Here's my combo:
71 400(+.030) block and 71 heads. Cast flat tops with 2 valve reliefs per piston. Rings unknown. Comp Cams Magnum roller tip rockers with hardened pushrods (no guides). Unknown type valve guide seals. Edelbrock Performer (not RPM) intake with Edelbrock Perf 750 carb w/elec choke. Stewart hi-flow water pump. Dynamax ceramic coated headers with 1 5/8' primaries. Torque Tech 2 1/2 " exhausts w/straight crossover. HEI with Accel Supercoil, MSD module and Crane adjustable vacuum advance. Believe curved to all advance in by 2800rpm.Comp/Cams 268H 218/218@.050 w/.454 lift. TH350 trans with Transgo shiftkit. 2:73 open 12 bolt rear. Questions are: What compression ratio do you estimate with the flatops and stock 71 heads? Other than my obviously weak rear end gear, how does the rest of the combo look for a street engine in a weekend cruiser trying to stay limited to 93 octane reformulated gas? I am not thrilled with the Edelbrock carb and have been considering a Sean Murphy Induction Q-Jet. Any experiences with them? The engine has never met my expectations.

Feeling like the Maytag repair man with no one replying to my post yet. Not having dyno simulator
I was also wondering if someone could estimate the horsepower for my combo.

Can you get the casting number for the heads. It will be under the valve cover.

I'm sure I wrote the head casting number down during the rebuild and the heads date to a 71 model. I'll have to find out quickly where I scribbled it!

I built a 400 with cast dished pistons 1.94 heads and the same comp 268h. I was dissappointed with the power it made. When the cheap head gasket let go I took the heads off, had them cut for 2.02/1.60 valves. After reinstalling the heads it was a new engine. Much more power, pulled to 5500 instead of previous 4500, spin the tires at will. If you ever (re)build a 400 don't economize on the heads.

i don't like the 268H cam, but that thing should run pretty darn good. do you have any ET's from a dragstrip? i had a bone stock dish piston 400 with a General Kinetics 288/.480 cam, rpm intake, 1 5/8" headers, 2 1/2" exhaust, 3310 Holley, 3.55 gear, 3000 stall, and it ran 8.40's in the 1/8mi with stone stock 71 heads, little valves and all, with stock rockers too. how much total timing do you have in it?
i would think your compression would be around 9.5 to 1 if your heads are 76cc's.

I have receipts going back to '86 on the car but couldn't locate last night either the casting numbers for the heads, which I feel sure are 76cc, or the timing specs, which I had my previous mechanic write down. Got all receipts I have absolutely no use for! Will search again tonight. No drag strip numbers, as I have a thing about drag racing in brick-shaped convertibles. While it may be unlikely, upside down at 90mph in a raptop is not where I want to be. I had also guessed around 9.5:1 compression.

why not go with a holley instead of a qjet?

Adman, perhaps the new Street Avenger series Holleys are different, but I have car-buddies with tales of previous Holley's and rebuilding them, along with adjustments. I just don't have the skills, although I'm no wizard with a Q-Jet.I'm about to take the car to a new mechanic (see looking for a perf tuner in the Houston area post)highly recommended by another Team member. I may consider one if he recommends it and knows them well.

Originally posted by Bruce_H_Miller:
but I have car-buddies with tales of previous Holley's and rebuilding them, along with adjustments.:eek:

IMHO, QJets might be a better carb from a functionality standpoint, but when it comes to making changes and calbrating them to your needs, give me Holley anyday. Much easier to work on, and tons of parts to work with. Other people may disagree, but why do all of the performance people use Holleys as the base for their racing carbs?

mr71-initial timing is 12 deg and 32 total, all in by 2800rpm. Very little vacuum advance set with my adjustable Crane advance. Vac advance off timed vacuum port on card vs. manifold vacuum port. I believe the stock timing on a 71 400SB from an Impala was 8 deg. I'm also concerned that my Accel Supercoil might not like the increased initial timing. I believe their tech web site mentions staying with stock timing, but why wouldn't that vary widely w/peoples's mods?

tpshea-yes you are obviously correct about Holleys and racing. Mine is street only, although I like to thrash it, and I thought perhaps the smaller primaries might work better. Your thoughts?

Bruce,

Don't get me wrong, I think QJets are great carbs. I just don't agree that they are the easiest thing for tuning. Holley makes soooo many choices including vacuum secondary spreadbores which would bolt right in place of the QJet. I had one of the Edlebrock carbs probably just like yours, it reminded me of one of the Carters from the old days. All it did for me was drink gas. I switched to a small Holley (600 CFM vac sec/square bore) and both mileage and performance perked right up. I have a ZZ4 about ready to fire up, and I put on a Holley Avenger 670. Those carbs sound like a great choice just due to the fact that they are actually calibrated for a specific HP range. I know it is smaller than what GMPP suggested, however saeveral guys have opined that it is probably a better choice than the 750 that GMPP said to use.

tpshea- what is the HP range for the 670 Avenger you mentioned? My Edelbrock experience is the same as yours. I can't figure out why you see them on 75%+ of all street rods around my parts. Must be the attraction of being simple.

You're probably better off with a smaller carb. I read somewhere that it is always better to under carb your engine than over carb. I think what I read says that the smaller carb will give you torque and good throttle response and vacuum, whereas the larger carb can just cause the car to run rich and have off idle stumbling and hesitation. Please feel free to correct me if I'm wrong. I'm just going from memory.

three85stroker-you are probably right about under vs oversizing, up to a point of course. Guy who build the engine insisted on the 750cfm vs the 600cfm I had from the previous engine. That is part of why I'm considering the QJet with it's small primaries, yet flows up to 750cfm. JET Perf and SMI both will calibrate the carb to your combo. I'm wondering about the 670 Holley Street Avenger though with all the adjustability they're advertising. Meanwhile, just discovered part of why it's started running badly recentlt. Distributor hold down must have loosened because I just measured 18 deg initial timing with my gun. Backed it down to 12 deg and running much better although still has a miss.

Bruce,

Here is the PN for the Avenger I bought. 510-O-80670 It is rated 300 to 400 HP, so my ZZ4 is right in the middle if it. The last 3 digits indicate the CFM, so mine is 670. Here is the whole list from Jegs. You save about $40 to $50 going with the manual choke, but I like the automatic choke just fine.

510-O-80570 Up to 300HP 570 cfm
510-O-80670 300-400HP 670 cfm
510-O-80770 400-500HP 770 cfm
510-O-80870 500HP+ 870 cfm
510-O-81570 570 CFM AVENGER M/CHOKE
510-O-81670 670 CFM AVENGER M/CHOKE
510-O-81770 770 CFM AVENGER M/CHOKE

Does anyone else have any positive or negative experiemnces w/ the Avengers?

Originally posted by Bruce_H_Miller:
tpshea- what is the HP range for the 670 Avenger you mentioned? My Edelbrock experience is the same as yours. I can't figure out why you see them on 75%+ of all street rods around my parts. Must be the attraction of being simple. Because they are great for a car that needs to be fun to drive and run hard, I think . I have a 625 Road Demon jr on my daily driver and I love it. I haven't found any Holley parts that don't interchange. I would also recomend a street avenger. Both have power valve blowout protection built in.