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Travis

351 compression

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28 minutes ago, Travis said:

I’m running the crow cam 21649, not sure if that helps at all, it has the 351 crank and the 302 rods

 

 

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you might be better off asking crow directly?

 

i asked them about something a while back, they replied next day

link to the cam here for people like @gerg  @Thom perhaps

 

https://www.crowcams.com.au/FindaProduct/tabid/92/ProdID/15400/21649__FORD_CLEV_CAM.aspx

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As Dean mentioned, cam choice Is the main factor. Also, open or closed chamber makes a big difference to how much comp it can take and what fuel you can run

If running the 302 heads, comp will already be up around 11:1. That might be OK with the camshaft you're running, which is pretty radical.

First, you have to decipher the cam specs into intake closing ABDC.

Use this calculator:

http://www.wallaceracing.com/cam-deg-calc.php

Then, punch in the specs of your head. You have to know what chamber you have and how much has been taken off. Closed chamber 2Vs are 56-58cc, open are around 76cc. Subtract 1 cc for every 5 thou taken off on a closed chamber, 1cc every 3 thou on an open.

Use this calculator:

http://www.wallaceracing.com/cr_test2.php

Then, with this info you've derived, use yet another calculator to determine what dynamic compression you will end up with. This takes into account the intake valve closing event and static comp. On a healthy street engine, aim for around 8:1 if running 95 or 8.3:1 if on 98. If running open chamber, aim for 8:1 on 98. You may just already be in the ballpark with any luck.

Here it is:

http://www.wallaceracing.com/dynamic-cr.php

So armed with all this info, you can dial in what comp you want based on the cam and head design you already have.

Here's a real-world example....
I got to 7.9:1 dynamic on a closed chamber 302. It's running around 10:1 static with a Crow 21602 which is 208/208/110. I say "around" 10:1 because I'm not 100% on how much has been taken off, but I guess around 0.030" in total. This brings the chamber down to 50-52 cc. I have run it purely on E10 without pinging issues in the past before getting the heads shaved but I haven't driven it on the street yet with the new combo. The closed-chamber design is very efficient.

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As Dean mentioned, cam choice Is the main factor. Also, open or closed chamber makes a big difference to how much comp it can take and what fuel you can run

If running the 302 heads, comp will already be up around 11:1. That might be OK with the camshaft you're running, which is pretty radical.

First, you have to decipher the cam specs into intake closing ABDC.

Use this calculator:

http://www.wallaceracing.com/cam-deg-calc.php

Then, punch in the specs of your head. You have to know what chamber you have and how much has been taken off. Closed chamber 2Vs are 56-58cc, open are around 76cc. Subtract 1 cc for every 5 thou taken off on a closed chamber, 1cc every 3 thou on an open.

Use this calculator:

http://www.wallaceracing.com/cr_test2.php

Then, with this info you've derived, use yet another calculator to determine what dynamic compression you will end up with. This takes into account the intake valve closing event and static comp. On a healthy street engine, aim for around 8:1 if running 95 or 8.3:1 if on 98. If running open chamber, aim for 8:1 on 98. You may just already be in the ballpark with any luck.

Here it is:

http://www.wallaceracing.com/dynamic-cr.php

So armed with all this info, you can dial in what comp you want based on the cam and head design you already have.

Here's a real-world example....
I got to 7.9:1 dynamic on a closed chamber 302. It's running around 10:1 static with a Crow 21602 which is 208/208/110. I say "around" 10:1 because I'm not 100% on how much has been taken off, but I guess around 0.030" in total. This brings the chamber down to 50-52 cc. I have run it purely on E10 without pinging issues in the past before getting the heads shaved but I haven't driven it on the street yet with the new combo. The closed-chamber design is very efficient.

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couldn't have put it better myself, about the oly thing I'd have to add is the closed chamber by design is better at resisting detonation compared to an open chamber head and also tends to work better with unleaded fuel and most aluminum heads have a more modern combustion chamber design and quite often resembles a closed chamber combustion chamber (you can usually get away with a bit more comp on alloy heads due to the more modern chambers and aluminum dissipates heat better than cast iron)

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Check the block hasn't been shaved as well as this will increase the comp way to much for pump gas.

 

I had a 351 030 (Block deck to 0) and CC Heads and it was a pinging nightmare with unleaded, even 98 was only a little improvement. Change to a wilder cam made a little difference but it then suffered on take off, increased stall and that helped but was still not fun. We estimated it had 11.8:1 comp as on Avgas it was a weapon, you could advance the timing from 0 to about 10degs and the change was awesome

 

Mate had the engine after me and he replaced the heads with a set of shaved & Ported OC reco heads and back to the original Crow cam and it was a total different beast, no over heating and ran really nice as that was just over 10.3:1 compression

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Check the block hasn't been shaved as well as this will increase the comp way to much for pump gas.
 
I had a 351 030 (Block deck to 0) with 302 Rods and CC Heads and it was a pinging nightmare with unleaded, even 98 was only a little improvement. Change to a wilder cam made a little difference but it then suffered on take off, increased stall and that helped but was still not fun. We estimated it had 11.8:1 comp as on Avgas it was a weapon, you could advance the timing from 0 to about 10degs and the change was awesome
 
Mate had the engine after me and he replaced the heads with a set of shaved & Ported OC reco heads and back to the original Crow cam and it was a total different beast, no over heating and ran really nice as that was just over 10.3:1 compression

So the engine builder has come back and said if I use my close chamber heads it will put the compression up to 10.5:1, I’m not sure if that’s good or to high,


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Should be ok running 95 or 98, I do a poor man's version if I get a shitty tank of E10, I go to a servo that has E85 and slurp some of that in. I've run up to a guestimate of 25% ethanol with no dramas except a little edge knocked off the power. Runs very smooth though. I do this only when I really need to.

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I had a 351c with a 30 over bore built a long time ago that ran 2V CC heads, from memory the comp was pretty much bang on 11:1. Cam was around the 520-530 odd lift and 220-224 duration Crower.

I sold it off before it was fitted to the car, the engine builders had done a few to the same spec and they ran good...the person who bought it from me never complained.


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I had a 351c with a 30 over bore built a long time ago that ran 2V CC heads, from memory the comp was pretty much bang on 11:1. Cam was around the 520-530 odd lift and 220-224 duration Crower.

I sold it off before it was fitted to the car, the engine builders had done a few to the same spec and they ran good...the person who bought it from me never complained.


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This has happend to me on every single clevo i have built over 20 years when using cc heads ,ok im talking run on after turning key off,the 400 i just built gave its first indication the other day when it was running hot as hell ,could be the reason of only a tiny bit of run on , i only use 98 fuel,hell i dont even know what the comp ratio is maybe gerg can estimate 400 plus 030 with cc heads milled slightly im guessing at least 10.1 comp piston is 060 under deck roughly but i do not know the piston cc when i asked manufacturer they said um errr we dont know wtf ,im guessing about 20cc dish speed pro new pistons maybe some Google reasearch can find this.

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This has happend to me on every single clevo i have built over 20 years when using cc heads ,ok im talking run on after turning key off,the 400 i just built gave its first indication the other day when it was running hot as hell ,could be the reason of only a tiny bit of run on , i only use 98 fuel,hell i dont even know what the comp ratio is maybe gerg can estimate 400 plus 030 with cc heads milled slightly im guessing at least 10.1 comp piston is 060 under deck roughly but i do not know the piston cc when i asked manufacturer they said um errr we dont know wtf ,im guessing about 20cc dish speed pro new pistons maybe some Google reasearch can find this.

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You're running those ported closed 2Vs right? A 2V that's been cleaned up on the deck should be between 56 and 58cc.

With that inputted, I'm getting 9.47:1 with 20cc dish and 60 down the hole.

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You're running those ported closed 2Vs right? A 2V that's been cleaned up on the deck should be between 56 and 58cc.

With that inputted, I'm getting 9.47:1 with 20cc dish and 60 down the hole.

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Yes sealed power piston not speed pro

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In any case, I don't think you're going above 10:1 and you have a bigger cam than me. If running on is an issue, try a tank of E10. The ethanol content increases the burn stability way beyond the percentage that it takes up. Mine has never run-on, even when the fans didn't cut in and I pulled in the driveway with the temp in the red. I've nearly always run E10 so I reckon that's what helps the most. My comp is (I think) around the 10:1 mark

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In any case, I don't think you're going above 10:1 and you have a bigger cam than me. If running on is an issue, try a tank of E10. The ethanol content increases the burn stability way beyond the percentage that it takes up. Mine has never run-on, even when the fans didn't cut in and I pulled in the driveway with the temp in the red. I've nearly always run E10 so I reckon that's what helps the most. My comp is (I think) around the 10:1 mark

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But isnt yours a 302c with 9.1 ?

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But isnt yours a 302c with 9.1 ?

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Can the 650 holley brawler take e10 ? With no mods

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But isnt yours a 302c with 9.1 ?

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302s were 9.4 to start with, mine's been shaved I gather 30 off the head and at least 5 off the deck. I calculated with 20 down the hole Hypertec pistons, roughly 10:1.

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Can the 650 holley brawler take e10 ? With no mods

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Might need another 2 jet sizes if it's jetted spot-on now but otherwise will be fine

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Might need another 2 jet sizes if it's jetted spot-on now but otherwise will be fine

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You mean bigger jets ?

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i would never dreamed on putting anything less than 98,but last say 10 switch offs no run on,also have very low idle timing on msd about 12 deg ,like what if i set it at 20 deg at idle would that cause it to run on or not,cause im very surprised at power at even very low timing curve from idle.

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