Acid 67

hi,
i want to upgrade my carb.
i was thinking about a bary grant, but i dont know which one i should use.
i ask the tech support from BG and they recommend the 750 Speed Demon with annular boosters ( pn 1402020) .
but after a look at the BG carb selection guide it seems to big.

at second i asked yearone and they recommend the h80770 street avenger.
which one is the best choice ?
what do you think ?

druckle

I have the same engine and they also told me a 750 double pumper. I tried the Holley double pumper and couldn't get it to run right. I tried a 670 street avenger and it ran good but not great. I didn't like the vacuum secondaries. Finally I went to the 650 speed demon and it runs great. No off idle hesitation. I did have to lean it out a little other than that it was good out of the box. Runs strong up to 6000 rpm and I never go beyond that. It does seem to have more left. I know they dyno those engines with a 750 but that is to get top end hp.

Acid 67

at the moment im using the 670 avenger too. out of the box it stumbled a little bit, so i rejetted it to 68 pri. - 73 sec. it feels a little better, but i think the engine dont have the power it should have.
which 650 speed demmon you put on ??
where did you set your timing ? ( initial - total )
are you using vac. advance ? ( ported or manifold )
how much vac. advance you add. ?

73'Vette

I have the same engine, but with forged pistons. Since I plan on using the car for street/strip, I went with a 750 double pumper. I haven't started any tuning, so I can't offer much advice on the carb setup yet. My engine dyno'd at 416hp and 455 ft lb tq with the 750 double pumper. What kind of exhaust are you running?

Acid 67

@ 73'vette

this is one thing where i loose some power for sure.
at the moment i use some cc90 sanderson blockhugger headers into a short 2 1/2" pipe into a sidepipe.
i know its not the best way to create power but i have to use the short headers because my exhaust is to close to the frame.
if i would use some long headers i have to install the pipe under the frame.
while driving they sometimes would hit the floor and will be damaged.
there is not enough room to go this way.

i thought about to order some hedman headers ( 68500 ) on summit and try to build a better exhaust pipe.

i tryed to put a pic in but i dont know how to do it.

73'Vette

I removed my "fake" (4 into 1) side pipe setup in favor of a true hooker-style side pipe setup. To further decrease horsepower loss, I am in the process of ripping out the glass packs in the side tubes to install a set of STS baffles. You are correct in considering a better exhaust setup to free up some more ponies. Once I get the exhaust completed and do some tuning, I plan on seeing what it can do at the drag strip. Do you remember your dyno sheet numbers?

Acid 67

my dyno sheet shows the maximum of torque from 432,2 @ 3700U/min and max. HP from 412,3 @ 5900 U/min.

how should a good exhaust pipe look like?
whereat the focus i like on torque @ lower rpm.

very interessting for my is the timing.
in germany you can get 91 - 95 - 98 octane.
the engine was dynod with 93 octane, with a total timing of @ 32 degrees.
i dont know if it make a big difference ?

73'Vette

Your engine dyno'd similar to mine. Mine was dyno'd with 35 degrees timing, so you could try adding in some more timing. I finally got my STS baffles installed, and I'm impressed. They sound great! I'm very anxious for a test and tune night at the local track.

marz

How many horses, tranny, torque converter? I have a 400hp 350 SBC and tried Edelbrock, Holley and eventually installed a 750 Speed Demon. Plenty of torque and power when I mash the gas. It's with a TH400 and 3000 converter. Mechanical secondaries. Did have to play with the jet size. Good luck.

Acid 67

@73'vette

im wondering a little about your total timing, on the same eninge.
everywhere i read vortec heads onla need 32* total.
how much initial you set ?

@ marz

wanne get about 400 HP
light car, about 2600 lbs. with a 5 speed TKO (1st 3.27 ), 3.05 rear end on 15" wheels with 265/60 tires.

marz

My timing I set at 36 and it liked a little more, but I left it at 36. I also plugged the vacuum advance and it liked that even more. If yours is anywhere close to the 400hp range I would go for the 750 cfm carb. That along with Hooker long tube headers for more torque and you should be in business.

Acid 67

how much vacuum you add ?

i think i will start at 9* ini and 34* total.the msd dizzy 8360 have 18 - 21 - 25 - 28 degree bushings for mech. advance.
and about 10* vac. at the manifold port.

you mean the 750 speed demon or a holley double pumper ?
i had a look at the 650 double pumper Holley 0-82651.

i only can use shorty headers because its to close to the frame.

Ganey

You need a 650 in Holley. DP are race carbs that work great on the street if you drive hard. Some prefer DP for strip & vac. sec. for street & gas mileage.

smon

I also have the Yearone 350. I was using my stock q-jet and had some trouble, but I rebuilt it with a cliffs ruggles kit and now it runs great except for off idle stumble when I floor it. I think my total timing is about 32*, but I think I am getting too much mech adv. I was afraid to go over 32* total with vortec heads and I can only get 91 octane here.

What vacuum advance can are you guys running with this engine? I can get mine to pull about 11-12* vacuum.

I recently bought an LM-2 wideband o2 sensor and just started tuning with it. I found out that I was pretty rich all the way around, probably losing WOT power. I haven't spent much time trying to get it in a better range, but I'll see how lean I can go without detonation or surging at cruise.

Sean

73'Vette

I'm using this MSD distributor because of the built in rev limiter:

MSD 8365

I haven't played around with the advance curve or the vacuum canister yet though.

druckle

I have the speed demon 650 with mech. secondaries. No off idle hesitation and great acceleration when the secondaries kick in. With the street avenger with vacuum secondaries you dont feel the surge because they only open with the amount of vacuum you have. You can change to a lighter spring to make them open quicker but it still doesn't compare to mech sec. I had to set my timing to 34 degrees total with no vacuum advance because of spark knock. I am running hooker full length headers with 2.5 in true duals and turbo mufflers. It isn't loud but it sounds good.

Ganey

Sean
The idle mixture affects off idle & there is limited adj. towards rich.
The accel. pump has adj. holes on the lever & another can be drilled.

73'Vette

I finally got a chance to play around with the jets a little. I ended up with 75 secondary and 69 primary. I did 7 passes at the track tonight with a best of 8.87. Once I find someone who knows how to weld stainless steel, I'll get a bung welded into my collector. From there, I will use a friend's LM1 and tweak the carb further. I'm hoping to get the times closer to 8.5 sec. (1/8 mile track)

Acid 67

what are the next biggest cams i can use on this engine ? without i have to change something like valve springs or anything else.
its possible to change it one on one ?

Ganey

You really need better exhaust first. The Dynomax Corvette SB Cerama-Coat full length headers fit & flow great.