Carb Suggestions

[Alan_Mac 48]

  I have Bigs (4150) 950 Stage 5 carb and think it is too big. No bog or anything just not as responsive as it should be.  It has been tuned with an innovate.  I am thinking either a Quick Fuel 750 with MS or a 780 with VS. I also want a choke. Here is my application. 

Street warrior 
1970 Mustang Mach1 (likely around 3500 lbs with a full tank and me in it)
6200 RPM Max 
418W
AFR 205's
10.5:1 compression
Lightweight forged rotating assembly
Custom roller cam split duration @0,50, intake 219 exhaust 239
Mildly ported and flow balanced performer RPM intake
TKO 5 speed 3.27:1 first gear
3:50 rear 

Recommendations from carb experts requested!  
Alan

[barnett468 418]

what is your exhaust?

 

who told you to use a 950?

 

who made that cam?

 

throw that girly cam in the trash and get a mans cam

 

780 with NO CHOKE

 

set your timing CURVE for optimal perf.

[jholmes217 65]

Is your car a street car, street/strip, or full race?  For a street car I'd say 750 cfm with vacuum secondary, but I'd go bigger for a street/strip or full race.

[Alan_Mac 48]

what is your exhaust?

 

who told you to use a 950?

 

who made that cam?

 

throw that girly cam in the trash and get a mans cam

 

780 with NO CHOKE

 

set your timing CURVE for optimal perf. 

 

You obviously don't like my car,  950 mistake, I had a 780 before.  The cam is from long ago with an FMX.  FPA 1.75 headers magnaflow exhaust.  Who makes a 780 w/o a choke? 

[barnett468 418]

why is it obvious that i don't like your car?

[barnett468 418]

this will work fine with that wimpy cam

 

https://www.summitracing.com/parts/qft-sq-750-vs/overview/

[MikeStang 247]

Ha Damn Barnett My Cam isn't much bigger than his ... 228/236@50 563/571Lift on a 113LSA...Do I have a

Wimpy Cam also?.

On a side note I dynode with an HP 950 off of my 77Trans Am with a 455 and the carb was dead nutz on when we dynode the motor.

I have almost same build as you do buy run a Vic Jr. intake and only 408 cubes .. made 550hp at the crank.

I have tried a few different carbs on my car, and while I am running a 4R70W trans and 3.73 gears all of the carbs seemed pretty decent to me in terms of throttle response.

Here is what I have tried.

 

1. Holley Street Avenger 770CFM...This was probably the most peppy in terms of throttle response, but lacked a little in power compared to the rest..It was Vac secondary with elect choke.

 

2.Holley Street Avenger 870CFM.... less peppy on the throttle response but better top end power...Always seemed to run rich.... Vac Secondary and elect Choke.

 

3. HP 950 Built by Tom Vaught on the Performanceyeares.com boards...Was built and used in my boosted application on my 455 Pontiac...This is the one we dynode the 408 with, it made best HP and target AFR's were spot on for a NA motor... No choke. manual secondaries

 

4. Holley 850 Double Pumper with elect choke... This is what I currently have on the car right now.

I went back to a manual secondary carb so I could use my Top Shot N2O kit, and 850 seemed to be a good compromise between the 750's and 950, plus it has an elect choke LOL.

This seems to be the best compromise and gives me all of the stuff I want/need in a carb.

I need to tune it with my LM1 to get it dialed in perfectly but out of the box with stock jetting its pretty darn close and throttle response is instantaneous.

 

I am seriously considering the FiTech EFI unit however LOL, but this carb just works pretty damn good so I am on the fence ATM

[barnett468 418]

Ha Damn Barnett My Cam isn't much bigger than his ... 228/236@50 563/571Lift on a 113LSA...Do I have a

Wimpy Cam also?.

 

 

No, but that is the smallest one I would use.

[Alan_Mac 48]

So what cam do you recommend?  

 

[Max Power 74]

why is it obvious that i don't like your car?

 

 

Perhaps it is because of the tone of your responses.

[barnett468 418]

Perhaps it is because of the tone of your responses.

 

You are misinterpreting the "tone" of my responses/comments, plus, they are clearly in reference to the cam, not the car which is why I asked the question . They are also meant to be humorous while suggesting that there might be a better cam for his app, however, I do realize that unfortunately, some people have no sense of humor.

[barnett468 418]

So what cam do you recommend?  

 

It depends on what you want the engine to do and what trans and gear ratio you have etc . It is possible that the cam is contributing to part of what you are complaining about but we would need a lot more info to determine that . I can also tell you that a 20 degree difference in duration in the lobes is massive and that "should" be less than optimal for your app and it could be causing some problem . I have never seen that much in my life and I have seen a LOT of cams, plus the ratio of intake to exhaust flow is fairly high on those heads and the typical rule of thumb is that the closer the flow ratio is, the closer the duration the in and ex lobes can be to each other . Maybe around 90% of the cams made have no more than 8 degrees difference in duration @ .050 lift . A few have 12 but the ones with 12 are getting into being more for a highly specialized app like for turbos etc.

 

It often happens that people have a problem with their engine but are attributing it to the wrong part and are therefor asking the wrong questions . This isn't suggesting that your carb is not part of the problem . It is merely to suggest that there may be others like the cam in addition to the carb.

 

My guess is that your cam has only 10 degrees difference in duration and that you either made a typo or "misremembered" what it actually is, but even if it is only 10, it is still slightly more than what would typically be used on those heads unless the exhaust system was excessively restrictive which is why I asked what your exhaust system was.

..

[Alan_Mac 48]

Barnett, I appreciate you taking the time to respond.  The cam was designed by Jay Allen long ago when my car had a FMX.  Although I am a mechanical engineer and very mechanical, I do not know much about picking a cam.  Link for cam specs here      http://s124.photobucket.com/user/Alan_MacDougall/media/side%20marker%20dimensions/1970%20Mach1%20Strip%20and%20Letter%20Dimensions/cam_zps5vreqlsh.jpg.html ..  Exhaust system is 2.5" magnaflow true X.  FPA full length headers 1 3/4.   I found Pro systems makes a 780 without the choke.   

[barnett468 418]

Barnett, I appreciate you taking the time to respond.  The cam was designed by Jay Allen long ago when my car had a FMX.  Although I am a mechanical engineer and very mechanical, I do not know much about picking a cam.  Link for cam specs here      http://s124.photobucket.com/user/Alan_MacDougall/media/side%20marker%20dimensions/1970%20Mach1%20Strip%20and%20Letter%20Dimensions/cam_zps5vreqlsh.jpg.html ..  Exhause ststem is 2.5" magnaflow true X.  FPA full length headers 1 3/4.   I found Pro systems makes a 780 without the choke.   

 

 

Wow, I have never seen a cam like that before . Far be it from me to to suggest to Jay Allen how to design a cam but I wonder if he might use something a little different these days . Also, since we don't know what you told him you wanted the engine to do we don't have much info to go on but I would say that if it had a 750 before and it was properly jetted and the engine was properly timed and you didn't like it, I would put a different cam in because you have now also tried a much bigger carb so you would have pretty much covered both ends of the spectrum that way.

 

 

The cam below is one of a few different types I would run but my goals may be different than yours.

 

http://www.lunatipower.com/Product.aspx?id=1670&gid=289

 

282 290 .  231 239 . 1.6 rockers 571 587 . lsa 110 . icl 106

 

 

the cam below is one of the smallest i would use and i would use 1.7 rockers with it.

 

http://www.lunatipower.com/Product.aspx?id=1669&gid=289

 

272 280 . 221 229 . 1.6 rockers 549 565 . lsa 110 . icl 106

.

[Alan_Mac 48]

Thanks for the cam recommendations,  The first cam seems like a better choice.

 

 The Jay Allen cam was designed for street use, idle ~800 RPM automatic trans with 2300 stall converter, 6500 red line, 350 gears, the engine was in the process of being built but generally the specs were as above except 408W and smaller headers, and a stock RPM intake.  The cam is decent for the street, idles great 850-900 but I expect leaves some power on the table.  The car with the FMX and the 780 VS had an awesome kick in the pants response. When I changed from the FMX to the TKO I also changed to a 950 MS and mostly lost the kick in the pants response.   Here is some feedback from carb manufacturers; 

 

Holley / QuickFuel;  Recommended a 1) Street-Q Carburetor 750cfm MS or VS 2) SS-Series Carburetor 780cfm VS

 

Holley CFM calculator: (6400 RPM 830 CFM) (6300 RPM 750 CFM) no choke, MS   

 

ProSystems: PRO SERIES XC series HP double pumper. Although the specs will vary a little when I am flowing it for the application, your supplied tech sheet follows the carb around the shop during the build.   We'll size it for the exact cfm range when it is on the wet flow bench to match your programs needs.  But it'll probably end up being in the 830-840 REAL cfm range.

  

I am going to measure my 950 venturi and throttle plate opening for comparison.  As i remember they are smaller than the 850.    

[barnett468 418]

Thanks for the info . If you were to put a different cam in it like the first one I posted or a similar one, I would keep the carb you have and try it first to see if you like the way it runs as this might save you some money . If you want the best throttle response you can get with a bigger cam I would consider a quick fuel mechanical secondary annular booster 850 carb with the optional slow secondary linkage rod, unfortunately that carb is not cheap.

 

The first cam I posted is a popular one for 410 and 418 ford strokers etc so it is nothing unusual and would be considered about in the middle for a performance street cam , some people that want much more of a street strip car and fairly nasty/rough idle would use a bigger one.

 

I would also try your engine with a 1" spacer if you have hood clearance . I think you will find that you will gain some power but you my need a drop down air cleaner for clearance which would put the lid very close to the top of the choke housing which will cost some hp which is one reason why you should not run a choke.

[Max Power 74]

You are misinterpreting the "tone" of my responses/comments, plus, they are clearly in reference to the cam, not the car which is why I asked the question . They are also meant to be humorous while suggesting that there might be a better cam for his app, however, I do realize that unfortunately, some people have no sense of humor.

Yes, many people have misinterpreted the tone of your responses on various forums over the years. It's all them, not you....LOL! I would say we have an outstanding sense of humor here.

[barnett468 418]

Yes, many people have misinterpreted the tone of your responses on various forums over the years. It's all them, not you....LOL! I would say we have an outstanding sense of humor here.

 

ummm...your attempt at sarcastic "humor" needs some serious improvement imo, therefore I suggest you stick to something you are better at for the time being .  Now, let's get your "facts" straight . There were basically three people that were causing a LOT of trouble here and they were causing it with more than one person . I know that one of the moderators dealt with all three of them in one way or another . I believe he banned one, if not two of them . The fact that I am still here and they are not should speak for itself.

 

I knew two of these people from other forums where they also initiated problems by making unwarranted, rude, and disrespectful comments to others, unfortunately, they are friends with the moderators on a couple of those forums so the moderators don't address this issue with them for fear of damaging their friendship, plus, on two of those forums, the moderators even contribute to the problem . These people did this so frequently (almost daily) that I could copy and post over 100 examples of this, however, this thread is NOT the place to do this, nor are other peoples threads really the place for people to air their grievances with others like it seems that you are doing here with me to some degree.

 

I made no sarcastic or inappropriate comment about you whatsoever, therefore, I see no reason for you to make any about me . Also, the fact that at least one person "Liked" my comments regarding a sense of humor suggests that in their opinion at least, I am correct . Other peoples opinions may vary like yours obviously does.

 

There is a simple saying I like and agree with which I think would eliminate a lot of the problems on forums as well as in other situations in life which is, "Don't start nothin and there won't be nothin." . I also think that it is peoples duty on a free public forum like this one to try and make the lives of forum moderators as easy as possible by not causing problems . They put time and effort into these sites with no reward and really shouldn't have to play babysitter, especially for grown adults . I think that some people forget that ALL of us on these forums are here by the good graces of the people that run and/or own them.

[barnett468 418]

.

Alan, sorry for my lengthy response to Max Powers post . I won't reply to any more of his comments to me if he makes any more and hopefully your thread will stay on track.

 

Here's the 850 Quick Fuel carb I was referring to.

 

https://www.summitracing.com/parts/qft-q-850-an/overview/

 

[BuckeyeDemon 211]

i'm curious to know which 950 you have.  I know there are true 950 cfm carbs and the 950 hp's that are much smaller.  I have the 950hp which has the smaller venturi on mine and it wet flowed 830 cfm (memory) from Pro-Systems.
 
 

I am going to measure my 950 venturi and throttle plate opening for comparison.  As i remember they are smaller than the 850.

[fvike 173]

I just learned about a device that is supposed to help carb throttle response, on a Facebook group. Has anyone tried it? Looks and sounds to work in the video.

 

http://www.thompsonperformance.com/

 

I guess it won't cure a over-carbed situation, but could optimize a correct size carb.

[barnett468 418]

I just learned about a device that is supposed to help carb throttle response, on a Facebook group. Has anyone tried it? Looks and sounds to work in the video.

 

http://www.thompsonperformance.com/

 

I guess it won't cure a over-carbed situation, but could optimize a correct size carb.

 

 

I haven't tried it but I have seen it . Certainly doesn't look like it could hurt anything other than possibly loosing a little air flow thru the carb so it seems to me like it would be worth a try if it isn't too expensive, however, this only affects throttle tip in which is just one area of performance so it likely won't make a large difference if a carb is already jetted properly.

[1969_Mach1 333]

I just learned about a device that is supposed to help carb throttle response, on a Facebook group. Has anyone tried it? Looks and sounds to work in the video.

 

http://www.thompsonperformance.com/

 

I guess it won't cure a over-carbed situation, but could optimize a correct size carb.

My opinion.  I don't now???  Watched most of the video.  The fuel looks to atomize into a finer mist.  But on a down side it certainly stops the fuel from getting to the center of the venturi where maximum air velocity occurs, which is one goal of the accelerator pump nozzle.  And I didn't see a difference in throttle response.  Why didn't they try their devise with the tube style accelerator pump nozzles?  Most old school mechanics know the tube style nozzles do a better job of directing the fuel at the boosters and the center of the venturi than nozzles without the tubes. 

 

Might help, might be just a gimmick.  I wouldn't spend my money on it.  I've seen DaVinci reworked Holley HP style carbs respond like turning on a light switch without any additional devise to help atomize fuel from the accelerator pump nozzles.

[BuckeyeDemon 211]

I just learned about a device that is supposed to help carb throttle response, on a Facebook group. Has anyone tried it? Looks and sounds to work in the video.

 

http://www.thompsonperformance.com/

 

sure looks like they are hitting the throttle faster and farther when the device is installed (around 5 min) (maybe just me?).

 

seems like a good idea, but wonder what really happens under the throttle blades, if the fuel just drops out anyways (e.g. open throttle, air speed drops considerably, fuel drops out of suspension, which is why the need to add a lot more fuel).

[1969_Mach1 333]

I also noticed the throttle being opened faster and farther after the devise was installed.  The engine still didn't seem to respond any better.