XFfalconman95 25 Posted July 4, 2015 Hey all just wondering if anyone would be able to give me a pointers tuning my 250 crossflow? Engine is cammed, with 2 wire dizzy and 350 holley. If more details on engine are needed just ask. Any help would be much appreciated, thanks in advance. Share this post Link to post Share on other sites
slydog 7,873 Posted July 4, 2015 Whats wrong with it ATM ? Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 4, 2015 Running rich as and I just cant seem to get it right. Share this post Link to post Share on other sites
slydog 7,873 Posted July 4, 2015 Rich @ idle or the whole range ? A bigger cam WILL always be richer @ idle due to the engine not been efficient till later in the RPM thanks to the camshaft duration. If you have a REAL big cam it will run rich but read lean on a 02 sensor due to the oxygen in the pulses been greater and not mixed with fuel as well @ low RPM. Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 5, 2015 Ok cool thanks. Just seems to be way to rich at idle. Share this post Link to post Share on other sites
broken-wheel 659 Posted July 5, 2015 how much vacuum are you pulling at idle ? Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 5, 2015 Unsure. Need to get my hands on a vac gauge during the week Share this post Link to post Share on other sites
ando76 4,354 Posted July 6, 2015 Set idle mixture to give you best vacuum possible at idle. Best way without an o2 sensor and then size your pv to suit. Half idle vacuum is a good start. As everyone has said above it will be hard to get perfect at idle without the use of adjustable air bleeds but you should be able to make it acceptable. From there is it just a matter of plug reads but a decent AEM afr guage can be had for under $300 delivered (search e bay) and you will be able to get is bloody close with careful monitoring whilst driving. I have used the AEM units for years and even on methanol the sensors survive very well. I love the gauges that much I have one on my boys single cylinder buggy engine. 2 Outback Jack and PRO250 reacted to this Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 6, 2015 Legend thanks for that Share this post Link to post Share on other sites
broken-wheel 659 Posted July 7, 2015 don't be scared to push your idle a little to get best vacuum or close to it as morning starts will love you, with the power valve every motor is different, i'll probably go against the grain but what I do (this is on 4bbl) is this. I go on the highway and see what vacuum i'm pulling at 100km/h, i write this down. I go doing 60 km/h on a slight hill and see what vacuum i'm pulling then I write this down, I average these and this is what I'm choosing when looking at the PV, you don't want enrichment before whatever vacuum you're pulling at 100km/h or doing 60km/h on a very slight incline or you will just throw money down the exhaust pipe. Share this post Link to post Share on other sites
ando76 4,354 Posted July 7, 2015 and when you do that, how different is it from if you just halved engine at idle? like more than 3 sizes??? Share this post Link to post Share on other sites
broken-wheel 659 Posted July 7, 2015 idle vacuum is dependant on way too many things, for starters cam and rings make a huge difference power valve is an enrichment and should not be doing anything under light load or cruising, if you follow your formula it might not work will all cams, also i see no need of an O2 gauge for adjusting/selecting PV Here is some reference on where the PV comes into play This is specific to Holley but makes you wonder why people say the Holley 350 is a bucket with a hole in it when in fact it's probably tuned to shit. When you have big overlap below say 1500 rpm half the cyl fill in one cyl comes from the exhaust of another cyl so it will be drawing fuck all vacuum but will sound bad ass, if you go by your rule then you will select a PV that will dump fuel in like 14 year old on red tube Share this post Link to post Share on other sites
ando76 4,354 Posted July 7, 2015 ok that's all great information but I would really like you to answer my question. when you do your way of power valve tuning, how different is it from half vacuum at idle? That's what I'm keen to know. PS - half manifold vacuum at idle is not 'my theory' - it actually comes from a Holley in their own YouTube videos as a baseline. Oh and read my post - I was not suggesting you need an O2 sensor to size power valve. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
broken-wheel 659 Posted July 7, 2015 yes, so does the "drop two sizes from your idle vacuum in Drive and that's your PV size" but that is with a stockish cam and then it's all OK but once you have a bigger duration cam then things change as your mercury at idle is lower, even a mild cam can lower the mercury to 9 so you then fit a 4.5 instead of the stock 6.5 or whatever comes with the stock Holley? then I bet if you hook up a A/F gauge you'll be in the mid 11's when cruising which is not very good. Now some people think old school and want a FAST PV so instantly adds fuel when you smash the pedal and whoops more fuel at cruise and part throttle. It will stumble when you want to take off and you get frustrated and try stupid shit like playing with air bleeds and poking wires in them and all sorts of shit until you get sick of it and take it to a pro and let him fix it. I'm not trying to have an argument with you but I have seen so many people complain about fuel usage even when their carb is set up by a "gun" but as soon as you put an A/F gauge on it the bullshit stops and you tune for what the engine wants. I think my old motor was pulling 7 inches and i had a 6.5 valve which gave me 14:1 at 95km/h with 3.27 on the rear, this dropped to 12.5:1 at 100km/h! yes I could of tune it further but 95km/h was ok for cruising, if i would of followed the /2 i would of had a 3.5 valve and dump fuel like nobody's business, i think i would of been on the PV while doing 90km/h Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 7, 2015 If you need it i can get a photo of my cams spec sheet Share this post Link to post Share on other sites
ando76 4,354 Posted July 7, 2015 Nah mate - not interested in an argument - just interested to hear the answer to my question and you have done that. I build and tune these things for a living so I'm always interested to hear other theories as no one knows everything. I spend a stupid amount of hours dyno tuning these engines - some meth - some petrol and one thing that has taught me is that there is no one size fits all approach the OP was asking for advice on tuning his engine and suggested it was rich at idle. That's why I gave him baseline advice - straight from the Holley book as often - simple baseline tuning is adequate to cure most situations. after that AFR's are a must. that's why dynos exist and O2 sensors are a massive part. so back to the OP - have you got this solved yet. Share this post Link to post Share on other sites
ando76 4,354 Posted July 7, 2015 cam specs will help. Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 7, 2015 http://i1049.photobucket.com/albums/s393/Crazy_Wolfman95/20150611_214657_zpsiymswgne.jpg There we go. Hopefully that works. Where abouts are you located for tuning ando and how much do you charge if you dont mind me asking Share this post Link to post Share on other sites
broken-wheel 659 Posted July 7, 2015 has a bit of a lope at idle that one Share this post Link to post Share on other sites
ando76 4,354 Posted July 7, 2015 overlap puts it in the street performance range. Not overly big on the lift tho. I'm at the other end of the country mate - Cairns. Share this post Link to post Share on other sites
XFfalconman95 25 Posted July 7, 2015 Hmmm yeah just a tad far. Ok thanks for all the help. Will give this engine a tune to get me by until my new engine arrive. 1 Outback Jack reacted to this Share this post Link to post Share on other sites
