[Z Code 400]

I was ordering a UD hydraulic roller for a friend's 421 this morning when Tim Goolsby and I started talking about my Pontiac 350 Project. I told him about the recently completed '092' heads and how I was using a lot of stuff that I just had lying around, NIB, to complete the project. I also explained to Tim that I am very conscious of the DCR of any street engine that I build and I always work to keep DCR around 8.00:1 whenever possible. This got our conversation off on a discussion about fast ramp cams, cylinder pressure bleed-off, lobe separation angles and octane requirement.

During this discussion, Tim asked why I didn't step up the cam in the 350 from the .466".467"/270°/276° @ .006" - 220°/226° @ ,050" - 111.5° LSA (which Tim feels is good for 340/350 HP) to my UD .495"/.500" - 288°/292° @ .0045" - 231°/235° @ .050" - 110° LSA, which he feels is good for 370-375 HP.

The IC event of the 220°/226° - 111.5° LSA camshaft is 39.5° ABDC (installed on a 109.5° ICL or 2° advanced) and the IC event of the 231°/235° - 110° LSA camshaft is also 39.5° installed on a 104° ICL or 6° advanced. Either one is in the 8.00:1 DCR neighborhood and can be built with parts I currently have in stock.

The 1966 '092' heads have been trued to 72cc's, have new .500" OD guides, stainless SI valves (stock sizes) mild bowl work, screw-in studs, stock Pontiac retainers, lowered spring pockets, Crower 68405 springs @ 1.700" installed height, no splash shields and positive seals along with stock 'O' rings.

With a 4-speed (2.52 first gear) and a 3.23:1 rear axle, I have quite a bit of flexibility. The exhaust on the car is excellent, with 1-7/8" headers and full length, 2.50" mandrel-bent exhaust. I have both a Performer Intake and access to a Tomahawk single plane, both of which will fit under my fully-functional 1975 Ram Air Hood.

Of course, my biggest concern is the ability to run as much initial advance as possible and be able to run on fuel with varying qualities that I frequently encounter when I travel. My current HEI is setup with an MSD low resistance bushing and is curved for 20° initial, 16° mechanical and 8° of vacuum advance. While the Formula will see a drag strip run here and there, it will be Auto crossed more than anything else. I also have a trip to Laguna Seca planned for early next year as this car's theme is geared more towards road racing than anything else. I will probably drive the car to work one of two days a month to keep it maintained, but I won't drive it daily like I did last year when I racked up 24,000 miles driving it back and forth to work.

I have a 412 on the stand that will likely be equipped with aluminum heads and a roller cam, so the 350 is what I have chosen to build. I do not want to get into a 'bigger is better' discussion, because I have never cared for engines with anything more than a 3.75" stroke. I would invite some honest opinions on 350's approaching this power level from guys like GoQuick and others who have actually built them. I will probably drive this 350 for a couple of years while I save up to complete the 413.

I am using 1.52:1 rocker arms and was planning on using my 65,000 mile original stamped steel rockers. However, I found a set of Comp Cams Roller Tips (1.52:1) that were given to me that I could use, but I have heard both good and bad from forum members on this topic.

Tim also feels that a single plane intake, with the UD 231°/235° - 110° LSA on a 104° LSA, would be a better choice from a power output standpoint than the Performer.

Basically, since I already have all of this stuff, I want to make the best choices possible and would like to solicit advice from the forum as which way to go.

I appreciate your time and hope others find this thread useful...Robert

[tom s]

FYI,my 366 engine is 10-1.Cam is 236-242@50.110 in at 106.Street roller CC lobe number 3316 and 3317.Lift is 572 and 594 with 1.65s.The car is a 69 bird.3.90s in the back with a 2.20 first gear muncie OD trans.4th gear is equal to a 3.36.Car runs fine on our 91 gas with 38 total lead.I can start the car off in second and shift to 4th from 3000 RPMs with no lug at all.Tom

[Z Code 400]

Tom,

What bore/stroke did you end up with????

[70GS455]

I think it's not the best practice to use .050" valve timing events in computing DCR, especially with an un-symmetrical cam.

[Z Code 400]

Originally Posted by 70GS455

I think it's not the best practice to use .050" valve timing events in computing DCR, especially with an un-symmetrical cam.

Typically,

Most computations of DCR use events @ .050" + 15° or the .006" (SAE) figures...Robert

[70GS455]

If you have trouble starting it with lots of initial advance, a little trick is to use the 5-pin module from a 1980 Olds 260 HEI w/ "EMR" (electronic module retard) which, when triggered will pull 10 deg of retard. Just ground the 5th pin while cranking, then release it when running.

[70GS455]

Originally Posted by Z Code 400

Typically,

Most computations of DCR use events @ .050" + 15° or the .006" (SAE) figures...Robert

In your above examples, the first cam is 270 @ 0.006" and 220 @ 0.050" . So that is (270-220)/2 = 25 (if it is a symmetrical profile) from .050" to .006". So you will need to add 25, not 15, and now you are 10 deg off.

In the second example, it's 231 @ 0.050" and 288 @ 0.0045" (ok, so it's not exactly .006 but it's closer than pulling a number out of the air). Thats (288-231)/2=28.5, assuming it is symmetrical, which we know it's not. So now we are 28.5 instead of 15 and the error is 13.5 degrees, which in actuality is another 3 or 4 deg since UDH's profiles are un-symmetric for a grand total of 17.5 deg off.

If you can get the actual seat values from the cam card you'd be better off in both cases.

[tom s]

4.150 by 3.375.Short deck 6.1 rod.I think a std deck would have more TQ for a street motor.If me,I would offset grind a 3.75 crank to a 2in rod to shorten the stroke and have the bore be what you want.Tom

[Z Code 400]

Originally Posted by 70GS455

In your above examples, the first cam is 270 @ 0.006" and 220 @ 0.050" . So that is (270-220)/2 = 25 (if it is a symmetrical profile) from .050" to .006". So you will need to add 25, not 15, and now you are 10 deg off.

In the second example, it's 231 @ 0.050" and 288 @ 0.0045" (ok, so it's not exactly .006 but it's closer than pulling a number out of the air). Thats (288-231)/2=28.5, assuming it is symmetrical, which we know it's not. So now we are 28.5 instead of 15 and the error is 13.5 degrees, which in actuality is another 3 or 4 deg since UDH's profiles are un-symmetric for a grand total of 17.5 deg off.

If you can get the actual seat values from the cam card you'd be better off in both cases.

70GS,

Thank you for this information. Here is a scan of the 288/292 card. Tim Goolsby says the numbers shown @ .006 are actually @ .0045" lifter rise.

The events @ .006" for the 220°/226° - 111.5° LSA camshaft (109.5° ICL) are as follows:

IVO: 25.5°
IVC: 64.5°
EVO: 71.5°
EVC: 24.5°

The events for the 231°/235° - 110° LSA camshaft (106° ICL) are as follows:

IVO: 35.5°
IVC: 67.5°
EVO: 77.5°
EVC: 29.5°

Hope this is helpful and thank you for your insight...Robert

[Z Code 400]

Originally Posted by 70GS455

If you have trouble starting it with lots of initial advance, a little trick is to use the 5-pin module from a 1980 Olds 260 HEI w/ "EMR" (electronic module retard) which, when triggered will pull 10 deg of retard. Just ground the 5th pin while cranking, then release it when running.

70GS,

When we were racing, we used to run a dual point on one set of points and switch on the second set in 4th gear which gave us about 6-8° of retard. Years later, Hays offered a Stinger ignition that would drop-out 2° every 1,000 rpm above a certain rpm threshold. This is great information. I would say ground it with a switch in 4th gear for those long pulls...Robert

[Z Code 400]

Any comments on the rocker arm question from post number one????....Robert

[Z Code 400]

Now, knowing that engine simulations are just 'guesstimations,' especially the less elaborate ones, I decided to put this combo in for fun anyways.

When I run this engine combination through my Dyno 2000 simulator, with 9.49:1 SCR, 210 cfm @ .600" intake and 160 cfm @ .600" exhaust, dual plane intake, big tube headers and mufflers, the 'big cam' version (231/235-110) comes up with 362 HP @ 5500 and 377 lbs/ft TQ @ 4500 rpm. The 'small cam' version (220/226-111.5) comes up with 357 HP @ 5500 and 387 lbs.ft TQ @ 4000 rpm.

Interestingly, both 'guesstimations' are very close to what Tim Goolsby predicted. However, I would have thought a greater spread between HP and TQ.

Thoughts????....Robert

[Z Code 400]

Anyone have an opinion on the best, most accurate DCR calculator???? I would like to iron out a few details and decide which way to go before assembly this weekend. Thanks to all who have posted....Robert

[quicksilver97ta]

I like the Pat Kelley calculator. I used this on my last iron headed Pontiac build with 8.3:1 DCR and a true 10.5:1 SCR. Always on pump premium, never experimented with midgrade or lower, maybe this winter. Also, it had no overheating problems this summer.
I also used that calculator with my 383 LT1 build. Of course it's reverse cooled aluminum headed but I run 9.2:1 DCR and 12.5:1 SCR with premium pump gas.

[Z Code 400]

Is it available online???? I would like to run this combination and see where I am at, inlight of the new valve timing events. I am shooting for 8.00;1 DCR...Robert

[quicksilver97ta]

Here.
http://www.empirenet.com/pkelley2/DynamicCR.html
At the bottom of the page, you download it and install it. This is great so you don't have to be online to use it. It's very handy when playing with timing events.

[Z Code 400]

Thank you!!!!

Unfortunately, my laptop doesn't like this file and won't open it....:-(

[Murf'sDad]

Originally Posted by Z Code 400

Unfortunately, my laptop doesn't like this file and won't open it....:-(

You'll need to download WinZip, if you don't already have it. I downloaded the calculator this morning and all is well.

My scr calculates to 9.8:1 and my dcr comes out as 7.6:1, with this calculator. The other calculators came out a point to a point and a half higher.

FWIW, Stewart

[Z Code 400]

Murf's Dad,

You care to run this combo in your DCR calculator????

[Murf'sDad]

Originally Posted by Z Code 400

Murf's Dad,

You care to run this combo in your DCR calculator????

Works out to 9.03:1 scr and 7.21:1 dcr.

I used your deck as .020" in the hole, a .039 gasket with a 4.2" gasket bore, and 5.5cc of dish/valve notches.

HTH, Stewart