'68 327 c.i. - Is it 250 or 275 HP? [Archive] - Impala Tech

: '68 327 c.i. - Is it 250 or 275 HP?


ed68
10-17-2008, 08:27 PM
I understand that Chevy had at least two versions of the 327 c.i. engine in 1968, one producing 250 HP and the other 275 HP. How can I tell which one is in my car? It's a '68 Impala convertible, 327c.i., Quadrajet carburetor and single exhaust. It is equipped with a 3-speed automatic transmission. It is all factory installed equipment. Is this enough information to determine which HP engine would have been put in the car? Is there some other way to determine which engine it is? Thanks for your help.

maas restorations
10-17-2008, 09:12 PM
I think there's a post on here about it. Something about two different carbs available.

Found it:

The 250 hp had a Rochester 4GC carb. The 300 hp had the Carter AFB which is cloned now as the Edelbrock so it is easy to compare. There are several other differences, but this should be quick. -Michael9040 (http://www.impalas.net/forums/showthread.php?p=3446)

Hope this helps

dgwar
10-17-2008, 11:43 PM
I bet the 300 HP had dual exhaust too.

maas restorations
10-17-2008, 11:52 PM
I bet the 300 HP had dual exhaust too.

I second that

62BillT
10-18-2008, 01:55 AM
The Standard 327 HP rating in Full Size cars '65 and back is 250 (altho in '65, many if not all, had the smaller Double Hump heads). The Standard 327 HP rating in '66 to '67 was 275 (These engines have a Q-J carb). After doing a little research it looks like in '68 they did reduce back to a 250 HP engine, as well as having the 275.

Ed, Post your engine code on the pad on the front of the engine and we can determine exactly what you have, altho with the Q-J carb I'm going to say you have a 275 HP 327.

Bill

ed68
10-29-2008, 01:45 PM
Ok, Bill. I finally got the engine code off the pad on the block. It is V0527HN. I've done some research and found that the "V" means it was made in the Flint plant. The "0527" means it was made on May 27 ( I assume in 1968). The "HN" designates the the engine displacement, horsepower, and what model it was intended to be installed. I haven't been able to find that information online. Do you know what the "HN" designation tells us?

ed68
10-29-2008, 02:16 PM
I did a little more research and found that the "HN" part of the engine code means it is a 327 V8, 275 HP, with a 4-bbl carb and a compression ratio of 10.0:1. The compression ratio for a 327-250HP is given as 8.75:1 and also has a 4-bbl carb. I found this info at YearOne.com.

62BillT
10-30-2008, 07:03 PM
Ed,

I've done a little research on the '68 327, as up till you posted it the other day, I always thought all '68 327's in passenger cars had 275 HP. I found out a few different things from different sites.

The HN Suffix Code was also used for other year engines ('65, '68 and '69) according to 2 sites anyway. So I would try to verify the year, altho the date code is on the back of the engine and it may be difficult to see.

Also, the Year One info may be wrong. Two other sites list the '68 HN different.

http://www.chevy-camaro.com/chevy-camaro-engine-codes.asp

http://www.nastyz28.com/chevy-engine-code-stampings.php

Also, check to see if you have the Double Hump markings on the front of the heads. That would also tell us something.

Bill

ed68
10-31-2008, 12:04 PM
Bill-

What a can of worms! Both references you give say the "HN" engine is coupled with a Powerglide. Both say that an "HM" suffix is for the Turbo Hydra Matic, at 250hp. I have a Turbo Hydra-matic transmission, but my suffix is "HN". One reference I found (which I have not located again) said that the higher horsepower was coupled with the Turbo Hydra-matic, if I remember right.

The original Owners Manual for the car does state that there are two available HPs for the 327, those being 250hp and 275hp, with the compression ratios I found at Year One.

How can I identify the Double Hump markings you mention?

ed68
10-31-2008, 01:57 PM
I found a picture of what the Double Hump looks like. It looks really kind of like a double-humped camel back with rounded humps. My engine does not have that shape on the castings but rather has two squared off rectangular shapes on the passenger side head and two rectangular shapes sticking up from a lower rectangular shape on the other head, kind of like a mutant camel with square humps. I assume these are not the Double Hump markings we are looking for.

Steve Nagel
10-31-2008, 05:13 PM
I thought I'd just add some dirt to the can of worms. In the tag team forum, last spring I'd posted some questions about nearly the same topic regarding engine codes and 275hp vs. 250hp. I moved the thread to the top. In any case, I still haven't figured out the 1968 codes for 275hp. In Colvin's book a 327, 250hp TH w 4bbl is HM code. 275hp is HF.
Steve

Steve Nagel
10-31-2008, 05:42 PM
By the way Ed, your car looks very nice. My '68 is very similar to yours other than condition, I have more rust than metal. I was curious what other options yours has such as PS or PB, drum or disc? I'm wondering if there is more to these codes based on options the car was built with that would effect how the engine was assembled prior to installation in the chassis.
Steve

62BillT
10-31-2008, 11:15 PM
Ed,

While I was doing some searching the other day, I also found out the casting numbers for the heads on a '68 327/250 which is #3917293. The markings you described sounds like these.

Steve,

You might want to try the links I posted above to try to find out more info on your engine.

Bill

Big Dave
11-01-2008, 08:10 AM
Just out of curiosity dose the speedometer have the word certified on it? If so all bets are off as it is a used cop car which is a COPO car so any combination is possible.

My mothers black over white 1968 four door hard top Caprice Classic was special ordered for the Chief of police for the City of Clearwater Florida. It had a 327 that had been destined for a Corvette and had a TH400 transmission with oil and tranny coolers, four puck disc brakes on all four wheels and Corvette 15x8 15" Rally wheels with trim rings and power disc brake hubs. The city commission got the tab for the car and nixed the sale, so my dad was able to pick it up for a song from the dealer because it idled funny compared to the other Impalas (solid lifter cam). The chief wanted the fastest car in the fleet and it had more luxury items in it than the mayor's car (power everything including split bench seat and antena).

Big Dave

ed68
11-01-2008, 10:25 AM
Bill-

I'll take a look at the head casting numbers you referenced. Thanks.

Thanks,
Ed

ed68
11-01-2008, 10:42 AM
Steve-

I reviewed your post in tag team and, indeed, we have a very similar dilemma. I've found several sources with either conflicting or incomplete information regarding the suffix in my engine code. Very frustrating.

To answer your other question, my car has power steering and power drum brakes. Although I haven't seen any sources that link the engine codes to options other than the transmission, whether or not other options affect which engine was installed is a good question.

Thanks,
Ed

ed68
11-01-2008, 10:48 AM
Big Dave -

Your mother's cop car sounds like one heck of a sweet ride! But, I am sure my car was not a police car. It's a convertible. I would like to have seen THAT get by the city commission!! :)

- Ed

ed68
11-01-2008, 11:01 AM
This is very frustrating trying to find an answer to this question, but I am learning quite a bit while looking.

Year One Tech has a good article about Chevrolet Engine Decoding. Here is a link to it:

http://www.yearone.com/updatedsinglepages/Id_info/gm_engine_id/engineinfo1.html

It is several pages long (click the "NEXT" button at the bottom of each page to proceed). At the bottom of the last page there are links to Nova, Chevelle, Camaro, and Impala Engine Codes by year.

Check it out. It is the most thorough treatment given on the subject that I've found on the Internet so far.

TAR6569
11-01-2008, 12:55 PM
let me clear things up:
L30 - 275HP 327
HA - manual trans
HB - manual trans/heavy duty clutch
HC - powerglide
HF - TH400

L73 - 250HP 327
HG - Powerglide
HF - TH400
HH - TH400
HI - Manual
HJ - powerglide
HK - powerglide
HL - Manual/Heavy Duty clutch
HM - TH400
HN - TH400
HQ - Powerglide

I have confirmed all of these suffix codes on actual cars or protectoplates except for HB and HQ. There are also 2 COPO suffixes for the 68 327 both L30. One is HR with supposedly came with a manual trans and the other HS, I believe with automatic ( I think TH400) has just been confirmed. Both had the COPO 9665 option which was some special transmission.

Warren

ed68
11-01-2008, 05:34 PM
Warren-

Thanks for the info. I like the fact that your information has been confirmed with real-world applications. It is frustrating and confusing that the published information on the subject is full of conflicting and incomplete information.

So, based on your experience the suffix on my engine, "HN", tells us it is a 250 HP V-8 with a TH400 transmission. This is probably correct because I have a TH. Most of the documentation for "HN" specify 250 HP but with a Powerglide. Yours is the first reference to a Turbo Hydra-matic.

So, based on that, it is looking like it is a 250 HP engine.

It will be interesting to see if others concur.

Thank you,

Ed

TAR6569
11-02-2008, 12:27 PM
Right. And I would imagine that since the engines were so similar, that a HN engine could have been mounted to a powerglide by mistake.
On some protectoplates I have seen, a 68 impala had a 307 engine but the code for the TH400 was actually for a 327. I imagine the differences were very minor so these mistakes could happen.
Yes, I like to confirm all of these engine codes before I tell others what they mean.
Warren

Don41
08-19-2009, 07:23 PM
I understand that Chevy had at least two versions of the 327 c.i. engine in 1968, one producing 250 HP and the other 275 HP. How can I tell which one is in my car? It's a '68 Impala convertible, 327c.i., Quadrajet carburetor and single exhaust. It is equipped with a 3-speed automatic transmission. It is all factory installed equipment. Is this enough information to determine which HP engine would have been put in the car? Is there some other way to determine which engine it is? Thanks for your help.

I realize this is an old thread, but I just came across it. Since I recently researched this same question, I thought I would add what I learned.
My source of info is 'Ultimate American v-eight engine data book'.
For 1968, the full size chevy cars with 275 HP 327's were suffix coded HA HB HC & HF. The 250 HP cars were HI HL HG HH HU HK HN & HM. Also, of this latter group, only the HM code was mated at the factory with a TH transmission. The HI and HL codes were manual shift, the rest were factory mated to a power glide. Hope this sheds some light on the confusion!

ed68
10-27-2010, 12:47 PM
Don, I was just looking at some of my older posts and responses and found your response detailing the suffix codes. If you are correct that the HM codes were mounted to a TH transmission and the HN codes to Powerglides, then I must assume my engine was replaced at some point. My suffix code is HN and I have a TH transmission. Up until now, I was pretty sure I had the original engine in the car, as it only has 43K miles on the odometer. But I really don't have a detailed history of the car, so anything could be the case.