[Stan Weiss]

[QUOTE=68WarDog;6458622]

Originally Posted by Stan Weiss

OK, UltraDyne does have some splid roller lobes which could have IVC 104 ABDC depending on ICL.

IMO I would not be running any of them in these


Stan, the 10.4:1 engine uses the R81/R88 lobes. At the time when building this engine, I was looking for a solid roller comparable to the comp 290 b6 solid flat tappet, almost 20 years ago. There may be better lobes since then, but this cam has a brutal mid range and respectable 1/8 mile time with a 3400 10",Continental converter and 3.70 gear.
What is it about these lobes you don't like?

The 12.1:1 engine has the R79/R80 lobes, this engine wasn't built by me,and I will be replacing the 72cc Eheads with the 87cc version for pump gas safety.

What ICL is the R81 in at?

Have you ever done a cranking compression test on the engine with the R81.

Stan

[68WarDog]

[QUOTE=Stan Weiss;6458631]

Originally Posted by 68WarDog

What ICL is the R81 in at?

Have you ever done a cranking compression test on the engine with the R81.

Stan

R/81 ICL 104
Yes, iirc it range from 190-205. It was many years ago and posted here.

[Stan Weiss]

[QUOTE=68WarDog;6458639]

Originally Posted by Stan Weiss

R/81 ICL 104
Yes, iirc it range from 190-205. It was many years ago and posted here.

R/79 ICL 102
No cranking for on this engine yet.

In your first post you showed the ICL as IVC for calculating DCR.

Using 190 psi I get 7.7:1 DCR

Using 205 psi I get 8.1:1 DCR

Stan

[68WarDog]

[QUOTE=Stan Weiss;6458645]

Originally Posted by 68WarDog

In your first post you showed the ICL as IVC for calculating DCR.

Using 190 psi I get 7.7:1 DCR

Using 205 psi I get 8.1:1 DCR

Stan

I may not be using the calculator correctly. Thanks for the information 👍.

[68WarDog]

UD Solid roller

[Singleton]

Cam card is showing Intake Valve Close @ 69 ABDC. The 104 is Intake lobe centerline, the 116 is Exhaust centerline. Sort of a confusing card imo.

[johnta1]

The cam is being installed 6º advanced I think?

[Singleton]

Originally Posted by johnta1

The cam is being installed 6º advanced I think?

Confusing part is the listing of the intake and exhaust centerlines in the same row with the valve events. I think that’s where the OP mistook the intake close for 104 abdc.

Install at 104 ICL according to card, but where did the builder actually degree the cam to? (Question for the OP)

[68WarDog]

Originally Posted by Singleton

Confusing part is the listing of the intake and exhaust centerlines in the same row with the valve events. I think that’s where the OP mistook the intake close for 104 abdc.

Install at 104 ICL according to card, but where did the builder actually degree the cam to? (Question for the OP)

The cam actually came in closer to 105 by Joey Arrington Speed Sport. And this 455 runs 170-180 in the NC summers.
Back in the 90s I use to run comp "magnum " sr lobes, they were both noisy and hard on valve train, one of the reason I switched to UD.
UD appears to be less harsh and quieter, even with .020 lash.

[Jay S]

That cam card is from back in the days that some cam company’s ground cams with 2* extra advance from where the were designed to run at. The installed ICL is 104*, but the seat timing as shown on the cam card is 106*. I have been slow to change on that, I still use the old way. I calculate DCR on my engines, I plug in -2* from were they are installed at. Plus the closing side is usually 4* to 6* longer than what the cam card says. Your actual intake closing is likely in the lower 70s ABDC.

The lash can swing the intake closing another 6* either way too, sometimes more than that. I will tighten the intake lash to nearly zero to spread compression out on some pump gas engines, usually can make big changes on the closing.

I usually check the intake closing after the lash is taken out for when the valve is .009” open. Lash divide by the ratio plus .006” is what I check. Aftermarket .006” tappet ratings are a close equivalent of .020” tappet rating on mechanical cams as long as the lash is set close to .020” with 1.5 rocker arms.

[68WarDog]

Thought I needed to come back and correct some information about my engines. Engine # 1 did have 195-205 cranking compression when initially built about 15 years ago using Ace Brewer 16cc pistons , 6.8 rods with a 4.19 bore and 72cc Ehead . About 6 years ago I did a engine refresh using 20cc dish pistons, lowering static compression from 10.8:1 to 10.3:1, but I have not repeated the cranking compression test. Before the refresh dynamic compression was 8.33 , one of the reasons I believe Joey decided to use a bigger 20cc dish, dynamic compression now is 8.03, with a IVC 69 ABDC, thanks Stan for helping me figure this chit out. ��

[68WarDog]

Engine #2
With a 4.21 ob/.005 deck, 4.21 stroke, 87cc Ehead. Static compression 10.3 and IVC 62* ABDC. I'm looking at 8.42 dynamic compression. Shouldn't this be ok for pump gas? I think I understand Jay from the old school about tightening up the lash , opening the IV early , but with the 8.4 DC, I might not have any room for errors?

[Jay S]

Tim at Bullet told me once the .3883 and .4176” profiles when ground on 108 LSA will act like the engine has more compression than it actually has. On 108 LSA with those cam profiles people have thought their engine acted like it has 11 or 12:1 compression, but may only have 9 or 10. You will have to be on top of your tune running it on pump gas, but on the plus side, you won’t loose much power lowering the compression for pump gas.

At 10.3 it should work on pump gas, better yet with big flows from the heads, induction and exhaust. The DCR won’t be as high as your thinking it will be, the cam closes the valve about 4* later than what the cam card says, and can gain more yet with the intake lash on the tight side. With the lash tighten up it may only pump 180 lbs, with the DCR in the mid to upper 7s.

Stan posted a DR file of an older Ultradyne profile that has a very similar lash ramp design. Same .01733 lash ramp design as a .3883” profile. You can compare and see how the intake closing changes with different lash. Tightening the lash a ton won’t change the octane tolerance as much as the drops in DCR and pumping pressure would indicate, but on the razors edge with pump gas it is a noticeable change. It is something to experiment with after it is together and your tuning it.