Trickflow as cast 220
I understand that, but how much compression is too much for a street car? Not all of us are after max effort track setups. I was under the impression that around 11:1 static compression is about ideal for a pump gas motor. I am not sure I would want to push past 11.5:1 on pump with todays inconsistent fuels. With E85 different story of course.
You can run 12:1 if your cam is big enough with a late enough IVC @ .006" to determine your cranking compression/DCR. I used the Polluter as an example. It's a 239/244 112+3. It's IVC is 73.5 degrees at advertised. With a 58cc Chamber, .040" Cometics and stock flat tops, you're around 11.95:1 CR and 8.8:1 DCR with that cam. Really that's an ideal setup with that camshaft. Had I know about the TFS 205s when I bought my heads, I would have gone that route and did something similar to the Polluter which is slightly bigger than my cam and has a little more overlap - but the later IVC needs more compression.
You need a pretty big cam to get by with 12:1 on 93. Or you're going to run into issues with timing and KR. And I'd rather run 27-28 degrees without KR and a safety margin with slightly less compression than 12:1 at 20 degrees with little to no safety margin and the possibility of KR with a tank of bad gas.
You need a pretty big cam to get by with 12:1 on 93. Or you're going to run into issues with timing and KR. And I'd rather run 27-28 degrees without KR and a safety margin with slightly less compression than 12:1 at 20 degrees with little to no safety margin and the possibility of KR with a tank of bad gas.
Ok I see...so for more of a max effort setup going with the 205's and a 240 duration cam would be a great combo, but the 64cc TFS-220's will work better with a 229/231 cam or something in that area?
I'd like to see Martin comment on this, but even with big big cams there's a limit on static/dynamic compression.
Say you're at 12:1, even if you have a can that drops you down to around 8.3 DCR, you'll be fine at lower rpm's, but you might run into problems in the higher RPMS when the engine gets more efficient, or in tune, with those cam specs. It will start sucking in more total air/fuel that the larger duration and later IVC will allow. Actual compression and cylinder pressure will increase because of scavenging, pressure waves, and what not.
I'm not the best at putting thoughts into words, but basically the DCR isn't truly a fixed number, it will increase nearing peak torque, which is where you'd run into problems with a big cam and that much compression.
Martin might comment on this
Say you're at 12:1, even if you have a can that drops you down to around 8.3 DCR, you'll be fine at lower rpm's, but you might run into problems in the higher RPMS when the engine gets more efficient, or in tune, with those cam specs. It will start sucking in more total air/fuel that the larger duration and later IVC will allow. Actual compression and cylinder pressure will increase because of scavenging, pressure waves, and what not.
I'm not the best at putting thoughts into words, but basically the DCR isn't truly a fixed number, it will increase nearing peak torque, which is where you'd run into problems with a big cam and that much compression.
Martin might comment on this
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I'd like to see Martin comment on this, but even with big big cams there's a limit on static/dynamic compression.
Say you're at 12:1, even if you have a can that drops you down to around 8.3 DCR, you'll be fine at lower rpm's, but you might run into problems in the higher RPMS when the engine gets more efficient, or in tune, with those cam specs. It will start sucking in more total air/fuel that the larger duration and later IVC will allow. Actual compression and cylinder pressure will increase because of scavenging, pressure waves, and what not.
I'm not the best at putting thoughts into words, but basically the DCR isn't truly a fixed number, it will increase nearing peak torque, which is where you'd run into problems with a big cam and that much compression.
Martin might comment on this
Say you're at 12:1, even if you have a can that drops you down to around 8.3 DCR, you'll be fine at lower rpm's, but you might run into problems in the higher RPMS when the engine gets more efficient, or in tune, with those cam specs. It will start sucking in more total air/fuel that the larger duration and later IVC will allow. Actual compression and cylinder pressure will increase because of scavenging, pressure waves, and what not.
I'm not the best at putting thoughts into words, but basically the DCR isn't truly a fixed number, it will increase nearing peak torque, which is where you'd run into problems with a big cam and that much compression.
Martin might comment on this
I personally would keep the SCR around 11.5-11.7:1, possibly 11.8:1 tops.
The DCR is not a set number that will stay put as the engine runs through the operating range is the simplest way I can put it.
I will say I have had a number of customers run 11.8-12:1 SCR with 93 pump gas and run fine, but there are many variables that can come into play in allowing it to work.
I think you did a great job explaining it!
I personally would keep the SCR around 11.5-11.7:1, possibly 11.8:1 tops.
The DCR is not a set number that will stay put as the engine runs through the operating range is the simplest way I can put it.
I will say I have had a number of customers run 11.8-12:1 SCR with 93 pump gas and run fine, but there are many variables that can come into play in allowing it to work.
On that note, how would you say the as-cast TFS 220 heads do in that regard? And the 205s? Figured I'd ask since its the topic of the thread.
That is correct. Without going back and looking through a lot of old emails, I believe the highest CR I've had someone run with the As Cast 220's is 11.7-11.8:1.
I don't have any experience with the 205's. I had a customer purchase a camshaft for a set a while back, but I believe he changed combinations.
I don't have any experience with the 205's. I had a customer purchase a camshaft for a set a while back, but I believe he changed combinations.
~11.7:1 SCR on a 408 with as-cast 220's
I run a 239/247 comp cam currently on 93 with no issues.
I've run the TFS220's with PM valve guides, Ferrera valves, stock rockers (with trunnion bearings), 63cc chambers and a VRX5 .609/.605 cam for 6k miles no issues whatsoever on 93 octane. I opted out of porting as the extra 10hp wasn't worth the price. To each their own, though.
I've run the TFS220's with PM valve guides, Ferrera valves, stock rockers (with trunnion bearings), 63cc chambers and a VRX5 .609/.605 cam for 6k miles no issues whatsoever on 93 octane. I opted out of porting as the extra 10hp wasn't worth the price. To each their own, though.
I've run the TFS220's with PM valve guides, Ferrera valves, stock rockers (with trunnion bearings), 63cc chambers and a VRX5 .609/.605 cam for 6k miles no issues whatsoever on 93 octane. I opted out of porting as the extra 10hp wasn't worth the price. To each their own, though.
440/403 no track numbers. I've added a few other tweaks it will probably be around 450whp now. This is with small 1-3/4" headers and an LS6 intake also. It's a good setup.
I have a small issue to sort before going forward. Currently tracking down a tick that runs down the passenger side header. Top side of the engine is dead quiet, no signs of leaks anywhere, but I am noticing a persistent ticking sound when fully warm at idle.
Thread Starter
Staging Lane
Joined: Sep 2008
Posts: 86
Likes: 0
From: Cincinnati Area
Congrats and Nice numbers! I have 1 7/8 kooks with their true duals now. Debating on keeping the LS6 or ponying up for a Fast.
I have a small issue to sort before going forward. Currently tracking down a tick that runs down the passenger side header. Top side of the engine is dead quiet, no signs of leaks anywhere, but I am noticing a persistent ticking sound when fully warm at idle.
I have a small issue to sort before going forward. Currently tracking down a tick that runs down the passenger side header. Top side of the engine is dead quiet, no signs of leaks anywhere, but I am noticing a persistent ticking sound when fully warm at idle.