REPRINT FROM OLD HTT: 10.5 COMPRESSION AND DELPHI BAD IDEA?

[ClassicRider2002]

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DISCLAIMER: THIS IS A REPRINT TOPIC FROM "OLD" HTT

I have saved many great topical discussions as "links" over the years and would hate to see these lost, so I am reprinting this TOPIC here, which may "perhaps" help some.

TOPIC:  10.5 COMPRESSION AND DELPHI BAD IDEA?  03-04-04


From: SeabrookTrickBagger  (Original Message) Sent: 3/4/2004 8:03 PM    Message 1 of 5 in Discussion
I would like to go with the correct compression with my 37g cams.  I asked Andrews for high and low CR with the cam, but they ignore my emails.  My builder states that "everytime I go 10.5 cr or near it with Delphi, I get bit."  He means that high CR and delphi's don't mix.

The branch heads and JE Branch pistons are 10.5 cr on a 95 c.i..   I have a delphi, 2004 on an A engine.  Should I steer away from the 10.5? 

I noticed Hippo's statement which may  be out of context: 
"I rather leave a little on the table then push Delphi's into areas they may not like, it's not like you get a big prize if you win."

Does this mean:  stay away from 10.5 cr with delphi due to intake pulses screwing up the intake/efi.?

STB   

[ClassicRider2002]

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From: blktrain Sent: 3/4/2004 8:15 PM   Message 2 of 5 in Discussion
Seabrook,
I'm running 10:5/1 on a 95" B engine (FXSTBI) and have had zero problems. None! Starts every time fast, no pinging, pulls hard. I did install a set of Yooper cables that L-Bar insisted I get. One of the best best single up-grades I made (thanks coldrider). I am very pleased with this build, and. like most folks looking for more. I just posted basicly the same question for Hippo on the thread you referenced. Good luck.   Bill


From: SeabrookTrickBagger Sent: 3/4/2004 8:36 PM   Message 3 of 5 in Discussion
I don't know if my builder is trying to squeeze every horse out of the engine when he says that high CR and Delphi efi don't mix or what.  It is kinda like if he says don't do it, we don't do it.  He is the expert. But, my job is to question and kinda push him. 10.5 with releases does not bother me since I run more than 1.5 extra quarts of oil and a Jagg cooler to compensate for the extra engine heat/power and the hot Texas weather.  I kinda feel I stepped down on the cams to 37g instead of the Wood 6hg, so I would like to compensate with a bit of extra compression to push the 37g cams with the Branch heads to a near limit of performance.  We will decide on the CR in a few days and order the pistons and bore to 95 etc..  I don't want to screw up the build, but nothing ventured, nothing gained; he who hesitates is lost; [I'm trying to convince myself to go 10.5]. 

Anyone with an opinion is welcome to express it.

STB


From: wideglidebob Sent: 3/4/2004 8:57 PM   Message 4 of 5 in Discussion
Here is what the guys at nightrider emailed me when I asked them about compression ratios....
"...Even the 10:1 compression ratio is going to be marginal in its resistance to detonation. Unless you are willing to ride and keep the RPMs high, either of these engines is going to detonation. Under 2500 RPMs is where the problem will be prevalent.  For the maximum in streetability (no significant worries over detonation and overheating), I prefer to keep compression ratio's at 9.5:1 especially since most HD riders like to lug the engine.

A TC95 with HTCC heads and flat top pistons gives you a 9.4:1 compression. A 103 with flat tops and HTCC heads gives a 9.8:1 compression. Either of these is better for street riding.

With the lower compression, you can use the SE-251 cams which should give you enough torque to pull stumps out of the ground. Second choice SE cam would be the SE-257, but I like short duration, high-lift cams in strong street engines (SE-251)..."


From: HIPPO_ Sent: 3/4/2004 9:50 PM   Message 5 of 5 in Discussion
Your guy is basically correct.
10.5 on a 95 with 37's is going to be a very unhappy bike, to run that CR you need a much later closing cam and then you start pushing the TQ peak higher into the rpm range.

You run much more then 180 psi cranking pressure on a Delphi and you will see a lot of knock retard. The few I have done at that CR were done with a 625 cam and for people that I positively knew what they primarily were looking for and how they ride. I would take a 9.8 CR bike with a S&S 570 any day and I will beat them most of the time in all around situations despite the lower dyno numbers.  They are real nice with the 37's at 9.6 and the mapping is manageable.    

[ClassicRider2002]

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This THREAD went on for a while longer but I always find HIPPO's responses the most interesting of all....concise and to the point.....


Anything added beyond this point is new information.

Regards,

"Classic"

[ClassicRider2002]

PROVIDING A "LINK" TO THE THREAD BELOW TO PROVIDE ANOTHER OPINION, SIMPLY CLICK, VIEW, & READ:

ANYONE RUNNING S&S 570s AT 10.5:1? 11-19-2006