kalli

hi all,

maybe boredom, or wanting to upgrade, or curiosity, or simply stupid ...

http://cgi.ebay.com/ebaymotors/QUICK...Q5fAccessories

I'm thinking about that one. it's REMAN, but would save me 200$ ...

opinions? should I, should I not. Can i expect a big improvement from a holley 570? probably not ?! (assuming they're both tuned right)

my77stang

i think with the heads and cam you have now that 570 is small, i'd be looking at between 600-650 but keep in mind your MPG will probably drop.

have you tried that holley 650 you got from me on there yet?

67mustang302

I prefer mechanical, but it would work great. You can tune it to get mileage. My 650 mechanical QFT gets better mileage than the 570 I was using before.

kalli

mystang77: that holley 650 went into a different car, i wanted that 570 with my old 289, guessed I'd have no need for it. According to all maths the 570 should be fine, but it is like that it's dropping in power above 5500 (going flat), which doesn't make sense with my current cam profile. so i was thinking bigger (than 570) might be better in this case.

67M302: i'd love a mechanical with my light car, T5 and 3.5:1 (i think that would suit). But i'm really afraid of bad gas/mileage in cruise. There's nothing stopping the secondaries opening (better said the secondary jets feeding) during cruise at higher speed. or do I have this wrong? but then again you say you have ok gas/mileage

Kalli

my77stang

you can have the secondaries starting to open at a certain point though, its not always all 4 immediately. when your cruising at speed, you usually don't have your foot too far into it so you'd be running on the primaries only.

cprstreetmachines

Find out how much vacuum your engine is making at the top of 3rd gear to really find out if the carb is too small. There are a few reasons it could be laying down. This will at least lead you in the right direction.

kalli

mystang: very true
cpr: the simplest ideas are always the best ones. i never come up with them though :-) i'll get a long vacuum hose and tape the gauge to the window or something

67mustang302

The QFT's all come with different secondary linkages. They're set standard at 60%, meaning the primaries have to be open 60% of the way before the secondaries open. I basically never have all 4 barrels open unless I go WOT. They also come with a 40% and a 1:1 linkage.

cprstreetmachines

Sorry, sorry, do it in 4th gear for accuracy. thought for some reason you had a 3 spd, and I know you have a T5. doh !
Carbs are rated at a certain CFM. If you are at the vacuum reading at the top of 4th, you are flowing what it's rated at, 570. If you are higher, then you are flowing more than it's rated....if it's way too small, and starts pulling say around 6 to 7 in of vacuum, the power valve will flutter(because most holley's come with power valves around 6.5) and start to close on you leaning you out. But gotta be pretty small to do that though. Hope it helps.

kalli

uh :-) go easy on me. 5500rpm in 4th in my car is already 120mph :-) my car has never seen that speed. what would be a reaslistic difference between 4th and 2nd anyway (apart from the fact that I have less time for reading the gauge) ? the amount of mixture the engine is demanding should be the same in 2nd gear at 6500 and 4th at 6500. shouldn't it?