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Old 03-26-2020, 12:32 PM
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Those #76 heads are stated to have a 68 cc chamber, but have you confirmed that they are by CC checking them.

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  #22  
Old 03-26-2020, 12:34 PM
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+.050 locks will increase installed height.


.
Yes, but I will get more clearance between retainer and guide. I will shim the springs around 0.100" to get the 1.550" installed height.

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  #23  
Old 03-26-2020, 12:52 PM
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Those #76 heads are stated to have a 68 cc chamber, but have you confirmed that they are by CC checking them.
I think the are stated as 70cc and #77 heads 68cc?My heads are milled previously and measured 66cc. The machine shop shaved them another 0.006" to get them perfectly straight now. Guess I have to unshroud the valved guite a bit to get them back to 69-70cc.

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  #24  
Old 03-26-2020, 03:19 PM
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I would not run the smaller cam. Your SCR is pretty high.

I'm running the 703 in a '69 firebird with a 400 bored 0.030 over. 1968 #15 heads with 74cc chambers, no porting or other mods. This yields a little below 9.5 SCR. I get between 175 to 180 psi cranking compression. Its running a TH400 with 3.55 rear and 27 in tires. It behaves real nice on the street, excellent throttle response and pulls hard through 5000+ rpm. My only complaint with this cam is that idle is a little more aggressive than I expected--this may not be an issue for you since your SCR is higher. I need to keep it at 700 to 750 in drive to keep everything happy. Vacuum at idle in drive is about 8 to 9 inches--just adequate for power brakes. I know I'm running a lighter car, but hope this helps.

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Old 03-26-2020, 04:15 PM
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Plug the numbers in some time on a cam timing event calculator and compare a 702 and a 703. The Intake closing is 1 whole degree different, if the 702 is installed on 109 Icl they are identical. Even the exhuast opening is with in a couple of degrees on the two cams. Mainly the extra performance of the 703 comes from the overlap and a little more lift. Most of the time a 703 outperforms a 702 almost everywhere, but it has a rougher idle and less vaccuum. The only time a 703 would not run better is if for some reason the overlap was causing some sort of reversion or dilution issue, possibly from a really restrictive exhaust system...like log manifolds and a 2” exhaust.

A cam with a wider 114 lsa would better for this, such as a 2802 summit or a 278H or 288H Crane. The Lunati will work great if you can get the compression down. You have the right idea trying to find some extra cc’s unstrouding and opening the heads up to drop the scr down.


Last edited by Jay S; 03-26-2020 at 04:19 PM. Reason: Edit
  #26  
Old 03-26-2020, 05:14 PM
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Originally Posted by many birds View Post
I would not run the smaller cam. Your SCR is pretty high.

I'm running the 703 in a '69 firebird with a 400 bored 0.030 over. 1968 #15 heads with 74cc chambers, no porting or other mods. This yields a little below 9.5 SCR. I get between 175 to 180 psi cranking compression. Its running a TH400 with 3.55 rear and 27 in tires. It behaves real nice on the street, excellent throttle response and pulls hard through 5000+ rpm. My only complaint with this cam is that idle is a little more aggressive than I expected--this may not be an issue for you since your SCR is higher. I need to keep it at 700 to 750 in drive to keep everything happy. Vacuum at idle in drive is about 8 to 9 inches--just adequate for power brakes. I know I'm running a lighter car, but hope this helps.
Thanks for the info, it's good to hear how the cam acts on the street in a similar engine! With a .030 over 400 and 74cc heads wouldn't your engine be closer to 10:1 or do it have dished pistons? I prefer a choppy idle as long as there is enough vacuum for the power brakes, so that's no problem. Do you remember were the intake centerline was installed at? I have read that the Voodoo cam runs a little better with the intake advanced 6° or with the 703 cam at 104°. Do you have stock converter or a higher stall converter?

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  #27  
Old 03-26-2020, 05:14 PM
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Originally Posted by Jay S View Post
Plug the numbers in some time on a cam timing event calculator and compare a 702 and a 703. The Intake closing is 1 whole degree different, if the 702 is installed on 109 Icl they are identical. Even the exhuast opening is with in a couple of degrees on the two cams. Mainly the extra performance of the 703 comes from the overlap and a little more lift. Most of the time a 703 outperforms a 702 almost everywhere, but it has a rougher idle and less vaccuum. The only time a 703 would not run better is if for some reason the overlap was causing some sort of reversion or dilution issue, possibly from a really restrictive exhaust system...like log manifolds and a 2” exhaust.

A cam with a wider 114 lsa would better for this, such as a 2802 summit or a 278H or 288H Crane. The Lunati will work great if you can get the compression down. You have the right idea trying to find some extra cc’s unstrouding and opening the heads up to drop the scr down.
Jay,
I don't have cam DR files for these lobes so I generated some lift files using spline curves. What do you think about using the 702 with 1.6:1 rockers.

Stan
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  #28  
Old 03-26-2020, 05:42 PM
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Quote:
Originally Posted by Jay S View Post
Plug the numbers in some time on a cam timing event calculator and compare a 702 and a 703. The Intake closing is 1 whole degree different, if the 702 is installed on 109 Icl they are identical. Even the exhuast opening is with in a couple of degrees on the two cams. Mainly the extra performance of the 703 comes from the overlap and a little more lift. Most of the time a 703 outperforms a 702 almost everywhere, but it has a rougher idle and less vaccuum. The only time a 703 would not run better is if for some reason the overlap was causing some sort of reversion or dilution issue, possibly from a really restrictive exhaust system...like log manifolds and a 2” exhaust.

A cam with a wider 114 lsa would better for this, such as a 2802 summit or a 278H or 288H Crane. The Lunati will work great if you can get the compression down. You have the right idea trying to find some extra cc’s unstrouding and opening the heads up to drop the scr down.
I have log mainfolds, ported and outlets opened up to 2.2" with 2.5" downpipes and 2.5 " mufflers. From the mufflers and back the exhaust is 2". I know I should have chosen a wider LSA but didn't think of that when I ordered the cam. I calculated the DCR to 8.03, assuming 275° advertised duration, ICL @ 104° and 9.8:1 SCR if I open up the chambers a bit. To high or could it work?

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  #29  
Old 03-26-2020, 09:03 PM
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Jay,
I don't have cam DR files for these lobes so I generated some lift files using spline curves. What do you think about using the 702 with 1.6:1 rockers.

Stan
I really like the 702 with 1.6 rockers. That is more inline what I think of when trying to run log manifolds and make power in spite of the logs.

Usually when I figure dcr I add 2 degrees to the intake Icl since the engine is running. ICL on 104 runs on 106icl. I don’t know what altitude this combo is at, I usually add that in too for dcr and v/p index numbers. This is high enough compression that the V/P should be looked at as well, it climbs faster. I was thinking the 703 had a seat timing duration of 273*. If I recall, the .842 lifter adds 5*, and the .904 lifter adds 3* on the voodoos from what they are advertised at (268). I do not alway remember correctly though. Correct me if I am wrong.

JMHO, 8+ on the DCR is really high on a iron head for a cam and engine of this size. Especially if that is after an altitude adjustment. Could easily require 95-98 octane. Not sure what that would be using the Ron numbers. With a cam with intensity like a voodoo you don’t want to be much past 7.5 dcr. Maybe could go as high as 7.7 dcr if your a good tuner with the 703, which is around 10scr. A 1.6 rocker would help some too.



5cc of unshrouding from a 66cc head could get the compression down to 10scr at zero deck with a 11cc dish and a .043 gasket. That would be getting close to the 7.7 dcr for 93 octane.

  #30  
Old 03-26-2020, 11:28 PM
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I just looked at the cam card for the 703 cam and the adv. duration is 275/281, not 268/276?
I think some cam companies mislead us about the tappet lift that seat duration is measured at. I’d say the cam card is showing duration at .006 lift on the opening and closing. But they advertise the seat duration at something like .006 lift on the opening and .009 on the closing. This is done so the lobe appears more aggressive and the companies can then market them as such. Look at the comp xe cams. The hft cams have a difference of 44 deg between the .006 and .050 numbers. The 703 has a difference of 41 degs suggesting its more aggressive. Yet it’s common knowledge that the xe cams set the valve down to aggressively and the voodoo has a more gentle closing ramp. This would suggest the voodoo is less aggressive. Comp cams seems to be the only large cam manufacturer that is consistent with their hft seat durations. In short use the 275/281 numbers, it’s probably at .006 tappet lift.

  #31  
Old 03-27-2020, 09:12 AM
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I agree with PMD400’s comment. My bad, that is correct, use the 275. I probably shouldn’t have said add 5 degrees to the advertised. I should have said add 48 degrees to the .050” numbers. Would have have been more accurate.

If you want to make a dcr calc more accurate yet use the 275 (or 276 if you happen to run 1.6 rockers) to get the Intake closing event, then after you get the calculated number add another 4 degrees to the intake closing event for .009” at the valve. That will give you a close “actual” IVC number. Those cams have different acceleration on the opening and closing side of the cam. It is one of the reasons they often “rev” more than what they appear they would looking on paper at the “average” seat numbers that do not include the cams asymmetric’s. IRC the actual IVC number is around 67 to 68 ABDC.


Last edited by Jay S; 03-27-2020 at 09:14 AM. Reason: Edit
  #32  
Old 03-27-2020, 10:21 AM
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I have a similar bullet cam in my 400, I have a little more gear at 3.42. Great cam, no problems, its on a 112 LSA. I think you'll be just fine with the 703, I would not step down to the 702. I didn't see the 400hp with a 702 post, but just because someone else made that HP with a 702 doesn't mean you will, it seems a little sporty to me.

  #33  
Old 03-27-2020, 11:40 AM
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Bullet has some profiles that are later Ultradyne designs that are really similar to the Lunati voodoos. They have the same 48* intensity with less lift. They are my favorite flat tappet .842 hft lifter profile when used with 1.65 rockers. The 274/282 Bullet .312 profiles on 112 lsa with a 1.65 rocker would have been better for the high compression than either of those off the self Lunati cams. I am guessing that is what 1funride has. Lunati can also move the LSA out to 112 on the 703, that would have been a better choice yet since this engine has 1.5 rockers. They do not charge to do that, but they get you on the shipping cost versus a off the self cam from a mail order company off the self cam. For the compression with the logs i think it would even better moving the LSA out to 114 and a little extra advance. It smooths out the power and would be easier to tune with the extra compression when the exhaust is holding the engine back.

There is also some port work you can do to the intakes ports to help run some more compression. It involves the diameter of the valve to the ratio of the diameter to the throat of the bowl right under the valve. Then that has to be matched that the port size. It is a lot of work, and you have to spend some time working on the rest of the intake tract to make it work right. That might also be an option if you working around to much compression with a smallish cam.

  #34  
Old 03-27-2020, 12:39 PM
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Quote:
Originally Posted by Jay S View Post
Bullet has some profiles that are later Ultradyne designs that are really similar to the Lunati voodoos. They have the same 48* intensity with less lift. They are my favorite flat tappet .842 hft lifter profile when used with 1.65 rockers. The 274/282 Bullet .312 profiles on 112 lsa with a 1.65 rocker would have been better for the high compression than either of those off the self Lunati cams. I am guessing that is what 1funride has. Lunati can also move the LSA out to 112 on the 703, that would have been a better choice yet since this engine has 1.5 rockers. They do not charge to do that, but they get you on the shipping cost versus a off the self cam from a mail order company off the self cam. For the compression with the logs i think it would even better moving the LSA out to 114 and a little extra advance. It smooths out the power and would be easier to tune with the extra compression when the exhaust is holding the engine back.

There is also some port work you can do to the intakes ports to help run some more compression. It involves the diameter of the valve to the ratio of the diameter to the throat of the bowl right under the valve. Then that has to be matched that the port size. It is a lot of work, and you have to spend some time working on the rest of the intake tract to make it work right. That might also be an option if you working around to much compression with a smallish cam.
Jay,
would you have anymore information about these lobes? When I look at the Bullet lobe list this about the only 312 lobe that looks close.

Master______Adv__050__200____Lift__Lash__Type

H286/312____286__237__146___.3120__.000__CRA

Stan

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  #35  
Old 03-27-2020, 01:07 PM
Steve C. Steve C. is offline
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Stan check the UltraDyne lobes

http://www.bulletcams.com/Masters/ultradynemasters.html


( Side note. If anyone wants to avoid the Lunati conglomerate I can highly recommend Tim at Bullet Racing Cams. He worked with Harold Brookshire for 21 years )





.

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Last edited by Steve C.; 03-27-2020 at 01:17 PM.
  #36  
Old 03-27-2020, 01:28 PM
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Steve,
Thank you. My bad. I have the ultradyne master list on my computer and just never though to check it.

Stan

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  #37  
Old 03-27-2020, 02:15 PM
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Your welcome.

Recently I consulted Tim at Bullet about a new custom UltraDyne cam. I had on hand a cam previously ground at Bullet with one lobe slightly damaged and since I was reducing the lobe lift we used it.
I sent it to him and one week later the new cam was delivered.



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  #38  
Old 03-27-2020, 03:19 PM
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You found a profile from same cam profile family Stan. The older list, which is listed as Ultradyne are the old masters from before everything went to CNC. The Bullet profile like the one you found is the same profile now converted to CNC. All the profiles are converted to CNC now. I think they have the .312 profiles available in 2 to 3 degree increments. They are not all listed on the website. Some of the profiles on the Bullet list have Ultradyne origins.


Last edited by Jay S; 03-27-2020 at 03:24 PM. Reason: Edit
  #39  
Old 03-27-2020, 04:24 PM
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Call Lunati and discuss with them what you want with a cam. I did (had to call a few times) and they recommended a cam grind in between the two advertised grinds and made it for me. The cost was the same as a stock grind. They have a lot of different cam profiles and lobe separation options and just put a common spread in the catalogs.

Paul

  #40  
Old 03-27-2020, 06:48 PM
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Thanks for all the help in this thread. I have decided to try the 703 cam with intake centerline @ 104°-105° and unshroud the valves to drop the compression to just below 10:1. Tomorrow I gonna pick up at set of #670 heads as a plan B if I can't get the chambers in the #76 heads to at least 70cc.

/Eric

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