Calculating DCR with a solid roller cam?
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Calculating DCR with a solid roller cam?
Hi, I'm hoping some of you experts can help me out here.
What intake valve closingtime (IVC) should I use when calculating the dynamic compression ratio (DCR) for my new engine?
The IVC on my solid roller cam is 72dgr after bdc at 0.015 lift on the tappet and 53dgr at 0.05.
On the KB-Silvolite calculator I'm using it is stated that I shall use the 0.05 IVC and ad another 15 deg but I have the feeling this is more relevant on a hydraulic cam compensating for the lifter flexing.
When I'm calculating my setup with 72dgr. I'll get 7.8 DCR which I find too low and doing the same with (53 + 15)dgr puts me in the better 8.2 DCR level.
What advice can you give me on the IVC so I can decide for the right cc on my heads? Thanks in advance.
What intake valve closingtime (IVC) should I use when calculating the dynamic compression ratio (DCR) for my new engine?
The IVC on my solid roller cam is 72dgr after bdc at 0.015 lift on the tappet and 53dgr at 0.05.
On the KB-Silvolite calculator I'm using it is stated that I shall use the 0.05 IVC and ad another 15 deg but I have the feeling this is more relevant on a hydraulic cam compensating for the lifter flexing.
When I'm calculating my setup with 72dgr. I'll get 7.8 DCR which I find too low and doing the same with (53 + 15)dgr puts me in the better 8.2 DCR level.
What advice can you give me on the IVC so I can decide for the right cc on my heads? Thanks in advance.
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I have seen 10 different variations of DCR calculators. Each one has some spin. The reason is that it's very hard to account for VME. A well tuned motor using intake raming effect can actually overfill a cylinder at certian rpm with over 100% Then you have plain jane low compression motor with lots of residual burnt gas and 80% fill. It can run a higher DCR and never ping.
What is your ci and .050 duration. I know enough to tell you what static you could run.
What is your ci and .050 duration. I know enough to tell you what static you could run.
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Hi Gkull, and thanks for your reply.
I'm not sure what you mean with ci but I have the following cam specs at 0.05: 9 deg open / 53 deg close total 242 and LCA 112 and 0.608 lift with 1.6 rockers.
My comp is 10.35:1 with my curent parts but I could have the heads milled for a higher ratio.
On the other hand I'm planing to run the engine on 95 octan Europe fuel which should be similar to 90 octan in the US and I want to keep away from knocking-problems.
Looking forward to hear you recomendations and best regards, dk-corvette.
I'm not sure what you mean with ci but I have the following cam specs at 0.05: 9 deg open / 53 deg close total 242 and LCA 112 and 0.608 lift with 1.6 rockers.
My comp is 10.35:1 with my curent parts but I could have the heads milled for a higher ratio.
On the other hand I'm planing to run the engine on 95 octan Europe fuel which should be similar to 90 octan in the US and I want to keep away from knocking-problems.
Looking forward to hear you recomendations and best regards, dk-corvette.
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From: Plano TX
For this to work you need aluminum heads and quench is critical. The bigger your bore, the more likely it will ping. 10.35 will be a challange on low-octane fuel. If you are set on regular fuel I'd lower the compression to just under 10:1.
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
My present 383 Solid roller runs fine on our local 91 octane. With 11.24 static compression. 4.030 X 3.750 = 383 64cc heads and .041 quench
My .050 cam is Intake BTDC 12 ABDC 46 Ex. BBDC 60.0 ATDC 6.0
238/246 LSA 112 installed 2 degrees retarded .635/.644 with 1.65 I rockers
My .050 cam is Intake BTDC 12 ABDC 46 Ex. BBDC 60.0 ATDC 6.0
238/246 LSA 112 installed 2 degrees retarded .635/.644 with 1.65 I rockers
Drifting
Joined: Sep 2003
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From: FRANKLIN GA
A 242 duration cam should handle the 10.35:1 with alum. heads and 90 octane gas. Quench will be an important factor with that low of an octane. You can get a thinner head gasket to help with this without having to mill the heads.
What is your deck heighth? head combustion chamber cc's?
I'm getting away with 11.2:1 static with a total quench of .031 (0 decked with a .031 gasket) on 93 octane. I do have to retard the timing a few degrees in the summer to control the ping.
What is your deck heighth? head combustion chamber cc's?
I'm getting away with 11.2:1 static with a total quench of .031 (0 decked with a .031 gasket) on 93 octane. I do have to retard the timing a few degrees in the summer to control the ping.
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I have had the following cam grinded at Comp for me:
At .050 cam is Intake BTDC 9 ABDC 53 Ex. BBDC 53 ATDC 9, 242/242 LCA 112 grinded on a small base circle for stroker. It might be necessary to advance the timing 2 or 4 deg. we'll see on the dyno.
The block will be 0 decked. Probably end up somewhere between 0 and 0.005 and together with a 0.04 packing it gives a quench round 0.045.
bore and stroke is 4.03 x 4.0
I have a nice set of 68cc AFR heads that I planed to use for a 383. Then I decided to go for a 4" stroke instead but with 68cc this will put my comp to 11.1:1 which I'm afraid will be too high for the fuel. DCR 8.4 -8.7 depending on IVC but compared with Gkull's data this might work?
Therefore I'll think about selling them and get another set of heads in the 75cc size instead. Such will lower me to the mentioned 10.35:1 and a DCR 7.8 - 8.2.
What do you think about all of this?
At .050 cam is Intake BTDC 9 ABDC 53 Ex. BBDC 53 ATDC 9, 242/242 LCA 112 grinded on a small base circle for stroker. It might be necessary to advance the timing 2 or 4 deg. we'll see on the dyno.
The block will be 0 decked. Probably end up somewhere between 0 and 0.005 and together with a 0.04 packing it gives a quench round 0.045.
bore and stroke is 4.03 x 4.0
I have a nice set of 68cc AFR heads that I planed to use for a 383. Then I decided to go for a 4" stroke instead but with 68cc this will put my comp to 11.1:1 which I'm afraid will be too high for the fuel. DCR 8.4 -8.7 depending on IVC but compared with Gkull's data this might work?
Therefore I'll think about selling them and get another set of heads in the 75cc size instead. Such will lower me to the mentioned 10.35:1 and a DCR 7.8 - 8.2.
What do you think about all of this?
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Team Owner
Joined: Apr 1999
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
How much in negative cc are your pistons dished? Because my cam is retarded 2 degrees the real world numbers are 12 48 58 8 which is very simular to yours if you install at 2-4 degrees advance. With 11:1 i wouldn't worry about it. It's going to be a TQ monster with a good intake and free flowing exaust.
Last edited by gkull; Nov 6, 2006 at 04:45 PM.
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Hi Gkull,
The pistons are Mahle flat top 5cc. They have an incredible low weight of only 380g!!
The idea behind the cam was to make a real TQ-monster to match the 3.08 rear and the TH400 / 2400 stall the car has now. Inspired of the great results that Motorhead has with his cam setup we decided to use the same grinding from his inlet to both my inlet and exhaust.
With the fast acceleration cam grind together with the 1.6 rockers we hope to have something close to an "on/off" opening and closing of the valves ensuring an big opening area within a relative narrow (242) deg. The overlap was reduced by the 112LCA for reduced fuel consumption and driveability. It looks rather close to your cam but with the extra 25 cui of my engine it should go more in the TQ direction. I hope it will work.
I have a RPM airgap intake and a set of Hooker super comp 13/4" headers. Haven't decided for a carb yet. The engine builder suggests a Holley 750 DP but I am more in for a Mighty Demon 750-825 with ann. boosters. Any suggestion? Best regards.
The pistons are Mahle flat top 5cc. They have an incredible low weight of only 380g!!
The idea behind the cam was to make a real TQ-monster to match the 3.08 rear and the TH400 / 2400 stall the car has now. Inspired of the great results that Motorhead has with his cam setup we decided to use the same grinding from his inlet to both my inlet and exhaust.
With the fast acceleration cam grind together with the 1.6 rockers we hope to have something close to an "on/off" opening and closing of the valves ensuring an big opening area within a relative narrow (242) deg. The overlap was reduced by the 112LCA for reduced fuel consumption and driveability. It looks rather close to your cam but with the extra 25 cui of my engine it should go more in the TQ direction. I hope it will work.
I have a RPM airgap intake and a set of Hooker super comp 13/4" headers. Haven't decided for a carb yet. The engine builder suggests a Holley 750 DP but I am more in for a Mighty Demon 750-825 with ann. boosters. Any suggestion? Best regards.
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
yes my JE pistons are 419 grams. Most anyway i figure your static with 68 cc heads gets you right at 11.2 with ..040 quench. Not a problem with aluminum heads and 242 intake duration.
My original 427 small block came equiped with a comp cams 242/248 110. It was really mild for that many CI. My compression has me limited to not to radical duration.
My original 427 small block came equiped with a comp cams 242/248 110. It was really mild for that many CI. My compression has me limited to not to radical duration.
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I think the added 15 degs is just an average for "normal" cams to make sure the valve is closed, then they know where to calculate from. Your intake valve is still open 15 degs past 53 ABDC @ 0.050". It gets worse, you can add another 4-5 degrees on to the 72 deg @ 0,015" too, that is where the valve will be completely closed, so your DCR will be even lower than you already calculated.
This is where picking the correct parts and compressin ratio is critical. You need to be in the 8-8.5 DCR range, any lower it's a lame duck, any higher and you have detonation problems. I am impressed that you are at least looking into this before bolting a motor together and wondering why it runs like crap with no power later. You need at least 11:1 CR to run a 240-250 deg cam, now you know why
This is where picking the correct parts and compressin ratio is critical. You need to be in the 8-8.5 DCR range, any lower it's a lame duck, any higher and you have detonation problems. I am impressed that you are at least looking into this before bolting a motor together and wondering why it runs like crap with no power later. You need at least 11:1 CR to run a 240-250 deg cam, now you know why
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Hi Motorhead,
That is exactly what I am afraid of too.
With the right inlet valve adjustment of 0.016 the valve will first be fully closed at 75-77deg ABDC. At this deg. the DCR will be in a much to low 7.6 level with 75cc heads but with my 68cc DCR will be perfect at 8.2.
Based on your great help I will therefore start out with the 68cc heads I already have. Thank you very much for your great advice.
That is exactly what I am afraid of too.
With the right inlet valve adjustment of 0.016 the valve will first be fully closed at 75-77deg ABDC. At this deg. the DCR will be in a much to low 7.6 level with 75cc heads but with my 68cc DCR will be perfect at 8.2.
Based on your great help I will therefore start out with the 68cc heads I already have. Thank you very much for your great advice.
