CR and pump gas question

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zsn0w

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For my 408 stroker build, I'm looking a a combination of the Scat cast crank and forged pistons kit 1-98113BI, edelbrock 60779 heads, and this Hughes cam Hughes Engines . I'm wondering if I should go with the open chamber edelbrock heads (60179) instead to help keep the CR down a little further? I'm looking at around 10.1:1 with the closed chambered heads and 9.9:1 with the open (assuming I don't need to deck the block at all, although I could use a thicker head gasket to compensate for that anyway so I'm not too worried about that). I want to be able to use pump gas. 93 is easy to get around here so I'm fine with needing that, but is that even possible at 10.1:1 with this cam? Everything seems to come together well with the parts I've picked, but this is worrying me a bit, as there aren't any sets that I can find with forged dish pistons that are higher volume. I think icon sells some, but not in any of the kits I've seen. I know CR is kind of a point of debate, but I'd like to at least know if I'm completely out of the advisable area for pump gas. Thanks.
 
Ran the 60179 heads on my 416 with 11.9 to 1 compression using 93 octane no issues (by the way they're for sale here..
 
Who picked the cam? If you get the correct cam, and can do basic tuning, you can run a bit higher CR than what you are doing. But it has to be right.
 
Who picked the cam? If you get the correct cam, and can do basic tuning, you can run a bit higher CR than what you are doing. But it has to be right.
I picked the cam after a lot of research. Wanted to go with a Hughes and it seemed like the best fit to maximize performance while keeping it drivable.
 
I picked the cam after a lot of research. Wanted to go with a Hughes and it seemed like the best fit to maximize performance while keeping it drivable.


I'd suggest that you let the cam grinder pick your cam. Unless you are 100% confident in what you are doing.

The number 1 mistake when trying to run what some consider high compression on pump gas is cam timing. There are some who love to take away intake duration, add exhaust duration and then open the LSA up so the RPM range is what you want.

That is a 100% power killer every time.

Don't know what heads you are using, but more than a couple degrees split on gasoline says the cam grinder is trying to get tricky and that's never good.
 
Closed chamber will allow better quench.
I would think there would be a larger spread in CR between the open and closed.
 
Closed chamber will allow better quench.
I would think there would be a larger spread in CR between the open and closed.
I could be wrong about the CR for sure, I just approximated them based off the advertised CR for the stroker kit. 62 CC was 10.2 and the closed chambers have 63cc. 68cc was 9.6, so doing the math for 65cc (the open chambers) I got around 9.9. It seemed like a fairly linear progression from the three examples they gave for 62(10.2), 68(9.6), and 70cc(9.4), so I would think my estimates are within .1 of the actual values at least?
 
Sounds reasonable.
I assumed the volumes were further apart.
Yeah, I was kind of surprised it was only a difference of two cc as well. I think it's because the open chambers are just so stock 340 pistons can fit, though?
 
something does not add up
If I remember correctly (lotsa luck there) the recess is .100 on those heads
sounds like more than a few cc to me
"I'm wondering if I should go with the open chamber edelbrock heads (60179) instead to help keep the CR down a little further"
absolutely not
No quench and
do you have 93 in your area ? AWOL here in SOCAL
with those heads it can be done but everything has to be right they work better with high octane and lower gears and looser converter- motor revved up
compared to closed chamber they do not like a long pull up a hill (or towing) as much
run the closed chamber with the piston cc AND gasket to get the CR you want then pick the cam - much more leeway with octane and timing and cam
do not increase the gasket with 0 deck over .040 just to lower compression- it's counter-productive
in otherwords deck clearance + gasket .030-.040 with closed chamber heads
as yr says they have to go together
Typical Hughes lack of info on that cam- you can't tell what the seat timing is so you cannot determine where the intake closes so you can't determine your Dynamic CR or estimate your cranking compression
Check Howard's website for a lobe similar .050 and lift to the Hughes and write it down then someone can advise you and Dynamic compression and detonation restience
allow for carbon buildup if this is a street machine
also check lunati Voodo and Bullett they all have similar shelf cams with different LCA s depending on what you need
 
something does not add up
If I remember correctly (lotsa luck there) the recess is .100 on those heads
sounds like more than a few cc to me
"I'm wondering if I should go with the open chamber edelbrock heads (60179) instead to help keep the CR down a little further"
absolutely not
No quench and
do you have 93 in your area ? AWOL here in SOCAL
with those heads it can be done but everything has to be right they work better with high octane and lower gears and looser converter- motor revved up
compared to closed chamber they do not like a long pull up a hill (or towing) as much
run the closed chamber with the piston cc AND gasket to get the CR you want then pick the cam - much more leeway with octane and timing and cam
do not increase the gasket with 0 deck over .040 just to lower compression- it's counter-productive
in otherwords deck clearance + gasket .030-.040 with closed chamber heads
as yr says they have to go together
Typical Hughes lack of info on that cam- you can't tell what the seat timing is so you cannot determine where the intake closes so you can't determine your Dynamic CR or estimate your cranking compression
Check Howard's website for a lobe similar .050 and lift to the Hughes and write it down then someone can advise you and Dynamic compression and detonation restience
allow for carbon buildup if this is a street machine
also check lunati Voodo and Bullett they all have similar shelf cams with different LCA s depending on what you need
I do have 93 available here. It's actually really hard to find 91 anywhere, goes straight from 89 to 93, which was a huge pain when I used to drive a 3000gt that needed at least 91 but I had to shell out for 93 because it was all I could find. I calculated the DCR with a calculator I found linked from FABO somewhere and it was giving me around 9.35:1. The intake closes 40 degrees after BDC, it has it kind of further down the page in the table. Yeah, I wasn't sure if the quench difference would offset the CR drop in those heads. Haven't really read much about the open chamber ones, so that's what I was wondering. Seems like they aren't worth it. Still, wondering if I can run 91 or at least 93 with a CR that high and that cam.
 
Stay away from the open chamber ede heads.... run the closed chambers.

JMO, why push the edge on compression and tune up when the marginal gains from an extra .5 in compression are usually minimal. Street car, run compression at a level where even if you had to put some rancid pump piss in it, it would run.
 
Stay away from the open chamber ede heads.... run the closed chambers.

JMO, why push the edge on compression and tune up when the marginal gains from an extra .5 in compression are usually minimal. Street car, run compression at a level where even if you had to put some rancid pump piss in it, it would run.
I agree, I'm not trying to push the compression to run it as high as possible. I'd much rather run around 9.7:1. The stroker kits available are either a forged piston at this CR 10.1:1 CR or a hypereutectic piston at around 9.5:1. I'd much rather go forged with the numbers I'm looking to make, but if I have to put together the kit myself to get some other pistons rather than use the preassembled kit ones, I'm going to be paying a lot more for basically the same exact thing but with like .4 lower compression...
 
FWIW.... The so-called 'open' chamber Edelbrocks have .060" deep recesses.

If the dished Icon pistons for that kit are IC745's (20.5 cc dish + eyebrows), then you have about 9.8 Static CR with a .039" thick 1008 head gasket, the 60779 closed chamber heads, and a nominal LA block height. If they are the Icon IC984's, then they would be about 0.3 points lower (despite the catalog saying the CR will be the same) due to a .020" lower compression height.

I would be tempted to use a Mr Gasket 1121G (028" thick) to get the gap from the heads to the pistons down close to .040" (with the IC745's and a nominal LA block height) and have better quench effect; that is always a good detonation fighter.

BTW, IMPORTANT:
You run DCR numbers with the advertised duration valve events, NOT the .050" valve events. It looks like you used the 40* ICA from the .050" valve events, and that would falsely elevate the DCR to that 9.35 number and probably is what scared you! That is not a correct number. That is what is wrong (IMHO) with the Hughes cam advertisements.... you have to make a good guess at the advertised durations to get to a DCR number.

I'm gonna guess that the Hughes cam you linked has at least a 280 advertised duration; might be a bit more. If so, then DCR is around 7.8 installed straight up (ICL=106*) and this should be easy-peasy to run on 93 with AL heads... easy to tune, and easy to avoid detonation.

FWIW..... I personally would not be scared to run hypers at this level with AL heads. I've run them with 14-15 psi boost in a rally car engine all day long... avoid detonation and you are fine. In fact, my son's 340 is at 8.0 DCR with KB hypers and the 60779 closed chamber Edlebrocks..... never has hinted at detonation on 93. 15 degrees initial and 35-37 degrees total for ignition advance numbers.
 
BTW, IMPORTANT: You run DCR numbers with the advertised duration valve events, NOT the .050" valve events. It looks like you used the 40* ICA from the .050" valve events, and that would falsely elevate the DCR to that 9.35 number and probably is what scared you! That is not a correct number. That is what is wrong (IMHO) with the Hughes cam advertisements.... you have to make a good guess at the advertised durations to get to a DCR number.

I'm gonna guess that the Hughes cam you linked has at least a 280 advertised duration; might be a bit more. If so, then DCR is around 7.8 installed straight up (ICL=106*) and this should be easy-peasy to run on 93 with AL heads... easy to tune, and easy to avoid detonation.

Ah okay, that makes sense. Thanks for clearing that up. I got in contact with Hughes and they actually recommended I go up one camshaft to this Hughes Engines which surprised me. Would you say this should be just as good to go with 93? I figured that would be too much for the low end power I want, but they said that would work better for a stroker. Thanks for the help.
 
Ah okay, that makes sense. Thanks for clearing that up. I got in contact with Hughes and they actually recommended I go up one camshaft to this Hughes Engines which surprised me. Would you say this should be just as good to go with 93? Thanks for the help.


Doesn't surprise me one bit. That's why you are better off to call the cam grinder.
 
For my 408 stroker build, I'm looking a a combination of the Scat cast crank and forged pistons kit 1-98113BI, edelbrock 60779 heads, and this Hughes cam Hughes Engines . I'm wondering if I should go with the open chamber edelbrock heads (60179) instead to help keep the CR down a little further? I'm looking at around 10.1:1 with the closed chambered heads and 9.9:1 with the open (assuming I don't need to deck the block at all, although I could use a thicker head gasket to compensate for that anyway so I'm not too worried about that). I want to be able to use pump gas. 93 is easy to get around here so I'm fine with needing that, but is that even possible at 10.1:1 with this cam? Everything seems to come together well with the parts I've picked, but this is worrying me a bit, as there aren't any sets that I can find with forged dish pistons that are higher volume. I think icon sells some, but not in any of the kits I've seen. I know CR is kind of a point of debate, but I'd like to at least know if I'm completely out of the advisable area for pump gas. Thanks.
I run a .030 over 340 iron head roller engine with 10.5:1 on crap 91 octane fuel all day - no issues. You need to tune for what is available.
 
I agree, I'm just over 10.5-1, iron heads on 91 Ca pump pis but you better know what you're doing. With aluminum heads I wouldn't even sweat it.....
 
as nm said that intake closed is at .050 which is for degreeing in the cam not for calculations
worthless for calculations
do as I suggested and look at Howards cam master catalog and match it up with the hughes numbers - Howard will give you the timings - ask themif they are .006 or .008\
nm can do the rest
as I said you can run open chamber heads - but why?
try those compressions in a boat or truck or motorhome or in a street car with stock converter and tall gears and see how much fun it is something where you are putting a load on the motor below the torque peak
"better off to call the camgrinder" Hughes is not a camgrinder
is the second cam better?
Depends on where you want your rpm band to be what rpm at cruz are you happy with
then get your build to match
I must be as good a tuner as Yr- sure of that

key quote
avoid detonation and you are fine.
also what crackedback said
just because an expert can do it does not mean you should do it
 
"better off to call the camgrinder" Hughes is not a camgrinder

is the second cam better?
Depends on where you want your rpm band to be what rpm at cruz are you happy with
then get your build to match
Who grinds Hughes cams?
Also, I want the hp and torque at low rpms. Going to be a street motor. Does the larger can help with that? I assume they recommended that because they thought the smaller one I was looking at would be the restriction at all rpms.
 
You can also have a relief cut made to the chamber to unshroud the intake valve, opening up the chamber a bit more. I have that done on every ede head I use.
 
I would always run the closed chamber Edelbrocks over the open unless you NEED the open chamber heads (like with stock 340 pistons).

Aluminum heads dissipate heat much better than iron, that is why you can run more compression with aluminum heads and not run into detonation. Typically, you can get away with premium pump gas and 10.7:1 (even higher compression depending on cam selection).

Also to note, stroker motors eat up cam duration...meaning, you can run a larger cam and it will "act" like a smaller cam...if that makes sense (max power will be at a lower RPM than advertised).
 
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