[F ROCK]

what heads are "heads from a 78 trans am"?
i'm no expert but that thing is probably 7.7:1 compression and 180 hp.
maybe 8.1:1 and 200 hp.
maybe if you didnt have to push the pedal so hard to get power, you'd get better gas mileage.

my completly stock, (exept RA manifolds and 2.5" exhaust) 1971 ys 400 gets around 15 mpg. and smokes the tires effortlessly. 2.78 gears.

[Sporter]

My heavy loaded out '67 Firebird convertible (4000+ lbs), with a 068 cammed 455 and Qjet, headers, 2004r with lockup converter, 3.55 rear gears and 28" radials in the rear averaged 19-20 mpg at 75 mph with the top down. Never checked it with the top up but the top down has got to add some drag.

Most late model V8 cars I've owned that weigh close to my convertible (ragtop BMW 645 and 650) made around 23 mpg in the same situation. Both of my wife's two C5s weighed far less with far better aerodynamics but barely got 26 mpg at 75 mph. My Dodge Ram is only slightly heavier than my Firebird, has a Hemi, overdrive and gets a whopping 17 mpg at 75 mph. Not much aero at work there.

[Cobrabill]

Originally Posted by bryansMtngto

well we've sort of got off topic. 1)But sorry to tell you Cobra have converted many engines to FI and to EFI. Some basic systems, some full blown Sequential. I do know what it takes. 2)And the comment about boost just like earlier in this thread, 3)For N/A applications Carbs work just fine when tuned right, and since his only concern is MPG dont think theres a need to spend $$$ on EFI. But since we have strayed to FI or EFI apps. Think you need to do some more research. 4)For something besides Fords, 5)The GM aftermarket is growing with new EFI stuff almost daily. 6)But then again from you posts you hate GM so dont even know why your here.

1)We can't tell from the way you post.
2)For the 3rd,4th or 5th time-WE AREN'T TALKING ABOUT BOOSTED APPS!!!!
3)ABSOLUTELY-that is my point!
4)I've never owned a Ford.
5)Really?I guess i don't know a thing aboutFI & boost-do i?


6)Yes,GM does SUCK. But since this isn't a GM board,so what's your point?

[trshman]

Originally Posted by Half-Inch Stud

Okay. Sorry, I was not referring to a Tune-up. I was referring to the Total Advance Tune.
--> What is the Total Advance at 2800RPM (2800 thru 3300) (with Vac-Adv vacuum disconnected)?

See if the Total Advance was 24Degrees, that would be 70% of 34. That would "Run" but yield terrible MPG.

No problem Charlie set the timing at 36degrees total advance @ 2500 rpm. When I asked why he found it off by so much his guess was that whoever worked on it up here must have set the timing at idle and never checked it advanced. You can bet I won't use him again trshman

[bryansMtngto]

never said you didnt have or can't do an fi set up. But comments you have made previous show you dont know whats out there for Pontiacs. And your on a Pontiac-Street Forum so if you hate GM yes I think you in the wrong place. We can agree to his original question Dont think EFI will benifit at this time. and whats the vehicle in your pics. Dont see it being a Pontiac either.

[Half-Inch Stud]

Originally Posted by trshman

...Charlie set the timing at 36degrees total advance @ 2500 rpm. ... trshman

A possibilty: 36 is LIKELY too much advance at 2500 RPM. See the Advance can still climb on the way to 3300, 3600 RPM. Perhaps RE-Time the Total ADV to 34Deg at the Highway RPM (3000?). Peak MPG may occur ~32DEg +/-2DEG on the 455 stroke. I dunno about the 400 stroke.

Also may want to re-Gap the Plugs down to .045" rather than the big GM gaps.

[trshman]

Originally Posted by F ROCK

what heads are "heads from a 78 trans am"?
i'm no expert but that thing is probably 7.7:1 compression and 180 hp.
maybe 8.1:1 and 200 hp.
maybe if you didnt have to push the pedal so hard to get power, you'd get better gas mileage.

my completly stock, (exept RA manifolds and 2.5" exhaust) 1971 ys 400 gets around 15 mpg. and smokes the tires effortlessly. 2.78 gears.

The heads were done by the previous owner so I can't give specifics. We did a compression leak test and all but one cylinder came in at 160, one came in at 155. I don't know what that converts to as far as compression . I was satisfied with the readings being so consistent. I've never checked HP. I didn't get the car for that. I want to go places with it. I want reliable. Whatever the HP is it pulls to 100 easy enough to keep me happy. trshman

[Cobrabill]

bryansMtngto
Senior Member Join Date: May 2011
Location: Salem,WI
Posts: 239

efi

--------------------------------------------------------------------------------

never said you didnt have or can't do an fi set up. 1)But comments you have made previous show you dont know whats out there for Pontiacs. 2)And your on a Pontiac-Street Forum so if you hate GM yes I think you in the wrong place. 3)We can agree to his original question Dont think EFI will benifit at this time.4) and whats the vehicle in your pics. 5)Dont see it being a Pontiac either.

1)Wrong-i DO know what's out there-and what's out "there" doesn't work.
2)Wrong AGAIN.This is NOT a GM board.Pontiac has NOTHING to do with GM.Get that thru your skull.
3)So then what's your point?
4)240-Z
5)Yeah, i know-sorry about it being faster than your GTO.

[MrElectric03]

Youd be better off going to a different transmission or an overdrive unit. My 01 Trans Am was pushing 400hp at one point with a cammed LS1 and still got over 25mpg highway with the T56 manual which is a double overdrive.

[Cobrabill]

Originally Posted by MrElectric03

Youd be better off going to a different transmission or an overdrive unit. My 01 Trans Am was pushing 400hp at one point with a cammed LS1 and still got over 25mpg highway with the T56 manual which is a double overdrive.

An O.D tranny is not a good match to a "2 series" gear.

[MrElectric03]

Originally Posted by Cobrabill

An O.D tranny is not a good match to a "2 series" gear.

Meaning the differential gears? Can you explain what you mean? Not saying you are wrong at all just trying to learn a bit. Im in the process of getting my 68 going but have mostly only built up more modern cars.

[bryansMtngto]

Well cobra GM did own Pontiac and they sank it like the Titanic afraid to say.and I know guys on here and other boards and at the track that have EFI systems on there cars and they run Fine. and 3rd always like Datsun's but if you think that lil car would out run my GTO sorry i gotta ROFL. But guess everyone has their Dreams.

[trshman]

Originally Posted by Half-Inch Stud

A possibilty: 36 is LIKELY too much advance at 2500 RPM. See the Advance can still climb on the way to 3300, 3600 RPM. Perhaps RE-Time the Total ADV to 34Deg at the Highway RPM (3000?). Peak MPG may occur ~32DEg +/-2DEG on the 455 stroke. I dunno about the 400 stroke.

Also may want to re-Gap the Plugs down to .045" rather than the big GM gaps.

I appreciate the suggestion but I would never suggest changing anything Charlie does. He owns Warpath Performance in Opa Locka, FL. All he does is build Pontiac engines and I've found he's pretty well known for it. I consider myself lucky to have found him and to call him a friend. He didn't build this one so the aftermarket cam in it is a question mark and may mean he's using his best judgement for the timing and that's fine with me. Again I appreciate the suggestion but from what I'm reading here I think the Q-jet is my best bet to improve my mpg. thank you one and all. trshman

[Cobrabill]

Originally Posted by MrElectric03

Meaning the differential gears? Can you explain what you mean? Not saying you are wrong at all just trying to learn a bit. Im in the process of getting my 68 going but have mostly only built up more modern cars.

2 something gears and a .85(or so) O.D. ratio will put cruising rpm in excess of 80 MPH

Originally Posted by bryansMtngto

1)Well cobra GM did own Pontiac and they sank it like the Titanic afraid to say.2)and I know guys on here and other boards and at the track that have EFI systems on there cars and they run Fine.3) and 3rd always like Datsun's but if you think that lil car would out run my GTO sorry i gotta ROFL. 4) But guess everyone has their Dreams.

1)Irrelevant.Pontiacs we love HAD(pre-81) NOTHING to do with GM.
2)And?Do you even know what you're argueing about?
3)There's that smug Detroit superiority complex-
4)I sold my 427 Side-oiler Cobra so i could go FASTER..and it does.But we digress.

[Cobrabill]

Originally Posted by trshman

Again I appreciate the suggestion but from what I'm reading here I think the Q-jet is my best bet to improve my mpg. thank you one and all. trshman

I think you're on the right track(pun intended).THe ROI on FI just isn't there.Keep playing and wring everything you can out of the combo you have.

[goatwgn]

Originally Posted by Cobrabill

An O.D tranny is not a good match to a "2 series" gear.

Very true. When I installed the 2004r in my car (Previously had a TH 400) even with a 3.08 rear end, the engine was just above idle at 60 mph. Effectively turned the 3.08 into a 2.07 final drive. Felt kind of weird. Was like the engine was turned off on a trip I made down US 460. I actually installed the OD with the intent of changing the rear gears anyhow. I installed a 3.42 gear and the rpms were still a lot lower than with the TH400 at highway speed, (now a 2.29 effective ratio) but cruised at an rpm closer to the beginning of the powerband of the engine. About 1800 now at 70mph.

[big_gto]

I don't what I did right but I had a `70 LeMans 4 dr wit ha 350 2 bbl & a 2.73 rear & dual exhaust and got 19 mpg, twice. Two consecutive tankfuls each at 21 gallons, going 400 miles using 91 octane gas. this was mostly highway under 60 mph. But usually got at least 375 to a tank. wish I had that car now.

[Ragtop Man]

Late to this party, but, just bolting on FI won't change a whole lot. FE is a total vehicle solution that affects ever part of the build.

TBI is a half-measure, because there is still wet flow in the manifold, which causes a lot of the issues with poor fuel atomization. Port FI is much better, because if properly installed, you can aim the fuel cone straight into the point of highest port velocity and get very good distribution with comparatively less fuel.

Failing that, I would urge anyone seeking higher FE to get the low hanging fruit, first. Ignition has to be top-notch, preferably a multiple spark system. Carb needs to be built for the application, then tuned on a chasssis dyno with a wideband O2 sensor. Gearing needs to put the engine at approximately 50%-60% of the rpm necessary for peak HP at cruise (i.e. peak at 4500; roll at 2250.) Cam timing has to be conservative to hold peak cylinder pressure, and maintain high intake velocity. Run the highest static CR your Pontiac can stand, every point is power and mileage at the same time.

Get rid of fat-@ss tires that suck up power, they are probably past their expiration date anyway. Align everything, twice. Lower it. Get the junk out of the trunk. Consider an OD conversion, depending on your car either a TH200 built up, or a Gear Vendors splitter for autos, a Tremec / T56 for manuals.

There is a lot more, but realize, these old Pontiacs (well, all old cars) are relative barns to push through the air, with heavy drivetrains and high rotating mass that exact a fierce parasitic loss compared to new cars and trucks. Shoot, even in the '80s, Pontiac made a training film about how they lowered rolling resistance, showing a truck pushing a '77 and '81 B-Car at the same time... the '81 coasted almost twice as far.

You can do a lot, but you will only get so far. Good luck!!

[quicksilver97ta]

Originally Posted by trshman

I appreciate the suggestion but I would never suggest changing anything Charlie does. He owns Warpath Performance in Opa Locka, FL. All he does is build Pontiac engines and I've found he's pretty well known for it. I consider myself lucky to have found him and to call him a friend. He didn't build this one so the aftermarket cam in it is a question mark and may mean he's using his best judgement for the timing and that's fine with me. Again I appreciate the suggestion but from what I'm reading here I think the Q-jet is my best bet to improve my mpg. thank you one and all. trshman

Hunting mpg, why not get a wide band and just see whats going on at your cruising rpm?

[old66tiger]

Well, I might as well throw my 2 cents in. I have had several motors in my GTO starting with the 389, 455 and finally my 461. The 389 lived a useful life with the tri-power until #5 cylinder started blowing past the piston rings like a girlfriend going after a diamond ring. The tripower had its wow factor under the hood but every time the weather changed and my source of fuel varied, gremlins would appear. I usually found myself leaning over the fenders trying to figure out what when wrong and trying to explain to my wife that old cars are supposed to stink. In the end, I attributed the problems to heat induced fuel expansion causing fuel creep past the needle and seats. I also ran the tri-power on my 455 and it was nothing to write home about.

I ran a highly modified Q-Jet for some time on my 455 and then on my 461 and it was a good carb. I had some nozzle drip at idle that I could never get under control, but the carb worked well every place else. I despised tuning the Q-Jet because any changes to the idle circuit or bypass air meant opening up the carb and leaning over the fenders again. The only complaint that I had with the Q-Jet performance was the AF would go fat when I cracked the throttle wide open and take some time to lean out until the air doors would catch up. I futzed around with this for some time, but the fat condition was hard to get cleaned up.

As my signature shows, I am now running FAST EZ multiport. This system uses a bank to bank injection where the ECM is given a clean tach signal from the MSD box and the timing of the injectors is based on the number of pulses that it sees from the MSD box. Being bank to bank, there is no timing sequences of the injectors, just a double squirt with every crank revolution. Richard Nedbal (FastMan) said that when he was doing EFI development years back, they tested bank to bank against sequential and found that the gains noticed with sequential are modest when considering the added complexity. Yes, sequential is better and more efficient, but for engines like ours that are retrofitted with FI, gains are hard to measure.

In my opinion, this system works very well. I set my targets from my driver’s seat, and as conditions change, the ECM compensates for it. With a 1250 CFM throttle body, the potential of the EFI to feed my 461 is only limited by the size of injectors and the fuel pump pressure. Behind the wheel, there is virtually ZERO lag in throttle response. Let me restate that…ZERO lag. When I crack the throttle open, it is there…right now. The car flat ass flies. I can monitor the AF, temps, RPMs, etc from the hand held. I wish it had data logging feature like the XFI, but for the time being, it is not a necessity. I remember when I first installed the system, I had a very slight lean surge condition under light throttle and was able to tuned it right from the driver’s seat.

OK, so what about mileage? It is crap. Come to think of it, my mileage with a tri-power and the q-jet on the 455 wasn’t any better. What can you expect from 500+ HP in an old school package. But it sure does move this heavy car down the road nicely. In the end, I spent a lot of money and gained the ability to hit the key and tune from my seat. Was it worth it? Yup! Would I do it again…Actually, I would build an LS7 next time and then FI comes standard.

FWIW, there was a guy at the Chicago Corvette and muscle car show with a 69 Camaro that won the Optima battery challenge. LS9 with north of 700 HP. You could balance a glass of milk on the engine cover. When that car went through the course, it was simply amazing.

Let the comments fly…that’s OK.