I've just installed the new 4.6 and I'm not sure about the timing. I dont have any info on the RR engine. My old 3500 ran at 8 degrees of advance at 1000 rpm with the vac disconnected.
I've set the new one to this and it idles ok.
But I dont know how much vac or centrifugal advance the 4.6 should have. I have the kit to alter the mallory dissy so any advice would be appreciated. My old low comp 3500 was happy with 20 degrees of vac advance.
I am having other probs with the new engine which I will post about in a different thread.
Thanks
Perry
Timing on a 4.6
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Timing on a 4.6
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
I forgot to mention, it is a 4.6 with 4.6 Thor heads. I havent used my old 3500 heads. Mind you, apart from the slightly lager ports, I cant see any difference from my 3500 ported heads. Both heads seem to have the same size valves as well.
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
-
CastleMGBV8
- Top Dog
- Posts: 2334
- Joined: Sat Aug 18, 2007 5:09 pm
- Location: Sidcup, Kent, UK
Perry,
The timing recommendations I have for the Rover engine are 10* advance at 1000RPM and all in at 34* by 3500RPM obviously with vacuum disconnected. The figure you stated for vacuum advance seems to me very excessive and although in a wide open throttle situation there should be very little effect on timing you could still be getting a lot more advance than you really want, also when you lift off the throttle suddenly say at the end of a run, the dizzy will go to full advance and could in combination with a slightly weak mixture, have been responsible for the damage in the old engine. Personally I would disconnect the vacuum when doing runs at the strip it shouldn't effect performance.
Re the heads, yes the valves are the same size as the SD1 and far too small for a performance 4.6 you really need to take them out to at least
1.63" In. and 1.4"Ex. and if using nitrous of which I have no experience I understand you should increase the size of the exhaust valve in relationship to the inlet.
Kevin.
It's also very important to open up the throats to maximum seats size to maximise flow, I would also as a minimum Bullet the valve guides and just clean up the ports, this is good for 30+BHP on a 3.5 and a fair bit more on a 4.6.
The carb will probably need to be jetted back to the original base line spec if you changed it for the 3.5.
The timing recommendations I have for the Rover engine are 10* advance at 1000RPM and all in at 34* by 3500RPM obviously with vacuum disconnected. The figure you stated for vacuum advance seems to me very excessive and although in a wide open throttle situation there should be very little effect on timing you could still be getting a lot more advance than you really want, also when you lift off the throttle suddenly say at the end of a run, the dizzy will go to full advance and could in combination with a slightly weak mixture, have been responsible for the damage in the old engine. Personally I would disconnect the vacuum when doing runs at the strip it shouldn't effect performance.
Re the heads, yes the valves are the same size as the SD1 and far too small for a performance 4.6 you really need to take them out to at least
1.63" In. and 1.4"Ex. and if using nitrous of which I have no experience I understand you should increase the size of the exhaust valve in relationship to the inlet.
Kevin.
It's also very important to open up the throats to maximum seats size to maximise flow, I would also as a minimum Bullet the valve guides and just clean up the ports, this is good for 30+BHP on a 3.5 and a fair bit more on a 4.6.
The carb will probably need to be jetted back to the original base line spec if you changed it for the 3.5.
Thanks for the info guys. I'll be right on those suggestions every evening this week. I have all the tuning bits for the dissy and carb etc.
thanks
Perry
thanks
Perry
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
Spot on Kev.
I just did a static TDC setting again. Warmed her up and set the idle to 1000 with the vac off and the vac port on the carb capped. I set the 1000 rpm timing to around 8-10 BTDC (hard to see with these wimpy marks). Then brought the rpm slowly up to 3700 where it topped out at 30 degrees.
The advance was smooth all the way up.
She now picks up quite quickly and I can hold her at any rpm from 1000 to 4000 and she is now steady.
I didnt want to rev it anymore as she has only done about 10 miles so far.
I have another question about stting the initial static TDC, but will post that separately.
Many thanks for your rapid input chaps
Regards
Perry (a very happy bunny tonight)
I just did a static TDC setting again. Warmed her up and set the idle to 1000 with the vac off and the vac port on the carb capped. I set the 1000 rpm timing to around 8-10 BTDC (hard to see with these wimpy marks). Then brought the rpm slowly up to 3700 where it topped out at 30 degrees.
The advance was smooth all the way up.
She now picks up quite quickly and I can hold her at any rpm from 1000 to 4000 and she is now steady.
I didnt want to rev it anymore as she has only done about 10 miles so far.
I have another question about stting the initial static TDC, but will post that separately.
Many thanks for your rapid input chaps
Regards
Perry (a very happy bunny tonight)
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
-
CastleMGBV8
- Top Dog
- Posts: 2334
- Joined: Sat Aug 18, 2007 5:09 pm
- Location: Sidcup, Kent, UK
Perry,
Sounds great and if your intending to use nitrous probably as much advance as you need. The curve certainly looks to be about right and if with gas you need to limit max advance, you can always back off the initial timing a couple of degees, might be wise on the first couple of runs to see how it behaves and then gradually increase and see if it's any quicker.
Do you know what year your engine is, I looked around for a decent 4.6 half engine and couldn't find anything which didn't sound like it had problems. I'm prepared to rebore the block as I intend using larger flat top pistons but didn't want to go to the expence of Top Hat liners and then boring out to take the new pistons, so now intend to go with a 4.2 which will end up as 4310cc and be big enough for the big valve Buick 300 heads
virtually a TVR BV 4.3 and hoping for about 1 BHP per cubic inch (260BHP) which is realistic with a fast road cam
Kevin.
Sounds great and if your intending to use nitrous probably as much advance as you need. The curve certainly looks to be about right and if with gas you need to limit max advance, you can always back off the initial timing a couple of degees, might be wise on the first couple of runs to see how it behaves and then gradually increase and see if it's any quicker.
Do you know what year your engine is, I looked around for a decent 4.6 half engine and couldn't find anything which didn't sound like it had problems. I'm prepared to rebore the block as I intend using larger flat top pistons but didn't want to go to the expence of Top Hat liners and then boring out to take the new pistons, so now intend to go with a 4.2 which will end up as 4310cc and be big enough for the big valve Buick 300 heads
virtually a TVR BV 4.3 and hoping for about 1 BHP per cubic inch (260BHP) which is realistic with a fast road cam
Kevin.
Hi Kev
I can retard the timing from inside the cabin.
I've got an adjuster hooked up to the Mallory AL6 thing.
I can take up to 15 degrees out of the timing. And when I get my boy to adjust it while I've got the strobe on it does just what it says on the tin.
I got the engine in a fluke ebay auction last year. I believe the guy buys a shed load of engines for customers cars from V8 Developments. Sometimes the deal gets changed and he sticks them on ebay. This one is a crossbolted 4.6, fully balanced, line bored etc and assembled. It was still in the packaging with a ticket from V8 Devs unopened. They normally go for around £1900 + Vat from V8 Devs. I suppose he gets a good discount so can sell a bit cheaper and still make his money back. The auction didnt attract much interest near Xmas and I snapped it up for just over 900 quid inc delivery.
He forgot to put a reserve on, but he still honoured the deal and when I told Shaun at V8 Devs about the price he flinched and said Ouch, well done mate.
The engine number is 60D 1008(or3)9A
Which seems to tell me its a factory 4.6 from a Rangie 1998 onwards.
I can retard the timing from inside the cabin.
I've got an adjuster hooked up to the Mallory AL6 thing.
I can take up to 15 degrees out of the timing. And when I get my boy to adjust it while I've got the strobe on it does just what it says on the tin.
I got the engine in a fluke ebay auction last year. I believe the guy buys a shed load of engines for customers cars from V8 Developments. Sometimes the deal gets changed and he sticks them on ebay. This one is a crossbolted 4.6, fully balanced, line bored etc and assembled. It was still in the packaging with a ticket from V8 Devs unopened. They normally go for around £1900 + Vat from V8 Devs. I suppose he gets a good discount so can sell a bit cheaper and still make his money back. The auction didnt attract much interest near Xmas and I snapped it up for just over 900 quid inc delivery.
He forgot to put a reserve on, but he still honoured the deal and when I told Shaun at V8 Devs about the price he flinched and said Ouch, well done mate.
The engine number is 60D 1008(or3)9A
Which seems to tell me its a factory 4.6 from a Rangie 1998 onwards.
Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
-
CastleMGBV8
- Top Dog
- Posts: 2334
- Joined: Sat Aug 18, 2007 5:09 pm
- Location: Sidcup, Kent, UK
Perry,
That was a nice Christmas present then.
I have just posted a link under Enjoy these V8's There is a tip from a guy called Bill Guzman on how to improve traction and anti tramp on a B very simple very cheap if youve got an old pair of springs and could help you get of the line a bit quicker, not that you need it turning 12.4's
Lots of lovely stuff in the newsletter I'm still reading it.
Kevin.
That was a nice Christmas present then.
I have just posted a link under Enjoy these V8's There is a tip from a guy called Bill Guzman on how to improve traction and anti tramp on a B very simple very cheap if youve got an old pair of springs and could help you get of the line a bit quicker, not that you need it turning 12.4's
Lots of lovely stuff in the newsletter I'm still reading it.
Kevin.
