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Another PB for the MGBV8 today at the Pod.
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mgbv8
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1975 MG MGB GT V8

PostPosted: Sat May 30, 2009 7:07 pm    Post subject: Another PB for the MGBV8 today at the Pod. Reply with quote

What a cracking day !!

No cigar or fat lady singing re the 10.99 second pass. But I did PB's for the first 3 runs of today. The best being 11.08 @ 124.84mph.

This pass actually had two PB's in it. I've hit my goal of the 100mph 1/8th mile speed.
7.1 seconds to 100mph Smile

The last few runs were duff due to me farting around / experimenting with settings and the traction just dying off between 3pm and 5pm. Oh! and the gas running out.

I'm still happy though. She's back home in one piece and she lives to fight again at North Weald in 2 weeks time.

The slight beefing up of the rear suspension has done something though. Its made the power transfer to the rear a bit quicker. But, it also started developing some tyre shake and she has become difficult to keep straight in the first 100 feet or so. So now its time to start tinkering again ready for the next outing.
My 0.3 of a second reduction to reach the 10.99 goal has now dropped to 0.09 of a second.
I really thought I was going to bag it today.

And the good news is. I PB'd on less gas. The first 11.08 today was with a 200 shot at 123mph. The second 11.08 was with a 225 shot but at nearly 125mph.
I have previously been running a 250 shot. But I found a small problem with the feed to one of my pulsoids. So I sorted that and took 50hp off for the baseline run today. How nice it is to run a PB straight off the trailer eh?

Oh well!
Back to the drawing board eh?

http://www.youtube.com/watch?v=fH2vsboOXbM
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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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Tricky
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PostPosted: Sat May 30, 2009 8:25 pm    Post subject: Reply with quote

Happy dayz Perry well done Very Happy
you so deserve that 10.
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topcatcustom
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PostPosted: Sat May 30, 2009 8:30 pm    Post subject: Reply with quote

Nice one Perry, have you done any weight shedding yet? (The MG Laughing )

Also can you go any thinner/lighter on the front wheels/tyres? Perspex side windows? Brainstorm session coming on!

TC
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mgbv8
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PostPosted: Sat May 30, 2009 8:44 pm    Post subject: Reply with quote

Thanks chaps!

The only weight shedding has been to ditch the big rubber bumpers and throw out the passengers seat Tom.

There aint much more I can lose really. My mate was on site today with his truck. He has steel rims for his Hoosiers and they are a fraction of the weight of his alloys. My wheels are quite heavy. But getting lighter ones come with a hefty price tag eh?

I'll just keep chipping away at this now. If I can nail the rear end down a bit more I reckon I might make another 10th in the 60 foot which might just see me through to the ultimate goal. Very Happy

This 10.99 has been a long time coming though. Confused
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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: Sun May 31, 2009 7:34 am    Post subject: Reply with quote

Nice one Very Happy ,you will get there, ive been having a think (i got headache know), could you lower the back down ,so the weight is already over the axle using less energy to force the arse down ,?? Smile see you at nth weald Very Happy rich
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CastleMGBV8
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1975 MG MGB GT V8

PostPosted: Sun May 31, 2009 8:17 am    Post subject: Reply with quote

Perry,

Great stuff, so near but so far if only less than a 10th.

Looking at your numbers, if you are getting to 100MPH at the 1/8th it seems you are only adding a further 24 MPH to the 1/4 so clearly aerodynamics are almost certainly holding you back.

Try one of the ST front air dam/spoilers not the Sebring stlye ones which are less efficient, their only about 35 from Honeybourne Mouldings and (seriously) remove the wipers to reduce turbulence to the air stream as it passes over the car.

I know you have RV8 type manifolds that go through the inner wings but I would also increase the air flow out of the engine bay to the front wheel arches, as they are low pressure areas and this will further reduce drag.

Wouldn't hurt to get the front of the car a bit lower either, the less air that goes under the car the better.

I haven't accurately measured the frontal area of a BGT but it has got to be in the region of 20 sq ft and if you apply it to the figures in this article it will give some idea as to what effect drag is having.

http://www.trackaero.com/factors1.html


Kevin.
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Ian Anderson
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PostPosted: Sun May 31, 2009 11:22 am    Post subject: Reply with quote

Hey guys STOP giving Perry advice - he's going to be difficult enough to beat at the Pod in July without him doing any more modifications and taking on advice!

Seriously though Perry those are great times - what revs are you running at the 1/4 - and are you already over the power "hump" max on tha engine? If so time to go for a longer 3rd or even 4th gear - but then each gear change loses some drive time.

And aerodynamics play a huge part remove external rear view mirrors and wipers and run with windows closed (the GT40s at Le mans dod not run with rear view mirrors and also had an 8 inch long by 1inch angle perspex about a foot infront of the windscreen on drivers side - this caused so much air movement that very few bugs and rain drops actually hit the screen!)

Perhaps also fitting spinners / hubcaps to cut the drag arund the outside of your rims

And to get even more keen masking tape over your door seals to avoid turbulence happening.

The trial day becons!

Ian
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mgbv8
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PostPosted: Sun May 31, 2009 12:17 pm    Post subject: Reply with quote

I suppose there are lots of little tweaks to start looking into now eh?
I'm already on course for an ST spoiler because I know I need to stop so much air getting under the car. I've already taken this car up to 140mph in standard trim, so I know she can make higher speeds. But that was when I had 4 gears + O/D. Now I only have 3 gears.
She is topping out at around 5000rpm at 125mph. So I know I have some revs left, but at that rpm I'm over the summit of my peak torque band.

I've got some more caveman style mods to do to the rear suspension so I can test at north weald. Its obvious from the video that its steering from the rear now. By fitting the taller bump stop I have limited the downward travel on the drivers side rear. This seems to have made the axle pivot sooner on this bump stop and there is more force on the passengers side rear wheel so its digging in and trying to make the car turn right. I can see this from the tyres. The near side tyre is showing a little bead of rubber snot all around the edge where the tread meets the wall. This is not happening on the other side. I suppose I should swap them over for the next meet eh?

Now!
I dont want to go farting around with even bigger rear tyres. And there is no way I can afford another gearbox for extra legs. So what about making the engine develop its torque at a higher rpm! Feasible??

Cam change?? Cam timing?? Bigger ported heads??

Food for thought. But in the meantime I'll get it locked down a bit harder and look at sticking more gas on. Laughing
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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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topcatcustom
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PostPosted: Sun May 31, 2009 4:34 pm    Post subject: Reply with quote

Not sure what the others think perry but I would be tempted to try out an offy 360 manifold instead of the eddy performer you have on there, supposed to be much better for high rpm but lose a bit of low down torque, I would also remove the choke flap from the carb, only a restriction and more turbulence and a 5 minute job, just plug the holes the bar went through after! If you look at nascar holleys they are completely smoothed for nice airflow. Also what air filter are you using? If it's a round type you may consider replacing the solid top with a filter (like the one I bodged up in my mx5 thread!)

Just more thoughts re the engine! Also I think Kevin and Ian are right about the aerodynamics, at 125mph they play a big part!

TC
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Darkspeed
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PostPosted: Sun May 31, 2009 7:25 pm    Post subject: Reply with quote

What size are the exhaust valves / ports and primary diameter and lengths

But like others have said aero mods even the smallest thing like using gaffer tap to smooth ridges will offer gains from 60mph onwards. Race track guys were using plasticine and gaffer tape in body ridges and shut lines back in the 60's to gain the odd tenth here and there.

Andrew
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mgbv8
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PostPosted: Mon Jun 01, 2009 11:06 am    Post subject: Reply with quote

Andrew
They are stock 4.6 heads, but with a bit of port matching done at home. Exhaust is RV8 style with the collectors cut to 3". Then 3" secondaries of approx 20" each side.
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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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CastleMGBV8
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1975 MG MGB GT V8

PostPosted: Mon Jun 01, 2009 4:19 pm    Post subject: Reply with quote

topcatproduction wrote:
Not sure what the others think perry but I would be tempted to try out an offy 360 manifold instead of the eddy performer you have on there, supposed to be much better for high rpm but lose a bit of low down torque, I would also remove the choke flap from the carb, only a restriction and more turbulence and a 5 minute job, just plug the holes the bar went through after! If you look at nascar holleys they are completely smoothed for nice airflow. Also what air filter are you using? If it's a round type you may consider replacing the solid top with a filter (like the one I bodged up in my mx5 thread!)

Just more thoughts re the engine! Also I think Kevin and Ian are right about the aerodynamics, at 125mph they play a big part!

TC


Tom,

Not sure where you heard that the offy 360 flows better than an Edelbrock Performer. Most opinions are that the edelbrock is superior all the way from idle to 5500RPM, I've also seen back to back dyno tests and with the carb optimised the Edelbrock was up to 20 BHP better!

It can get confusing as people state the Offy manifold is a good manifold to use in certain applications but this is solely down to it being approx 1/2" lower and works well in say in MGB with limited space under the bonnet.

FWIW

Kevin.
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Darkspeed
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PostPosted: Mon Jun 01, 2009 5:03 pm    Post subject: Reply with quote

Thats my understanding of the 360 as well - good for bonnet clearance issues but thats about it.

I have a Wildcat Spider on mine that gets pretty good revues and must admit that it seems to work quite well on my car.

It's the primary diameters and lengths that are the important factors - and for torque and power I think that your first priority would have to be with bigger exhaust valves - what goes in must come out and the engine is gonna choke at some point with all that charge going in there.

First job would be the exaust ports and fitting medium valves - and using 1 5/8 bore primaries at least

Andrew
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topcatcustom
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PostPosted: Mon Jun 01, 2009 8:22 pm    Post subject: Reply with quote

Sorry I rekon you are right about the offy as it is a low riser- but am I still correct thinking that 360 degree manifolds (high riser variety) are generally better for high rpm as an oppose to 180s like the eddy performer? (just I thought the EP was made for all round driveability which isn't important in Perry's situ!)

TC
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mgbv8
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1975 MG MGB GT V8

PostPosted: Mon Jun 01, 2009 8:27 pm    Post subject: Reply with quote

My thoughts too Andrew!

The performer seems to handle this setup better than the 360 did.

But a lot of this will be down to just how much the stock heads can breathe eh?

I just wish I could data log as she runs like a nutter up to the 1/8th mile marker and then just dies away. 100mph at the 1/8th marker, then only 125 at the finish ??

Now!
To test this even further I suppose I need to up my nitrous quite a bit, but with a slower build time on the controller. By the time I hit the 1000 foot marker I feel like I need another bit of boost as she is revving in the high 4000's with not a lot of torque.

But as the engine is revving faster there is only so much juice it can drink in a given cycle eh?

I know she will take a 200 shot all day long with a fixed hit of 60hp off the line and the other 140hp coming in over 2.9 seconds.

Maybe I should up the nitrous to a 300 shot and increase the build time to say 5 seconds.

I've got a few idea's floating around in my head to try this at the Retro Show in July.

I've just started modding the rear suspension again ready for the 14th at North Weald. So I'll keep the settings I've got for that to see if the mods work or not Smile

I tend to get a bit carefree near the end of the season so I may just aim for that 300 shot in a few of months if all goes well in July...Then I'll know just how much these stock heads will handle.
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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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