question on 3400 cylinder heads

[Mach 5]

I have a question on setup before I buy parts. I have a 1990 Racer X TGP 3.1 lg5 turbo. roller cam conversion and crane roller lifters w/ link bars, TCE drtc, Manton pushrods, JE forged pistons, H beam rods, custom crankshaft. Turbo is going to be a gtx3582r. Im looking for a set of race heads and intake but unsure what year to buy from wottech.. meaning early gen 3 3400 or the 2000 style? I would like to keep my 1.6 comp roller tipped rockers if possible but do the heads flow the same if race ported? and also depending on what year do I buy for the intake? I didn't know what the differences were. cant seem to find the right answer im looking for.


Thanks for all your help!
-Jarek

[ericjon262]

you might email ben on this one direct. are your rockers roller fulcrum too? the GEN 3 heads use a roller fulcrum and are pretty good out of the box.

[Mach 5]

Thankyou. I did get in touch with ben. You can use non roller rockers on heads with 10mm.

[geoffinbc]

Make sure you get ones with M10 threaded holes for the rocker studs and not the newer ones with the M8 holes. This way stock adjustable (gen I) studs or aftermarket M10 to 3/8" conversion studs will screw right in.

[ericjon262]

they make 8mm conversion studs too.

[geoffinbc]

That's true but right now it looks like he has the COMP Magnum rockers which use the stock M10 studs. So if he would like to keep them as is he needs the heads with the M10 stud threads.

Plus if you did change to high ratio rockers and higher spring pressures the M10 threads will simply hold up to more abuse than the M8 threads of the newer heads.

[Mach 5]

thanx for the input everyone! My question has been answered. Very confusing I can figure out why GM would go with a smaller bolt size in later years. I just said screw it and ordered a set of pre 2003 3400 rockers from GM. I think the Comps I will use for my other car.

[3400-95-Modified]

Very confusing I can figure out why GM would go with a smaller bolt size in later years.

I know it reads like a different language but the thread diameter is less relevant to strength vs the height of the thread.

Influence of tap-drill size on thread strength
In tapped holes, the thread height is dictated by the diameter of the tapping drill. To reduce the risk of failure, the Design Engineer is often cautious and specifies high percentages of thread height in tapped holes. From a production standpoint these higher percentages of thread height result in higher tapping torques, increased tap breakages and, as such, are not favored. For short lengths of thread engagement, the minor diameter size - resulting from the tapping drill - has a significant effect on assembly strength. Studies have shown that for threaded assemblies of usual proportions, tap-drill size is relatively unimportant so long as the percentage of thread height is greater than 60%. Tapping costs are likely to be lower if the lowest possible thread height is used.

The effect of a low proportion of thread height is to reduce the shear area of the external thread, this is illustrated in figure 1. For very low thread heights, the shear plane through the threads need not be parallel to the thread axis, this is illustrated in figure 2. Such failure modes are difficult to predict and can be easily eliminated by maintaining a reasonable percentage thread height.

[Mach 5]

now that makes sense. so pretty much strength vs cost.

[3400-95-Modified]

I'm guessing the did testing and determined they could use a smaller diameter bolt in that position which would allow them to beef up the pedestal of the roller rocker (more important if you ask me) and in doing so they didn't loose any strength the bolt was providing regarding holding the rocker to the head.

If your really concerned the only issue is the fact that they don't helicoil the threads... Straight aluminum threads can be worn down easily by constant use so when helicoiled they will last much longer. I did that to all my exhaust head threads... Debating doing it to the rocker threads next time I have it all apart.

[Mach 5]

That's a good idea! I usually just do the intake bolt threads Ive had issues with those center 4 holes stripping

I'm guessing the did testing and determined they could use a smaller diameter bolt in that position which would allow them to beef up the pedestal of the roller rocker (more important if you ask me) and in doing so they didn't loose any strength the bolt was providing regarding holding the rocker to the head.

If your really concerned the only issue is the fact that they don't helicoil the threads... Straight aluminum threads can be worn down easily by constant use so when helicoiled they will last much longer. I did that to all my exhaust head threads... Debating doing it to the rocker threads next time I have it all apart.

[Driver_10]

Meh... I feel pretty confident in the 3500 stock rockers and m8 threads. I stopped worrying about that a while ago.

[caffeine]

That guy that ran 10s in his Cavalier had a rocker pull out of the head. Then again others have had rockers pull out with stock engines. I think like others have said it comes down to how much use the threads have seen.

[Driver_10]

That guy that ran 10s in his Cavalier had a rocker pull out of the head. Then again others have had rockers pull out with stock engines. I think like others have said it comes down to how much use the threads have seen.

Im thinking of sending in a set of 3400 heads to John and Ben later to have them fully race ported as alternates. (from what I hear, the 3400 heads can be ported for more flow than the 3500 castings can)

Right now I'm more concerned with getting this car on the road than I am with doing anything else to the engine. I have a 480/463 lift cam and comp 26986 springs with stock rockers. If the rockers pulls out, so be it.

[3400-95-Modified]

I think like others have said it comes down to how much use the threads have seen.

That's the biggest issue I had with my header threads and why I helicoiled them.