gwarren612
Registered Member
Have any of you ever ran a 327 in their k5? And if so, what carb and tranny did you use?
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327 sb in a k5?
- Thread starter gwarren612
- Start date
Stomis
Professional Amateur
There is no difference between any peripheral needs to run a 327 in place of a 350 or 305. For a typical not crazy built motor any carb is going to run a a 327 just fine that was running a 305 or 350 with a little rejetting.
Now if its going into a TBI truck you're going to need a retune on the computer.
The only thing to watch out for is that lots of 327s had camel hump heads on them with no accessory holes. That will get ya.
Trans is really null and void. All that stuff crosses over no problemo. Run a 700r4, TH350, TH400, Sm465, NV3500, NV4500, doesnt matter.
Now if its going into a TBI truck you're going to need a retune on the computer.
The only thing to watch out for is that lots of 327s had camel hump heads on them with no accessory holes. That will get ya.
Trans is really null and void. All that stuff crosses over no problemo. Run a 700r4, TH350, TH400, Sm465, NV3500, NV4500, doesnt matter.
gwarren612
Registered Member
Thank you Stomis. The 84 k5 I recently got my hands on has had a 327 dropped in it at some point in its life. It came to me with an edelbrock c3bx intake, quadrajet carb and hei distributor. Now I didn't realize this at first, but the c3bx intake wasn't designed to except the newer large diameter hei distributors. When I picked the truck up, it hardly ran well enough to get it home. The previous owner blamed the carb and said he had had trouble ever since he put the quadrajet on. Got it home and got to looking, and discovered that, to make the hei dizzy seat, some dumb a$$ had ground down the top of the last air horn on the intake and ground so much off that I could stick my entire thumb in the hole... HUGE vacuum leak! I was low on funds at the time and needed the truck on the road so my temporary fix was to pull the dizzy out and cut a chunk out of the base with a hack saw ( the part of the base that would bottom out on the top of the air horn ), and fill the huge hole with quick steel apoxy putty. That helped drastically but still had issues. Since then I have replaced the intake with an edelbrock performer eps and replaced the quadrajet with a holley 600cfm 4bbl. I think the quadrajet I took off is a 750cfm carb. I'm wondering if the difference in cfm between the two would give me enough performance increase to justify rebuilding the quadrajet and putting it back on top of the new intake. I'm not sure what the optimal cfm rating is for a carb going on a 327. Any thoughts?
Stomis
Professional Amateur
Well carb sizing is dependent on two things, RPM and cubic inches. If you refer to this LINK Its a very quick calculation. Typical driving with a 5800 RPM redline (which is probably above what you'll take an unknown motor to IMO) with a 327CI requires a mere 466CFM to properly run on the street. At WOT in a racing/high load scenario the recommendation is 603 CFM. So your edelbrock is spot on and if its working for you I would certainly suggest you leave it alone.
That quadrajet is more than likely from a big block car or truck. Im no quadrajet guru but I dont believe any small block used a carb that large from the factory and the performance model small blocks used a holley style carb off the line IIRC. That quadrajet would be more suited for a builtish 383 that you still wanted good street manners on. Way to much for a average 327.
gwarren612
Registered Member
Thank you very much 
I guess I will use the quadrajet to barder with then. Yes, the carb on it now is working great. Was just wondering if I would see a performance increase but sounds like, if anything, it would hurt my performance. I'll find something good to trade it for 
I guess I will use the quadrajet to barder with then. Yes, the carb on it now is working great. Was just wondering if I would see a performance increase but sounds like, if anything, it would hurt my performance. I'll find something good to trade it for 
I don't think that there is a Q-jet that is any smaller than 750. They can do it because of the air valve above the secondaries. That is why GM put them on lots of engines. Even 305s had them.
Now whether or not you would get any performance gain, I would guess not much if it was tuned perfectly. But I would bet that you could see some improvement in driveability and mileage, IF the carb was set up correctly. But if you are happy with what you have, I don't know if you would want to mess with it. So I am just throwing out some information from what I have learned.
Now whether or not you would get any performance gain, I would guess not much if it was tuned perfectly. But I would bet that you could see some improvement in driveability and mileage, IF the carb was set up correctly. But if you are happy with what you have, I don't know if you would want to mess with it. So I am just throwing out some information from what I have learned.
gwarren612
Registered Member
Thanks for the info 6872xtc. I had originally planned on rebuilding the quadrajet and then seeing which I liked more. I might still do that. I'll just put off trading it till I'm sure which one I want to keep.
Stomis
Professional Amateur
Ah see you learn something everyday. Apparently from googlefu GM used some sort of restricters to size them for different motors but theres only two sizes 730/750 and 800.
Qjets are a whole facet of knowledge that Ive only ever dipped my little toe into lol.
Now see, I didn't know about the 730 cfm, but Sean at SMI told me that the air doors on top of the secondaries is what made them work on lots of engines by somewhat varying the cfm. He did an awesome job on my carb!
don't forget the various rods, jets and hangars that vary them from app to app too...
FWIW the 305 trucks got 800's. Not sure that is ALL 305 trucks, or just some years/applications, but I know at least some did, I had one.
GM also used the 800's on the 307 Olds in cars (while the HO 305's in Monte's got 750's?!). I recall reading something somewhere, may have been from David Vizard, the lead me to think that somehow, even though it's counter to what is commonly thought, that more flow actually helps torque. It was specific to the carb sizing, it wasn't a general rule, but there must be something to it, as the 800's made up the flow difference on the primary side. It also proves (IMO) the carb CFM calculators are overly simplified. Vizard has proven this, he's spent a fair bit of time testing this, and has made more power with carbs that common belief holds would be way too large for the applications. Here's one of his articles on it http://www.hotrod.com/how-to/engine/0511phr-carburetor-boosters-tech/
For what pretty much anyone is ever going to do with these carbs, that 50CFM isn't going to make a difference at all. I doubt many here will argue that the Q-jet is the best all around carb available...not the best at anything, but a more well-rounded design for street and offroad than others.
GM also used the 800's on the 307 Olds in cars (while the HO 305's in Monte's got 750's?!). I recall reading something somewhere, may have been from David Vizard, the lead me to think that somehow, even though it's counter to what is commonly thought, that more flow actually helps torque. It was specific to the carb sizing, it wasn't a general rule, but there must be something to it, as the 800's made up the flow difference on the primary side. It also proves (IMO) the carb CFM calculators are overly simplified. Vizard has proven this, he's spent a fair bit of time testing this, and has made more power with carbs that common belief holds would be way too large for the applications. Here's one of his articles on it http://www.hotrod.com/how-to/engine/0511phr-carburetor-boosters-tech/
For what pretty much anyone is ever going to do with these carbs, that 50CFM isn't going to make a difference at all. I doubt many here will argue that the Q-jet is the best all around carb available...not the best at anything, but a more well-rounded design for street and offroad than others.
You may notice the 327 has less low end power than a 350,it has a shorter stroke,and will want to run best at higher rpm's than a 350 or 400 sb would..
They like to rev,and if you have low gearing it will perform better..
Q-jets can work on many engines due to the air valve secondaries--GM even put them on the Pontiac OHC 250 straight sixes back in '69...by limiting how far the secondary air valve can be opened,it makes the carb "self limiting" in a way..kind of like a variable venturi..
Most guys here who ran 283,307 & 327 engines and some 350's on dirt track cars found they often performed better with the 2 barrel carbs,many classes restricted them to 500 CFM carbs or less..many used the Holley 2300 2 bbl or the 2 Rochester stock 2 bbl carbs,that were available with 1-1/4" or 1-1/2" throttle butterflies..in my experience the smaller carbs made more low end power than a 4 bbl did..
They like to rev,and if you have low gearing it will perform better..
Q-jets can work on many engines due to the air valve secondaries--GM even put them on the Pontiac OHC 250 straight sixes back in '69...by limiting how far the secondary air valve can be opened,it makes the carb "self limiting" in a way..kind of like a variable venturi..
Most guys here who ran 283,307 & 327 engines and some 350's on dirt track cars found they often performed better with the 2 barrel carbs,many classes restricted them to 500 CFM carbs or less..many used the Holley 2300 2 bbl or the 2 Rochester stock 2 bbl carbs,that were available with 1-1/4" or 1-1/2" throttle butterflies..in my experience the smaller carbs made more low end power than a 4 bbl did..
