Rover 4.6 power issue at higer rpm

ghw70mgv8 · Post by **ghw70mgv8** » Mon Sep 30, 2013 11:32 am

Thanks for your comments Sidecar, the 143 - 147 rear wheel kW is low in my opinion and really frustrating. Compared to the 3.5 I am replacing the 4.6 produces 70-80% more torque and power up to about 3500 rpm the really trails off to only a 30% increase at approx 5500 which pretty much equates to the increase in cubic inches from the 3.5 to 4.6 and a pretty worn out 3.5 to a relatively high spec newly built 4.6 at that!!!!!

Perry, the engine build and car restoration have been long in the planning. I used to live in the US where I purchased the carb, inlet manifold and other parts from D&D. I've since relocated back to Australia and now have the opportunity to put the plan into action.

Thanks Graeme.

Darkspeed · Post by **Darkspeed** » Mon Sep 30, 2013 11:59 am

Pictures required.

kiwicar · Post by **kiwicar** » Mon Sep 30, 2013 12:00 pm

Hi
I wouldn't be too upset about 200 odd bhp when the AFR is that far out, get it sorted and you will probably pick up 15 to 20%. That would be a pretty healthy output for a rover, you will also be able to get the ignition timing sorted out then and that will probably pick you us another 5 or 10 bhp. I would not be surprised about the fact that nearly all the gains are at the bottom end, the heads are the limiting factor, if the heads flow around 160 cu ft/min sticking a bigger engine under the heads still leaves them flowing the same amount so ultimately they will make very similar power. Where a bigger engine gains a bit is in that you can use more cam timing and still have the same power low down and keep it drivable, this gains you a bit at the top end but it will still end up with peak power lower than the smaller engine. What you end up with with bigger rovers is a narrower power band the bigger you go until you start to need a much closer ratio gear set just to keep it in the power

When I was into tuning Minis people worked out how to get 1620cc out of the A series, they consistently disappointed because they did make decent power on a full race cam and they would still pull away from the lights people found a 1400 engine on the same cam and using a special exhaust to tame the cam gave you a much wider power band that gave a much more drivable car that was quicker on both track and on the road, it was the same issue with the A series, lousy head flow.
best regards
Mike

ghw70mgv8 · Post by **ghw70mgv8** » Mon Oct 07, 2013 5:51 am

Time for an update, the tuner is back from holidays so I caught up with him today. He said that I had misunderstood his message about the 11:1 AFR through the rev range, it was to indicate that had got it to run that rich as a way to demonstrate there was not an issue with fuel pressure / flow and leaning out in the higher rpm range. From the dyno curve it seems to be running pretty consistently between 12.9:1 and 13.2:1 AFR @ WOT. Unfortunately the car has been held up on the panel shop with delays in final assembly so will not go on the dyno this week. Now it looks like the week starting Oct 21st. I have attached a photo I took of the dyno screen showing one of the previous runs with power and AFR. It seems as though with the AFR pretty much right I am – almost – back at square one. BTW sorry everyone for the misleading info.

http://i818.photobucket.com/albums/zz11 ... db8b1c.jpg

The tuner said he believes the issue is the manifold height is so low that at this higher engine rpm / air speeds through the carby, the air comes through the carby bores, runs straight into the floor of the manifold then turns 90 degrees before entering the cylinder through the very short – almost nonexistent - inlet manifold runner then the head inlet port. There is no time for the air / fuel mixture to straighten out. So maybe the Edelbrock performer might be a better option. Thoughts……

Thanks heaps again, Graeme

ghw70mgv8 · Post by **ghw70mgv8** » Mon Oct 07, 2013 6:23 am

some photos,

as you can see the car is nearly done. If anyone is interested I can post some earlier photos as well

http://i818.photobucket.com/albums/zz11 ... 48d891.jpg

http://i818.photobucket.com/albums/zz11 ... e16c85.jpg

http://i818.photobucket.com/albums/zz11 ... fa64d9.jpg

http://i818.photobucket.com/albums/zz11 ... c8d2e7.jpg

Hope you enjoy.

Darkspeed · Post by **Darkspeed** » Mon Oct 07, 2013 10:58 am

Has the manifold been ported ? - has the divider been removed etc.

ghw70mgv8 · Post by **ghw70mgv8** » Mon Oct 07, 2013 12:34 pm

Yes Darkspeed the manifold has been ported. it was done in two stages. First the ports were opened especially in the inner radius of the runners and any sharp angles radius'ed. The gave approx 20% ave increase in flow across the ports. When I went to put the manifold back on I found the ports weren't quite aligned so I carefully measured the ports in the head and corrected the ports in the inlet manifold. Also the bends were further radius'ed and some material was taken out of the floor of the ports with the view of allowing better flow from the manifold in the "upward" angle of the ports in the head. The dividing wall is still fully intact (no cut outs, no holes etc.) Despite the extra flow, when the car was dyno'ed again rwkw went from 143 to 147 - maybe 3%

. It lost a little at lower rpm and gained a little at high rpm which is what you would expect. The difference in power could also be down to variances in the dyno and ambient conditions??

Thanks Graeme

Darkspeed · Post by **Darkspeed** » Mon Oct 07, 2013 8:15 pm

Remove that divider it serves no purpose other than to mess up flow. Unless you have a flat plane crank fitted

ghw70mgv8 · Post by **ghw70mgv8** » Tue Oct 08, 2013 10:03 am

Thanks Darkspeed, I will run it on the dyno first with the Edelbrock 500 carb to see what the result are then I will look at getting the manifold futher modified. Thanks Graeme

ghw70mgv8 · Post by **ghw70mgv8** » Thu Nov 28, 2013 11:15 am

OK everyone, I have finally had the carbys swapped over and run the 500 Edelbrock on the dyno as a back to back comparo with the Holley 650 and the results were surprising to say the least. I expecting a small difference but it was significant. As can be seen from the photo in the attached link the Edelbrock performed worse across the whole range and 126rwkW versus 144rwkW at peak.

I can't really believe the size of the difference. The Edelbrock was setup with baseline rods and jets. The engine tuner was really surprised as well and checked a few time that the secondaries were opening properly etc. He said that the Holley has zero vacuum at WOT whereas the Edelbrock had 2.5 in Hg at WOT. He said this indicates the carb is restricting flow. No doubt the rod and jets sizes need to be optimised but this shouldn't affect manifold vacuum at WOT should it??

This seems to fly in the face of a lot of people saying that the Edelbrock 500 is a great carb for a 4.6!!! What am I missing here????

Thanks heaps, Graeme[/img]

ghw70mgv8 · Post by **ghw70mgv8** » Sat Jul 05, 2014 12:53 pm

OK just to close this post out, after much pulling my hair out researching and trying to figure out what the issue was....changing inlet manifolds and everything, The guy that was tuning the engine found that he had been using the wrong mark for TDC on the balancer. It was out by almost 30 deg advanced. Honestly and surprisingly the engine was not pinging its head off - the engine builder (not the tuner) said it would have had non-audible detonation! By correcting the timing the power went up by 30 rwkW!!!!

Earlier on the forum post Darkspeed mentioned cam timing so he was on the right track.

Unfortunately very soon after this was solved the engine experienced oil pressure problems which led to more headaches!!!

Needless to say that guy is not tuning my engine any more!!!!!!

Thanks everyone for your help and advice. Cheers Graeme

ghw70mgv8 · Post by **ghw70mgv8** » Sat Jul 05, 2014 1:01 pm

Sorry Darkspeed and others mentioned the cam timing so eventhough it was not the direct root cause absolutely on the right track guys....well done.

ghw70mgv8 · Post by **ghw70mgv8** » Sat Jul 05, 2014 1:03 pm

Sorry........ Darkspeed and others mentioned the cam timing so even though it was not the direct root cause absolutely on the right track guys....well done.

sidecar · Post by **sidecar** » Sat Jul 05, 2014 4:05 pm

With regards to the Eddy 500 then yes 2.5" at WOT would indicate that the carb was restricting the engine, this does seem surprising to me as I know that my 4.6 does not show this sort of vacuum drop at WOT.

With regards to the jet and rods then yes they would need to be changed in order to get the right AFR's across the board but I doudbt that this would account for the big difference in performance between the two carbs.