924Board.org

[931fan]

Hi Guys
I've been lingering a while on this really great site but wondered if you could help me out?

I'm in the UK and thinking about a N/A 924 for the Historic Sports Car Championship 70's roadsports class see

http://www.hscc.org.uk/

I've raced a 924 in the Colway tyres series back in the mid 90's (that's me in red 57) so have some experience with car prep but I'd would really like to get stuck into a car build specifically for the 70's Roadsports as above.


To get competitive I really need make more power as, according to the regs the weight has to be 2376lbs.

The cam, compression, valves sizes, piston (+40 thou is allowed)and combustion chamber shape, exhaust and manifold can all be modified but I would have to run it on the standard K jet induction.

Has anyone been down a similar route to try and maximise what's possible bearing in mind the limitations? Failing that can anyone hazard an experienced based guess on what sort of power that I could reasonably expect if all the parts were optimised as above and the usual gas flowing, blueprinting, lightening steps were taken?

Thanks all

Steve
_________________
Whether you think you can or think you can't - you are right.

[ideola]

I doubt CIS will be your constraint on an NA. Dave Dennet's car is the most powerful (documeted) NA I am personally aware of (not including the factory D-Prod cars...). Details are here: http://www.924board.org/viewtopic.php?t=23247
Note the discussion around displacement, though...there is no evidence that the car actually had 2.4L of displacement...the specs seem to suggest 2.2L. FWIW, a board member here, daveo, now owns that car, but last I knew had some engine internal issues. See these threads:
http://www.924board.org/viewtopic.php?t=29085
http://www.924board.org/viewtopic.php?t=29837

I believe 924RACR has achieved something in the 130-140 BHP range, and that's with the limited mods allowed by ITB. So 140 should be fairly easily obtained with high compression oversized pistons and a big valve head, plus a header. You could consider a stroker, but not sure the ~$2500 cost would be warranted. You might be better served to knife edge the crank and run the lightweight Crower rods we commissioned; also add in a crank scraper.

For cam, I would recommend discussing your plans with Steve Greunwald at Integral Cams. For a full-on race application, I suspect his Stage 2 or Stage 3 would pair nicely with the other mods discussed.

And now for the obligatory shameless plug: I can help you source virtually everything you would need, minus the cam (go direct to Steve). That would include all of the performance bits, as well as the standard rebuild components like gasket sets, plug wires, etc. You can see a list of all the available components on my website with pricing:
http://garage.ideola.com/prod-2LEngineMods.html
http://garage.ideola.com/prod-Kingsborne.html
http://garage.ideola.com/prod-Kits.html
I have shipped extensively to international customers, so no worries there. Everything but the crank could be shipped fairly economically, best to have your crank work done locally. I can also get the crank scrapers, although I haven't added them to the site yet. Feel free to PM or email: dan DOT beckett AT ideola DOT com.
_________________
erstwhile owner of just about every 924 variant ever made

[fiat22turbo]

Spend all of your money on fixing the flow in the head.

I repeat:

Spend all of your money on fixing the flow in the head.

There are some interesting links in the Performance Upgrades section, check out the sticky post at the top and kick back with a good beverage and do some reading. There's one thread that shows a cut away of the intake and exhaust ports for the NA and turbo heads. They aren't very good ports.

The rest is just parts and careful assembly. Head work requires lots of experience, labor and testing to get it right.

Some thoughts off the top of my head:

Up the compression as high as you can (depending on the gas you want to or can run)

Lighten the rotating assembly as much as possible by knife-edging the crank. Use custom rods to increase high RPM durability. Build an aluminum flywheel with a lightweight racing clutch. Build an oil scraper to keep the oil in the pan and off the crank/rods.

Can you increase the stroke of the motor? offset grinding the crank journals can help increase displacement, which helps with torque output.

Then look at where the next bottle neck is. My guess would be the intake system. The extra turns the air takes into the engine doesn't help flow. See if you can straighten it out a bit more. I've also heard someone mention that the flapper in the fuel distributor can be effected by the G-forces in the car. So while investigating the air flow, look at what happens to the flapper when the car is most likely to be heavily loaded or have to change directions quickly.

I might look at a Lehmann inspired intake to improve distribution to the cylinders (not necessarily increase flow, but certainly to even it out, ensuring each cylinder is making the same power).

http://www.jasperintegration.com/distribution-plenum.html

http://www.bufkinengineering.com/intake%20manifolds.htm

http://www.elitedubs.com/index.php?topic=2275.0

http://forum.miata.net/vb/showthread.php?t=300335

At the very least a stock intake bottom combined with a larger plenum and throttle body could be a decent gain provided the K-jet doesn't become a restriction at that point.

A UT-CIS might also help you fine tune the fuel delivery while still keeping the K-jet, but that depends on the rules and what they'll allow.

http://unwiredtools.com/utcis.asp

A Franco Automatic timing gear can help widen the power curve a bit, but they are rare, expensive and add to your maintenance cycle. It will however help maximize the larger race cams because you're not having to sacrifice as much power at one end of the power curve or the other.

http://thorin.adnc.com/~figf/

http://forums.vwvortex.com/showthread.php?678454

Claims of gaining 5-10hp doesn't seem like much until you look at the power curves on the dyno plots and realize that while peak power changed only slightly, the area under the curve increased quite a bit, which is important in engine tuning. If you can make more HP at a lower RPM than your competitor and continue making power all the way to redline, then you'll be able to accelerate faster than they will and you'll be able to do it nearly anywhere.

Programmable ignition will help widen the power output as well, many people have found power in tuning the ignition on these cars. If you happen to find and use one of the Franco gears, keep in mind that the timing gear will also alter the ignition timing at the distributor.

A knock sensor might be a worthwhile investment to protect the internals in case you go too far with the tune. Certainly a wide band oxygen sensor and a set of EGT's that you can log their data will help in tuning.

For longevity's sake, you can look into improving the cooling system by using an electric water pump and reversing coolant flow through the engine. Seems to help reduce hot spots on the turbo cars, so a high compression NA motor should see some improvements as well.

I could guess at power figures, but I'd probably be wrong. Just figure that you'll be starting at 125hp and heading towards 200hp, if everything was perfect, in reality you'll be somewhere in the middle.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[ideola]

I'm pretty sure the G-sensitive AFM is only an issue on the 931, as the flapper travels the opposite direction than on the NA cars...

[zimm]

Hi,

nothing to add to the above technical advice really, the heads the biggest issue with regard to power

do everything and i'd guess you'd be around 140bhp @ the wheels on a good day.

this may be a good starting point for you if its still there ..

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330441014706&ssPageName=STRK:MEWAX:IT

not mine.. i viewed it a few weeks back as a potential parts car for another build, but something else came up. They were very open to offers, just want the space back.
_________________
6 bikes, 9 cars, 1 van.... the more you have the less they work.

[931fan]

Big thanks for all your help guys.
It would appear that I have some reading to do!!
If I could get to 140 at the rear wheels along with a set of 'short' ratio's it would definitely make the car competitive in it's class.
I'll let you know how it goes.
Fantastic site ideola I'll be visiting again for sure when my engine spec has been finalised with the builder.
Steve
_________________
Whether you think you can or think you can't - you are right.

[931fan]

[ideola]

Also, be sure to check out posts from 924RACR and his website, complete with build pix. Not all of the build details are the latest version of his car, but it will give you insight into things a real racer has done to milk power out of the 2.0L lump.
http://www.vaughanscott.com/
http://www.vaughanscott.com/construction.htm
_________________
erstwhile owner of just about every 924 variant ever made

[924RACR]

Perhaps an easier way to do this would be to figure out, based on your weight, how much power you'd need to make to be competitive, and then figure out what it'd take (in resources and cost) to make that happen.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Joes924Racer]

The colway series looks nice.. very nicely prepped cars and fun
smashing time I bet. I think all items you mentioned if done right
would net you more that 140 more like 150 - 155. Youd have
a huge enough increase in performance to give you a new
grip on racing.

A better breathing head is nice with a big open set of headers &
a ignition kick ... plus the cam.. Being Ive there done that only on
the street .. though.

Nice pics yea theres a few good people here youll step up and
give you a hand here anytime .. thats nice.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

[931fan]

[fiat22turbo]

It would have to be a pretty stoutly built motor to get that. It all comes down to Volumetric Efficiency.

http://en.wikipedia.org/wiki/Volumetric_efficiency

Unless someone knows what happened to the gentleman in the UK that was doing a lot of the work on our cylinder heads (including research into Porsche's decisions behind them) I'd probably start making inquiries into local cylinder head porting geniuses and speak to them about your goals and what they can do to improve the head. I would inform myself ahead of time of the basic terminology and make sure they do a before/after flow bench test to ensure an improvement was made and that it is even across the cylinders.

Here's some interesting articles for porting 101, it isn't Porsche related, but it gives you an idea of what can be done and why:

http://www.allpar.com/fix/holler/porting.html

http://www.allpar.com/fix/holler/porting2.html

http://www.allpar.com/fix/holler/head-porting.html

http://www.allpar.com/fix/holler/head-porting2.html

http://www.allpar.com/fix/holler/exhaust-porting.html

http://www.allpar.com/fix/holler/polyquad.html

http://www.popularhotrodding.com/enginemasters/articles/hardcore/0412em_porting_cylinder_heads/index.html

http://www.popularhotrodding.com/tech/0610phr_cylinder_head_porting/index.html

http://hubpages.com/hub/Cylinder-Head-Porting-101

Expect to spend a lot of hours there and expect to need a few heads to work with.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

[zimm]

[ideola]

[924RACR]

That'd be pretty tough to manage, but I think with the right budget, and no limitations, you might be able to pull it off. In addition to getting the '24 down to weight.

Not the cheapest way/place to play...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype