Help choosing cam

[Nova1975]

Hi all.

I'm in the process of trying to get my 75 Nova a little more streetable and would like to replace the cam and convertor.

I have SBC 400, 30 over with 5.7 rods. Flat top pistons calculated compression 11.1.
Dart 64cc (very first version) iron heads, 2.02,1.60 valves. They have been worked over and milled.
Bowtie Vic Jr manifold, Holly 750DP.
4:56, 28" tire, TH350.
Manual brakes.

I do not have a good convertor so I want to match a new one with the cam. I wouldn't mind going back to my 3:70 gears, but not sure if that is possible without changing my heads, manifold, carb.

My current cam is a solid roller and I would like to go with another so I could get away with not replacing the lifters. I have been looking at Lunati VooDoo cams that pull to 6500-6800 but I'm afraid they may be too small for a 400.

I know this sounds like I am all over the place with what I want. It is not a daily driver, but I wouldn't mind driving it 30 miles at a time. Hopefully I gave enough info.

Thanks for any help.

Darin

 

[Indycars]

Hi all.

I'm in the process of trying to get my 75 Nova a little more streetable and would like to replace the cam and convertor.
What does more streetable mean to you, more low end torque ???

I have SBC 400, 30 over with 5.7 rods. Flat top pistons calculated compression 11.1.
Dart 64cc (very first version) iron heads, 2.02,1.60 valves. They have been worked over and milled.
Bowtie Vic Jr manifold, Holly 750DP.
If you are looking to more more torque lower in the RPM range, then a dual plane manual would be a step in the right direction.

4:56, 28" tire, TH350.
It would be more expensive, but going to an Over Drive trans like the 200-4r would allow you to keep the 4:56 rear end. A 4:56 rear end and an OD trans (.67) would be the same as a TH350 with a 3.06 (4.56 x .67 = 3.06) rear gear, the best of both worlds.

Manual brakes.

I do not have a good convertor so I want to match a new one with the cam. I wouldn't mind going back to my 3:70 gears, but not sure if that is possible without changing my heads, manifold, carb.

My current cam is a solid roller and I would like to go with another so I could get away with not replacing the lifters. I have been looking at Lunati VooDoo cams that pull to 6500-6800 but I'm afraid they may be too small for a 400.
What is your present cam specs, model number ???


I know this sounds like I am all over the place with what I want. It is not a daily driver, but I wouldn't mind driving it 30 miles at a time. Hopefully I gave enough info.

Thanks for any help.

Darin

 

[grumpyvette]

yes I concur it would help a great deal to know your current cam part number and manufacturer and swapping too an over drive top gear transmission with that 4.56:1 rear gear would be a good idea.
youve posted much less info than would be ideal, but lets discuss basics a bit here!
ID SUGGEST CALLING BOTH CRANE AND CROWER CAMS FOR THEIR SUGGESTIONS
you can,t make good choices unless you know exactly what your trying to accomplish and exactly what your currently using so you have a firm basis for making any changes required.knowing your true static compressions a first step,knowing your cam specs, head flow and a dozen other factors like the drive train gearing, ignition advance and fuel/air ratio sure helps., because without knowing that your going to have a very difficult time making power without getting into detonation or tuning issues. and having iron heads , due to their slower heat loss rate, limits your engine flexibility a bit
lets look at a few things,in an ideal world you try to optimize the combo.
from purely a math stand point, you can calculate whats required to lower the cylinder pressure, but other factors like header scavenging and coolant temps, oil temps and ignition advance will effect your results and if you run E85 you can run significantly higher cylinder pressures and get away with it without detonation...
(1) as mentioned swapping to a good dual plane intake like a ededlbrock rpm air gap, is a good first start, as it increases mid and low rpm torque.
(2) with 11:1 static compression ratio your going to need to calculate whats needed in cam timing to get to about 8:1-to-8.3:1 dynamic compression and with about the lowest duration imposable on about a 110-114 LSA to increase the cars street manors if you want to run pump high test fuel.
wider LSA tends to bleed off more cylinder pressure
a few calculations show that will require about a 60 degree intake close point at .050 lift, but we also have the option of installing a cam a few degrees retarded to further bleed off cylinder pressure

http://www.kb-silvolite.com/calc.php?action=comp2

viewtopic.php?f=52&t=324

now you look at cam timing numbers, in these charts on a 114 LSA, and we find were looking at cams with about a 258-264 intake duration at .050 lift so that certainly won,t be a super street-able cam

viewtopic.php?f=52&t=4299

you should be looking at cams in this design range and the second or lower cam looks like what Id suggest, be matched with the 200r4 trans and edelbrock dual plane intake

 

[Nova1975]

What does more streetable mean to you, more low end torque ???


If you are looking to more more torque lower in the RPM range, then a dual plane manual would be a step in the right direction.



What is your present cam specs, model number ???

My current cam rpm range is 4000-7800 with 106 lobe separation. I will get my cam card and post as soon as I can. Even with that big a cam and not the best convertor, I didn't really have any low end torque problem. It would break loose my slicks if not heated. In fact, when I raced my friend at one race, we were pretty much dead even until we hit upper part of 3rd gear and he started walking away from me.

I currently have way too much compression (12.5). When I built it, that was all I could find in a forged piston for a 5.7 rod. That was fine when I was racing it and buying racing fuel. With it being torn apart, I wanted to go ahead and get a more street-able cam.

Thanks for the replies. I will get back with more details as soon as I can.

 

[Nova1975]

Part number 50124

Lobe Separation 106
Lift at valve .622 IN, .624 EX
Duration @ .050 262 IN, 271 EX
Adv Duration 300 IN, 310 EX

 

[grumpyvette]

it looks like the person selecting that current cam either knew what he was doing to avoid detonation issues OR just lucked out in getting a good choice
now obviously you can select a milder cam, but doing so will tend to increase effective true compression,so the first step is to do a compression test and find out what your TRUE cylinder pressure IS, youve stated it 11:1 and 12.5:1, let me know what a compression test shows with the tested cylinders rockers BOTH on, with the valves adjusted normally and then tested again,with the rockers REMOVED

http://www.harborfreight.com/quick-conn ... 95187.html

you also obviously have the option of both a milder cam and a set of flat or dished pistons (what ever is required) to drop the true static compression down to a more pump gas octane and street driving rpm range, dropping the static compression to lets say 9.8:1-10.3:1 and using a cam like I,ve used on several engine builds like this one below, may help

ID SUGGEST CALLING BOTH CRANE AND CROWER CAMS FOR THEIR SUGGESTIONS but first step is verifying EXACTLY what compression ratio you have, before making ANY changes

 

[Nova1975]

http://www.summitracing.com/parts/SLP-L2477F/ These are the pistons I have. It is apart, so I cannot take compression readings, wish I had done that. The block and rings only have about 200 miles on them. Plans are to mill the dome off the pistons and reuse the rings instead of buying new pistons, rings and re-hone. With my current piston, gaskets and heads, I was told it calculated to 12.8 (sorry I posted 12.5). By milling the .145 dome + .10 he said it would be around 11.06, which is still not ideal for the street.

The current cam was good luck. It was bought by a friend to put in his 406 trying get get more hp, but a cylinder shelled out on him. I picked up cam and lifters barely used for $300. Seemed to work okay on the track and actually not that bad around town. Just thought since I had it apart, I would get a more streetable cam. Maybe I shouldn't and let the current cam handle the higher compression.

Thanks again for your time and information you posted. I still need to study the information more.

Darin

 

[Indycars]

Something doesn't add up from what I can see. His head has 64cc chambers, but it's been milled. I used 64cc in my calcs. I also used a quench height of .045". Used the cam spec Darin posted.

Engine 1
Assuming he installs the cam dot-to-dot (4 degrees ADV) IVC of 72 ABDC, I get a static CR of 13.39 and DCR of 10.05

Engine 2
Retarded 4 degrees or IVC of 76 , I get SCR of 13.39 and DCR of 9.68.

Engine 3
If milling the dome off increase the combustion volume by 10 cc, then I get SCR of 11.79 and a DCR of 8.55

Did I get a number wrong somewhere ???