My Starlet is currently running a 38/38 DGES with a header, open exhaust, and some intake manifold porting. I couldn't really ask for better performance. However, I am planning on building another 1.3L 8 valve four cylinder for the car with a mild cam, 10.5:1ish compression, and mild head porting. I can't run DCOE sidedrafts in the engine compartment due to strut tower and brake master cylinder/booster clearance issue. That leaves downdrafts.
Could I get any improvement in going to DCNF or IDA? Also, I know there are tricks to modify a 38/38 but searching the internet reveals little info. It seems like working with Webers is becoming a lost art--fuel injection seems to have made them almost obsolete on anything except vintage period correct vehicles.
Thanks
JP
RX-7 sidedrafts use a 180 degree manifold. Could you fab up something like that?
I'm looking at running a 38/38 on my GLC 1.3L race motor. I'm currently using the 32/36 but I think the sequential setup will give me better performance. I just need to get the race motor off the jack stand, etc., etc.
I have also considered trying an ITB setup (either carb or FI) off a ~1L motorcycle engine. The intake would have to be custom but I have seen it done. Another option if you have limited room on a side draft set up with DCOE's it to look at the Mikuni 40/45's. They are a lot shorter and are supposedly butt simple to tune.
If class rules allow it, can you run bike sidedrafts? Quite often they are very short for packaging reasons and can be bought cheep on the Bay of E. Interesting adaptation of CBR900RR carbs:
Woody said:
RX-7 sidedrafts use a 180 degree manifold. Could you fab up something like that?
I could indeed fab up something like that and have thought about. The question then becomes what do I gain by going DCOE over 38/38 DGES? I've seen RHD Starlets run two DCOEs giving one throttle plate per cylinder and they certainly "sounded" good. That seems like a lot of carb for 1.3L...And, if I fabricated a 180 style manifold the runners would be long--that's going affect the powerband, no? I'm weak up top but nice in the low to mid range. My cam was selected to keep this characteristic mostly intact. If I remember right longer runners usually improve low-end? Might work out okay if that's the case.
hobiercr said:
I'm looking at running a 38/38 on my GLC 1.3L race motor
Do it. Once you go 38/38 with the right jetting you will NEVER go back to a 32/36. There is no hit on mpg and everything--I mean everything--else improves.
Curmudgeon said:
If class rules allow it, can you run bike sidedrafts? Quite often they are very short for packaging reasons and can be bought cheep on the Bay of E. Interesting adaptation of CBR900RR carbs:
I can run whatever I want--they'll just bump me up which doesn't bother me. Flat-slide bike carbs tend to be the most compact, correct? I was under the impression that they were still kind of expensive. I don't know much about tuning them--is there like a "Flat-Slide/Bike Carb" GRM type forum? Books maybe?
And I don't think I've ever seen bike carbs on a Ford V8...
Here you go. (vw vortex link) Not sure how helpful it'd be but bike carbs were (are) popular swaps on VWs. You may find some tuning hints there. I had a DCOE manifold for my Golf but could never afford Weber sidedrafts so I toyed with using bike carbs instead. Never did it though.
A buddy of mine converted his 2.0L SOHC motor from a single throttle body to a set of ITB's and gained 12hp with no other changes than retuning the EFI to account for the change in the amount of air available.
So, yeah throttle response typically improves along with power output at the expense of mileage. Proper sizing of the throttle plates will go a long way to ensuring they work well and there are equations available to calculate the throttle plate size based on your engine configuration.
The caveat with ITB's or multiple carbs is the potential challenge in proper balancing of each throttle body/carb and properly tuning them.
Yes, longer runners will improve your low end power curve at the expense of the higher RPM ranges. If you want to experiment with some curved, 180 degree runner, look at the early (77-79) BMW EFI motors, they have a set of runners that bolt to the intake manifold and form a pretty decent 180 degree turn with fairly easy to work with flanges at both ends. Some work with a grinder and you can clean them up pretty well. 4-cylinder cars had slightly larger runners compared to the 6-cylinders.
http://77e21.info/mstunedintake.htm
In reply to Curmudgeon:
Do you have a link to that? that is of great interest to me. I had an idea to run 8 carbs on an SBF, but didn't find anything at the time...
In reply to redvalkyrie:
My original race motor had dual DCOE 40's on a 1.3L engine. With an aggressive cam and custom long runner intake it was amazingly strong for a small displacement motor. Torque for such a light car was phenomenal. When I switched classes from GT5 to HP I had to go to a stock intake and the weber.
I've got a photo of my setup somewhere.
In reply to hobiercr:
I'm definitely be interested to see your setup!
I know tricks exist to hot up a 38/38. Nobody is very clear on the internet as to what to modify. Anyone here know of any 38/38 tricks? Any good books on 38/38 carbs?
Thanks
JP
redvalkyrie wrote:
I don't know much about tuning them--is there like a "Flat-Slide/Bike Carb" GRM type forum? Books maybe?
And I don't think I've ever seen bike carbs on a Ford V8...
They're really simple(at least the ones I've cleaned for people on various old bikes), you've got an idle jet, main jet (WOT mixture), you adjust the needle on the slide for midrange, then there's an accelerator pump and a cold start jet, that about covers it. The style with the diaphragm running the slide on a vacuum line is called a "CV carb" and is tuned more or less the same way, can't recall the point of them though.
The 38/38 is a step up from the 32/36, and pretty much a bolt on. I'm not sure if a DCNF would gain you anything over a 38/38, especially since it has a different base and will require an adapter.
The IDA, on the other hand, is pretty much a DCOE standing up and can offer quite a bit more airflow over the 38/38.
Over on opelgt.com there are some good tuning threads for 32/36 and 38/38s if you can't find more general info anywhere.
As to bike carbs the biggest issue is part throttle stumble because most bikes are so light the engine can speed up quickly enough for a throttle change that the carbs have little or no accelerator pump action. Toss those carbs in a car and they don't enrich well enough for good tip in response without being pig rich.
