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Discussion Starter · #1 ·
First and foremost, I am not very mechanically inclined, I am really just learning about motor work etc. As mentioned previously, my grandfather sold me his 1970 goat. Talking with him tonight, he told me the car has the original 400 YS 4bbl in the car (rebuilt around 8 years ago, and driven maybe 200 miles since) He told me the motor has been bored .30 over and has a chevy 454 carb on it right now???? He said he has the original carb but it is leaking.... As a favor, he is having the motor/heads redone again, apparently they are at the machine shop as we speak. With all this said, is this a good mixture with the carb and bore, or does it really matter. Hell, I may even need more info about the carb. Does anyone know what kind of output this setup might have?? Also, is it difficult to rebuild the original carb, or should I let a pro do the work?? Any help is appreciated. P.s. The car is still in Illinois, so I can't provide any additional details right now.
 

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I don't know a whole either, but .30 bore is pretty common.

After my engine was rebuilt, they dyno tested it for hp and torque. I would suggest you have the same done.
 

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The 454 Chevy carb is a 750cfm Q-Jet just like your original Pontiac carb. The only real difference between the Chevy carb and the Pontiac is that the Chevy has the fuel inlet on the forward passenger side of the carb, while the Pontiac has the fuel inlet straight in the front of the carb. Thus, you can't use the stock Pontiac fuel line with the Chevy carb. The Chevy also has different choke linkage - the Chevy divorced choke operates opposite the Pontiac choke.

Correctly set up, either carb will produce the same level of performance. Jet the carbs to their stock specs for the carb number - not for the application. The Q-Jet is not difficult to rebuild, but there are some things to watch for. If you give me the carb numbers, I can give you the correct jetting specs for each carb. Also, I have several papers available on setting up Q-Jets and identifying problems. If you'd like a copy of these, drop me an e-mail request:
[email protected]
 

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there are several things you need to look at before you go with any carb. The 454 carb may be fine for everyday driving however if you make a drastic gear change in the transmission or the rear end differential you may need a carb that can supply more fuel. If the engin is rebuilt with stock parts you probably wont have any issues. It may run a little rich because the carb's cfm rate and fuel jets are set up for an engin with 50 more cubic inches. After you get everything put back together don't drive it hard until you bet at the very least 500 miles on it, it gives the engin and parts time to settle and if there are any problems you should know fairly quickly. You will know if it is running rich because it will idle a little rougher and the spark plugs will be black like, what you dont want is for them to look white. If you are running rich and you want to keep the 454 carb what you can do for a little more performance is a K&N air filter and a full exhaust with headers. Hooker headers are ok, personaly I would go with stainless steel long tube headers. If you go with FlowMaster mufflers, get the 3 chamber. I had a 71 cutlass 450 HP and running a full exhaust with 2 chamber FM's, It was to loud, sounded like a NASCAR, but was badazz :D . Post what you decide to do, I would love do read about it. On a personal note, Dyno it before you go making any mods, making the wrong nods you may loose power, you will get more satisfaction if you know were you started and where you might be in the future. Good Luck on your Goat

Aaron
 

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Discussion Starter · #5 ·
Thanks for the replies, I am shipping the car next month, so I can't wait to get her!! I am really expecting the car to be mechanically sound upon arrival. It should have the original 3.55 axle on it and I don't have plans to change it unless you all know something I don't.
Lars, once I receive the car and all the extra parts (q-jet) I will relay the numbers to you for the correct specs.
 

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Braman'sGTO said:
if you make a drastic gear change in the transmission or the rear end differential you may need a carb that can supply more fuel.
That's not correct. Rear end ratio and tranny gearing has no effect on the carb's performance. The carb responds to the engine's metering signal and will produce the same A/F ratio regardless of gearing. The 750 cfm Q-Jet, whether Chevy or Pontiac, will keep up with any demands of a 400 engine regardless of gearing.

Braman'sGTO said:
It may run a little rich because the carb's cfm rate and fuel jets are set up for an engin with 50 more cubic inches.
The 454 Chevy carb is the same size Q-Jet as a Pontiac OHC-6-cylinder carb, and the same size as any other Pontiac carb. All Q-Jets are 750 cfm except the 455SD Pontiac carbs and the Stage 1 455 Buicks: these are 800 cfm. A big carb does not run rich: it actually works the other way around. If a carb is too big for the engine, you get a lower metering signal to the carb and it leans out. But you can run the Chevy carb with no problem - in its stock form, it will perform very well on virtually any engine, even with some modifications.

Braman'sGTO said:
After you get everything put back together don't drive it hard until you bet at the very least 500 miles on it, it gives the engin and parts time to settle
Modern piston rings require that you get an immediate high load on the pistons and rings as soon as possible after initial engine startup. The high cylinder pressure will force the rings into the cylinder walls and makes the rings seat. If you run the engine lightly, the rings will fail to seat, and you will end up with excessive oil consumption. Recommended engine start-up and break-in procedure is to get the engine fired and run at 2500 rpm for about 15 minutes to assure proper cam lubrication during cam break-in. Once done, get the car out and put several hard wide open throttle passes through 1st & second gear to seat the rings. Once done, the engine is ready for normal service. We run these engines on a dyno right after we finish building them: we break in the cam and get the engine up to operating temp. We check lash and timing, and then do wide open throttle dyno pulls. No problem.

The 3.55 gear is a very good all-around setup. It will produce very good torque and response from a standing start, and is usable for highway cruising. Sounds like you have a great platform to work with - some simple and precise tuning should get you a great performing car.
 

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Im not disagreeing with what you are saying, I was working on an olds rocket 350. That is a different beast altogether form pontiac and chevy, but not all Q-jets are 750 cfm, the 350 rocket came with a 650cfm Q-Jet. I did also forget that you cant change the the jet size on a Q-Jet either without drilling it out. As far as the break in goes you are right about the piston rings and cam, tkinion was talking about having the heads worked on and I should have been more specific about that. If the valve assembly is not installed correctly it can cause major problems if run hard in the first 500 miles. Because of the cam in my 350 rocket the Q-jet could not keep up, 4000 rpm and up it would start to run very lean. That is were I went to a Holly 700cfm dual feed dual pumper. Thanks for correcting my mistakes and helping to get tkinion a good running Gaot.

Aaron

By the way with that 3.55 gear, if you dont already have a posi unit from the factory it may be worth investing in one. I had in my cutlass and recommend Auburn Gear Pro Series Differentials. Good luck and most of all have fun.
 

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Aaron -
Actually, all Q-Jets are 750. Some Q-Jets were cfm-limited by the factory for various reasons by limiting the secondary throttle opening angle and by limiting the secondary airvalve angle. But if the limit tangs are corrected, the "smaller" Q-Jets flow exactly the same as all the others at 750 cfm. There were some truck Q-Jets with triple booster venturies, and I have found these to flow slightly less, but they were still promoted as 750 carbs.

It's interesting to note that Pontiac actually did this Q-Jet cfm limiting in 1967 - 1969: Pontiac had made the marketing decision that the GTO was to be the flagship performance car. However, the Firebird was available with the exactly same 400 engine as the GTO, and the Firebird was lighter. So the Q-Jet carbs installed on the 400 Firebirds had their secondary throttle blade angle limited so that the Firebird 400 engine only produced 335 horsepower versus the GTO's 350 hp. Yet the engines are identical.... To make the Firebird run circles around a GTO, you simply bent the secondary throttle tang to make the secondaries open all the way.

Finally, there is no reason to drill jets on a Q-Jet. All jet sizes from 66 through 79 are still availaable, and the jets are easily changed. There is never a reason to do any drilling.

Lars
 

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I read a performance manuel on the q-jet a few years back and they were the ones talking about drilling the jets. I would personaly never do that, its easyer to buy what you want. The problem these days is if you do enough research you can run into conflicting info. That brings up a question, does the pontiac run a chevy block and is it a true 400? I thaught I remember reading that each of GM's brands ran different engins. Oldsmobile being a perfect example of that, they used the same block for the 330, 350, and what they called a 400 but was actualy a 403. Did the GTO ever run the 3 duce carb setup on there 400's?
 

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lars said:
the Firebird 400 engine only produced 335 horsepower versus the GTO's 350 hp.
Lars
The 67 firebird (400 with q Jet) was rated @ 325 hp, the 67 GTO was 335 hp, the HO and the Ram Air GTO's for 67 were rated @ 360 hp.

The only reason for restricting the carb on the firebird was because of GM's vehicle weight to HP restrictions.

I remember some of my buddies with firebirds changing the intake manifold and carb. They would smoke my 67 GTO HO.
 

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Aaron -
The Pontiac engines are true Pontiacs - they are not Chevy-based engines. Pontiac, like the other GM divisions, started using "corporate" engines in 1977, and 1979 saw the last year for "real" Pontiac engines.

The Pontiac 400 has a bore x stroke of 4.12 x 3.75. This makes it actually a 399.9 cube engine, which is pretty darned close to a 400. A .030" overbored 400 is a 406 (405.8), and a .060" over 400 is a 412 (411.7).

All Pontiac blocks are visually identical in terms of size and overall configuration - Pontiac managed to vary bore & stroke within the physical envelope size of their same engine from 265 cubic inches through 455. Thus, there are no "big block" and "small block" Pontiacs. Rather, there are "small journal" and "large journal" Pontiac blocks. This makes it nice for parts interchangability, since you can really mix and match parts between the various Pontiac engines to obtain the engine parameters you want.

No, Pontiac never installed the Tripower - or "Triple Power Pack" - system on the 400. The Tripower was used only on the 389 and the 421. Last year for the Tripower and the 389 was 1966. However, since Pontiac intake manifolds will interchange between heads, the Tripower system can be easily installed on any 400 or 455 engine/head combination, and you will frequently see 400 GTOs with the Triple Power Pack installed. Although visually very cool and much better performing than the Carter AFB 4-barrel, the Tripower system does not perform as well as a single 4-barrel of the correct size, since 3 2-barrel carbs cannot feed 8 cylinders as uniformly as a single 4-barrel system. Further, the 3 individual air filters used on the GTO Tripower systems were very restrictive, and actually limited the cfm capability of the system. But I've run Tripower systems myself on 400 and 455 GTOs just for the cool factor in spite of their limitations.
 

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05GTO said:
The 67 firebird (400 with q Jet) was rated @ 325 hp, the 67 GTO was 335 hp, the HO and the Ram Air GTO's for 67 were rated @ 360 hp.

The only reason for restricting the carb on the firebird was because of GM's vehicle weight to HP restrictions.

I remember some of my buddies with firebirds changing the intake manifold and carb. They would smoke my 67 GTO HO.
05 -
I stand corrected - you're right for the 67 model year. I was pulling the numbers from memory and missed the Firebird rating by 10hp.... The 68 & 69 GTO 400s (standard engine) were rated 350 (WT, XZ, XH, YS, WX engines), and the Firebird was 335 (WQ, WZ, WI, XN, YW engines).

I did an interview with Jim Wangers (Pontiac Motor Division PR & Marketing in the GTO era) back in the late 70s. Although the Firebird's reduced hp rating was attributed to the "GM Policy on weight to hp," Wangers told me that it was in reality a marketing tool used to make sure that the GTO was the faster of the two cars when the magazines tested them and when the "official" performance numbers were published: Pontiac specifically wanted the GTO to post the better numbers of the two, since the GTO was to be the performance "flagship."

The intake manifolds on the two cars were the same. The only difference was the secondary engagement tang on the Firebird was bent back to preclude full secondary throttle opening. All you had to do was bend the tang to the GTO position and the Firebird would come alive.
 

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Braman'sGTO said:
Lars,

I just read your profile and found that you have been into GTO's since they have been around.
When I bought my first '69 Ram Air IV GTO for $500, the car was 4 years old, and you could still buy new GTOs at the local Pontiac dealer...

I had a chance to drive the new GTO out in LA before they were released to the dealer showrooms. I was impressed with the overall balanced level of performance (the car actually corners and stops), and I was very impressed with the interior finish and fit. I think it's a great total performance package. I share the same issues that have been aired by most of the enthusiast magazines and editorials: high price and rent-a-car looks. As big of a fan and supporter as I've been of the GTO for the last 30 years, I think I'd rather throw in another $10K, get a Vette, and keep my Judge.

Hey Troy - will I get banned from this Forum for saying that...? :cheers
 

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Discussion Starter · #16 ·
I was looking at NADA for the ballpark value of my Goat for insurance purposes when I noticed the car was more valuable if it has the 400 4bbl (30% increase) instead of the 400 Ram Air (25% increase). Anyone have any idea why this may be or is it possibly an error.
 

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There's something wrong with that: The 400 4-bbl is the standard GTO engine, and there is no increase in value for the standard 400. There is a 30% increase for 400 Ram Air IV, and a 25% increase for Ram Air III. There is no increase for the base 400. I think they got their 400-IV and the 400-4 bbl mixed up...

I suggest you not use the NADA for value on your GTO - Use the CPI Guide - it's the accepted standard in the collector hobby, and they do their homework a little better than NADA.
 
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