lack of vacuum on 200 with 250-2v head

dawnovsky

Well-known member
Hi,

i am still havin a bit of a hard time in getting my engine to work properly.

i have remove the cylinders head recently to change the cam after i have found camshaft was damaged.
when i fisrt installed the head a few months ago, i get perfect vacuum immediatly.
since i have change the cam (i don(t know if it is cam related or not for now) i only get vacuum reading of about 13-14.
accordingly, advance have to be pushed further to get engine to work properly on idle.
compression test (dry n cold) show correct value between 135 and 150 psi (read cold, dry, wot, after 4 compression cycle).
i have track down few vacuum leaks already, and carburator , adaptor plate, and intake manifold gaskets are new.
PVC valve is connected at carb base plate port, and advance and tranny vacuum lines are connected at the vacuum port of the intake manifold ( cylinder 6 intake) of the stock 250-2v intake manifold.
there is still a tinny leak between the tranmission modulator and solid tranny vacuum line, but really something minor i ll try to have fix asap;
i don't now where to investigate now.

the cam is said to be a 264/110 from claysmith.
lifters are new from CI ( claysmith).
head had been tested year ago and new valves installed (slightly oversized exhast as stock were not available).
carb is a holley 350 (purchased new when head was first installed 8 months ago).
carb plate is new.
ignition is a ds2 with manifold advance, cap and plugs cables might need to be replace (on order).

i have been able to get descent idle condition, and good on drive idle once engine is hot, but, vacuum still low, advance is high (about 20 initial), and performances not to bad, but not as they should (just guessing).
could this be cam related? i don't think so as it is not a aggressive cam.

what is your opinion ??


regards
 
dawnovsky":3b5wbeb4 said:
Hi,

i am still havin a bit of a hard time in getting my engine to work properly.

i have remove the cylinders head recently to change the cam after i have found camshaft was damaged.
when i fisrt installed the head a few months ago, i get perfect vacuum immediatly.
since i have change the cam (i don(t know if it is cam related or not for now) i only get vacuum reading of about 13-14.
accordingly, advance have to be pushed further to get engine to work properly on idle.
compression test (dry n cold) show correct value between 135 and 150 psi (read cold, dry, wot, after 4 compression cycle).
i have track down few vacuum leaks already, and carburator , adaptor plate, and intake manifold gaskets are new.
PVC valve is connected at carb base plate port, and advance and tranny vacuum lines are connected at the vacuum port of the intake manifold ( cylinder 6 intake) of the stock 250-2v intake manifold.
there is still a tinny leak between the tranmission modulator and solid tranny vacuum line, but really something minor i ll try to have fix asap;
i don't now where to investigate now.

the cam is said to be a 264/110 from claysmith.
lifters are new from CI ( claysmith).
head had been tested year ago and new valves installed (slightly oversized exhast as stock were not available).
carb is a holley 350 (purchased new when head was first installed 8 months ago).
carb plate is new.
ignition is a ds2 with manifold advance, cap and plugs cables might need to be replace (on order).

i have been able to get descent idle condition, and good on drive idle once engine is hot, but, vacuum still low, advance is high (about 20 initial), and performances not to bad, but not as they should (just guessing).
could this be cam related? i don't think so as it is not a aggressive cam.

what is your opinion ??


regards

You didn't mention whether you had manual or auto trans. I installed the exact same cam in my 200 with an Autolite 2100 carb (245 CFM) and a C4 auto trans with a stock converter. I also had about the same vacuum that you are reporting. I think the relatively narrow 110 degree lobe center separation makes this cam profile a bit aggressive for a 200 (for a 250 it would be a bit milder). Not only did I have difficulty getting my 200 to idle, but it would stall at traffic lights. However, the 200 pulled strongly at mid-range RPM.

I also think 350 CFM is a lot of carb for a mildly built 200.

Bob the Builder
 
Yep, I agree with Bob on both counts. That's probably the best vacuum you will see from that grind. :( your combination is likely mis-matched and this might just be the best you can do with it. Even though the duration is not too wild, the overlap is quite high especially with an auto with stock-ish converter. You will likely have to set the timing when it is warm and as low an RPM as you can manage and also continue running manifold vacuum to the distributor can. If it runs well at 20 degrees initial and doesn't experience detonation or run hot, leave it that way.

If it aint broke, don't fix it. :beer:
 
I run the 264/274 110* CAM, and it' getting 7-9 vacuum, but as you mentioned the bas plate for the carb to the head was leaking... currently the head is getting rebuilt (the 2bbl conversion I used putty, someday brazing will fix it once and for all)

once I get the head back I bet I'll get 10-12 vacuum if I can seal it all up properly. but you vacuum seem great. it's all you're gonna get.

I've been running this cam with the same 250 head, 350cfm carb, and 264/274 110 cam for about a year now, recently just switched over to a GM type TBI setup. and it still did the same before the intake broke.
 
You've done well, and clearly read through the earlier post on the four things you needed to do. viewtopic.php?t=69008

You still need to double check your intake manifold for leaks.

Now, you've done everything except reposition your cam, ignition and converter stall ratio change.


The 264 is not a screamer cam, but it is just a very high intensity cam which just needs 9:1 compression, good effective compression and with the big port area from the Aussie head, it's right on the cusp of getting good performance.

There are three things to do now. See if Cam reposition helps, then igntion curve, then stall ratio for converter. I'd say that we can eliminate increasing the valve clearances manually by using the adjustable rockers, it won't help idle or cold cranking compression.

STEP 2 is to look at the ignition curve and then,STEP 3 lastly, converter stall ratio change if those first two don't fix your problems

Your cold cranking compression is quite low. I'd expect more compression, but it may be all you'll get.

If your idle is still a concern, then its time to look at the distributor advance curve. This may be the whole problem. The use of the right curve can turn a latent engine into a raging bull. If it likes 20degrees, then if might like a different, fast advance curve than what youy have. If you think its giving less than its best, its more likely advance curve than the converter ratio.

The Clay Smith cam requires good compression, and will work best with just the right combination of the 2V heads great port area, a good 2-bbl carb like you have, and a little work with getting the cam postion right for your engine mighr be all that's needed.

Just one other question!

Could you please tell me if you have the stock 25 thou steel gasket, or the 41 thou composite, is the chamber still 59 to 61 cc, and are your pistons the stock 5.5 cc dish items.

Your cold cranking compression is really low, and maybee you don't even have the bare minium 9:1 compression ratio you need to make this cam work.
 
My setup is pretty much what xtasy said, I have the 264/274/112.
I've recurved the dizzy, installed cam advanced, ported head, and had the stock converter tweaked. They were able to get it to about 2200rpm. I have a 1946 carb with an oversize jet and a hole drilled in the throttle plate. Steel head gasket, maybe 9.1:1 CR.
Vacuum is pretty much the same as yours. Idles around 9-10 when warm and 13-15 at highway cruise. Idles at around 800rpm in neutral and 750 in gear, but the idle is lumpy.
buggitybruggitybruggitybrugbrugbrugbruggitybrugbrug :LOL:
I chalk that up to poor fuel atomization although I've found it's sensitive to transmission fluid level too. If it's too low the idle gets more rough.
This cam does not like to idle around and loves to wind up above 3000rpm.
And it doesn't like the cold.

But yah if you haven't shaved the head and used a new composite gasket in your head swap your CR will be too low.
 
hi guys

thanks for answer.
it start to makes sens.

what would be a good compression reading for cold engine ?
rings are kinda news (4-5 years old and not much miles)
i m using a composite head gasket
head was milled before. i have mesure it to about 55 cc, but it was not state of the art mesurement so it might be a 1-2 cc more or less.

idle and drivibility is now not too bad (once vacuum leak from C4 tranny fix).
A bit high hot, a bit low while cold.
choke not installed currently, as 350 choke is a pain to conect with a 250-2V head in a mustang.
i also had hard time to have the choke operate properly. it seems even very little variation of the choke plate makes the engine stall.
i have then remove the choke plate ans use the system has a idle corrector with good result, but my cable is a piece of crap that i need to replace.
 
xctasy":1vju1lmi said:
If your idle is still a concern, then its time to look at the distributor advance curve. This may be the whole problem. The use of the right curve can turn a latent engine into a raging bull. If it likes 20degrees, then if might like a different, fast advance curve than what youy have. If you think its giving less than its best, its more likely advance curve than the converter ratio.

what would you recommend to curve the dizzy.
springs and cans can be sourced, but plate (10L-13L it think that s what i have) don't seem to be easy to find.
If you know a dealer, let me know.
regards
 
You have the good plate.
All you need is Mr Gasket 925D spring kit.
Although there will be those that say it must be done a machine.
 
hi

something i always forgot to considere when reading either shopmanual or forum is that, in europe (this is including New caledonia as a french oversea territory) we are using 95 octane gasoline. This is allowing to push ignition advance way further than US 87 - 89 octan regular gasoline.
It might be part of the picture.
 
dawnovsky":11kbmve1 said:
hi

something i always forgot to considere when reading either shopmanual or forum is that, in europe (this is including New caledonia as a french oversea territory) we are using 95 octane gasoline. This is allowing to push ignition advance way further than US 87 - 89 octan regular gasoline.
It might be part of the picture.

Different ways of measuring, US uses an average of the Research Octane Number and the Motor Octane number (sometimes called Anti-Knock Index or AKI), while most other countries use the Research Octane Number only. RON 98 equals to about US 93 AKI rating, while 95 RON is equivalent to around 89 AKI.

Pretty good chart here:

http://en.wikipedia.org/wiki/Octane_rating#Examples_of_octane_ratings
 
I read it all in 1988, when David Vizard opened the whole (RON+MON)/2 thing in Modiying Fords SOHC. He discussed the cost plus margin issues with higher test fuels, and why the US lowered the fuel octane requirement for all vehicles in 1972, that it was an economic excerise. The days of Sonoco 260 and Five Star fuel in the US and England ground to a halt in with the Yom Kipper war, and the critical break even economics of fuel production govern the percentage of high to ultra high octane fuels around. In a finacial crisis, oil companies need to be able to limit the higher octanes, and adjust (inflate) the price of it by under production. Nothing has changed since 1972, although in Japan, 100 RON octane fuel is used for there Type R Hondas, and some cars are no longer able to operate on US 87 AKI fuel. Other engines have 4 rated horsepowers, 87, 89, 93 and 95 AKI (91/95/98/100 RON), with the cars able to adjust timing via piezo electric knock sensor.


I think the US rating is sensibile, but a few sources, like Motor Trend in the 80's, made incorrect references to RON being the " at pump rating" when it was actually (RON+MON)/2 rating. That has made it hard to convert to what is now called AKI. US cars since 1972 ,Japanese cars since 1975, and all Australian and European cars since 1986 have been designed for 87 AKI (our 91 RON). Some German cars, like some Bugs and many Steyr Puch Mercedeas G wagons, Porsches and even some Italian cars like some Ferraris have been designed with 87 aki capability since the late 70's. (Unlike our OHV engines, Ferraris don't need 11:1 compression).Specific models have a 95 RON (89 US AKI rating), like the Turbo Volvos, the 1997 Ford Falcon EL GT with the US GT40 Cobra SVT 5.0 Windor OHV, and US Type R Hondas, but can run on the mandated 91 ron at a pinch with a specified horsepower loss.

So a Kiwi, Aussie or French Pacific Territory owner has 91, 95 or 98 pump gas(Regular, Premium/Super, Ultra) which are your US 87, 89 and 93. Pretty simple.

All our Falcons, right up till the cross flow were designed for 97 RON leaded, (your old 92 Super) and then got downagraded to 91 octane( your 87) in 1986. But special Taxi versions of the Falcon, Fairlane and Cortina were around that ran on Aussie Standard gas from 1961 to 1981, then they stopped when unleaded started to get phased in.

One other thing though. US fuel, although it varies hugely over the US, its not aromatically inferior like other Pacific fuels...its total amount of benzene/tolulene based aromatic series is mandated to low amounts for public health reasons. NZ fuel especially the 89 and 93 (RON+MON)/2 equivalents, are very high in thinners to get the RON target, and its shelf life is short. And as we are now learning, benzene/tolulene in cross sectional studies has proven to be more or a health hazard than tetra ethyl lead ever was. Which is way Avgas for air planes has always stayed with its 105 RON rating, high lead content. It meets the public good by not dropping out of the air due to fuel system failure and octane attenuation that is common with high aromatic fuels.

I love free market economicis, but I do I like the lower grade gas, and doing the modifications to run it seam more sensible than paying the game of chance when petrochemical companies to raise the octane for you. Flex fuel has been a way of car makers to cover the risks of alcohol blends, but no-one is going to provide a service for free, so high octane blends are always going to be a risky proposition for most of us.
 
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