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Posted: Thu May 17, 2012 1:25 pm
by mgbv8
kiwicar wrote:mgbv8 wrote:Another issue I would expect with the single plane mani is the front cylinders of the engine leaning out when racing. I have to put up with this on mine. Its not uncommon but it does need to be taken into account when tuning for racing with hard acceleration for sustained periods.
Its all down to budget really I guess.
This happens with or without boost when you stick a big carb on an open inlet manifold. It still happens on dual plane mani's but to a lesser extent.
I tune mine on the front plugs to make sure I have my safe mix up front for drag racing. I will soon be able to remove this issue when I fit my direct port nitrous injection kit. I will then be able to jet and tune fuel and nitrous to each cylinder.
This would be the formula I use for sizing a carb on your engine.
215 ci X 6000 max rpm / 3456 = 373.26 cfm.
Add in the boost factor. 1 bar is atmospheric pressure so 7psi of boost = 1.5 bar total pressure.
373.26 cfm x 1.5 = 559.89 cfm required from carb.
For 15 psi, call it 1 bar of boost you would need….
373.26 cfm x 2 = 746.52 carb cfm required
So the carb sizing is ok in my book for a drag race application where we dont really bother about part throttle use. I tune mine on the dyno at wide open throttle only and this has been fine for me
Interesting, not how I would calculate it on a blow through set up. May be suck through but not blow through
Best regards
Mike
I only know suck through Mike. Its all I've done so far
Posted: Thu May 17, 2012 3:36 pm
by stevieturbo
If it ain't blown, it sucks
Posted: Thu May 17, 2012 4:24 pm
by kiwicar
Hi Perry
I always used a rule of thumb, for a road car or bike that the total throttle plate area seen by any cylinder should not be more than about 1.75 X valve curtain area (circumferance of valve times lift) other wise the throttle ceases to be effective, ie from about 2/3 peddle movment the throttle is effectivly fully open. certainly for a normally aspirated engine it is a good guide, for a blow through carburetor you might want to work of 1.5 X curtain area.
For a suck through carb then it is different as you have a constant draw on the carb from the blower and the air passes through uncompressed, I think your calculation is OK for that situation, mbut for this chap, I think he will have issues unless he screws the secondarys shut. I have seen a recent article in Car craft on a 454 chevy with a blow through turbo using a 650 mechanical secondary carb with 750 throttle plates, and it was not under carbed.
Best regards
Mike
Posted: Thu May 17, 2012 7:54 pm
by mgbv8
stevieturbo wrote:If it ain't blown, it sucks
Love it Stevie !!!
Posted: Thu May 17, 2012 7:56 pm
by mgbv8
kiwicar wrote:Hi Perry
I always used a rule of thumb, for a road car or bike that the total throttle plate area seen by any cylinder should not be more than about 1.75 X valve curtain area (circumferance of valve times lift) other wise the throttle ceases to be effective, ie from about 2/3 peddle movment the throttle is effectivly fully open. certainly for a normally aspirated engine it is a good guide, for a blow through carburetor you might want to work of 1.5 X curtain area.
For a suck through carb then it is different as you have a constant draw on the carb from the blower and the air passes through uncompressed, I think your calculation is OK for that situation, mbut for this chap, I think he will have issues unless he screws the secondarys shut. I have seen a recent article in Car craft on a 454 chevy with a blow through turbo using a 650 mechanical secondary carb with 750 throttle plates, and it was not under carbed.
Best regards
Mike
Like I said Mike!
I dont blow. I only suck
Posted: Fri May 18, 2012 6:20 pm
by mgbv8
stevieturbo wrote:Ran mine for years blowing thru a carb and single plane. Never had any issues with mixture distribution. It is not a concern.
I have to dissagree on that one Steve. Mainly from my own findings with plug readings between dyno and the 1/4 mile.
Other guys I race with have experienced the same. Under hard acceleration the fuel does tend to lag behind the rate of acceleration inside the manifold on a carb setup. Especially with an open manifold nasp or supercharged.
I'm talking purely 1/4 mile runs here mind. In many cases we can get the front plugs leaning off and melting the earth strap if we dont over fuel a bit.
I can do a dyno pull and get even plug readings. But on the track the fronts will show a leaner mix than they did on the dyno.
Thats why EFI and DP injection on nitrous systems is the best way to go when using large hits of gas.
When I say plug readings I mean with a clean shut off after the power pull on dyno or track so the plugs dont get contaminated on the over run.
Just my own experiences mind.
perry
Posted: Fri May 18, 2012 7:03 pm
by stevieturbo
It's maybe something unique to a suck through carb setup.
Certainly nothing I ever had a problem with, and I ran mine twin turbo for several years with the single plane.
Posted: Fri May 18, 2012 7:21 pm
by mgbv8
stevieturbo wrote:It's maybe something unique to a suck through carb setup.
Certainly nothing I ever had a problem with, and I ran mine twin turbo for several years with the single plane.
Food for thought???
Next year I would like to attempt a turbo or pro charger setup on one of the engines so this would be an interesting thing to observe.
Pro charger is my ideal aim for the V8 Escort though.
Posted: Fri May 18, 2012 7:27 pm
by stevieturbo
If you want to make power, turbo is definitely the way to go
A Centrifugal can also make power, but does have good points and bad. But for drag race only if that's what it's for, turbo will be faster easier.
Posted: Sat May 19, 2012 9:13 am
by Boosted LS1
I used twin rotomasters in my Tr8 with a 4.5 engine and a holley 600 dp in a simple blow through configuration. Never had any problems with it. That was many moons ago. It was defo a fun car.
Posted: Tue Jun 19, 2012 1:20 pm
by thewedgeshop.com
Car should be up and running shortly. Had some issues with plumbing in a return line the way I wanted. Should be done this week.
Will post pictures and videos.
Thanks
Clint
Posted: Wed Jun 27, 2012 12:33 pm
by thewedgeshop.com
It runs. Should have more video and update on how it drives shortly.
http://www.youtube.com/watch?v=6xbAQXerlr4
Thanks
Clint
Posted: Wed Jun 27, 2012 7:12 pm
by stevieturbo
good stuff. Very interested to see how the carb works out.
Posted: Wed Jun 27, 2012 9:08 pm
by john 215
Hi Clint,
Sounds great mate
Looking forward to seeing a video of it running down the road
Cheers John
Posted: Wed Jul 25, 2012 1:59 pm
by thewedgeshop.com
Some quick vids of it running.
Car still has some bugs to work out, currently is running great on 10psi at half throttle, but is having some issues at full throttle. Will try to sort it out in the next two weeks.
http://youtu.be/ecIH4YAtBxg
http://youtu.be/cMqX5duPgOM
Thanks
Clint