I am currently starting a 68 firebird project. I am trying to build it like I would have had in high school if I had any money. My question is this. I am getting a offenhauser 360 equiflow duel quadrajet intake and I was wondering about the cfm requirement for the heads to run this intake. Can I get ported 6x heads with enough cfm? I would really like to stay with iron heads for a early 80's build. Where I am currently at is a 68 400 firebird, 73 455, th400 with 10" torque converter and a dana 60 with 3.54 gears. The car is minitubbed with ca chassisworks subframe connectors and a ca chassisworks 4 point roll bar. I am having a small issue finding any information on this intake so any information would be very appreciated. Thank you.
hello, i see you are new, welcome.first i will say that, that is a ridiculous intake to run imo, i love it.are you building from scratch?can you photo the intake runner and post a photo here or on flickr etc. then post the link to it here.it's really better to tell us what type of perf you want or what cam you have.can you measure the intake port size at the end that bolts to the head and tell us what it is?do you want a 7000 rpm engine with a stupid nasty idle etc?what gears will you run?fwy, street or both types of driving?are you going to run race gas?you can get huge flowing heads but if your cam is not a "big" cam then it will not be matched to everything.for a mild to moderate build you need around a 700 - 750 cfm carb max. with 2 carbs you need 2 375 cfm carbs but because you may be opening 4 barrels at a time with dual quads instead of 2 like yiu would on just 1 4 barrel depending on what linkage you use,a pair of 300 cfm carbs might be better. they do mot make 300 cfm 4 barrel carbs so you can see a possible prob.yes you can run 2 450 cfm carbs and it will be over carbureted but it will work. the factory buick gs dual quad cars worked ok but they were 455 ci.if you use linkage that opens only 2 barrels until around 1/3 throttle the cylinders in the rear will be much farther away from the 2 barrels that are opening.i suggest you look into how the buick linkage set up worked.HEADS - You can not use any 6x heads on a perf built 400 because the chambers are way too big so you will not have any compression.you need some 72 - 78 cc heads 67 or newer with big valves off the link below.http://ronspontiacpage.com/reference-pages/stockheadspecs.htmlooks by the link above that you need either casting code 9787671 or 9773345 with either a 1966 or 1967 date code. they are 72 cc the 671 has screw in studs, you need to add them to the 345's.the 671's may flow better stock. they both may be made to flow the same once both are ported but i don't know. member rowsley or another might.
Thanks for the reply and yes I am new here.I am starting from scratch with this project but I do have some parts. I want to run pump gas so I am looking at 9.5 cr for iron heads. And as far as rpm I am looking at 5800-6000 due to the 455 I am starting with. As far as gears I have 4.10 now but am looking at going to 3.54. Driving will be street strip. as far as the port sizing I do not have the intake yet. Vince at Offenhauser found 2 castings and is machining one for me. Should be here next month. the intake is not a square bore intake it's a spread bore intake. 2 quadrajets. Looking at putting 2 chevy quads on set up for a 307. I have a set of 72cc heads I cannot use because of the valve spacing, they are 77's. I was looking for off the shelf pistons and I was coming up with to much compression with the 72cc heads. The 4x heads I also have are way to big at 114 cc.As far as cam I was looking at comp cams hydraulic roller xr-288hr. In your opinion can the 671 heads be ported enough to support this setup?
ok great i got confused by your 68 firebird 400. i thought it was a 400 ci.without much more infolate 1973 or 1974 #46 89 cc 211 in 166 ex = 9.63 comp on a .040 455 screw in studs69 - 70 #64 are 87 cc 211 in, 177 ex, = comp screw in studssome 73 and 74 4c and 4x heads are 98 cc 211, 166, must mill them .025" from stock to 94 cc = 9.24. deck the block to .010 and have 9.45 or leave the heads at 98 cc and deck the block to .005 and have 9.24 comp.one of the 74 - 75 #5c and #68 heads are 211, 166 98 cc.1977 #68 head 211, 166 = 94cc6x-4 heads late 75, 76 and all 77, 211, 166 = 94 cc.one of the 1978 6x-4 is 211, 166 = 94late 78 and 79 6x-4 is 211, 166 = 94 cc 71 and 72 7k3 is 211, 166 = 96 ccthese are all on the list i gave you and they will all workbuy them at frankspontiacparts.comraciingjunk.compontiacengines.comCAMS - The following are almost identical and meet your rpm criteria and will work well with both gears you mentioned and will haul the mail without being excessively big and therefore not traffic friendly. Use around a 2400 stall with them and your gears.lunati 60904http://www.lunatipower.com/Product.aspx?id=1777comp xe274hhttp://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1204&sb=0here's the next step up in brutality and need around 2600 stall, very good flowing heads requiredcomp xe284hhttp://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1205&sb=0lunati 60905http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60905ROCKERS - Scorpion race series alum rollers, see at summitracing.com
welcome to the forum!The 455 you have, is it 4 bolt mains? How about the internals? are you going forged on the pistons/rods? what crank do you have? How about oil pump?You do realize, even with small dual 500-550 CFM carbs, this manifold is a 7,000 RPM manifold? with dual quadrajets (I am assuming they are 750 CFM), your power band won't even start until 4,500 RPM and runs on up to 8,000 RPM.For any Pontiac iron head, regardless of CC, it's going to take some serious port work to utilize the flow at those RPM's. Other wise, you're only utilizing half or less of what the intake is good for. IF memory serves me correctly, I believe the ports come sized for RA-IV heads. ( it was 16 years ago I bought mine)Here is a link to the Offenhauser catalog @ Exeter auto supply.http://www.exeterautosupply.com/Offenhauser%20Catalog.htmlIf you're only looking at max 6,000 RPM, you're better off with 500 CFM carbs. They will even run you to 7,000 RPM.With any RPM range above 5500, I'd seriously consider a mechanical roller instead of a hydraulic one due mainly to hydraulic lifter float at the higher RPM's. But that entails some seriously high spring pressures.The 670 heads you mention are closed chamber design and their very design negates a lot of flow due to the shrouding of the valves. If you go with iron heads, I'd try to find some post 67 as Pontiac opened up the chambers starting early 68.I can only say all this as I'm running that very manifold on a modified 428 w/Edelbrock round port heads and both manifold and heads have been ported and gasket matched. 2 500 CFM carbs, hooker super comp headers w/2" primaries. Bottom end is forged and balanced and a Crower mechanical roller.
Hello MY71In case he has no thtrottle linkage can you tell him how yours operates and where you got the parts.Any photos?Are you running q jets?Will your linkage work with q jets and/or spread bore holleys?
My71Thanks for the reply. My 455 is a 2 bolt main. And honestly I am going to do this build around this intake so if a mechanical roller is needed than that is what it gets. I am going with forged pistons and h beam rods regardless of anything else. If I am going to do a forged crank I was thinking on a 4' stroke out of a 428. That would bring the rpms up about 500 in the power band. Also due to the rpm's needed for this intake should I look at converting to a manual? Did you have any clearance problem between your exhaust gas crossover and your valley pan? I spoke to vince at Offenhauser and according to him the only intake that would fit was the hi rise due to the thermostat housing clearance. Vince spoke to Bruce Fulper and they say this will fit under my hood. How is your hood clearance? I am currently finishing up a ford project and this will be my first Pontiac project so any information you can give will be very appreciated. I think it is about time I did this car because I have only had it for 16 years.
"My 455 is a 2 bolt main. I am going to do this build around this intake so if a mechanical roller is needed than that is what it gets."The mechanical roller has nothing to do with the intake.mechanical lifters develop more hp and tq than a hydraulic ones but they perform better at higher rpms and/or with heavy spring pressures than non hydraulic ones.roller lifters reduce friction therefore providing more hp, quicker revs and lower cam and oil temps. in other words they work xlnt on any size cam but are a necessity on monster size cams with steep ramps.your intake does not need an engine that turns a lot of rpm unless the eng is a small displacement or the intake is super high rise. what it needs is air flow. this air flow is acheived by a high revving small ci engine like a 350 chev at 8500 rpm or by a large cube engine operating at a much lower rpm.as i mentioned in my previous post, a similar intake was used on a production 64 buick gs with a 455 engine which had poor flowing heads. the car was a slug with a small cam but it still ran fine with no hesitations or flat spots so you absolutely positively do not "need" high flow heads and a monster cam for it to run without problems especially since it is on a big engine that will move a lot more air than a smaller engine at the same rpm.this is why as i mentioned, the more important thing is what exactly do you want and how much money do you have to get there.xxxxx"If I am going to do a forged crank I was thinking on a 4' stroke out of a 428. That would bring the rpms up about 500 in the power band."i would not do this unless you simply want an engine that turns high revs. "There is no replacement for displacement."see reply above.xxxxx"Also due to the rpm's needed for this intake should I look at converting to a manual?"see reply aboveman or auto doesn't matter, you might consider using an "anti balooning" torque converter if you get over around 45o hp or 6000 rpm. xxxxxI spoke to vince at Offenhauser and according to him the only intake that would fit was the hi rise due to the thermostat housing clearance.the orig 64 gs dual quad low riser might fit if your t stat housing is in the same location as a 84 engine. see photo below in post 11.http://forums.aaca.org/f177/hard-find-correct-65-gs-dual-280861.htmlxxxxx "I am currently finishing up a ford project"oh i'm a big ford guy too so if you need any suggestions at all i'd be more than happy to help.
shyrgfuh3My intended goal for this project is to replace my high school car. When I was 16 I had a P.O.S. 67 firebird. So I am aiming to build a firebird that a 16 year old with funds would have in the early 80's. I got owned one night by a chocolate brown 69 firebird running this intake on a 428 with a 4 speed. That is why I want this intake. In that ere your mom ran an auto in the family wagon, 4 speeds were for muscle. That is why I was inquiring about a 4 speed. There were no aluminum heads available at that time so that is why I will be running iron heads. I do not know how this intake performs so that is why I was asking what it takes to run. MY71 said it likes rpm and high flowing heads. You say it just needs a bit of cam. In response to both of your posts what would a 16 year old with a muscle car want? If a little is good then more has to be better. I understand that a mechanical roller has nothing to do with the intake. I also understand that a mechanical roller will keep the lifters on a big cam at higher rpm longer than a hydraulic cam. My current project has a 428 Fe edelbrock nhra heads, comp mech roller 288r with Harland sharp shaft mounted roller rockers with the needle bearings, duel holly 600's off of a Shelby on a blue oval intake. She has eagle h beam rods with forged pistons static compression is 10.8. I had to have try y headers made due to fitment issues. It has a tci super street fighter c6 with a 10' torque converter with anti ballooning plate. I like feeling like a kid when I play with my toys. My new quest is to get a pontic 455 to run hard on pump gas with two quadrajets and iron heads. I am curious about the exhaust crossover clearance on that offy intake because I want to plumb nitrous under the intake. I feel that is the only way to get this car in the 10's on pump gas in street trim. If it is not street drivable on pump gas and I do not see 10.99 at 4800 ft elevation I will tear the car back apart and do it again.
shyrgfuh3My intended goal for this project is to replace my high school car. When I was 16 I had a P.O.S. 67 firebird. So I am aiming to build a firebird that a 16 year old with funds would have in the early 80's. I got owned one night by a chocolate brown 69 firebird running this intake on a 428 with a 4 speed. That is why I want this intake.oh i know the feeling, lol. i also was not looking for a reason for running it or trying to talk you out of it. i think its a great idea to run what you want. i was just letting you know some of the better items to run with it. xxxxxIn that ere your mom ran an auto in the family wagon, 4 speeds were for muscle. That is why I was inquiring about a 4 speed.Sure, i was only sating that you can run either with that intake. a properly set up auto will likely get you down the 1/4 a hair faster but i agree that it certainly is not much fun. i would rather have a 4 speed than an auto or even a 5 speed.xxxxxThere were no aluminum heads available at that time so that is why I will be running iron heads.]Oh sure there were, tri power vettes, 425 hp vettes, 375 hp 396 cars, buick gs dual quad, 69 full aluminum block ZL1 etc.xxxxxI do not know how this intake performs so that is why I was asking what it takes to run. MY71 said it likes rpm and high flowing heads. You say it just needs a bit of cam. please read my explanation again there is much more to it than that and a lot of info there, part of what i said is that it "works" fine on a stock type 455 but i was in no way suggesting that it worked better on a stock 455 than a dual plane single 4 would or that it would not work better than a 455 with high flow heads and a beg cam.the point is that you will gain nothing by running a cam that is capable of flowing more air peer se than the heads are capable of. there is a point of diminishing return. this is to say that one can not put 2 lbs of whatever in a 1 lb bag. i hope this makes more sense. i can assure you the my71 heads flow much more than stock if i remember right.some intakes work better with low air flow some work better with high flow, this is why they make low, mid and high flow intakes but it gets a bit confusing at times because they are rated for different rpms but what this really means in general is that they flow different amounts of air.xxxxxIn response to both of your posts what would a 16 year old with a muscle car want?If a little is good then more has to be better.well i agree therefore i like your intake plan but where you and i might differ is in where we want peak hp to occur. you seem to want it at 6500 with a 428 and i prefer it to be at 5800 with a 455 that's all. and i was simply trying to explain that with the 428 you are giving up low end power for high end powerthis being said, i had a 55 4 door chev with a 7500 rpm 327 and a 4 speed when i was 17.xxxxxI understand that a mechanical roller has nothing to do with the intake. I also understand that a mechanical roller will keep the lifters on a big cam at higher rpm longer than a hydraulic cam.they won't really keep the lifters on the cam any better but you may just be using different terminology than i am. they only reason they are required on some cams is because the ramp is so steep that the edge of a non roller lifter would catch it and kill the cam and lifter.rollers also are heavier than non rollers therefore they need stiffer springs.xxxxxMy current project has a 428 Fe edelbrock nhra heads, comp mech roller 288r with Harland sharp shaft mounted roller rockers with the needle bearings, duel holly 600's off of a Shelby on a blue oval intake. She has eagle h beam rods with forged pistons static compression is 10.8. I had to have try headers made due to fitment issues. It has a tci super street fighter c6 with a 10' torque converter with anti ballooning plate. like feeling like a kid when I play with my toys.now your talkin, what is it in?i've had plenty of 438 cj's boss 9's boss 302's etc. have a 70 428 r code mach at the moment.had a few 67 dual quad gt 500's, love just starin at dual quad cars with aluminum valve covers. still have a pair of 16 year old harland sharp fe's new in a box, lol. xxxxx My new quest is to get a pontic 455 to run hard on pump gas with two quadrajets and iron heads.as anyone here will tell you, you need big head flow, this can be achieved with some of the heads i listed for you. member rowsley and others will know better which ones can be ported the most but for now you can check out the stock flow rates at the link below.xxxxxI am curious about the exhaust crossover clearance on that offy intakei'm not sure what you mean there. if the intake has an exhaust port running through it i would block it off especially if you typically drive it in temps above around 75 degrees and run corn gas.xxxxxbecause I want to plumb nitrous under the intake. ok the trutrh finally comes out. you are a man after my own heart. guess you never forgot about gettin stomped in high school, lol.you should not run high compression with nitrous especially in a big block because it is so violent. i still have no idea just how fast you want to go but a 6500 rpm 428 like you want with around 8.75 compression and around a comp xe284h cam and 100 hp shot of nitrous would simply be scary to me. you have to give up some compression and subsequently some hp and tq when running without the nitrous button depressed to be able to run it with the button depressed.you can certainly build a 10:1 compression engine that you can run nitrous on but it will cost quite a ***i might also consider installing 4 bolt mains if you run nitrous.xxxxxI feel that is the only way to get this car in the 10's on pump gas in street trim. If it is not street drivable and I do not see 10.99 at 4500 ft elevation I will teat the car back apart and do it again.ok cool but heres sa new wrinkle, you loose around 4 lbs of cylinder cranking pressure and therefore some dynamic compression for every 100 ft increase in elvation.this means that in short yoi can run higher compression at that elevation than at sea level.if you have 10 at sea level it will be around 9 at 4500 ft etc.head flow chartsee 6x ported 255 in, 245 ex16 271 in 197 at.500 299 in, 222 ex at .700http://ronspontiacpage.com/reference-pages/stockflowcharts.htmDETONATION - If you want to do this on 93 octane you might look into running e85 corn gas. this is a new deal i know little about but it is purported that it is more resistant to detonation than regular gas and is on par with around 100 - 110 pump gas. this means that you can run higher compression than you can with regular gas. the down side is that it does not burn as well so you will not get a much power out of it so it is a trade off. is the trade off worth it, i don't know, i have only heard stories but until i see drag slips or dyno sheets i have no clue.PS - If you had mentioned you wanted to run 10's at 4500 ft with a 428 and nitrous in the beginning it would have only required 1 reply from someone, lol.
George, you certainly have a unique set of goals! Refreshing. Never seen one of those intakes but I'd like to.I probably shouldn't be involved in this discussion but had a couple thoughts-If t-stat housing clearance is an issue, chop off the coolant part of the intake and make a pipe to fit there, with a t-stat housing made onto it wherever it wants to be.If heat crossover clearance is a problem, block the heads off and hack away the interference area on the manifold, or create a custom valley pan of your own, or consider purchasing an aftermarket (flatter) type and modifying that if needed.Just tossing out ideas. Leave em lay if theres none you want to pick up.Two Q-Jets mounted on a Ponch is something I just gotta see. I'd walk a quarter mile round trip at a car show to look at it. I don't believe you'll have as much driveability trouble as one might anticipate. The truly glorious aspect of spread bore carb design is how it inherently sizes itself to the demands of a wide range of engines from mild to wild. But 10.99 with iron heads is a fairly ambitious goal depending on the extent to which the car is race-oriented. I reckon spray might get you there. Surely is an interesting project, I'll say that. Best of luck with it.
idrivejunkHi thanks for the input. I was thinking about cutting off the bottom part of the exhaust crossover if I had to, just thinking if I had to. as far as cutting modifying the coolant part of the intake I do not want any external modifications showing, that is why I will only cut the lower part of the exhaust xover off. I have to leave the upper intact because it can be seen. Just thinking like a street racer from 1982.I got the hi rise offy intake because according to Vince at offenhauser it is 1" taller than the low profile. The 2 are identical except for the carb heights. My plan is if there is hood clearance issues I will have the intake carb flanges milled to fit. I have 1" to play with on the intake body under the carb adapter flanges.
shyrgfuh3I have a 69 mach 1 that is currently going back to the original acapulco blue. Its a s code car with a automatic. I did not want to redo the 390 because the block is not original to the car so I did a 428 instead. same family so visually it would fit the car.As far as the aluminum heads in 1982 I know other makes had them but I did not think Pontiac had them available at the time. I could be wrong on this. As far as the 1/4 mile time that will be tricky. I believe it will be achieved with a minimum of a 200 horse shot on a timer. Planning on using the motor torque to get off the line then the bottle after the 60'. I can then adjust the timer to come on earlier. My perceived big problem is the weight. I want to do this with a full bodied car with full interior and steel wheels. Honestly for me it is all about the build. Once I achieve my goals I move onto the next project. And I believe this goal will be tricky.
what do you mean by full bodied?exactly where in the 10's is yiour realistic goal?yeah, no aluminum pontiac heads i know of, funny that chevs had them though isn't it?am i correct that you want to do this on straight pump gas also? obviously race gas will get you there without grenading.if it were me i would run race gas but no nitrous since i don;t think there was nitrous around in the early 70's but race gas was.i had an iron head 355 chev in a 68 camaro with nitrous that ran around 11 so it can be done some how some way with a 428.the taller your slicks are for any given width the more they will hook up also.do you know the safety requirements at your track for those speeds?i love acapulco blue.
My idea of a full bodied car is complete right down to the radio and sound deadener in the interior. I am looking at 10.99 at 4800' of elevation. By my math that is at least 500 horse 500 torque on the motor another 200 on the bottle and needing a cage at the track. I am loosing something around 100 horse due to the elevation. The elevation is a killer. I am putting in a 5 point roll bar with a removable side bar because of what I have seen happen to these cars. If they get upside down the top is even with the door locks. When I was 16 I worked at a machine shop where the owners kids had some of the fastest cars around. 1st gen Camaros running ls7's 454's with nitrous. When they hooked up on the street in street trim they would break the back windows and open the passenger doors if it was not locked. I need the 5 point to keep the car together. Besides race cars have cages I want a street car.