Primatech DOHC 6 head...

[Greg55_99]

This is VERY interesting. They're cutting and shutting two DOHC 3.4 heads to make a DOHC 6 head for the old Pontiac OHC 6 250. Very clean..

http://primatechmotorsports.com/products/pontohc/ohcdohc.htm

Greg

[SappySE107]

RE: Primatech DOHC 6 head...

Wow, thats quite a bit of work! I didnt check their entire site but im curious as to the performance gains from doing this on their motor.

[Kohburn]

would be a huge improvement I'm sure

but who the hell would think of doing that?

[SappySE107]

Im just surprised the bolt spacing and cylinder bores are that close of a match to do it. Just takes research sometimes to find a somewhat simple solution. Compared to making new heads, im sure their process is much cheaper.

[BMFH]

Hello All

The heads are being married to get a high flow, cross flow, 4 valve DOHC head for the ol'e OHC 6, (circa 1966-1969). The real gains will be at the higher RPM level's, much the same as the LQ1 does for us.

The really good news is that there will be little if any space constraints for custom induction or header systems.

I don't know if you know much about the 4.2L Vortec 6 that came out for the Chevy Trailblazer a few years ago, it's head design is very simmilar in design to the LQ1 heads, but its bore spacing is off.

The 4.2L's Debue was in the Baha race against a field of V8's, It recieved the best performance award for the race and WON THE RACE, AGAINST a field of V8'S I hear that it is a real contender in the Pikes Peak Hill Climb too.

In its race form it had around 600 H.P. at 7500 RPM's,
(Not bad for a straight 6)

The LQ1 and the OHC 6 have the same 4.4 inch Bore Spacing and uses head bolts almost in the same locations, it already almost fits in stock form, it is just too short.

So the potential is there for the OHC 6 also. The OHC 6 was buzzing 6500 RPM's and 207H.P. in 66 and 215 H.P. in 67 out of the box , (factory RED LINE). They were also the first production engines that they installed the Quadrajet on.

They were really a lot of fun when they first came out, and still are today.
Nothing worse, than getting our doors blown off by a Straight 6

If you want more information about the OHC 6 Retro-Fit head, talk to Q on this site, he is a really busy guy these days, so it may take him awhile to get back to you.

Food for thought, Isn't making it work, what HOT RODDING IS ALL ABOUT.

John

[Q]

This is a really long story, but I like telling it ...

I didn't think of the idea ... it's been done for years, but I was the one who pursued the LQ1 solution. There has been talk since 1966 of a "Hemi" head made for the OHC-6 that was a 2-valve cross-flow head. (The OHC-6 head isn't a cross-flow, which is one of the most limiting factors in its breating capacity.) The hemi-head never made it to production, and the few surviving examples that were actually cast have somewhat disappeared. Since that time, no new ideas ever made it to production for that little old six-banger.

Ever since '91, I'd wanted a GTP with the 3.4 DOHC. There is just something so cool about a dual cam, 4-valve head! I really wanted to own one. I never have. But I never forgot about the motor, either. In 2002 I bought a 1969 Firebird convertible with the OHC-6. I came within an inch of tossing the six and dropping in a huge V-8. I still have the V-8 on a stand in the garage.

Somehow, that little six hooked me. So, being restless and bored one day, I started to do some research.

I found out that the LQ1 bore spacing was the same as ALL of GM's motors since the dawn of time. Well, since the SBC in 1955 - maybe even before that. That was the clincher. I thought that if the combustion chambers were in the right place, I could probably make the rest work.

One of the guys that works in my plant is a welder - about the best welder I've ever known. He and I were talking one day and he mentioned that he used to work for a company that made racing cylinder heads, and it wasn't uncommon to weld bolt holes closed, build up bosses some where else and drill new bolt holes. Then I knew it could be done. I also have a very good working relationship with some guys at AFR. They offered me some great insight, and - as it turns out - another welder who knew what I wanted to do, and knew exactly how to do it.

Then, on a whim, I bought a pair of core heads and dropped the OHC-6 head gasket over them and almost shit in my shorts when I saw almost all the bolt holes line up.

The rest of it has been a "work while designing in progress" routine. One end of each head was sliced off and machined true. Then a plate was machined and welded into each head to compensate for the water jacket mis-match. The plan now is to mate the heads (on a fixture to control warpage) then heat treat them back to their aged condition. Once they are straightened and milled and the new water passages are opened up, the bolt bosses will be drilled through and enlarged to accomodate sleeves for the head studs.

We still have a long way to go, but this project will definitely be finished! And, a motor WILL be built for that head. Flow numbers will determine how the bottom end is built. We figure we can squeeze out at least 750 HP from the stock 250 CID block before we lose something important. The factory block was desinged for cross-bolted mains and a cap girdle, so we'll use them. The factory oiling system is a wet sump with an external pump, so we'll convert that to a multi-stage dry sump.

Unfortunately, this means very, VERY little to you guys. But I've had a great time so far, and I enjoy this site.

Thanks. This is probably the most flattering thing that's ever happened to PMI.

Also ... we're experimenting in a big way with stroking the OHC. Everything that's done to V-8's in that area applies to 6, either straight or V. If any of you are serious about expanding your bottom end, please look into it. It's a lot easier than you think. All you need to know is the width of the big end of the connecting rods, and we can spec out all the parts you'll need.

Q

[RednBlack]

Your work is sweet Q! I had a friend build a 250, "70s" style, 3 dueces and headers etc, and dropped it in a 66 Nova. I was impressed THEN. (1976) He would crap his pants if he knew this. I wish I knew his E Maill addy.

However, I will send this to a few people I know still humping straight 6s. Dirt trackers. Kudos!!

[OldSkoolGP]

I remember Q. He inquired about my 96 heads a few months back. Sorry if I didn't get back to you about those. My friend Ben has them right now for research and development.

[RacerX11]

I don't know if you know much about the 4.2L Vortec 6 that came out for the Chevy Trailblazer a few years ago, it's head design is very simmilar in design to the LQ1 heads, but its bore spacing is off.

The 4.2L's Debue was in the Baha race against a field of V8's, It recieved the best performance award for the race and WON THE RACE, AGAINST a field of V8'S I hear that it is a real contender in the Pikes Peak Hill Climb too.

In its race form it had 675 H.P. at 7000 RPM's, (Not bad for a straight 6)
John

I happened to be at Pikes Peak in 2000 for the race when GM Motorsports was the sponsor, and they brought something to race in just about every division. The GMC Envoy with the race version of the 4.2 DOHC was just awesome. The race engines were built/prepped by Rousch Industries, sharing the basic design, but no parts in common their production counterparts. The displacement was bumped to 5.0L, and they had custom cylinder head castings that had each valve canted in two planes, creating more of a hemispherical combustion chamber. This valve arrangement required the cam lobes to be ground on an angle. The custom 6-into-1 header was a work of art. The official numbers I read on the engine were 600HP @7500, and 450 lb-ft @6000. I have always been a big fan of the sound of a nice straight six, but they had this thing wound so tight, it sounded almost like an F1 car winding up. I took some video of it blasting past on the first straight just after the start line, and the sound is almost magical.

Larry Ragland drove the Envoy to the overall win in 2000, as several of the faster cars (namely Rod Millen) had mechanical breakdowns. He completely outclassed the other competitors in the High Tech SUV class, as well as the modified and open wheelers that should be faster. I had heard that GM had funded this race program to get some press on the new 4.2 Vortec I6 engine (which it did). They were very sucessful at it, but the costs were so high compared to the V8's, they only ran the I6 in the Baha circuit for a short time. They proved their point that a 6 cylinder could compete for raw power, as well as power density and fuel efficiency.

Marty

[your_I.D.]

Thats going to be a hell of a set of cams.
Very sweet Q!!!

[Q]

The cams are actually not that hard to concieve - just a little expensive to tool up for. Once we have it done, it should be a simple matter to offer blanks for the go-faster crowd here. Even though we are building a pair of long I-6 cams, the tooling and parts will be available for a set of the shorter V-6 cams. Stay tuned.

[Fierobsessed]

I love it. Thats the kind of engineering I admire. Can't wait to see the finished product.

[Q]

I don't want to let too much information get out before things are actually working, but we are also planning on having VVT on that head.

[your_I.D.]

VVT!! hmmmm DOHC v6 with VVT maybe

[OldSkoolGP]

VVT? That'd be it, then we could stomp on some L67s!