Hello Guys, I will try and make this concise as possible. I have searched this forum and found the Jim Blackwood thread to be the most comprehensive when it comes to the 340 build, but way overkill for my needs (and budget). I will also preface my request with the fact I am not a good mechanic. I am definitely handy so basic maintenance (plugs, oil, water pump, fuel pump, alternator, etc.) is in my capabilities, but as such I will be outsourcing this project. This obviously factors into the budget. I am looking for ideas where I should spend the budget to most effectively the goals below. There is limited 340 performance parts available outside of headers and cams, so I am looking for advice on how best/easy to achieve this. Goals: Increase overall horsepower to somewhere in the low to mid 300's. Higher is fine, but need to factor point 3. This is a weekend cruiser, so not looking for strip performance. Just looking to give the car a bit more gidde up because a bit underwhelming today. That said I love the car and really enjoy driving it. Increase HP, but maintain engine reliability, so want to minimize exotic options to keep maintenance a minimum. The ST300 concerns me too with increased HP. Vehicle Details: 1967 GS 340 California Stock 340 4BBl (Carter carb with original cast iron intake) Stock Super Turbine 300 Stock rear-end (not sure of ratio, but original) Dual Magnaflow exhaust (all bark no bite ) Cast iron exhaust manifolds Budget: $2k-$3k I could spend more, but I have about $6k into this car (above what I bought it for) adding power disc, dual exhaust, missing trim, new door panels and seat covers, steering wheel refurbish, 3 point seat belts, A/C change over, etc. Potential Suggestions: Port Matching/head porting New Cam Blow through carb (CSU appears to fabricate these) Fabricate new intake Turbo If budget allowed (meaning spend more) swap 340 for a Buick 350 or 455 and TH400. My concern would be budget, but sacrificing originality of the car. I appreciate the help and apologize in advance for the rudimentary knowledge. Thanks, Bob
Buick 350 would give you a great benefit on parts available. But pleny you can do with what you have. Call Jim at trishield and get the switch pitch restalled for more off the line.Jim can also recurve your distributer and convert it to magnetic .no more points. check your rear gear. You could benefit from a deeper gear. Send your carb to quadrajet power or everyday performance- I assume you have a quadrajet. Porting heads- and I believe the 340 has 1.77 valves so you would benefit by using 350 valves at 1.88 . Crower has some decent cams. Or custom ground from competition components-Scott brown. Its only 20 buck more than some cam companys. And will be more up to date tech. I assume 340 has steel head gaskets . replacements will be thicker and drop compression. So I would shave heads .030 and add the extra thickness of gasket being used(if gasket is .020 thicker then stock add .020 to mill .050 off head). I believe most of this work will get you there and give a much more powerful feel to your car.
My best recommendation is dropping in a 200-4r transmission and putting in 3.42 or 3.55 gears with posi in the rear. The swap is fairly easy for the transmission and will liven up your car in a big way. Look through my build and it will give you some info. I was able to do mine for under 600.00. Gears is next for me and it will only solidify my decision. I went from a 300ci to the 340 and was going to build it up but quickly found out it wasn't worth the effort given the mild return in hp. I am working on a plan for a 350 build right now for a future car.
A 350 trans with a 2000 convertor would show an improvement as it does have a deeper first gear than the 300. Usually pretty cheap and direct bolt in cept for adding the kickdown cable. Which you would need for a 2004r but the 350 doesn't need but you would have to manually downshift. . I think biggest downfall of the 340 is the valve size/port flow. Find used 350 heads and get bigger valves.
Not sure if its in the budget but the aluminum TA Rover heads will bolt onto the 340. Or do some basic home porting yourself, we all start somewhere when we learn how to do things like that. Decent advise to port your heads yourself can be gotten or found here. These piston can be ordered with a taller or shorter compression distance and a different dish volume at no extra cost to get your compression where you want it with less machine work; http://www.buyracingparts.com/pisto...stons/autotec-forged-350-buick-pistons-1.html I know these are sbb 350 pistons but they will work in your 340 because the bore size can be customized as well for no additional cost, that price includes premium rings and wrist pins as well. Your 340 should be able to handle a .050" overbore that will make it a 350 with a 3.800" bore or you can just do a .030" overbore and still order the above pistons that size because they're made to order.(the 3.800" bore would be a better choice because of the better ring pack selection) Matching the cam to the compression ratio to what grade of gas you want to run and the head flow should get you to 300 crank HP no problem with your 340. You should be able to use your stock rods and stock rod bolts at this low HP level, just make sure to have your machine shop check them to make sure they're still in spec. If the engine runs good now the best area to spend the $$$ is with some better gearing like a 200R4 and a 3.42 rear gear or numerically higher which would be a lower ratio. If the gear in the car now is in the 3s then you could consider a 700R4 will do good without having to do a gear change but the driveshaft will have to be shortened slightly. The gearing will give you the best seat of the pants dyno gains than even swapping in a BBB in front of the ST300 with its horrible gearing. People usually want to start with the engine on a car when the entire drive train should be factored in as a whole combination. Say you had a plan and knew what engine you wanted to end up with then the best bet would be to start with the rear gear and work your way forward to the trans then the engine as finances permit. Doing it this way you'll feel the gains right away that won't be as disappointing as a rebuilt engine behind the anemic gearing of the ST300 with a 2 or 3 series gear. GL Derek
Gsgtx did just what your talking about doing. I ported his heads and intake and he did a few other basic things and he was running around 14.2 in the 1/4. It was very streetable. That was with a 3.23 gear and 2 speed. I agree with the 2004r
I really appreciate all the great feedback. After considering option I really like the 200-4R with a better rear end. I will let everyone know once I have this in motion.
Cool. I should send you the heads from my 340 With the budget you have in mind my thought is T350 and posi unit. I had the ST300 in mine and it was ok with basically stock engine with a cam -old Poston 112 I think!!?? Trick with the transmission - to use factory rear gear order the low gear set in the T350. Get a little higher stall converter. Now the posi with original gears...will still give you highway comfort and low 1st/converter will get the car moving pretty well. It is a compromise, but with your budget that is what its is about. I still run a single exhaust too- it sounds great. Anyway that is what I did and I'm satisfied with the result.
A 340 4 brl is 260hp stock. You can get into the 300 hp range with a cam and headers. My GS340 came stock with a 3.23 rear which is a good all around ratio. I would take a TH300 switch pitch over a TH350 any day. A 200R4 would be a nice improvement and would work with the 3.23 rear. You don't need to get too carried away to spice it up a little.
My favorite gears are 3.23- I'm running them in the wagon and Stage 1-.did not know GS340 came with that standard. GS CA I think got the 2.78:1 like the automatic Specials. I tried to love my TH300 but even with the convertor from TriShield it cannot compare to the T350 I got from Transmission Specialties. They set that thing up right, probably makes the difference.
I had 2 67 340s, one was in a Skylark and the other was a GS340, The Skylark had a 2.78 as does my 65 Special 300, the GS340 had a 3.23. I still have that gear set in my attic. A can only assume the GS340 was stock.
I think Ted has it right on the CA GS 340 rear end (2.78:1). The CA is based on the Special body (2 door post) with a 340 engine. I definitely think the trans and rear end change will make the difference. I have already spoken with a guy that specializes in Buick's and specifically the 2004r. Thinks it will be a vast improvement over the ST300 and 2.78 in there now.
IF the switchpitch is working properly, and the 340 still has decent compression, the 3.23 rear is all it needs IMO. o No:
If he goes with a 200R4 he'll need at least a 3.23 rear, 3.42 preferred. To get the full MPG benefit from the 200R4 the metering rod springs will need to be changed so the rods don't start to lift until 9" Hg.,otherwise he'll be running on the interstate with the metering rods partially up.
I assume when the OP says he wants 300 hp, he is thinking 300 hp under the SAE standard used since 1972. To convert the pre-72 horsepower rating to today's standard, reduce 260 hp by 20% which yields 208 hp SAE net. Changing to headers and a cam are unlikely to make up a 92 hp. I would doubt these changes yields another and 50 hp.
Please explain further on this. I have the Carter AFV, 4330V I think. I plan on going to 3.55 gears here soon. Anything else I need to do? I have the 200-4r and the B&M lockup kit.
You will have to get carb adapter for trans cable. Do not run without cable connected and adjusted. You can wipe out a 200r4 trans very fast and it won't even need to be in gear.
I see a lot of people put overdrive transmissions in older and don't think about their carburetor. All carbs have some mechanisms to make the mixture richer during acceleration then go back to a normal base mixture at cruising speed. This is system is based on vacuum since it is assumed low vacuum means the engine is under acceleration and high vacuum means idle or low load. AFB style and Q-jets carbs have metering rods that are pulled down by vacuum (low load) and are pushed up by springs at low vacuum (high load). The metering rod is tapered so when it goes up in the jet the mixture gets richer. I know there are many different metering rods for Q-jets, different lengths, diameters, single, double and triple tapers are available. I can assume that there are as many available for the AFB style carbs also. The spring is what determines when, or at what vacuum, the metering rod begins to rise in the jet. If you compare the same car with and without overdrive, cruising down the highway at 75 MPH, the car with overdrive will have lower vacuum characteristics which may cause the metering rods to move up in the jet making the mixture richer when it's not necessary which will waste fuel. So, the carb needs to be tuned for the overdrive by changing the springs to a lower spring rate to push the metering rod up at a lower vacuum. A Holley style carb doesn't have metering rods, instead it has a power valve. They sell power valves that open at different vacuum levels, stock is probably 13 in Hg, for overdrive 8 in Hg would be better. They probably sell springs for AFBs and Q-jets for different vacuum levels as well. If you change to overdrive without modifying your carb you may go from 16 to 18 or 19 MPG, with the carb modification you may get to 22 or so. This is all an approximation since the mixture is based on one parameter, vacuum. A car with an ECU can do a more precise mixture adjustment because it takes vacuum, throttle position, mass air flow, vehicle speed, engine temp. and feeds it into algorithm to calculate the mixture. This is how a GN can run a 13 sec 1/4 mile and then get 28 MPG driving home from the track. Using only vacuum is crude science. My father had a 77 Nova, straight six, three on the tree that got 29 MPG, excellent for a 3,400 lb car. Here's how they did it: very wide ratio transmission with a 2.73 rear and a one barrel carb that had a non-vacuum modulated metering rod. The metering rod was mechanically coupled to the throttle plate, so, the mixture was determined by throttle position, not vacuum. One of my 65 Skylarks is a 225 V6 that I plan to put a 200R4 in. I have a 77 Nova carb that will bolt right on that engine, my goal is 30 MPG. Hope this helps.
That is some great information to check into. I have pulled some great mileage with my current setup so it seems close as is. 21 mpg's on a few trips. Once I put the gears in though I will have to check mileage and vacuum and see where I'm sitting at the new highway cruise rpms. Good next level tuning info to tweak the setup even better.
