HB250 3 Posted February 18, 2015 Gday guys, i have a issue which i am unable to sort on a moddified 250 crossflow. The engine is one of dave adams originals which i rebuilt. I did rings and bearings and shaved head the slightest to ensure flat. Specs are, 250 crank/rods - balanced Hp balancer Acl race pistions - 12.5:1 Work c2 head Dual springs 120seat Solid cam 600lift Cain 2 barrel manifold 650hp holley Avgas. 6al Ss coil Remanufactured dizzy locked at 25degs (it doesnt like more) Now the issue is, i cant get it stop missing, ive tried everything, and only luck i seem to have is removing the ignition box and running the dizzy module but even after time it develops a miss, ive changed boxes, plugs, leads, carbies, dizzys and cant get rid of it, Anyone ever had this? Is it possible dizzy doesnt send enought trigger for msd? I need help guys. Cheers, Share this post Link to post Share on other sites
slydog 7,873 Posted February 18, 2015 Halls effect TFI dizzy or electronic ? Sounds like it's a resistance/heat issue in the ignition. Are you running a colder plug ? For that comp I'd be running a REAL cold NGK bps8-9 even on the street as it has ALOT of comp and not much cam so dynamic compression would be high.Thats part of the reason you can't wind timing into it...and thats a bad thing. Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Good day mate, its electronic dizzy, im running ngk8s atm, i dynoed it today running on module only and 8s and it was smooth for about 5 runs but noises over early and later developed a miss again Share this post Link to post Share on other sites
slydog 7,873 Posted February 18, 2015 Electronic dizzy cannot keep up regardless of what anyone tells you. I'd ditch it an go straight to a TFI dizzy and then you get a solid square wave signal that is day and night compared to a electronic unit. You have too much comp for that cam and AvGas and will always be limited to how much timing you can give it which has you at detonation point constantly due to cyl pressure. Dave Adams was a guru for sure and no one will ever shit on his work but your sort of in the middle ATM. Hate to say it but perhaps a move to a programmable ignition is needed as well if your not willing to take some comp out. With that cam and bottom end how it acts I'd have no more than 11.7 @ most. Just saying bro... Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Perhaps i will change dizzy, where do you suggest i get a tfi? Still wire threw msd? This exact combo ran 11.4 all day mate it won 2 tri series and a xmas tree at some stage, before i rebuilt it, however had no dizzy and i switched carby. Ive tried it on e85 also and still doesnt like more than 25deg either. With comp test, only shows 185 do cam must be bleeding off fair comp? Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 And why is the hall effect elec sufficent with the hall effect sensor wires on the msd? Share this post Link to post Share on other sites
slydog 7,873 Posted February 18, 2015 After you throw the module off it MSD to TFI dizzy goe's like this,you use Black as the earth,Red as the power (12V switched) and green as the pip/trigger signal (white trigger from MSD) from the 3 wires off the TFI dizzy. Orange from MSD goe's to coil positive and Black from MSD to coil negative Done it too many times and yet to hear ANY ONE complain it didn't work.TFI is one step off crank trigger and it helps limit stop spark scatter plus you get a much stronger signal. Why not do it when all the fast guys do...? You can get 1 from a XE EFI car,wreckers or even a EST off a XF EFI car or late carb ute will work the same but the TFI is my favorite. So did you have it running 11.4 ? Have you got the same combo ? Is it in a Corty too and why did you change carbs if it was working before ? Why did you re-build it even ? If you can back step them changes you may find your answer somewhere but been so limited to timing shows a big issue. I run 12.3 comp in mine and have wound in 34 degree's before with zero rattle on a TFI dizzy but a designed chamber to suit. Ando will be on this soon and he may be able to help out too but he will tell ya to go programmable so you can dump timing then put it back in where it can take it.However watching mine on the dyno it loves timing as doe's Mossy's 11.0 NAT ASP xflow as it takes 32-33 every day locked aswell. Id suggest you could dump timing around 4800 and add it back after 5500-5700 as cyl pressure has dropped again by then if I know Ando LOL. Did you do your comp test WOT or closed ? I do mine open and find similar number but closed it's higher. I gotta leave for work. Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Sly, i really appreciate your help! i rebuilt it due to being due. It ran 11.7 @ 109mph with small miss, just before i bought it and previous ive watched it go 11.4. i rebuild it due to it breathing fairly bad and not being able to rev (weak valve springs)i changed carby due to original 1 being obsolete (top bowl feed holley) however ive tried both carbs back to back, and the dp does have slight increase. Its actually in a HB Torana mate lol. Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Sly i just remembered that on the dyno power starts to roll over at 5200 but increases alittle at 5600 is this due to timing and cylinder pressure? Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Sly, are ea distributors the same? They look the same? Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 Is it worth trying to get a thick head gasket or bigger cam to bleed off comp? Or is it possible cam timing could affect it? What do you recommend? Share this post Link to post Share on other sites
Thom 6,651 Posted February 18, 2015 Sly, are ea distributors the same? They look the same? dizzy drive gear is the opposite way up and they are a little different Share this post Link to post Share on other sites
ando76 4,354 Posted February 18, 2015 Gidday HB250. If you are running the XE style chopper wheel dizzy your problem will be right there. I don't care who modified it - or how good they are - the problem is not with the person that did it - it is with the design of the dizzy in HIGH RPM applications. I can not stress that enough. The chopper wheel dizzy in good condition, i.e. no wear in the top bush, is adequate for the street. Push them above 4500 consistently and they are next to useless. WHY I hear you ask. Because the wheel contacts the outer and creates a miss at high RPM due to harmonics created through the engine and transferred through the cam gear straight up into the dizzy where it rattles the shaft and BAM you have your miss above 5000rpm. My god if I had a dollar for every crossflow I've seen with this issue, I would be retired. Ditch it and go to a TFI dizzy - wire it as Rob has said and then you will cure that part of the problem. WHY? because the TFI (and the commonly hated on forums EST) dizzys only have a wheel with teeth missing, passing by a sensor with plenty of clearance. This means that even with the harmonics they still work. Yes you will still get a bit of spark scatter but you will not see or hear it as a miss - it will just lose 10-15hp over what it would make if you went to a crank trigger. You will still have issues unless there has been a shit load of good porting work go into that manifold. Those CAIN units have very uneven cylinder fill as cast - but if Dave has ported it - then it should rule that part of the problem out. I think the reason you are finding it wont take timing is within the Dizzy. Having said that there is absolutely no better way to make and build power than programmable ignition. I have made stupid gains with the 6AL2 Programmable units over locked timing on that many occasions it is not funny. But don't just take my word - Look at what Gerg did with his on his street car - its in another thread. It would be helpful to see a dyno graph of the engine as well - on that shows the AFR on the bottom as well as the power curve. I'm not interested in the HP numbers so you can cover them if you like. I just need to see the curve, RPM and AFR from the graph 1 Outback Jack reacted to this Share this post Link to post Share on other sites
ando76 4,354 Posted February 18, 2015 Oh and please tell me there is not a high volume oil pump in that sump? If so it needs to go ASAP. Don't get me started on those feking things..... 2 Ando81 and Outback Jack reacted to this Share this post Link to post Share on other sites
HB250 3 Posted February 18, 2015 You guys are absolute legands, i appreciate all input. If you send me you mobile number i can text photos threw? It only makes 200rwhp, who cares about the number lol. Runs time due yo 100% hopkup and no weight. Im graeme btw, new to xflows Share this post Link to post Share on other sites
ando76 4,354 Posted February 18, 2015 all good bud and welcome to the worlds most underrated engine. I have sent you a PM with my contact details Share this post Link to post Share on other sites
slydog 7,873 Posted February 18, 2015 So Errol Quartermaine car/engine? Share this post Link to post Share on other sites
HB250 3 Posted February 19, 2015 Excuse me sly? Unsure you reference. How ever thankyou to bout you guys, definetly running better now, could deffinetly reciece some gains with programable timing. Ans discussed with Terry, however ill runnit at drags on sunday and let you guys know. Makes over 200rwhp in the heat threw big convertor and 9inch with only 24-25 degress, should easily run 11s now. Cheers Share this post Link to post Share on other sites
slydog 7,873 Posted February 19, 2015 Errol Quartermaine from WA had a HB with a 250 in it...coincidence Share this post Link to post Share on other sites
wagoon 2,429 Posted February 19, 2015 HB would be really interested to see a few pictures of the car. Share this post Link to post Share on other sites
HB250 3 Posted February 19, 2015 Oh... Adelaide car mate. Hod do i post photos? Share this post Link to post Share on other sites
wagoon 2,429 Posted February 19, 2015 Photobucket. Free to sign up to. just upload pictures to photobucket and the click on IMG box which copies link then paste into the text box here. Won't show picture until after you post it Share this post Link to post Share on other sites
ando76 4,354 Posted February 19, 2015 Terry - my name is Tony - never mind at least it is running sweet now. Oh and another mystery solved by the OzFalcon team - Yahoo 1 gerg reacted to this Share this post Link to post Share on other sites
gerg 10,871 Posted February 19, 2015 So what was the reason for the miss in the first place... Or did i miss something? Share this post Link to post Share on other sites
slydog 7,873 Posted February 19, 2015 Don't lie Terry... 1 HB250 reacted to this Share this post Link to post Share on other sites
