Woke up at 3 AM this morning and it hit me:
Can using a 283 header on a 350 engine alter or affect in any way the vaccum of the engine?
Educate me por favor :)
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Woke up at 3 AM this morning and it hit me:
Can using a 283 header on a 350 engine alter or affect in any way the vaccum of the engine?
Educate me por favor :)
No.
Don
>Can using a 283 header on a 350 engine alter or affect in any way the vaccum >of the engine?
Probably not to any noticeable degree. Most off the shelf small block Chevy "street" headers are generic with regard to primary tube diameter. When used on a 350 instead of 283 (all else equal), exhaust gas velocity may increase by virtue of the increased displacment, but that ain't a bad thing.
Bob
The reason I ask is because the common complaints Eric and Lonnie (2 previous owners) have about my current 350 engine is that the vacuum is not 'quite' right. Hector (friend of Lonnie) measured it and said it did not match what a 350 vacuum should be. Said maybe there is a different cam on it (but I don't think so). Vaccum being off, the 3 deuce set-up has not been working. I am currently running on 1 carb.
Now I also know that Eric swapped the previous 283 Chevy engine (which died on his way to the NSRA nationals in 2002) with a crated 350 chevy. He did the swap while at the show, in one day.
The same headers that were on the 283 still are on my current 350 engine.
http://www.bettatalk.com/images/DSC04330.JPG
I don't know enough about engines yet to know for sure, but by simple logic, it seemed to me that possibly if the headers were restrictive it could create some kind of "pressure"...??
Or maybe I am completely losing it - since i have NO CLUE what I am saying LOL :LOL: :LOL: :LOL:
But just in case I may be right, I thought I'd ask. Is it AT ALL possible it might be affecting my vaccuum, throwing it off just enough to mess things up?
THose are whats called "rams horns" manifolds and they make a very distinct exaust note.
The manifolds you have are very good for that engine. If you have a different cam your vacuum will be effected. Could be a intake leak??? Have you had anybody look at it other than the people you bought it from???
>Hector (friend of Lonnie) measured it and said it did not match what a 350 >vacuum should be. Said maybe there is a different cam on it (but I don't >think >so). Vaccum being off, the 3 deuce set-up has not been working. I >am >currently running on 1 carb.
Vacuum is affected primarily by cam timing and the induction/intake system. It can vary from what you'd see on a stock engine to less vacuum on engines with more radical cams. Those look like small base Rochester 2G's on your three duece set up. I'm assuming you're running some type of progressive mechanical linkage?
>I don't know enough about engines yet to know for sure, but by simple logic, it >seemed to me that possibly if the headers were restrictive it could create >some >kind of "pressure"...??
You're not completely off base with your reasoning regarding the exhaust/vacuum relationship. Extreme restriction in the exhaust system can prevent complete purging of exhaust gas from the cylinder on the exhaust stroke. Any residual exhaust gas left after the exhaust stroke will diminish the volume of intake charge on the intake stroke and thus affect vacuum.
Bob
My guess is that you have a vacuum leak. Check all of your vacuum fittings to see if the are tight, and check the hoses to make sure none are cracked. Vacuum leaks can cause havoc with the way an engine runs. That is a nice looking engine BTW.
Faith,
If you have a stock 'mom and dad' car's engine, no matter what the make, the vacuum should be steady somewhere between 17 and 21 inches Hg (mercury) at idle speed (5 to 600 rpm). I prefer 19-21"Hg
A camshaft, different than stock can lower it - how much depends on the grind.
You have triple carbs - I almost can guarantee that one of them leaks vacuum somewhere, unless totally blocked off between the carb base and manifold. Possible leaks can be found at the throttle shafts, at the base and intermediate castings, cracked castings, missing vacuum takeoff point plugs or split hoses just to name a few areas. If triple carbs didn't look so great, my suggestion would be to put on a single 4bbl and manifold, but.....:LOL:
The intake to head(s) gasket may also leak.
The timing could be set incorrectly.
The mixture screws in the middle carb may be set wrong.
The mixture screws in the end carbs may not be seated - they should not be open at all on a 3x2 setup.
You may have valve, lifter or rocker problems.
You may have a leaky piston ring (or several).
You could have a bad spark plug or wire
You can pick up a vacuum gauge cheap at Auto Zone (or whatever you have there on the Left Coast) - but these are the kind of things that can lower vacuum readings - and on a pre-computer engine are the cheapest and best diagnostic tools available.
But since I've said all this, how does it really run? Skip, idle too rough, poor gas mileage, shift lousy(if it's an auto - I don't recall). If none of those are a problem, you may be worrying over nits.
Can you explain what you mean by a "distinct exhaust note" ? How does this differ from the way a 350 SBC sounds with headers or other exhaust manifolds? Thanks, Topless...Quote:
Originally Posted by shawnlee28
As the Irish guy said..........vacuum leak. If you are not using the other 2 carbs, it would be best to seal off those carbs. A simple sheet metal plate under the carb between 2 gaskets would do it.
Rams Horn exhaust manifolds are an excellent way to go.
Imo, they flow as good or better than most 'convenience' block hugger headers which are more manifold than they are headers.
If you have the time they can really look slick if you grind the casting down smooth, remove unecessary protrusions and bumps then coat them with anything from ceramic to Jet Hot.
As others have said, the cam profile (how radical etc.) makes the difference in vacuum at idle.
How much vacuum do you have and what RPM are you reading it at?
Fwiw, my 462" Buick runs 18.5" - 19" at 600 rpm idle at a 350' altitude with a very mild cam.
Very mild being a step or so above stock with timing figures of 260 & 266 degrees advertised duration.
(Don't confuse this figure with timing figures taken at .050 valve lift. They will be different to a considerable degree. This cam is 204-210 degrees duration at .050 lift.)
When the bigger cam was in, idle was 600-650 RPM and vacuum was 11" - 12" at the same 350' altitude.
286 - 292 degrees advertised duration in this case.
These lower vacuum figures due to camshaft profile and not vacuum leaks.
Once the engine is spun up to a no-load RPM of 1000-1200, vacuum levels are equivalent to a stock engine.
Keep in mind too that changing altitudes will change idle vacuum levels.
To the tune of 1" lower for every 1000' altitude gained.
The milder cam noted above idles at 15" - 15.5" at the cars present 3333' altitude.
When the engine is spun up to 1000-1200 no-load RPM, vacuum levels are the same as they were at the lower altitude.
Note that these lower vacuum levels - due to camshaft profile - require changes in carburetor tuning.
Different metering rod springs for Carter/Edelbrocks and different power valves for Holleys.
When these carbs are in standard - as received from the manufacturer - configuration they will be too rich on the bottom end (idle and low-mid RPM levels at light engine loads) due to the metering rods on the Carter/Edelbrocks will open dumping excess fuel in and the Holley power valve will open which does the same thing.
Along with the vacuum reading, what kind of cam is in the engine?
you could switch exhaust manifolds (headers are individual tubes going to a common collector) and probably not notice 1" of difference in vacuum....
I notice that you are runing and oil tube directly into the intake manifold and down into the valley between the bores. I am asking on the other side of the engine are you running a pvc valve out of the other rocker cover. Because sometimes the spring in the pvc valve goes soft and the engine will draw air and a little bit of oil mist into the intake. A sign of this would be low vacume and a little bit of blue smoke out the exhaust under load. Of corse the oil level in the sump would drop a little too. :HMMM:
I agree ..sounds like a leak some place. On another note I dont like ram horns. Have you ever considered a header that goes over the frame?Quote:
Originally Posted by rumrumm
Might not be the look or sound you are looking for but it is an idea
What is the vacuum reading and what rpm does the motor idle at in Park or neutral. How low can you get it to idle without stalling?
Could you explain EXACTLY what the people you have talked to mean by the vacuum being off and what vacume sourse you are using to get your vacume reading. A vacuum gauge can be a very good tool for diagnosing engine problems but different symptoms give different gauge readings and knowing what those readings are is the key to answering your question.
As mentioned the vacuum problem may be an external problem such as a mis-sized PVC valve, leaking manifold or the end carbs on your Tri-Power. Unless they are completely blocked off (i.e. a solid plate between the carb and manifold) you may have a vacuum leak originating from there.
From what you indicate it seems the intake worked well on the 283, but not so well on the 350......not a real big surprise considering it was now being asked to feed 67 additional cubic inches. That big of a jump would require major re-jetting and there is a good possibility the center carb should be changed out for a large base version of the Rochester.
The plates are simple to make and good tool for isolating a carb problem/vacuum leaks. Get a roll of roof flashing (any hardware store) which is simply thin aluminum sheet. Use a carb base gasket as a pattern and cut the plates with heavy scissors (bolt hole can be punched with a hollow gasket punch as a drill will tend to catch and twist the sheeting up. Install the block-off sandwiched between 2 carb gaskets (Car Quest part number G7327 are a good gasket to use) and then bolt the carb down. This will eliminate the end carbs as a potential problem, and either give you a place to look for a vacuum leak to move on to someplace else.
I can't tell for sure but it looks like your may be using an Offenhauser intake and these can be a little touchy to get dialed in correctly especially on an engine bigger than a 327. The manifold was originally designed in the early 60's when SBC engine displacement was only 283 and 327 cubic inches. Early literature I've seen from Offenhauser actually show them configured 2 ways....for "Economy" with a single 2 BBL carb in the center location and the end sealed with block off plates (in effect what you are doing) and for "Power" with a block off plate in the center and 2 end carbs installed. Based on this litterature it appears that Offenhauser never really intended to have these set up for 3 carbs with progressive linkage.
Configuring them for 3 carbs with progressive linkage is not a big deal and they do work well that way (personnal experience of having used the same manifold on a 307/327/383 and 350 (currently on a 72 LT1) they can definatly be made to work).
Anyway for now the best bet is to provide what the specific vacume readings are are concerning people to give people a better idea what is occuring.
Yes they have been plated )sealed off) already by last owner, who reverted to that to solve the problem. He tried to make the progressive linkage work, but the car would not idle right, it ran OK once going faster. He ran out of money and gave up LOL. He did not have money really and that is why he sold the car when he moved to Northern CA. he couldn't keep it financially. Anywhoo, this is WAY down on my list of "to do" things but I like to start investigating ahead of time so i am ready when the funds are.Quote:
Originally Posted by poncho62
Engine runs good, never stalls. It does seem to idel a bit rough (possibly - but not sure) and may be eating up too much gas (about 10 to 12 miles per gallon). Otherwise powerful and pretty fast.
Ok tell me why you dont like Rams horns?
Sorry i will make a post on it
They have a distinct sound that I dont like.... almost like marbles in a can at high RPM and I dont think they are very attractive to look at when showing your engine bayQuote:
Originally Posted by daveyboy1956
Quote:
Originally Posted by HiboyGal
I'm with Mike P, what is the vacuum reading, the idle speed and where are you sourcing the gauge from?
One experiment you could do would be to try each carb in the center position with the outer two carb mounts blocked off by a plate.
Sounds like you already have plates that would work.
If all the carbs function ok why not run them with straight linkage?
I've had many different multi-carb setups and ran them all with straight linkage.
Progressive linkage is ok . . . if you get a good one . . . there's a lot of junky stuff out there posing as progressive, but some of it is downright dangerous.
One setup I see now and then is nothing more than bent wire for the sliding part.
You can make a high quality straight linkage for about $30. - $35. for parts and a little time with a hacksaw, grinder and die.
Depending on what you're running for a throttle control (cable - ok, rod- best) you could make up a nice throttle rod setup to match.
HBG,
What you need to find is a greybeard that can tune a real motor.
Three two's should run fine on your 350 with straight or progressive linkage. If it has a stock cam (which I suspect) that would explain why it runs so well with end carbs. blocked off. Vacuum leaks and the way the pvc and breather are installed is something that should be checked. I have used a vacuum gauge to tune for years and it is how you adjust a carb. and I use it to set timing (although a race motor is another story). Some folks will probably not agee with this method but there's more than one to skin a cat.
I adjust carb. for higest vacuum reading (adjusting mixture and idle speed) and adjust dist. untill I get the highest reading. I usually have to back off timing a hair if I have trouble starting, but that is usually not a prob.
So much for my rambling. I hope you figure it out soon.
Keep on Truckin' (Roadsterin':confused: )
Jim
P.S. 12 MPG sounds awfull low, 18-20 seems more in line with your combo.
There have been numerous dyno tests on the SBC with 2 fours and with 3 twos ... a single 4 barrel carb on a aluminum performance intake always made more power ... gave better mileage and was a LOT easier to live with ...
That's why most folks use them ... over the old outdated multiple carb systems ... :3dSMILE:
They ( single 4 barrel setups ) also have less vacuum leak issues ... and are easier to tune :)
I would buy a new 600 CFM Edelbrock and a Edelbrock aluminum intake for it ... seal up the intake well and you would be amazed at the power gained and the mileage improvement ...
Yeah that is all well....but..... Those 3 x 2 barrels on that manifold blend in well with the rest of the roadster. They make it look "complete". 1950's style, it would be shame to wreck that look.
The other thiing is vacume leaks, try and locate the sorce of the leak manifold vacume lines, carbs.
Manifold - It has been around for a while it could of been decked to suit the other chevy, that is a new crate motor in there, so you could have a leak between the manifold and the heads from different angles and not lining up properly.
vacume lines probably the easiest fix, if they ar hard cracked or broken just replace them. Also while your at it check to see that the vacume advance canister on the distributor is not ruptured.
Carbs old worn linkages leak vacume from the slop caused by wear, see if you get much radial movement. If you want all 3 set up and going again, might pay to get them rebuilt and balanced, it is expensive for this plus getting the right linkage set up, you probably want with those carbs, using amechanical progressive linkage something like the 2 end carbs gradually coming in when the primary middle carb is around a bout half open. The whole idea being that the transition happens smoothly.
No, no, no I am not going to a 4 barrel :mad: i LOOOOVE my 3 deuces the only thing i like more than 3 deuces is SIX DEUCES :LOL: :LOL: :LOL: !!
http://www.bettatalk.com/hiboy%20images/DSC04540.JPG
Pretty sure those are 6 Stromberg singles, but we get the point...........
isn't it something? really beautiful....:)