The V8 Owners Forum -

Hi, I am new to posting on this forum and have visited it many times and read some great threads. I have an engine power issue I could really use some help with / advice on.
The background is I have recently had a new 4.6 Rover engine built for my MGB (previously 3.5). It was built by a very reputable company in Australia (in another state to where I live) and am having it installed and tuned by and another reputable mechanic and tuner located closer to home. Engine specs are 9.8:1 comp, stage 3 heads with large valves, roller cam, high quality electronic ignition system, Offenhauser 5165 360 single plane inlet manifold and custom 4-2-1 headers that are 1 5/8 primary pipes going into 1 7/8 secondaries. I already have an Edelbrock 500 but the tuner highly recommended at Holley Street HP 650CFM double pumper. The car is not on the road yet but engine has been run in and tuned on a chassis dyno. The engine builder swears and has many examples of where same spec engines with fuel injection make 200rwkw every day of the week. Because I am running a carby set up I am not expecting that power but my expectation is around 180rwkw (even 170rwkw would be nice). After tuning first power runs showed a disappointing 143rwkw.
The specs of the engine would tend towards (if anything) a of lack torque at low rpms and really come on strong at rpms picked up especially with the big Holley. However then engine is doing exactly the opposite – very strong down low (pulls like a train) but then really flattens out at 3800-4000 rpm. As a result I immediately went to inlet manifold thinking it was restricting airflow and some of the port matching was a bit out. I had the inlet manifold carefully port matched and ported and any sharp bends smoothed out. Back on the dyno, net impact was a whopping 4rwkw!!.... lost a little bit of torque down low and gained a bit up top which is what you would expect. From what the tuner tells me the ignition is advancing properly (14 deg static up to 28–30 deg full adv and what the engine builder wants). Interestingly, power did not vary much between 26 and 36 deg full advance.
So essentially I am 20% down on where I would like to be and am at a complete loss for where to go next. I am suspicious the Holley is just too big and maybe not atomizing the fuel correctly once the secondaries open (Kiwicar commented in detail on this in a thread called “Best set up for my Rover 4.6?” in Nov 2012). WOT A/F ratio is 11:1 through the rpm range which may be way rich causing manifold wetting /atomization issues….don’t know??
I am seriously considering an Edelbrock performer manifold if I would fit is under the bonnet (really, really want to keep the bonnet standard) but am not sure after reading the comments by “sidecar” (The eddy 180 has very good fuel distribution, the runners are all a similar length and the angles of them match the angles of the inlet tracks in the heads. This all gives good throttle response, good bottom end, mid range and reasonable top end…….. A 360 manifold may ultimately produce more peak power but can suffer in areas where the eddy does well) so am not sure if there is any more top end available with a 180 Edelbrock???
Anyway first step is to stick the Edelbrock 500 back on and test. Other than that I’m not sure if the performer manifold would be a good option (can’t afford fuel injection yet) and I am really open to other suggestions and could really do with some advice.
Thanks heaps in advance, Graeme.....sory for the long post!!

Are you sure the jets in the Holley ar the right size for the engine?

Thanks Chodjinn, to be honest I am not sure of the primary or secondary jet sizes, however I know the tuner has spent a significant amount of time on the dyno changing jets / boosters / air bleed values etc to get it to this point considering its a 650 on a 4.6

The dyno curve doesn't show a bog at WOT either.

Thanks Graeme

I would really have to question anyone suggesting a 650DP as a suitable carb for 4.6 RV8.

I would double check the cam timing valve lift and compression and if everything is OK there, then its just fuel and sparks the carb should not effect power providing AF looks fine - just drivability - so I would start with the spark energy - plugs - leads etc.

I run what I guess you would call a stage III 4.6 with an Edelbrock 180 and Eddy 500 carb. Dunno what kw is kicks out but its around 300 BHP at the fly. (Someone else can do the maths....). I can give you teh spec of my engine but I doubt that you need it really. The Eddy 500 is not too small for a 4.6, When running at WOT there is about 1.5"hg of vacuum which just about right for a 4 barrel carb. Of course any carb can get messed up with bad jetting and a restrictive air filter setup. I have seen setups which use a 2" drop base and a 2" high filter, now that ain't never going to work!

I dunno what your manifold is like but as long as its a true 360 and not a dual port 360 then I doubt that it would be restricting your engine.

I found that the standard ignition as not all that great at high revs, I had spent along time getting the advance curve and total advance that I wanted with a 35DML8 (or whatever its called) but when I changed the whole setup for an MSD system I reckon that I got another 15 BHP out of the engine at peak revs.


EDIT...170kw at the rear wheels is about 230BHP so your engine is not that bad, I guess 50 BHP may be lost in the transmission??

I thought cam timing too, the other thing i wondered was what fuel pump your running ?

Thanks for your feedback everyone it is really confirming the thoughts I have had.

Darkspeed, Ignition is high quality Australian made ICE ignition with booster and controller. It has been used on winning engines in the US engine masters challenge and reputed to be equal to MSD. Having said that I will take it back to make sure its functioning correctly.

Sidecar, Current inlet manifold is definitely 360 single port. The 3.5 Rover, I took out had a JWR dual port (actually made good power) so am familiar with the difference.

JSF55, I had the same thought about fuel pump and pressure and asked the guy tuning about it. He did not give me a pressure reading but said had been getting consistant 11:1 AFR across the rpm range, so from that stated the fuel pressure must be OK. I assume if the fuel pump can't keep up then AFR will really lean out.

Has anyone seen back to back comparisons of the Offenhauser 360 single plane and an Edelbrock performer??. If not maybe that will be a real positive that comes of this damn problem!!

Thanks again everyone!! Graeme

Hi
do you have a full spec on the cam? just any roller cam is going to be a custom job and it would be a good start to check the actual .05" points first, it would also be very informative on where the power should be coming in.
11:1 AFR seems very rich to me, I know some run around this region, but below 12:1 you are so far off the chemically correct ratio you are loosing loads of power. On any road engine you should not be dropping below 12.5:1 if you are having to to get best power then you have a serious fuel atomization issue that needs sorting out or/and you are coating the whole inlet tract in liquid fuel and then washing the bores with it. Really it sounds like you have a bad match of components leading to very poor atomization and a really inefficient burn.
Areas I would investigate are, finished surface of the ports and manifold runners, they should not be polished and shiny they should be finished with 80 grit emery in a die grinder. A smooth surface just leads to wetting of the port runners.
I would have a think about the inlet manifold plenum volume, with the small area runners of the rover head and the roller cam, especially if it is relatively short duration for the rest of the spec (say less than about 225 degrees duration and on a 108 degree LSA) and you have just the standard plenum you may be hitting the boosters with such a big pulse that boosters are dumping a very rich initial mixture into the initial part of the inlet charge that is leaning off very rapidly, the reading of 11:1 over all may be made up of an initial charge of about 8:1 with a latter part more in the region of 15:1, with the swirl free nature of rover chambers you could be trying to light very lean bit of the charge initially then that is in turn trying to ignite a really rich bit that has by now moved away from the plug, result very poor combustion that only partially burns the fuel. Many open port manifolds are actually never intended to run without at least a 1" open spacer and normally a 2" one, it is cheaper for the manifold manufacturer to get you to supply the top of the plenum after all you would probably be fitting one anyway, just get you to buy a thicker one. What I am saying is try a 2" spacer and I suspect that will help quite a bit as it will damp things at the boosters.
How close is the filter top to the of the carb top?
The biggest help here would be a cam chart .
I would not change any major components yet as this lot should work (but not at 11:1 AFR ).
Best regards
Mike

I would put the 500 carb back on and tune it properly.

You ideally need a carb with vac secondaries so the engine can pull only what it needs dependant on rpm and the VE of the enigne. If you are using a 650 double pumper you will be chucking in too much fuel at wide open throttle.

A really well tweaked 4.6 will only need 570cfm max IMO.

I bet if you looked in the 650 DP at wide open throttle on the dyno the fuel will just be dribbling in from the boosters instead of entering as an atomised stream.

11.1 AFR is way too rich for your engine !

Check cam timing.

Also run an AFR meter on the exhaust to see if the mixture is anywhere near.

Chris.

Thanks again everyone. I will confirm the cam duration and LSA, the engine builder in the past has been reluctant to let this info out. The tuner guy is on holidays at the moment so I will confirm with his offsider what the actual AFR is from the dyno runs.

As soon as I can I will ge my Edelbrock 500 on put the jets and needles that I got from D&D Fab and get the AFR right and see what happens on the dyno. If no real differnece i will try a 1" spacer as well. I will do that before getting into cam timing etc.

This may not happen until 8th or 9th of Oct but as soon as it happens I will post the results.

Thanks again Graeme

Also I have noticed the Offenhauser 360 manifold has a dividing wall between the two halves of the engine so one primary barrel and one secondary barrel are feeding one bank of the engine and the other side of the carb feeding the other bank, so it really is a single plane twin plenum manifold. Would there be any advantage in cutting a section out of the wall or removing it completely to make a true single plenum manifold? This may even out the pulses the boosters see?

Kiwicar, the walls, roof and floor of the ports in the heads seem to be sufficiently rough but the inlet manifold ports are definitely smoother so I might rough them up a bit.....thanks

Graeme.

ghw70mgv8 wrote:Also I have noticed the Offenhauser 360 manifold has a dividing wall between the two halves of the engine so one primary barrel and one secondary barrel are feeding one bank of the engine and the other side of the carb feeding the other bank, so it really is a single plane twin plenum manifold. Would there be any advantage in cutting a section out of the wall or removing it completely to make a true single plenum manifold? This may even out the pulses the boosters see?

Kiwicar, the walls, roof and floor of the ports in the heads seem to be sufficiently rough but the inlet manifold ports are definitely smoother so I might rough them up a bit.....thanks

Graeme.

That sounds like a 180 dual plane manifold to me, a true single plane would not have a dividing wall. If your right hand half of the engine feeds all of the right cylinders and the same thing happens on the left then that is not a good arrangement anyway, at least with the Eddy 180 the linking of the cylinders is done in such a way that the induction pulses are spaced out as far as the carb is concerned.


I would not cut the divider off, I know some books reckon that you can do this sort of thing at it may well work if your engine is 'under carbed'. I have ran an open wedge style spacer below my carb and I could tell that the throttle response was not quite as good as when I made and fitted a divider to it. I reckon that the signal at the primary boosters was not quite as good.

The 1.5" vacuum that my engine pulls at WOT would also indicate that the 500 carb is not too small for a 4.6 lump. In fact I fitted an Eddy 600 to my engine and ran it back to back on a roller against the 500. The 600 carb made no more BHP at the top end, interestingly it did make more torque lower down the rev range. On the road the 600 caused a big problem under braking, I spent days trying to sort it out, in the end I gave up on it. I've now modified my 500 carb so that the air valves open sooner now, it now at least feels like it has the low down torque of the 600.
(The main difference between the 500 and 600 is the size of the primary boosters)

Anyway back to the plot, the only Offy manifolds that I've seen are all low rise, or even worse low rise and dual port, they don't look very good to me!

I actually don't think that your engine is a bad as you might feel that it is, if its making 270 at the fly its not mega bad, it could be better though, I reckon that 300 at the fly is a really good figure for a road engine running a 4 barrel carb, throttle bodies and EFI might get this up to 320-330.

If you really want to cut the divider out then try an open spacer first! If it works I reckon that the underlying problem is the manifold setup!


EDIT, Just noticed that your lump is making 143kw not 170, that is quite bad as its only about 190 BHP at the wheels

ghw70mgv8 wrote:Thanks again everyone. I will confirm the cam duration and LSA, the engine builder in the past has been reluctant to let this info out. The tuner guy is on holidays at the moment so I will confirm with his offsider what the actual AFR is from the dyno runs.

As soon as I can I will ge my Edelbrock 500 on put the jets and needles that I got from D&D Fab and get the AFR right and see what happens on the dyno. If no real differnece i will try a 1" spacer as well. I will do that before getting into cam timing etc.

This may not happen until 8th or 9th of Oct but as soon as it happens I will post the results.

Thanks again Graeme

You had your carb spares sent into the UK from D&D fabs??

Dan and Mark are great guys. But you can buy all you need for the Weber / Edelbrock 500 here in the UK without having to pay for stuff from the USA.

Greetings from the north pole or thereabouts, well Finland to be exact. Morning temp is 0 C or 32 F whichever one likes. The season is just about over and 6 months of garage time looms ahead

I have done various dyno sessions with different setups. My engine is a 4,6 with Merlin heads, a Real Steel cam and CR at about 10,5. Can't remember the actual figure. I ran it with Performer dualplane manifold and with 500 carb ii got something like 280 hp. The power dropped at about 5500 rpm. I suspected that the limit of The Performed was reached and bought a Wilpower single plane manifold. It's From Australia like you probably know

With the same setup including advance and carb jetting single plane manifold scored another 20 odd hp at top end ... but lost about 40 lb ft in lower revs. Below 4500 rpm the dual plane was a lot better. A school book case.

Mine runs at about 30 degrees advane, 32 degrees is just on the edge of detonation. If your engine is that insensitive to timing I would guess that you have a combination of too little CR and too much cam. Possibly the cam timing is also off. Since it is a roller cam you need to ask nicely whoever had that cam made for any specs. If they are reluctant to aupply them ask for a recommendation regarding CR.

650db sounds overkill, maybe the guy just don't like Edelbrocl carbs.