Demps

95 ZR-1 W/ DUNN HEADS (1 OF APPROX 130)
RED/BLACK 2 TOPS VERY STRONG STOCK CAR
EXCELLENT DRIVER WITH VERY SOLID MECHANICALS
NOT A SHOW CAR BUT VERY CLEAN
49,800 MILES
$39,900

4cefed

Educate me on the Dunn heads.

Demps

Birmal made the heads for all LT5s except the last 130. They went out of business. GM contracted A.L. Dunn for the remaining engines. The Birmal heads were cast then machined to the current flow specs (as the original cast was done prior to the "better" flow design). GM made changes to the casting when Birmal went out of business and Dunn picked up. The remaining cast heads have more material (if porting is desired) and flow as good, or better, than the Birmal heads. Also, GM fixed the cam chain tensioner rattle problem by including the fix as part of the new heads. I talked to Graham Behan (Lotus engineer now working for LPE) and he said the Dunn head cars are very strong (stock) and will match the 90's performance--as the later cars got a little more luxurious, i.e. heavy.

Wide_One

Not significant most if not all after 92 i.e 405 h.p. should have the dunn heads. I have a 94 model year and a crate engine and I am positive that both have a.l.dunn heads by cast marking.

Demps

Not significant most if not all after 92 i.e 405 h.p. should have the dunn heads. I have a 94 model year and a crate engine and I am positive that both have a.l.dunn heads by cast marking.
[/QUOTE]

Not true. The 4-bolt main engines (405 h.p.) do have different machining in the heads. The Dunn motors were produced as the last batch in 1993 and put in storage. Supposedly only MY 1995 received these motors. The heads have a different cam chain tensioner adjustment cover. Look at the right head (on the car thru the wheel well opening). There is a cover at the front of the engine on the side. This cover is an oval with two screws (one top/one bottom) with the hex adjustment screw in the middle for Birmal. Dunn's have a golf tee shaped cover with two screws at the top and one at the bottom with the hex adjustment screw in the middle.


reference the zr-1 net and their FAQ list

Wide_One

Okay I give up ......you are an expert!

SPEEDEMON

The Birmal Foundry announced they were going out of business in 1992. Mercury Marine immediately order a years supply of the heads and then later Lotus modified the tooling and turned it over to another British Foundry, A. L. DUNN, to finish off the production of LT-5 Heads. A.L DUNN took Birmal’s tooling and made changes to resolve quality problems, and began making cylinder heads for MerCrruiser. The DUNN heads were a more refined head and only on the 95's, mostly the last 100 cars. The rest were all Birmal heads. If you own one of the last 100 cars made in 95 then your chances are real good that you have the A.L. DUNN heads. I understand the earliest VIN # for a 1995 that I know of with A. L. Dunn heads is #227. They were not consistently installed, so some later VIN's in 1995 had Birmal heads installed. As far as I understand it there were no DUNN heads in the 94 cars.

LEADFOOT_

I also heard that cars with the A.L. DUNN heads produced 5 to 8 horsepower more than the cars with the Birmal heads due to the refinement of the flow work that has been updated.

Wide_One

Okay double checked here .....and a correction is in order my crate engine which came as a 94 replacement engine built 6/93 does if fact have dunn heads with the exact markings described, the engine in the car has birmal heads. Both tags are just above the the number 3 exhaust.

Demps

First,Wide_One congrats on the crate motor. The Dunn heads truly are supposed to be "special"--if not just rare. Wish I had a spare motor!!!

Second, I consider myself lucky for the red/black has Dunn heads and is #161. My other car #258 is Blue/Gray and has them as well. The Dunn motors were made last but how they were loaded and stored made their use random. The red car is stock (K&N only) and the blue car has the K&N and flowmasters. The red one is a horse!!! Don't know what is different but it is stronger than the blue with exhaust. If you can't tell, I don't really want to sell either.

Cheers! Thanks for the discussion all.

Wide_One

Demps, thanks and sorry for the confusion I was reading from the Heart Of The Beast which states that the 94 1/2 model year was the start of using the dunn heads (in cars) but apparently this is not true verified by my own car being close to the model years end. But at lease I'm sure of the crate is and that was the reason for thinking both engines were the same. And you are quite fortunate having two rare cars. These things are great fun inside and out.

SPEEDEMON

Demps

Do consider yourself lucky. I have checked out some cars around the #270's and they still had Birmal heads. When I was in the market for a ZR-1 I made sure it had DUNN heads because that was pretty important to me. I also heard too that they do produce a bit more horsepower since they did some updating on the tooling.

Phil DeJohn

I got them on 95 # 229.

89'Bowtie

Interesting......Just make me want a "Z" even more. For something that ended only in 1995, Zr1's sure have alot of heritage, stories, and mystery.


89'

89'Bowtie

I am going to put a copy of this in my notepad for future ref.

89'