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Pre-Cup swap

6.5L

6.5L

Old Iron Runner
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Location
Northwest Wyoming
I have a Teds motor 6.5L NA(Square stamp pre-cups I believe). I have my old motor sitting at my shop (1993 599 block). I read in the other pre-cup post that the 1992-1993 T-stamp pre-cups were the next best at making power over the Diamonds. I also have a chance to pick up some Diamonds. Which would people do?
 
depends on what your goals are? for max power I would get Dennis's buddy Hank to make you some oversize ones. If you want good power without worrying about any compromises I would use the diamond ones.
 
6.5L said:
Would going from Square stamps to diamonds even make a noticable difference?
Click to expand...

They can. Smoke, MPG, and power all change with precup design. The turbo changes the game even more. Minimum precups to use are 6.5 NA precups. Larger appears to be better for power as other things on the turbo design eat MPG's of the smaller ones.

Check the precups for cracks before going too far. And if you have some surplus turbo precups you want to sell let me know.
 
I don't have money for dyno fun until next summer. Sorry AK. And WarWagon, you know the setup I am running. ATT.18-22psi at WOT. 1/4 turn on the pump and am planning headstuds and more fuel along with some lift pump upgrades. What would you recommend?
 
I lost low end power with the T's but gained top end. I ran the same motor with na 6.2 cups ,could spin the tires without boost.
 
I am looking to improve low end torque especially and just overall performance. Wouldn't less surface area in the pre-cup mean more heat transfer to the piston/more power? I am hearing arguments to swap and not swap. I have read through the other thread and most seem to lean towards swapping to diamonds. And 6.2turbo, you also have a lot more modified motor than I do.
 
I just swapped in a set of diamonds,I'll let you know how I like them. My motor and pump are stock at the moment. If you want low end I would leave the small cups in,and back off on the timing. Just don't rev it past 4k.
 
You can only move so much air through a small hole esp on fire. Then the lost art of mixing and burning in the cylinder from the precup design has a lot to do with your results.

The ATT I have runs better on the 6.5 NA precups than it does on military 6.2 NA precups. I would change them out and hit the dyno afterwards. You should also have a long discussion with Dennis about precups. There may be a point where you go too big, but, I can tell you what happens when you go too small with bigger turbo's and more fuel - lots of smoke.

The cam issue in these engines is something else I have been reading about for a RPM range. Something to look into.
 
6.2 turbo said:
I just swapped in a set of diamonds,I'll let you know how I like them. My motor and pump are stock at the moment. If you want low end I would leave the small cups in,and back off on the timing. Just don't rev it past 4k.
Click to expand...

My 1993 has lots more power with advanced timing. I can feel the cold advance kick off in the morning and hear it with the advance I am running. Clatters enough to slightly concern even me however.
 
Yeah, my advance is enough that when the cold advance kicks on, it has a slight haze out the exhaust pipe for about 2 minutes then it clears up. It almost sounds like it isn't running when the cold advance kicks off. I have even had a friend shut my truck off last winter after I started it and walked away to let it warm up because he thought I wasn't running any oil in it :) hahaha.

And I am not moving timing. I am at altitude and advancing it helps. But I do feel I may be running a bit tiny on the pre-cup. If I barely get into it enough to just climb rpm up to 3500 slowly, there is a minor haze at the exhaust. Could be not getting the air through my pre-cup hole fast enough. And my pump de-fuels at 4000rpm. It's fine
 
I also have a set that Hank modded for me, I don't think you should change the angle of the cup, the mouth is widened and the mouth angle is left the same. The angle is left alone to allow the flame front to run across the top of the piston, I wouldn't change that.
 
In the end I plan on running around 25psi through the ATT and 1/2 turn on my pump total. Diamonds or Wide-Mouths?
 
Are you sure there's another 1/4 turn to be had ? Would love to see some dyno results with ported cups.:thumbsup:
 
Yeah. When I had the pump rebuilt, they turned it up a 1/4 turn for me. I got 1/4 turn left. I may go up to diamond size.
 
Bringing this back to the top.

Where can I buy the diamond precups? Can new ones be bought or am I stuck buying used one?
 
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