engine, as it ought to fit even if you need to use the thin filter. Edlebrock probably won't fit, use the JWR if you want no issues at all with clearance and are less likely to rev the engine for fun where it begins to be restrictive, unless I was unlucky with mine.

[malcolm]

A bit off-topic (again) but I've got a modified original SD1/SU manifold with a holley sitting on-top.  The bonus of this set-up is that it retains the connection to the small hose from the header tank.  Would I gain significantly (in performance) from fitting the JWR dual plane manifold I have sitting in the garage?  Or by fitting an Offy??

 

I've left it alone on the "don't fix it if it isn't broken" principle as it does drive nicely as is.  :cool:

 

Malcolm.

[Guest ajttriumph]

Edelbrock is a much better manifold i have used the offy one and the edelbrock and the edelbrock produces more hp and torque originally on my 3.5l i ran a 390 holley with a 2" deep pancake filter, what you can do is press the centre of the filter so that it is dished and therefore sits lower.

[martynharrison]

JWR dual plane manifold I have sitting in the garage?  Or by fitting an Offy??

To avoid confusion, this is a Dual Port manifold, also made by Offenhauser.

[malcolm]

It is?  Shows what I know about V8 manifolds then.  I was really after words from the wise as to whether to bother to replace the modified SU manifold............

 

Malcolm.

[Guest ajttriumph]

Alec, i dont know about strangling performance the car did an offically timed 12.9 on the quarter mile in 30 degree heat with the 2" deep (paper) filter.

 

The 3.5l sucessfully competed in circuit racing and hillclimbs for several years with the two inch filter with a 7000 redline and i never noticed it being short of breath.

 

Car now has stroked 3.5 (to 4.4) and fuel injection so i cannot go and check it.

[tr7v8]

Just to add to confusion choice or whatever. I was looking at Jon Wolfe's TR7v8 at the international last year and he's running a wildcat single plain inlet manifold that seems to beat the offy and the edelbrook manifold - or thats what was said anyway, but judging on the cars performance in the race series it definitly seems to. Anyway the manifold is on this webpage and probably cost a small fortune....

Wildcat Engineering

worth a look round this site if only to realise your rover v8 is not really that powerful compared to some after all....

 

Tom Pringle

[Cinnobar]

I did enquire about this manifold and it was circa £ 250 complete which isn't bad, he did say it would be a month or so before being available. Single plane isn't necessarily what you want on a road car but it's fairly low profile. A guy runs one of their 6 litre engines in a circuit racing Lotus Esprit, I'll try and find the link in a mo.

 

Jim

[martynharrison]

Like anything else, you can't bolt on power as such. What you do, is remove restrictions.

 

A high flow, single plane manifold will permit more power at higher revs, e.g. at 6000 rpm you want a single plane manifold. At 3000 rpm you want a dual plane, a single plane is open and allows adjacent cylinders to rob each other of mixtures, unless they're 180 degrees out of cycle.

 

Like the cam profile, it needs to suit the application, a race engine is all about power, and you change gear so as to keep the engine on the cam while changing vehicle speed. This is no fun at all in a road car, where you would rather have grunt than outright power. Having it stall at the lights is embarrassing. Even Schumacher has done that.

 

You're not going to be seriously short of either in a 3.5 v8, though, so any choice will be pleasing to some extent.

[malcolm]

e.g. at 6000 rpm you want a single plane manifold. At 3000 rpm you want a dual plane....

Considering the characteristics of the Rover V8 engine, is a single plane manifold useful outside of competition?  The red-line on a proper TR8 tacho is only 5,500 and I wouldn't normally rev up-to that anyway - not even on a trackday.

 

Thoughts?

 

Malcolm.

[Cinnobar]

Malcolm, revs would depend on cam, mine was soft cammed with the defender cam and still made peak power at 5400RPM so with a slightly wilder cam say a Piper 270 then using 6000 isn't to bad. Engine in good nick is reckoned OK for 6500 with bursts to 7000. However agree that most "sensible" driving you probaly never exceed 4000RPM, one of the reasons that although I've upgrded the cam on the rebuild it's still quite genteel, an RC87 to be exact

[martynharrison]

Bit late on this question. The V8 engine probably doesn't care about revs, Cinnobar, as you say. But the hydraulic lifters won't react quickly (as the oil has to pulse the pushrods up the V) and basically the valves won't open much if you approach 6000 rpm so the engine can't develop much more power to get any faster revs.

 

So 'tis said. And in gear, obviously you can destroy the engine by revving it up until it goes bang, in neutral BTYKTA.

 

For lots of revs, the books / websites / racers say solid lifters, roller rockers and that sort of thing is necessary to get much out of the engine above 5500 rpm or so.

 

And that's the key question to what sort of airflow you might be anticipating, I reckon, road cars really are differently set up to race cars.

 

I'm open to hearing better information than I've got.

[SteveP]

I've just switched to a dual plane and it's much better on my mild-tune 3500cc 10.5:1CR. The single plane and larger single plane are only beneficial to racers running in the high rev bands most of the time, otherwise the torque isn't there lower down.