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ITBs
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friggin  



Joined: 30 Jul 2015
Posts: 39
Location: Montana

PostPosted: Tue Aug 04, 2015 5:23 am    Post subject: ITBs Reply with quote

hey guys, I'm looking at building my factory engine and am wanting to run an ITB setup. I've found pictures of them done online but wanted to see if anyone here has done them. If you have what all did you have to do to make them work? Thanks!
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Tue Aug 04, 2015 5:28 am    Post subject: Reply with quote

For starters, check out the references section of this post in the Performance Mods thread.
http://www.924board.org/viewtopic.php?p=218954#218954
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75 Fiat X1/9 | 80 US 928 | 80 US 931 '941' | 78 D-Prod Replica | 78 Poli-Form
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fiat22turbo  



Joined: 18 Jan 2006
Posts: 4040
Location: Portland, OR

PostPosted: Tue Aug 04, 2015 7:13 am    Post subject: Reply with quote

Yep. I've run 45mm DCOE style ITB's on my relatively stock 79 bottom end.

It kinda sucked.

No low end at all.

https://youtu.be/S4Xe2TSU8ko

Keep in mind, my 924 is pretty much a hot air balloon at this point. Stripped interior/sound padding, racing seats, fiberglass hood, quarters, nose, GTS headlights, no CIS or A/C, etc. Ford EDIS distributorless ignition controlled by MegaSquirt. The only places left to lose weight would be the glass (planned) and cutting out parts of the remaining sheet metal (possible depending on the time I have this winter).

Anyway, I used a higher lift cam, a Franco automatic timing gear and tuned velocity stacks to balance the power curve a bit more. It made a noticeable difference. Still only have about 110hp to work with.

Next step is to either up the compression ratio (with a block cut or new pistons) or move down to 40mm units as the 45's are just too big for the low compression motor.

Actually I'm going to turbocharge it with the BAE turbo manifold I have as I've already converted it back to a single TB. Might as well make use of this low compression motor as cheaply as possible! I may investigate going back to ITB's with the turbo once I get the tuning fairly close and get a season of racing under my belt. We'll see.

That said, tuning ITB's with whatever EFI solution you use is no where near as well documented or as easy as using a single throttle body is.

This lack of info makes it much more of a difficult project that seems to show little actual results over a single throttle body and that can be very discouraging. It becomes a matter of which you prefer more, building or driving?

Bottom line? I'd work on getting the engine healthy, improve the flow into, through and out of the head, then convert it to run on a single TB and tuned well. Then convert to ITB's once you have a good idea of what the engine is capable of and how to tune it.

Just my $0.02

CorsePerVita is also running ITB's on his 77 924 racer and we've helped each other quite a bit with sorting out the tuning as he is also running MegaSquirt. I'm sure he'll chime in here if he gets a chance.
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Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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MikeDanger  



Joined: 21 Nov 2002
Posts: 495
Location: Denver

PostPosted: Tue Aug 04, 2015 7:48 am    Post subject: Reply with quote

I'm working on using Hyabusa ITB's if you want to get in on it with me, as I build my kit.
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friggin  



Joined: 30 Jul 2015
Posts: 39
Location: Montana

PostPosted: Tue Aug 04, 2015 9:01 am    Post subject: Reply with quote

Thanks guys! I was looking to do a stroker kit, ITBs, a race head (or just get it ported), a bigger cam, and a good tune, then if it's still not enough power look into turboing it if I don't jack the compression to high with the stroker kit. I'm looking to get around 200-240hp for an end goal but I'd be very happy with 180hp NA if I could. I'll be using my car mostly for autocross courses. Is there anything else that can help make the car faster other then loosing weight? I plan on taking out the back seat to lighten it up a little but I'll be using the car for my DD in the summer so I want to keep some of the creature comforts. Thanks!
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Tue Aug 04, 2015 9:28 am    Post subject: Reply with quote

180BHP on NA is going to be quite a stretch. That's what the factory D Production cars were getting at 13:1 compression ratio and many thousands of dollars of high end race kit. I seriously doubt you can get those numbers without forced induction.
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motormouth  



Joined: 28 Feb 2010
Posts: 115
Location: Canton

PostPosted: Wed Aug 05, 2015 12:23 am    Post subject: Reply with quote

Have you finished the D Prod tribute car yet? I am curious as to how much power an turbo head being run NA is going to put out. How much better does the turbo head flow if the flow is the limiting factor in the NA head?
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Wed Aug 05, 2015 2:23 am    Post subject: Reply with quote

motormouth wrote:
Have you finished the D Prod tribute car yet? I am curious as to how much power an turbo head being run NA is going to put out. How much better does the turbo head flow if the flow is the limiting factor in the NA head?


No, it's still sitting in the shop in Plymouth. Next trip will be to bring the Club Sport back, and DProd after that. Last two trips will be for the UWB and then all the shop equipment.
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MikeJinCO  



Joined: 08 Jun 2010
Posts: 929
Location: Maysville, Colorado

PostPosted: Tue Aug 18, 2015 11:45 pm    Post subject: Reply with quote

My experience with cylinder heads and flow.

I have been tinkering around with both NA and 931 cylinder heads for 2 years on a homemade flow bench. In stock condition the NA and 931 have similar intake flows. On the exhaust side the NA is vastly inferior. It is easier to increase the intake flow with port cleanup and some porting as the intake port is a more conventional design for a NA head. It is still not good as the flow has to turn about 130 degrees in the head. I found that I could increase the intermediate lift flows on the 931 head, but when I got up to .450 lift it fell off. That could be a lack of bravery on porting, I really need a junk 931 head that I can saw up to see the port wall thickness. The NA has a classic asymmetric kidney shape around the turn, the 931 is round for a pressurized application
and could use more of the kidney shape to influence the flow toward the center of the cylinder rather than toward th partially shrouded cylinder wall side.

On the exhaust side the NA head with 33mm valves is hopeless. Besides the small valves the ports are rough, too small and flat sided around the turn. I have done everything that I can think of too do and the flow still doesn't reach that of a stock 931 exhaust. I even sawed up an old 38mm intake head the opposite way of the Boards porting work and the port walls are too thin to get a large enough port, particularly around the turn. A racer/race car shop owner I met near Denver with a flow bench and many years work on Datsun 240-280z's said that the trick on tight turn radius heads is to get the exhaust out more than getting the intake it. Notice all the threads about how adding headers has very little to no effect other than noise.

I am working on putting together a 931 head NA motor, but the car it is going into is currently getting taken apart rather than put back together and it will take at least another year or so..
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
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friggin  



Joined: 30 Jul 2015
Posts: 39
Location: Montana

PostPosted: Wed Aug 19, 2015 12:59 am    Post subject: Reply with quote

So you can use a 931 head on my 924? And it will make more power due to it having more flow? I believe my engine just lost all compression so I will be doing a complete rebuild and am looking for more power. I'm going to be doing a roots remote style supercharger to help.
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2038
Location: MI

PostPosted: Wed Aug 19, 2015 1:42 am    Post subject: Reply with quote

friggin wrote:
I believe my engine just lost all compression


Sounds like possibly a slipped timing belt if you lost all compression on all cyls at the same time..
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Wed Aug 19, 2015 2:12 am    Post subject: Reply with quote

931 head for NA motor requires extensive and expensive mods. It's not a bolt-on affair.
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MikeJinCO  



Joined: 08 Jun 2010
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Location: Maysville, Colorado

PostPosted: Wed Aug 19, 2015 3:03 am    Post subject: Reply with quote

Ideola's exactly right. On the exhaust the ports fit, but the bolt setup is slightly different. The intake ports don't quite fit requiring rework and again the bolt setup is off which on the CIS manifold could get interesting. Then of course the piston issue to have some compression means new pistons are required.

All doable but not to be taken lightly.
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Poco a Poco, #033 '78 Vintage racer, SCCA Dp-81
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Fasteddie313  



Joined: 29 Sep 2013
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Location: MI

PostPosted: Wed Aug 19, 2015 4:48 am    Post subject: Reply with quote

I wonder if you could deck the 931 head or NA block enough to get decent compression for a turbo and just install the complete 931 top end onto an NA bottom end to replace a 931 short block, and end up with a non-interference engine.. Like going VW flat tops..

What exactly does a 931 head on an NA bottom end yield for a CR? What does that piston/CR situation look like really?

friggin could probably just go with a 931 intake manifold to solve some of that problem no?
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motormouth  



Joined: 28 Feb 2010
Posts: 115
Location: Canton

PostPosted: Wed Aug 19, 2015 4:55 am    Post subject: Reply with quote

Ideola already talked about various combinations. There's a set of rods out there that can be used with a machined crank to get any CR you could possibly want. Then the 931 head and your set. Similar to the D production cars.

http://924board.org/viewtopic.php?t=36293&highlight=cheap+stroker
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