Discussion
Hi all,
At the mo, I've got a Demon 750 atop my 'ickle .350, which is good for 400hp.
Thing is, the car is running uber rich and from talks with Gail and Ted, isn't really that well suited to the engine. I can jet it down of course, but the fact that it's a bit worn (long story) and the butterflies have been drilled means that I'm considering replacing it altogether.
Gail has recommended either a Holley 650DP, or the 670 Street Avenger.
Now, the vacuum secondaries put me off a bit from the Avenger, but it is nice and shiny
Given that my car is supposed to be as 'street' as possible, is this a good bet, or should I stick to good old mechanical secondaries on the trusty 650 Double Pumper?
Opinions welcome
At the mo, I've got a Demon 750 atop my 'ickle .350, which is good for 400hp.
Thing is, the car is running uber rich and from talks with Gail and Ted, isn't really that well suited to the engine. I can jet it down of course, but the fact that it's a bit worn (long story) and the butterflies have been drilled means that I'm considering replacing it altogether.
Gail has recommended either a Holley 650DP, or the 670 Street Avenger.
Now, the vacuum secondaries put me off a bit from the Avenger, but it is nice and shiny
Given that my car is supposed to be as 'street' as possible, is this a good bet, or should I stick to good old mechanical secondaries on the trusty 650 Double Pumper?
Opinions welcome
I run a Cobra with a 351W H/O (350BHP) with a 650cfm Double Pumper, driveability is great and the full throttle air capability is more than enough to feed 350 BHP. Engine is more torquey with this carb which is great for plodding around in 3rd and 4th, fuel ratio's are spot on and the exhausts have that nice clean dark grey colour, that exhausts used to have!
Will follow with interest and also interested in debate on using secondary vacuum for our type of driving. I am told that advantage is that they do not lead to such an extent of fuel dump on full throttle. The double pumpers great on tract and wide open roads, our driving particularly in the South tends to be be full wack and stop, so huge amounts of fuel gets dumped in cylinders and does not get burnt.
Not an engineer so will be very ineterested on what people say on the difference in performance and will it make a difference.
Stig you can always try and convince me into secondary vacuum and then there would be a double pumper on offer.
Not an engineer so will be very ineterested on what people say on the difference in performance and will it make a difference.
Stig you can always try and convince me into secondary vacuum and then there would be a double pumper on offer.
I'm only familiar with edelbrock's - the secondary butterflies are connected mechanically via a progressive linkage to the primarys. But above those throttle plates is another pair of trap-doors (i'm avoiding the term butterflies, as you cant quite describe them as that) which only allow air into the secondaries when there is sufficient air flow (i.e. mid>wot). They also make the primaries smaller than the secondaries to maximise air velocity at low>mid throttle, therby improving drivability.
Ive got one (edelbrock 1405)sat on the shelf along with the full jetting kit that you could borrow to play around with one to see if vacuum route suits you.
Ive got one (edelbrock 1405)sat on the shelf along with the full jetting kit that you could borrow to play around with one to see if vacuum route suits you.
I ran a 770 Street Avenger in a 415 hp 350 ci engine. Usual very rich idle, but overall quite a nice set up for road use, I was always led to believe vac secondaries better for part throttle operation. I never managed to cure the stall under braking problem though. The carb is now excess to requirements due to upgrade to EFI and sitting in garage awaiting clean up and e-bay when I can be bothered. Available for experimentation if anyone wants it.
crazy of cookham said:
Will follow with interest and also interested in debate on using secondary vacuum for our type of driving. I am told that advantage is that they do not lead to such an extent of fuel dump on full throttle. The double pumpers great on tract and wide open roads, our driving particularly in the South tends to be be full wack and stop, so huge amounts of fuel gets dumped in cylinders and does not get burnt.
Not an engineer so will be very ineterested on what people say on the difference in performance and will it make a difference.
Stig you can always try and convince me into secondary vacuum and then there would be a double pumper on offer.
Not an engineer so will be very ineterested on what people say on the difference in performance and will it make a difference.
Stig you can always try and convince me into secondary vacuum and then there would be a double pumper on offer.
Actually Brian, Gail even recommended Charles Dunn to look at the carb! What's his opinion on vacuum vs. mechanical secondaries?
Why in this day and age does anybody mess around and use carbs, especially Holleys? O.K. I accept that they are simple once running right but as for economy, forget it. I also except EFI is nowhere near as inexpensive as carbs but if its the complexity that worries you, fear not, they are simpler in many ways than carbs. There is a lot more hardware required I agree but the benefits are well worthwhile I can assure you.
Charles is in discussion with Gail on this subject. He is trying to convince me to go with secondary vacuum. He tells at one time everyone raved about double pumpers and took off secondary vacuum and then coverted back just prior to fuel injection. I am told that the big advantage is that they just don't dump more fuel than needed. Power loss minimal and unless you are doing speed trials you would not notice. Drivability should improve. Bore wash on my car still an issue and seriously considering changing carb to help solve. I do not want to glaze bust once every 2 years. Suggest you give Charles a call or even better pop by with car and I am sure he will be happy to see you. Your reputation proceeds you sir.
bluesatin said:
Charles Dunn I believe has a couple of old carbs on the shelf that you could try. I would fit an air fuel meter to see what is happening- same for you crazy
Thanks Guy, I've got an air/fuel meter already - that's how I knew it was always rich
Will email you for his details...
crazy of cookham said:
Charles is in discussion with Gail on this subject. He is trying to convince me to go with secondary vacuum. He tells at one time everyone raved about double pumpers and took off secondary vacuum and then coverted back just prior to fuel injection. I am told that the big advantage is that they just don't dump more fuel than needed. Power loss minimal and unless you are doing speed trials you would not notice. Drivability should improve. Bore wash on my car still an issue and seriously considering changing carb to help solve. I do not want to glaze bust once every 2 years. Suggest you give Charles a call or even better pop by with car and I am sure he will be happy to see you. Your reputation proceeds you sir.
It makes sense as you say, because of our roads/driving style.
Mechanical secondaries dump fuel regardless of engine speed, so at low revs, if you floor it, in goes a shedload of fuel regardless of whether it can all be burnt or not.
Conversely, vacuum secondaries don't open until there's sufficient vacuum to operate them. So low rev/wide throttle will only operate the primaries until the revs rise. Obviously, because of this there can be a slight delay vs. the double pumper - BUT - you're not dumping fuel into the heads before it can be used (so improved economy too?).
Given that Ultima's are so light and therefore accelerate quickly anyway, I'm leaning more toward the vacuum secondaries (and the nice shiny Avenger 670
) I'd like EFI at some stage, but I'm waiting to see a tried and tested Ultima solution first (unless I've missed something and someone can point me at a fully working setup?).
GTWayne said:
I think GTRMikie will be at the open day on the 6th, he has injection on a relatively stock motor and swears by it (not AT it), have a chat with him.
Yep, my standard ZZ4 HO is fitted with a Holley PRO-JECTION4Di which was recommended to me by Real Steel when they supplied my engine back in 1999. It is a very simple, low pressure (15psi) system suitable for engines up to 500bhp. It consists of a throttle body containing four injectors which simply replaces the carb (uses the same manifold, air filter etc) It is fully programmable for fuel mapping and ignition, although I only have the fuel mapping option operating on mine, so all it really does is replace the carb. But my car starts readily, dosen't stall, has good fuel economy and low emissions. Mine was set up by Real Steel and I haven't had to change any settings in the six years I've had the car. However I'm not sure if Holley still market the system.
I am pretty sure USAGTRMAN retrofitted fuel injection on his Ultima too. Maybe Brad can speak up and provide you more info. Most guys I know of prefer fuel injection for overall driveability and ease of tuning (if you have the right eqiupment). It should definitely make your 'easy to drive' even better!
GTRMikie said:
Yep, my standard ZZ4 HO is fitted with a Holley PRO-JECTION4Di which was recommended to me by Real Steel when they supplied my engine back in 1999. It is a very simple, low pressure (15psi) system suitable for engines up to 500bhp. It consists of a throttle body containing four injectors which simply replaces the carb (uses the same manifold, air filter etc) It is fully programmable for fuel mapping and ignition, although I only have the fuel mapping option operating on mine, so all it really does is replace the carb. But my car starts readily, dosen't stall, has good fuel economy and low emissions. Mine was set up by Real Steel and I haven't had to change any settings in the six years I've had the car. However I'm not sure if Holley still market the system.
Problem with that, is that its still a "wet manifold" design - sorta like an electronic carb, Yes - better than carbs and easy to fit - but port injection (i.e. 8 injectors) is a better approach if you are starting from scratch or trying to choose between the two. (And the injectors are easier and cheaper to obtain too, as they are fitted in thousands of cars)
Edited by eliot on Friday 21st July 20:44
having seen the amount of mapping DW did on my can-am to get it to run right i'm not sure a standard system will work, the light weight and great aero package ment the light throttle work needed alot of sorting ,i think this is why the factory had problems with the early systems they tried .simon
Gassing Station | Ultima | Top of Page | What's New | My Stuff