z28maro

my motor, tbi to carb convertion, is almost complete and one of my last decisions left is choosing the carb.

I have a decent list of modification and expect to push around 300 hp. Among which is an edelbrock dual plane intake and an msd 6 ignition to burn whatever fuel i can put in.

i already blew out an old quadrajet but have since fixed some problems and am ready to try something new. i was looking at either a holley street avenger or maybe a lower end demon carb.

advice????

five7kid

iTrader: (14)

What transmission will you be running?

What will the car be used for?

Need more details about the modifications. This is still a 305, I assume.

z28maro

right now i still have the stock 4-speed auto and i have the same out of an 87 iroc i might put in but im not sure.
i do have the 305 bottom end in it still. however my cylinder heads are for a 350 and im currently instaling 1.6 roller rockers, autolite plugs, msd 6a, k&n with the top, and a cowlhood still sitting in my garage for when i get around to it, and i think thats it as far as fuel/air goes.

the car is going to be a summer car something to take around the block and showboat but i want a good 1/4 mile setup. ie i have a five hundred dollar race in a month against a some kid with a mint, stock, 92 rs needless to say i want to humiliate the guy in addition to taking his money.

firebird45331

you're putting 350 heads on a 305?

z28maro

yep its the same block so it fits but they let in more fuel and more exaust out. little more bang for the buck since i have the msd

firebird45331

you'll probably kill your compression though. What's your casting?

mw66nova

iTrader: (13)

your gonna be dissapointed when that msd doesn't do crap for your combo and the heads lower the compression enough to make your car slower. the 416's that used to be on the car will probably flow just as well, if not better than your current combo. i'm running some bonestock 305 h.o heads (416's) and have gone as quick as 13.7 and as fast as 100.5 mph in the 1/4. there is still alot left in the car too.

the msd will probably improve fuel mileage, but other than that, will not do much for your combo. you have to really be putting out some power to see an improvement with an msd box...shoot, i'm still running a stock ignition system! i have an accel super coil, and that's it, and i bought it when i was much younger and suseptable to gimics.

z28maro

i didnt buy the msd for horsepower i bought it cause i was runing way to rich and wanted to utilize not waste the fuelthat was getting in there and if your proud of ur 13.7 ive got a 4 banging saturn that does 14.2's at 98.

firebird45331

Well good luck to you then. I put 305 heads on my 350 and did much better than with the heads that were on it.

mw66nova

iTrader: (13)

wow...hey that's great about your saturn and all...and actually, a 13.7 is pretty darn quick.

but in all actuallity, you shouldn't be adding more spark to lean the motor out, you should be pulling fuel outta the mix....but hey, what do i know, i made a relatively stock 305 run mid 13's on 87 octane fuel in full street trim, and i happen to drive it everday cause it's my only car, etc...but i don't seem to know anything.








.5 in the 1/4 is alot of difference. i imagine that your 4 bangin' saturn weighs a ton less then my camaro. you seemed to be talkin' about these 350 heads and the msd like it was power from the gods given to you to make easy hp. look through what you wrote through the thread and tell me you don't sound like this.

firebird45331

i'd understand using ported 350 heads on a 305 if you were running some sort of boost, but unless you are you'll be disappointed cause you'll probably end up with less power than you started with.

IROC_385Z

Buddy I would not let pride get in the way and would listen to these folks.

Lets assume that your 305 had an 8.9:1 compression ratio with the 58cc 305 heads. If they were HO heads then the valves were probly 1.94/1.5, if not then 1.84/1.5.

Now you put on these 350 heads that have probly 76cc cambers. This will drop your compression to 7.44:1!! THAT is not good at all! NOW, if you could get some of the aluminum heads from a late 80s/ealy 90s vette, those have 58cc chambers, keeping compression the same, and would flow better than your 305 heads.

Better money could be spent with a camshaft.

Good luck with whatever road you choose. Just make sure that if you use the 350 heads that you get them milled to raise the compression to AT LEAST 8.5:1, 9.0-9.3 would be best.

IROC_385Z

BTW, to answer your actual question!!

on a 305 I would suggest staying near 600cfm. I know a kid that has a 305 HO (stock heads), performer manifold, mild camshaft (214/224 .480 lift) headers topped with a 600cfm edelbrock and his car moves quite well. I'd say the motor is making about 300hp/330lb-ft. A holley 600 vacuum secondary would work well. You could also look into the Street Avenger series. the 570 would probly be your best bet, but if you plan to setup up to a 350 then you may want to get the 670 model *the 570 is equal to 500cfm, 670=600cfm*.

You should really look into changing camshafts. With a stock cam you probly ever wont hit 300hp NA. With a stock cam and a 7.44 compression you wont hit 200hp. If you change cams then get the 670 or just a regular holly 600cfm.

again, GOOD LUCK!

five7kid

iTrader: (14)

Forget vacuum secondaries. Get a double pumper for drag strip performance. If your converter stalls at least above 1300 RPMs, a 600 CFM will be fine.

Otherwise, save your money and use the q-jet.

If this is a street race, then none of my advice applies.

z28maro

thanks for the advice on the carb sizes iroc. i just dont have patience for some of these cocky *******s who think theyve heard the whole story. im going to look up what cc those heads are and figure out my new compression.

right now im leaning towards a street avenger but i havent heard anything about a demon carb. i know they are reputible on a track car but are they any good on a street/strip vehicle?

thanks again

IROC_385Z

I have no personal expirience with demon, but its sounds like they are the cats-meow. Basically a holley but with all the tricks and better manufacturing. For what you are doing it would not be worth the cost, unless you want to drop a couple extra benny's to look pretty

five7 and his DPs...*shakes head, griningly* You will be happier with a VS.

If you need any help calculating the compression or anything let me know. I made a lil program to figure all that **** out and would be more than happy to run the numbers for ya. You can PM me or shoot me an email.

firebird45331

I sure hope you weren't referring to me as a cocky *******. I was just trying to help. If you were referring to me as a cocky ******* I really resent that. What part of ohio are you from anyway?

z28maro

ive been looking left and right but cant find the chamber size anywhere. they are heads off of an 1987 iroc-z with the 5.7 and auto tranny if any one knows what they are or atleast where to look it would be appreciated. and im not at home and wont be able to look up the cast #'s for atleast few days

and sorry i wasnt talking about you firebird, you too were being helpful.

Sonix

iTrader: (1)

Hold the phone! I thought you had a stripped down race car? well nonetheless, the part that impresses and inspires me is the 87 octane..... What's the trick??? Whats your static compression ratio and cam again?



maro: Most people assume if you're using "350" heads, they're from some '77 caprice or some crappy smog motor, they're 76ccs, and they'll DESTROY your power... Hence the comments to that effect. The heads you have are.... 093? I forget, it's fairly common knowledge around here, but i'll go out on a limb and say they're 64cc or something... Not terrible heads, BUT! Remember, if that's an LG4 that you started with, it had 8.5 compression or something, with 58cc heads, and now you're making them even larger, so you will lose some power due to that. Like someone already mentioned, milling the heads will help....

And finally, back to your original question, a q-jet might be a good carb for it, save you some $ for a cam or something that'll give a lot more HP/$.... Or yes, a demon carb is supposedly very good...

IROC_385Z

I wasn't able to find the chamber size but I wanted to say that they were 68cc.

11cc valve releifs with a 4.166x.042 gasket and 9.025 deck:

58cc = 8.54:1
64cc = 8.03:1
68cc = 7.73:1
72cc = 7.45:1
76cc = 7.20:1

mw66nova

iTrader: (13)

nope, it's got full interior and sub, full sized front tires, etc. all the horn/blinkers/lights/wipers etc. work. i just live without a/c and some other things.

trick? go easy on the timing! it's got 9.5:1 c/r and the cam is a crane cam with 214/224 duration .442/.465 lift. i think it's on a 112 lsa, but could be wrong.


oh, and so everyone knows, i'm the cocky ******* he's referring to...didn't originally mean to come across that way, i was just straight up with you. you took it the wrong way and where cocky and *******-like to me first, then i got cocky.

Sonix

iTrader: (1)

easy on the timing? that why you say you have more left in the car?

just out of curiosity, would that be less overall timing? ie. 30* instead of say 36* total? less base? vacuum advance on ported not manifold?

hmm, i'm hoping for similar results, albeit with a 350, slightly more duration, and roughly the same compression... (hmm, guess it's not that comparable... ) I just figured 9.5cr is about the most you can do with iron heads and PUMP gas (ie 94 octane or something...)
oh well, learn something new every day...




ok maro, theres your info, roughly low 8:1 cr..... might want higher.... I guess you could always use a cam that bleeds off less cylinder pressure.... oh well, now we're really straying from your original question....

IROC_385Z

my 385 currently has 10:1 with iron heads and a cam that is 218/224 @.050, 279/285 adv, with 112LSA. I run 92-94 and it does not detonate, well, once I fix the timing it wont. Right now my dist is letting in 50 degrees total at 2500 rpms, and it does have slight detonation at 2500rpm...but even at 9.0 cr it would detonate with THAT much timing.

mw66nova

iTrader: (13)

less overall timing, base timing is set at 6* i believe. can't remember, set it a while ago. that's one reason i believe it has more in it, as well as i have a tired 600vs and i'd like to put a 600 double pumper on it. should really wake it up.

one thing to remember is the overall package, not just engine. you look at the superstockers and see what they are running. 11's on stock 305 shortblocks with quadrajets! but they are also running cams with ridiculous duration and lsa's and the stall on the converters are normally in the 5500 rpm range and have something like a 4.56 or 4.88 gears, or higher in some cases.

i am running a well built 700r4 with a transgo shift kit and rebestas clutches and bands and a hardened sun-shell. a 2500stall ati 10" converter, 4.10 gears and an eaton posi fill the 7.5incher out back with some 275/60/15 m/t et street radials putting the power to the ground.

Sonix

iTrader: (1)

hmm, all helpful info, thanks.
I'm going by the article by damon on the main page, 36* at WOT, and 52* (ish) at cruise.... I wasn't sure if that was just for max power with good gas, or 87 octane or....

I'm also at higher altitude so i'll have to correct for that... I guess it's a matter of trial and error...

mrbulman19

305 heads suck for flow, they're really really bad. They're great for compression though. I agree that putting 350 heads will help with your flow and lower your compression... but all i have to say is this ...

get your 350 heads milled and it will bring your compression back up and give you flow.

i have a 305 and i ported all the burrs and other crap out of my heads and they're working a lot better now.

if your 305 has dish pistons i recommend upgrading to flattop or domed pistons, they will also increase your compression ratio if you decide to keep the 350 heads.

that's all i have to say.

mw66nova

iTrader: (13)

where do you come up with this stuff? the 416's have been proven to have some of the best flow numbers (ported or un ported) of any of the factory casting sbc heads!

mrbulman19

wow i don't know about you but have you ever taken a good look at the "416" heads? i can barely get my finger in the ports. hrm, well i guess i'm pulling this mostly from personal opinion then, but everywhere i have read about them i have read that they flow bad. i know for a fact that the 350 heads flow pretty good, but i've always heard that people who want to put 305 heads on a 350 for more compression need to port them because of their "airflow problems"... like i said, the ports are full of casting burs if you've ever had your fingers inside them... not to mention rather restrictive in the first place - not to mention smaller valve sizes than the 350 heads (if memory serves correct)... although i'm no scientist, i just know i ground a LOT of horrible crap out of those heads when i ported them.

go figure i can't find a single article either, oh well, looks like i'm going to eat this one.

so out of curiosity, what makes you think they're better than 305 heads? do they flow better for their bore/compression application than a larger SBC?

somebody out there knows the answer to this.