Question about a few modifications

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Odoyle
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Your car is a: 1983 Pinafarina Spider

Question about a few modifications

Postby Odoyle » Wed Oct 26, 2016 10:26 pm

I have some questions about a few modifications I've seen/heard and want to know if anyone has can confirm or deny their benefits.

1) Front brake banjo bolt mod enlarging the hole to 2.5mm in diameter. I assume this would be to increase rate and pressure of the brake fluid against the piston. Though I assume the existing hole is the size because the engineers designed it that way, but... who knows.

2) Drilling extra holes in the airbox (fuel-injected cars).

3) Seam sealing/stitch welding shock towers, frame, rear towers, obviously done to increase rigidity, but would it put increased strain on parts which are not seam welded?

4) Cutting a coil off rear springs, does the brake compensator need to be re-adjusted?

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RRoller123
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Your car is a: 1980 FI SPIDER 2000
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Re: Question about a few modifications

Postby RRoller123 » Thu Oct 27, 2016 7:17 am

2) better sound, very slight improvement in performance. perceptibly quicker, but only slightly. The original air box snorkel is a significant restriction to flow.
'80 FI Spider 2000 (rolling "resto")
'74 X1/9 (many years ago)
'79 X1/9 (fewer years ago)
'86 Jaguar XJ6 (2nd Hobby Car)
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/SB
2015 Keystone Montana High Country 343RL

carl
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Joined: Mon Oct 06, 2008 9:56 am
Your car is a: 1971 128

Re: Question about a few modifications

Postby carl » Fri Oct 28, 2016 1:04 pm

Drilling holes in the airbox will free up a little more power. There was talk many many years abo about enlarging the banjo bolt holes but I don't recall any consensus on the effects of that and really have not heard it mentioned in a long time. Make sure your brakes are completely up to snuff before worrying about that and if you can already lock up your brakes (easy enough to check on a lonely road) then your tires are currently the limit of your brakes. Don't know about seam welding the chassis but unless you plan to do some serious racing I don't think this is an issue. In theory, anytime you adjust the height of your spider you would have to make sure the compensator linkage is properly adjusted although many of us remove the whole compensator assembly and throw it in the trash.

klweimer
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Location: Arvada, Colorado

Re: Question about a few modifications

Postby klweimer » Fri Oct 28, 2016 9:21 pm

I would skip any modification to the brake system. There's almost zero fluid flow through through the brake lines when you step on the brakes. You don't need flow, you need integrity.

I would also skip any additional welding on top of the existing spot welding, unless the existing welds are falling apart. In which case, you have bigger issues.

Personal opinion.

Kirk

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Your car is a: 1982 131 Superbrava warmed 2.0 litre.
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Re: Question about a few modifications

Postby 131 » Mon Oct 31, 2016 4:14 am

Cutting springs is desperate ghetto behaviour. Lowered springs are not expensive or hard to find. You'd be hard pressed to show an improvement attributed to drilling the banjo bolt, the piston doesn't move much when brakes are applied, so a large volume of fluid transfer isn't required.
Mick.

'82 2litre 131, rally cams, IDFs & headers.

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Odoyle
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Your car is a: 1983 Pinafarina Spider

Re: Question about a few modifications

Postby Odoyle » Mon Oct 31, 2016 1:26 pm

Thanks for the feedback guys, at least I can put a few of these ideas to rest.
So for #2, is there any sacrifice on low end power? I would imagine the extra holes allow for better air flow at high RPM, but is there a measurable drawback for power in low RPMs.

carl
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Re: Question about a few modifications

Postby carl » Mon Oct 31, 2016 1:59 pm

I never noticed any reduction in power at lower rpm with a modified airbox.

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RRoller123
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Re: Question about a few modifications

Postby RRoller123 » Tue Nov 01, 2016 6:21 am

No reduction in power. Think of the snorkel as a resistor in a system with a set of resistors in series. The airbox holes are reducing, or basically eliminating the resistor from this initial section of the system. The next resistor is the air filter, then the AFM flap. The mass flow of air and its resultant fuel allocation is still regulated by the air flap in the AFM, but the flap can now react a little more quickly to this lower resistance just before it. At high RPMs it can allow a little more flow when the system starts to hit its flow resistance limits. Basically we are just making certain that the snorkel is no longer the highest resistor along the line. The intake manifold ports become that at higher speeds. (my best guess anyway, since I haven't actually measure any of this, just a thought experiment.)
'80 FI Spider 2000 (rolling "resto")
'74 X1/9 (many years ago)
'79 X1/9 (fewer years ago)
'86 Jaguar XJ6 (2nd Hobby Car)
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/SB
2015 Keystone Montana High Country 343RL


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