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School me in the ways of intaking fuel and air...

Posted by Mad Matt F 
Mad Matt F
Matt Follett
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Location: La Belle Province, Montreal
Join Date: 03/13/2006
Age: Midlife Crisis
Posts: 578

Rally Car:
Don't Laugh, the Justy is Fun!


Re: School me in the ways of intaking fuel and air...
February 05, 2017 05:57PM
winking smiley

So I stop just before I put dents in the hood?

Seems a 1000 more rpm isn't that much, and if it's still making power, there's no valve float right? So in theory the valve train is fine at that rpm?
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Robert Culbertson
Robert Culbertson
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Location: Portland , Or
Join Date: 08/15/2010
Age: Party Animal
Posts: 1,209

Rally Car:
MK2 VW GTI



Re: School me in the ways of intaking fuel and air...
February 05, 2017 07:06PM
What type of valve train does the mighty justly have? Direct acting or are there rocker arms?
What's the stroke of the engine?
How thick are the rods? Weight of the piston?

I do know that a stock b230 (80mm stroke) Volvo bottom end can sustain 8k rpm for a few seasons once you toss in some stiffer valve springs. I know nothing about the mighty justy.
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Mad Matt F
Matt Follett
Mod Moderator
Location: La Belle Province, Montreal
Join Date: 03/13/2006
Age: Midlife Crisis
Posts: 578

Rally Car:
Don't Laugh, the Justy is Fun!


Re: School me in the ways of intaking fuel and air...
February 05, 2017 10:14PM
Robert, thanks for coming in.

Data? Data?

What is this??? Can't we just theorise on some unknown and solve the problem???

Meh... I thought this was a site for bench racing... winking smiley

Okay best I can do at this time, is:

Single overhead cam… rockers, don’t have one to with me to measure right now.

Valve springs
length 45.5 mm
Diam 27.5mm
Wire diam 4mm

Cam
Intake
Valve Opening = -2.4 'BTDC
Lobe Center = 108.2 'ATDC
Valve Closure = 26.4 'ABDC
Duration = 204 Crank Deg
Max Cam Lift = .20673 IN.
Net Valvelift = .3101 IN.
Lobe Area = 16.34 IN. *Deg

Exhaust
Valve Opening = 29.3 'BBDC
Lobe Center = 109.4 'BTDC
Valve Closure = -2.4 'ATDC
Duration = 206.8 Crank Deg
Max Cam Lift = .21142 IN.
Net Valvelift = .31713 IN.
Lobe Area = 17.35 IN. *Deg



Bore x Stroke: 78 mm x 83 mm

Piston 234 g
Wrist pin 83 g
Rod 474 g
Rod, pin, piston 791 g
Rod centers = 13cm

I remember years ago JVL looking at a rod and commenting on how beefy it was for "such a pissy little motor" winking smiley

Compression 10.5:1



Edited 1 time(s). Last edit at 02/05/2017 10:16PM by Mad Matt F.
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Robert Culbertson
Robert Culbertson
Ultra Moderator
Location: Portland , Or
Join Date: 08/15/2010
Age: Party Animal
Posts: 1,209

Rally Car:
MK2 VW GTI



Re: School me in the ways of intaking fuel and air...
February 06, 2017 11:50AM
I forgot how beefy those engines were. We rebuild a few at my dads machine shop and we were really surprised at the size of the rods and crank in them.

So Mean Piston Speed is the deciding factor on RPMs if you're not worried about the rod and piston parting ways. As a general rule of thumb 20m/s-22m/s works with stock (thick) rings, cast pistons, and good oil.
The b230 volvo in the rally car has an 80mm stroke, and HEAVY cast pistons with decent rods. That engine has sustained 8k rpm for minutes at a time, and lived over 6k rpm for most of 25 rally races.
The MPS was 16m/s-21.3m/s for 6k-8k rpm.
If the valves aren't floating and you're still making power, there's no need to be worried in that range.

For the Mighty Justy: 16m/s is 5780rpm and 22m/s is 7950rpm... as a reference.

Also, you can still make power when floating the valves, if done properly. Read up on valve lofting, it's pretty cool!
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Mad Matt F
Matt Follett
Mod Moderator
Location: La Belle Province, Montreal
Join Date: 03/13/2006
Age: Midlife Crisis
Posts: 578

Rally Car:
Don't Laugh, the Justy is Fun!


Re: School me in the ways of intaking fuel and air...
February 06, 2017 12:56PM
Sweet!

Thanks Robert.

Pedal'er down! winking smiley
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