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I'm having it LARGE for 2010 :)
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mgbv8
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1975 MG MGB GT V8

PostPosted: Sun Nov 15, 2009 9:01 pm    Post subject: I'm having it LARGE for 2010 :) Reply with quote

I've fitted my new spider plate now. And a new Harcourt manifold, and a Weber 600. Absolute shite combo Sad

The weak link being the carb with vac secondaries. This big single plane mani does not develop enough vacuum at instant wot opening.

She rev's like a demon and very fast when I blip the pedal to full opening on the primaries. But if I try a quick opening to full throttle, she bogs flat dead when the secondaries go full open.

I've also done a lot of flow testing, and discovered a problem with my nitrous supply lines. Most of 2009 I thought I had been hitting my regular 10.6 1/4 mile times with a 300 shot of gas. But I have proved that I have only been flowing 240hp of nitrous. So all my dyno info is way off regarding the amount of power I've making for X amount of nitrous.

So!!!
I've got a nice Hoilley 600 double pumper on the way from the good 'ole US of A as I write. And a new set of MT slicks, but this time they are 27.3" diameter as opposed to my 26" diameter that I have been using. These are to go on my new 15" slot mags (for new read, new to me!)

My existing nitrous sytem can now flow a full 300hp of extra gas and petrol. And I've got another spare nitrous kit than can flow an additional 150hp of nitrous and petrol to bolt on if I need it to get me a 9.99 in 2010 Smile

I've decided I want to see just how fast she will go on stock heads and a tame cam before I do major engine work.

If all goes well I'll be doing shakedown runs late Jan or early Feb 2010. The reason being is that I want to try for a low 10 with the system as it is. If I can do this I'll leave it as is and be ready to race for the Fast Show.

Once I hit a sub 10.5 second pass. I'm going to stick more gas on to see how much she will take before she breaks.

I've also just bought another full manual auto gearbox with a transbrake kit fitted. That will surely kiss the old rear axle goodbye. Smile
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Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw

https://www.youtube.com/watch?v=eg3avnsNKrc&index=2&list=FLqIlXfSAoiZ--GyG4tfRrjw
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gelmonkey
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Joined: 27 Jun 2009
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Location: plymouth


PostPosted: Sun Nov 15, 2009 9:20 pm    Post subject: Reply with quote

Go for it Perry!!!
That is an awful lot of fun on the button Very Happy Very Happy Very Happy
Do you have a scatter blanket on your gearbox?
The one I bought will not fit my car because it is all so tight in the throat of the tunnel and is for sale now.
What axle are you running ?
cheers
P
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bones
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PostPosted: Sun Nov 15, 2009 10:39 pm    Post subject: Reply with quote

Go for it ,more gas is always fun Very Happy , will see you up at the pod early next year then Smile rich
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mgbv8
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1975 MG MGB GT V8

PostPosted: Mon Nov 16, 2009 9:37 am    Post subject: Reply with quote

No blanket Paul.
I'm stil running the stock MGBV8 axle as well. It has the pinion cogs welded together.
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Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw

https://www.youtube.com/watch?v=eg3avnsNKrc&index=2&list=FLqIlXfSAoiZ--GyG4tfRrjw
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Eliot
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Joined: 18 Nov 2006
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Location: Milton Keynes


PostPosted: Mon Nov 16, 2009 9:47 am    Post subject: Reply with quote

A weber has mechanical secondaries, which are progressivley opened.
There is an air flap above those mechanical throttles, to stop the very thing you describe i.e. bogging on WOT from idle. As the air flow increases, the flaps get pulled open and you keep your air speed.


A holley has no such thing and I can only see that it will be worse, because it just wacks all 4 throttles open resulting in no air speed, resulting in a bog.

On the Dakar 440 (chrysler big block 7.2L) it had a double pumper with mechanical secondaries which weren't progressive and if you hit the throttle, it almost stalled the engine, and 7.2 isn't exactly a small engine now...

So I'm not sure I follow your reasoning..
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5.7 Dakar 4x4, 4.6 P38 & BMW 750i
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bigaldart
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Joined: 20 Aug 2008
Posts: 469
Location: Chorley Lancs


PostPosted: Mon Nov 16, 2009 3:44 pm    Post subject: Reply with quote

Personally I think the 600DP will be a good choice for you. Compared to the Edelbrock design the Holley has the advantage of an accelerator pump for the secondaries as well. There is a progressive effect, the secondaries only start to open from about quarter throttle but open quicker so that all four barrels reach WOT at the same time. A little bit of work setting up the accelerator pumps properly will pay huge dividends. It should be possible to modify the other carb but for your emphasis on racing the Holley is the better choice. Unless you wanted street manners and economy. A friend had a 600 holley on a 3.5 with lots of gas and it got a very very heavy Cobra into the 11's, your bigger engine will be an even better match.

Alan
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kiwicar
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PostPosted: Mon Nov 16, 2009 4:44 pm    Post subject: Reply with quote

For my 2p worth
Where is the throttle plate relative to the transition slot when the engine is at idle? just if the car is ideling using the transition slot then the transition circute cannot be set up for transition to full throttle (and it will bog) a full discription is in the David Vizard book, which you are still welcome to borrow Very Happy Very Happy
Mike
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ian.stewart
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PostPosted: Mon Nov 16, 2009 4:55 pm    Post subject: Reply with quote

Double Pumper is probably better for Perrys application as he must be launching a near WOT
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kiwicar
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PostPosted: Mon Nov 16, 2009 5:23 pm    Post subject: Reply with quote

sorry, I must have miss understood when the engine was bogging, I presumed it was when he was on the line and transitioning from high revs low throttle opening no load high vacuum to (roughly) same revs, wide open throttle low Vacuum as he dumps the clutch on that new box of his and fires up the nitrous controller. From what you have said Ian it must be slightly after this as the should rise again as he moves off the line.
Mike
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Tricky
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PostPosted: Mon Nov 16, 2009 10:14 pm    Post subject: Reply with quote

Perry apart for the spacer you now have the same steup as me Very Happy

I think that the 600dp with single plane mainfold is a good set up on the Rover's for what we do with them Very Happy

you need to get loads of fuel in there one masive hit Laughing

I think the mainfold may cost you a bit of low down power but you should
gain a bit back at higer rpm

you be looking for a cam then soon????????????? Laughing Laughing
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Eliot
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PostPosted: Mon Nov 16, 2009 10:27 pm    Post subject: Reply with quote

I'll shut-up then Embarassed
Bloody carbs....mumble..grumble..
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Eliot Mansfield
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Tricky
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PostPosted: Mon Nov 16, 2009 10:37 pm    Post subject: Reply with quote

Eloit

I think Perry's getting a weak bog

When i was with him when it bogged there was no excesive black smoke
which i would expect if it was a rich bog
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Eliot
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PostPosted: Mon Nov 16, 2009 11:01 pm    Post subject: Reply with quote

Get a wideband and stop guessing!
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Eliot Mansfield
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mgbv8
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1975 MG MGB GT V8

PostPosted: Thu Nov 19, 2009 9:13 am    Post subject: Reply with quote

Its ok for afr at wot on the rollers. But thats with gentle throttle opening.

The problem is a lean bog when going from my launch idle of 1500 to wide open throttle in a split second.

I just need a big cupfull of petrol poured in the secondaries as I hit the pedal I reckon.
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Perry Stephenson
MGB GT + Rover V8
9.62 @ 137.37mph
Now looking for 8 seconds with a SBC engine
http://www.youtube.com/watch?v=nVscbPHgue0&list=UUqIlXfSAoiZ--GyG4tfRrjw

https://www.youtube.com/watch?v=eg3avnsNKrc&index=2&list=FLqIlXfSAoiZ--GyG4tfRrjw
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bones
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PostPosted: Thu Nov 19, 2009 10:38 am    Post subject: Reply with quote

not sure if its the same as a 390 set up, but can the power nozzle thing be changed, ive forgot the correct name for it, its at the top of carb, screw in the middle and 2 arm things coming out the side Confused just had a look, there called a discharge nozzle, or would a accelerator pump do it, or have you already got one,
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Last edited by bones on Thu Nov 19, 2009 10:43 am; edited 1 time in total
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