inline 6 conversion

Ok i just bought a 68 tempest custom it has a inline 6 and i want to give it more power without doing a motor swap everyone says the inline six sprint setup will keep up with a 350 all day long so i was wondering is there snything i have to change other than the intake manifold so nothing breaks?  

Not to steer you away from our great forum, but much of our discussion here is based on the Pontiac V8, so here's a link to great forum that deals entirely with Pontiac OHC-6 engines. You will find everything you need to know and more.
Steve

http://sohcsix.yuku.com/directory  
A little help... 'cause we don't all have to learn the hard way!

+1 Steve, its all there. Theres a lot more differences than just the intake and carb, as in compression and cam. Good parts are rare and if you do everything just right, you'll spend enough to swap in a V8 just to make 200 HP or so. They love to eat cam belts and cams. The base sixes with one barrel carbs are pretty limited, performance-wise. Still gotta love 'em.  

I had a tempest with the OHC 6 in it and loved it.  Personally, I never had any trouble with it and with gas prices as high as they are it may be worth keeping. Getting parts for them these days is hard though.  Visit the site Steve listed and make your decision.  Either way, we want to hear about your experience and what your doing to the car.

Milt  

hello tenpest 68

you have a hard road to hoe [or somethin like that]. all very good comments above. i had stock sprint in a 69 firebird, loved that car but it was slow. the sohc site is best. it really comes to what your idea of a "bit" more power is. the faster you want to go the more it costs and it can cost alot.

here's my view. the 6 cyl guys wish it would keep up with a v8, can't blame em ao did i however it would take big bucks to do that sooo... if you are NOT rebuilding the motor but want to increase the performance to a level you can definitely notice instead of just sort of notice like with a 4v from 2v intake on a v8 then this is the minimum you need.

1.mill head to increase compression, rebuild it while it is off.    
std compression is 9:1, sprint compression is 10.5:1. [will cause detonation]or buy sprint head.

2. pocket port head, very helpful. opt around $250.00

3. install hp cam, maybe nitride it if the sohc site says they eat cams like. idrivejunk suggests. there is a std sprint cam and an optional H sprint cam.

4.ask if there is anyway to improve oiling to cam'

5. you made hp or hv oil pump with cam upgrade. cost $60.00

6. buy sprint carb and intake or other brand.

7. buy a header or sprint ex, they just posted header dyno results on sohc.

pricing below is just a guess,

1. cam and springs 09690k orig sprint  $400
2. nitride process if needed                 $100
3. mill and rebuild cyl head w guides   $275
4. header or sprint exhaust                $275
5.gaskets                                          $30
6. carb                                              $275
7. intake used sprint                           $200  
8. upgrade exhaust if needed              $400
9. diff gears                                       $500
total                                                 $2455


NOTE - This following is one of the most overlooked and underrated items in your search for performance. The single most significant improvement to acceleration and increased hp "feel" is actually not in the motor, it is in the gear ratio. if you have $500 and want your car to feel faster i would change the differential gears first providing you are not planning on doing any long fwy trips. even if you spend all the money listed on the options above you will still NOT realize a substantial feel in increased performance if your gear ratio is too high. hp and gear ratios go hand in hand.

IMPORTANT - if you do these improvements on a stock used bottom end your motor may end up spitting out more parts than it started with. probably not but possible if you flog it often.

i'd suggest going 1 ratio lower than what you currently have example, if you have 273 go to 300 if they are 300 go to 323 etc. never go to 350 if you want to do much prolonged 60 mph driving at all.


check this out

http://www.overheadcammerschapter.150m.com/history.html


keep us posted. thanks  

Forgot to mention, if you search ebay and keep an eye out you can occasionally find parts on there. I recently saw a Clifford Inline 4bbl intake that bolts on to the 1bbl heads. One of the ebay stores (Falconglobal, I think) has complete rebuild kits including pistons, 4bbl cams and everything you need to rebuild. I believe Clifford also makes headers for the OHC-6. You could also swap to a later model overdrive trans and deeper rear gears to take advantage of the high rpm potential of the cammer.
Steve  
A little help... 'cause we don't all have to learn the hard way!

I actually still have a cam core around here somewhere, from a Sprint. With a flat lobe. Dad ordered his '66 Tempest Sprint with 3.23 posi and at some point he swapped the Muncie to a Borg Warner Retro T-50 five speed. The block was so worn out by that point that it was poked 1/8" over and used 327 Chevy pistons. I thought it was a pretty effective combo, very fun to drive but the six had trouble with the steep OD of that trans. Speed limit was 55 back then though!

tempest68, I have pics of the OHC6 section from a MOTOR repair manual if you need them.  

Okay thanks.guys this is a big help.but in your opinions would it b smarter just to.put a v8 in i have a fully bulit chevy small block i was going to put in it but i was worried it would decrease the value too much and then if i would ever decide to sell the car i would have more in it then i can get out of.it so what do u guys think would be my best option  

Man you're there with just a few Malibu parts to drop the SBC in it. Doing that and swapping to a Pontiac V8 ought to be a similar amount of work. But I and just about everyone else here will only clap our hands for a Pontiac V8. if I were you and I weren't in a rush, I'd putt around with the six and constantly search for the right deal on a nearby running Pontiac V8. Even a 350 would be worthy. Thats just the approach I would try, and what I think about it. I had a '71 Ventura with a Pontiac-installed Chevy engine so I'm not messed up about the brand thing, its just a shame to Chevy one that wasn't originally. Stash the OHC6 and sell it with, if/when you sell the car. Just my opinion.  

A 68 Tempest is not worth much so don't worry about changing the engine .I would look for a Pontiac v8 350's are easy to find at a low price .  

Back in the day I bought a couple of firebirds and put z-28 302s in that made a nice hot rod. Cut the emblems and put Z-bird on the front fenders. Buy it on Thursday cruzeing on Friday nite. Dual fours made her go.  
Drive it before your dead!

Hello tempest

Here’s my thinking like gtojack

I hate to change motors on original cars however since yours is a basic 6 and not even a sprint I would throw whatever v8 in it that is most cost effective for you including your chevy. When you go to sell it you can advertise it with or without the v8 motor. Take a video of it running before you yank it out then sell it separately if you want. Always keep the original 6. Since it was not a sprint I personally see the sense in investing a lot of money into a motor no one wants anyway.

hope this helps