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Discussion Starter #1
Looking for some advise. Getting ready to rebuild the top-end of my dads motor. 88-inch twin cam, going to 95-inch. Already has Headquarters HQ-0034 cams, SE air cleaner, rhinehart true duals. Plan is to keep cost low and reuse everything listed.
I picked up a set of 2008 heads also for the rebuild. My question is what to do with the heads, for maximum torque output. I was thinking bigger valves and light porting. But my dad thinks he will get better lowend performance with light porting and leaving the stock valves in the heads. Can someone share their knowledge with me, as to go bigger valves or leave stock? Goal is for more torque. Thanks in advance for input
 

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The HQ-34 is a low end torque cam, (a very good one by the way) so if it were mine I would do what most shops refer to as a street port with stock valves and good multi-angle valve job. Set the comp. at 9.7 to 1.
 
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By upgrading to the newer heads the HQ cam you currently have will be way less than optimal due in part to the better intake to exhaust ratio of the late model heads.
You will no longer need 14 degrees more exhaust duration to make up for the crappy intake port on the early heads and the late model heads are configured to accept more lift.

You can leave the stock valves in the heads and have a competent shop do a clean up and valve job,done right well worth the effort especially if the heads are off the bike.

Installing just a new intake valve without removing the guides will not increase airflow enough to warrant doing the job,either do the minimal clean up porting or go full on and have them fully ported,new guides/valves the works.
 
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we dont remove the guides on our street port heads (we do replace them on stage II or III headwork),with opening up the bowl for 1.900 intakes and conturing,they flow 155+ @ 10",
 
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If airflow numbers don't translate into power production,what would be the point of the extra work ?
 
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??? how you figuring air flow dosnt translate into more power???more air flow = more power
 
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still not following ya pal,if your saying stock heads flow mid 140`s your wrong (more like 125-130)plus a motor flowing 155 WILL make alot more power than heads flowing 140ish,after over 25 years of having my dyno (sold it when i moved to floida)ive seen power increases from 5 cfm increases
 
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Nobody is saying stock heads flow [email protected]"

Let me make this VERY simple

2 bikes same engine same cams....one with 140 cfm heads and one with 155 cfm heads....if they both make the same power OR the bike with 140 cfm heads makes more power...what is the point of the 155 cfm heads ?
 

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Incorrect.
If a larger intake and exhaust valve are used, and the seat throat/bowl area attended to..........correctly, leaving the guides in place, the cfm WILL jump from .100", .200"------.600" lift, as will the power when used in an application where the additional airflow will benefit.
Been there, done that waaaaaaaaaaay too many times to be told any different............... by anyone.
BTW we are on our flow bench EVERY DAY HERE.........so what could possibly know.......:D:D:D:D:D
Totally redundant argument.
Scott, out.
 
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Nobody is saying stock heads flow [email protected]"

Let me make this VERY simple

2 bikes same engine same cams....one with 140 cfm heads and one with 155 cfm heads....if they both make the same power OR the bike with 140 cfm heads makes more power...what is the point of the 155 cfm heads ?
im thinking you need to go back to "performance motors 101",if you have 2 idenical motors,one with heads flowing 140 cfm,one with 155 cfm heads,the one with the 155 cfm heads is going to make more power.period.been porting heads,building and dynoing HD performance & racing motors WAY before it was cool,so please dont tell me im wrong,cause im not
 

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Not to change the subject, but this is way more entertaining than reading the posts about puppy cages and cup holders for the bikes.
 

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Discussion Starter #14
So based on what i'm understanding. Leaving the stock size valves and having some mild porting done is what would be best for my application?
 

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So based on what i'm understanding. Leaving the stock size valves and having some mild porting done is what would be best for my application?
If retaining the parts you already have, that will work well for your application. Which I think was the original question!
 
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So the actual CFM requirements of an engine,more specifically a combination of parts according to both of you is not important ?

More is better reguardless ,bigger is better correct ?

So again ....if an engine or an engine combo makes the same or more horsepower and torque with less CFM .....does port design or port efficiency play into this at all ?
 
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unless the parts are miss-matched or the tune is off,a motor with heads flowing less cfm wont make more hp than a motor with heads flowing more cfm.(certainly not 2 idenical motors besides the heads),like i said,go back to "performance engine building 101",no bigger isnt always better and matching CFM requirments are important to a build.but ANY HD build can EASILY handle 140-155 CFM heads(we do have a discussion with our customer before ANY porting is done though,mild up to our stage III headwork).you really just dont get it and i hope your not REALLY designing & building motors for anyone.to answer the O.P. original question (i did PM him)if he`s staying at 88",i would stick with stock size valves (1.850 / 1.575) and do a SERDI radiused valve job & mild blending.if going 95",ide install 1.900 intakes
 

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Where's Max? ;-)

You guys rule. I'm in the more air in = more power out camp. Big fan of Physics.

As long as velocity doesn't drop...

If air flow stalls then you're flowing too much. Like the old oval port vs square port heads on Vettes and SS 396's. You can kill the low end chasing the high end horsepower.
 
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That would require someone to have equiptment capable of measuring a head at greater than 10" and find out where the head will actually stall neither Scott nor Kirby can do that.

While more air in and out is better in most cases,it comes down to the combination more than anything.
 
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very true,with the use of volocity probes,weather doing touring heads or heads for a very big inch WFO build,its important get the highest CFM while still retaining the highest volocity at the RPM the motor is expected to make power in
 
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