rickyrj1

I modded my 3k mile 95 haven't looked back since. Totally different car now. I could put it back to stock if I wanted but I NEVER will.
GO FOR IT!

If you need powder coating give me a shout, I can hook you up so you don't run into the same problem you had last time

xlr8nflorida

Everybody gets so caught up on NCRS deductions.

You can still top flight even with a powder coated motor.

I guess with NCRS, its all about your "Total Score" and the higher the better.

Even if you are a NCRS guy, I'd rather have a clean nice looking powder coated engine then a dingy LT-5.

If your motor is clean and nice leave it the way it came from the factory.

USAFPILOT

The ONLY reason those DUNN heads are valuable is because they can supposedly flow more when they are modded than the birmal heads. There is NO reason to keep a car with DUNN heads stock. MOD AWAY!

bb62

Actually, you have this backwards. Dunn heads flow better than Birmal heads WHEN stock. Once you decide to modify the heads, it doesn't matter which set you have.

The Birmal heads for the 405 heads were modified versions of the 375 heads and were machined to accommodate the modification. The Dunn 405 heads had the same modification, but it was done through a new casting design that yielded a smoother better flowing head. Still, the designs are identical - which is why the part numbers from GM are the same - and why when modified, there is no real difference between the two.

xlr8nflorida

It's as simple as GM finding a different manufacturer because GM ran out of the Birmal Heads.

If you have 95 then many have dual dunns. 94s often have 1 birmal, 1 dunn. Pretty much evidence that there is little or no difference between the heads or they would not have put the LT-5 together like that.

GTB/ZR-1

Stock is for sissies! j/k

Keep the stock parts to return it to stock config. Nobody is going to take it apart to ck for port/polish. Powdercoat? Your call...

Mod away & ENJOY!!!

Redline7g

Powdercoating is like putting on a set of chrome dress up parts. If the next guy that buys it wants to put the ugly factory stuff back on then he can do it. If I had the money to do it I would do it to mine. These things look awsome but the ugly gray powdercoating just takes away from the looks. The ones I've seen on here with the silver engine and black and red lettering are beautiful IMO. Who wouldn't want that?

illenema

Thats 3K ($) Le total des voitures différentes.

Id say just save up and do a 415.

USAFPILOT

This is info copied from ZR1.net regarding the differences between Birmal and Dunn heads.

Cylinder Head Differences:

The production cylinder heads for the LT5 engine were originally produced by Birmal, all engines right up to the last few of the 1995 MY were fitted with Birmal heads. The machined port matched and hand blended heads were all Birmal parts.



Originally when I returned from being Resident Engineer at Stillwater the changes for increased output for the 93 MY were intended to be increased lift and duration on the secondary cam profile from what was known as the 'B' profile to the 'RB' profile which had a further 10 degrees duration. This resulted in engines which achieved the power target but paid the price in terms of reduced low end torque, something for which the LT5 had always been criticized. Since this was now my responsibility we made a change in the design direction ie. we would stick with the same cam profiles, optimize the cam timing and devise a simple machining and hand blending operation for increased port flow. So the 1993 MY engines started to have a revised throat cutter diameter an increase in the primary and secondary ports and a simple blend at the junction of the two machine cuts. I would not really call the operation CNC porting because to me that implies some change in the fundamental port design which this operation certainly did not. Now the time frame for all of this was early 1991, Birmal advised us that they did not want to produce heads for the future model years, infact they wanted to get out of the semi-permanent mould business. So we looked for alternative sources. A.L. Dunn were selected and the tooling was transferred from Birmal. At this time because of the original production schedule and the cut back in the volume of cars produced there were sufficient Birmal heads for a large portion of the remaining engine builds. We decided that since the port core box needed refurbishment, we would take this opportunity to re-design the port so as to eliminate the need for machining and hand blending at Mercruiser. The final cast port actually flows better and more consistently than the machined part. This change was incorporated with the production fix to the right hand side chain tensioner reservoir for engines late in the 95 MY build. All A.L Dunn heads had these features incorporated. There were about 200 head sets cats by Dunns and I believe about 130 engines were fitted with them.



Above info provided by Graham Behan

horizontal rule


Cylinder Head Differences: Part 2


The following information provided by Mark Broin.



The latest two head designs had recast pockets for providing better oil retention for the cam timing chains. This reduced even further the possibility of chain rattling during startup, providing better dry start lubrication, especially after long periods of the engine not running. These heads were are referenced as the "A.L. Dunn Cylinder Head, First Design and Second Design" ( The latest Second Design Lotus Part Number was 550.4005.878A-RH and 550.4005.877A-LH) These second design heads were a design year change occurring sometime just before the final '95 designated engines were completed. The model year change specification documents were "ECH=3D 550.2680; MY=3D95A; ECA=3D1.0285". These heads did not include the CNC machining of the port runners when installed on the motors. The improved port matching technique was the same as the first design heads. GM's part numbers are 10228866-RH and 10228865-LH (Service part numbers are 10168655-RH and 10168654-LH. These are the numbers used internally for the construction of the motor).



The first design Dunn head included the CNC machining and better port matching technique to the manifold for '93-'95 applications, and also the revised oil retention pocket.



Again, the second design heads did not have CNC machined runners, and the casting walls were thicker. GM argued there was very little difference in flow rates between the cast runner and CNC machined runner sets of heads. Most of the horsepower increase in stock applications, anyway, was supposed to be from better port matching. When replacing heads, GM may inadvertently send one of each rather than a matched pair,ie., both machined or both cast runner. These heads are not uniquely distinguished by GM part number, so be careful when you buy to at least check for comparable runner treatment. The second design Dunn head is not uniquely part numbered from the first. Note: the thicker casting walls on the second design heads might be advantageous for machining out to even greater flow rates than achievable with any of the other head designs?



The high flow head work done early on by the fellows at Mercury consisted of refinements on the cast runners and port matching done by hand. From this work, patterns were developed for the horsepower bump work marketed through the rebuilders. This early modification work was all sub contracted to the two fellows at Mercury, Scott Skinner and another fellow named Greg VanDeventer, returned and then installed on customer motors.

DDSLT5

Port the **** out of it! You can easily get 400 rwhp with a top end port, headers, tune, exhaust. GIVE 'ER!

ZR-1DUDE

Corey Henderson repainted mine with a clear coat - looks awesome.

D.

hiznhrz

Consider taking the car to Marc for his 500Hp package less the single mass flywheel. Completely transforms the car yet it still looks bone stock. The Corsa exhaust might not be for everyone but I'm crazy about the sound of mine with NO unwanted harmonics.

96LT4

I can't afford Mark...I'm not putting another $20K into this car.

GS 163

I say, if it can be modded, then mod on.

FU

Experience say's that's the way to go.

DRM500RUBYZR-1

1-Do every single conceivable internal improvement / modification that you can afford!
2-Do every single reversable external improvement / modification that you can afford.
3-Give a lot of thought to the very few truly irreversable modifications.

Like it or not, the "future" of these cars will someday be in the hands of the NCRS / Bloomington crowd.

They will be the ones who will spend countless hours / years of their life bringing these back to their glory after we have put hundreds of thousands of miles on them, wrecked them, abused them, blew them up, watched mother nature destroy them etc, etc.

So have some heart!

Keep all that you take off, and when you or your heirs sell it, sell it with all of the takeoffs.

Make their future job easier.

This way, some kid who has not been born yet, may get to see what one of these looked like the day it was born.

While we all enjoy modding them, the majority of the truly great ones from yesteryear are the Blue Ribbon cars.

I would never undo many of the improvements made to my car.
But, it is fun toggling from modified to NCRS and back, and I know, and have known many others who enjoy the same.

Mod it;
Drive the hell out of it;
Then some day,
Restore it!
But most of all enjoy it!
It is your car, nobody else's.
( today)

Let us know what you do!
ps
There isn't much that can be seen that can't be reversed!
So have fun!

Marty
1FUNZR1

techvette

IMO, headers and exhaust are easy enough to swap out. If you really want ported heads, get a set of Birmals to port and leave the Dunns alone since they are so rare.

ZR-1DUDE

Exhaust is easy.

Headers not so easy.

Heads - I would not do it.

Plenum and injector housings - all good.

D.

96LT4

I think this may be the route I go...I was never going to port the heads.

Port and polish the plenum, airhorn, and FI Housings, and maybe go back to the 4.10 gear. I'll be under the hood Firday night and decisions will be made based upon how clean I can start getting this beast!