Geoffrey

Rods will be Arrow rods from England.

Kevin

This is the classic case in life where everything that would/could delay getting a custom designed set of rod could possibly happen, happened!!! There are alot of rod manufacturers around the world and I did make inquiries to eight of them. Prior to talking with the companies, I wanted to establish drawing and engineering specs that I could view and correct. Many companies will not allow this.. When you request and say "ask" and "custom" and "design" the cost goes through the roof.. My top three finalists were Pankl, Arrow, and Carrillo. I actually asked my friends at Sportec to help me with pricing, because my inquiries led to crazy pricing, reserved for F1 teams.. Even with some help, spending the monies similar to buying a used 993TT motor quickly moved me to Arrow and Carrillo.. Carrillo makes a good rod, I highly recommend there product!! There customer service was near the bottom of the list, but I have always supported there product. For the money you cannot beat there product. And believe it waiting 6-8 weeks 'IS" better than any other company that I talked to. One negative is that they will not release any engineering or drawings for the designed rod. It is one thing to submit basic dimensions, it's another thing to get engineering calcs for what you are building.

This leads me to Arrow. I have seen a PCA engine with Arrow rods and the finish and overall qualtiy wanted me to see if they would work with me. Rod vs Rod they will manufacture a lighter rod, lighter than Carrillo and various other rods that I has had on my scales. This application didn't have the budget for Titanium rods, nor did I want to tear the engine down every year to check and measure the Ii rods. Arrow's sales team, quickly got the engineering team involved and we traded drawings and specs. Arrow "DID" provide me all specs and engineering.. The "steel" rod is designed to spin at 8500 RPM all day with HEAVY Mahle 3.8ltr 102mm pistons... This rod will allow one to use the 996GT3R crank to be installed in any 993TT engine with stock pistons, 102mm Mahle's and 996TT engine.

I will edit this post and enter the weights of all the rods in the picture.



From left to right.
Stock 993NA, 993TT, 996TT 996GT2 Rod 566 grams (smallest rod of the lot)
Custom Arrow Rod 540 grams
Pankl 996GT3R Titanium Rod 423 grams
930/964 Carrillo Rod 585 grams
Stock 930 Rod measured with ARP rod bolts 658 grams

The 993TT996TT rod will not fit the GT3R crank the width of the rod journals are wider, similar to the 930/964 rod.. There are width difference between the 930 & 964 rod, another topic..

However the radius of the rod journal is smaller. What this leaves us is a larger rod in the big end of the rod required to handle the high RPM's The small end of the rod/wrist pin is actually physically larger than the stock 993TT rod. Please note that the diameter of the GT3R wrist pin is actually smaller at 22mm vs 23mm of the 993TT, 964 and 930.





One major design feature that I wanted to build into the rod was adding a taper. Heavy HP industrial diesel or natural gas engines will use a tapered rod to increase the stregth from high compression loadings put on the wrist pin and rod. A taper builds in strength and reduces the weight of the wrist pin end of the rod. This was the initial design I believe that Porsche wanted to use.. Because ALL of the 993NA, 993TT pistons including 102's have a taper that requires a narrow rod to fit the piston. Another words the top of the piston at the apex of the wrist pin is alot narrower than the bottom of the wrist pin. It is a design feature ready to be utilized. By adding a taper, we were able to add width to the rod and reduce the overall mass, because we would have had to increase the diameter of the top of the rod. In order to find out the maximum size for the taper, I had to digitally plot the stock TT and 102mm pistons.



The qualtiy and attention to detail that the folk at Arrow is at the top. Every surface is machine polished, no cross hatch honing. Precision finish honing similar to what you would do on a turbine wheel, or high RPM shaft.. The Brits did a awesome job holding the tolerances to 10ths.. I checked!! Another detail is the wrist pin oiling. In the top picture you can see the full radius groove that allow full oil flow around the wrist pin!! With the taper oil will also shed onto the high thrust side of the rod.

Marc in AK

I feel as if I am in Porsche Grad School when I read your posts Kevin.....always learning something!! Awesome!

BReyes

That is a fine execution of an ultimate motor. A good testement to your years of experience. Thank you. And thatnks to others posting techincal info. Reminds me when I was working my first rebuild. On my current 3.2 TT plans. And now taking forward planning to the next higher level, since it is a 3.8TT that keep coming up on on my mind.

I cant wait to catch up.

We'll keep an eye out for lo flyer.

Regards,

Bernard Reyes

foryorent

Kevin,

Where is your shop located? If you don't mind me asking?

Kevin

Good ol Pacific NW..

Kevin

I received my cylinder heads today. I am waiting for my new Billet camshafts, as soon as they arrive, I will be able to mock up the engine to dial in my valve pockets..

These heads have alot of labor into them and they still aren't done. I will surface the heads and then cut my EVO flame rings grooves. The heads have had everything replaced in them. New guides, seats, studs, and large valves, and pro-head porting. As in the earlier post I showed the rough in porting that I did. I decided to have them dialed in with the flow bench. It allowed me to see the difference with the stock valves and and more modern valve designs.






I did flow test these heads and will say that one can gain 12% CFM flow by just changing the design of the valve head. The industry calls it a "tullip" the less of a mass you have the less air restriction that you will have. We flowed back to back valves.. Stock valve vs small tullip and large valve vs small tullip and across the board we gained 12% which is significant. So one can retain the stock valve size and gain roughly 12% with the new smaller mass tullip. The big gains are with porting and stepping up to the larger valve diameters. To give you an idea of the size increase, I can take the stock valve and shove it through the new seat diameter. I tilted the valve to show the light coming thru.

The other picture shows the dramatic difference in the stock Tullip vs new design.




For this engine moving up in valve size, was not a penalty for weight. With the smaller mass tullip, even with the larger diameter, with the Titanium radial locks and retainer, I net a loss in valve weight.. The stock valves are heavy dogs..

TB993tt

Very interesting info on the "tulips" Kevin, thanks for that and the pics.

Is there enough room on that head surface to machine in the EVO ring/gasket groove - it looks really tight ?

Kevin

TB, the valves are custom made and the wait time is 8 weeks. If you look through this thread you will see the EVO rings. The actual groove that is cut into the head is smaller than the one in the cylinder liner. This is due to the step. Or "L" shape of the ring. There is plenty of room, infact more room than with the early 930 heads.

Miles965uk

Great stuff Kevin, keep it coming as you progress...

diabolos88

great thread, makes me want to go out and find myself a 993tt

ttAmerica RoadsterAWD

whoa, and I tought Jessica Rabbit was da bomb!

foryorent

any updates on this build? Any guesses on power output yet?

foryorent

How goes your ultimate quest?

Kevin

As with everything in life summer is extremely busy for me. I look at the engine on the stand everyday and wonder if/when I can spend a few moments on it. The rods are sticking out of the block.. I have my new camshafts. I'll try to post a few pics..