quiet riot
07-14-2005, 10:34 PM
So I got to dyno my small block this week after rebuilding from some torched pistons. Pretty happy with the results as I got 520 hp at 5400 rpm with a real flat curve holding over 500 hp from 5100-5900, will match the jet pump pretty good.
The same combo with a different cam and big tube headers got over 600 hp at 6200 rpms but I don't wanna spend the extra dough for jacketed headers and run a smaller impeller to get those r's so I'll stick with mine. Plus with the n2o I can get all the hp this little jetboat wants.
Learnings,
The proform base plate and main body was able to get within 7 hp of peak when compared to a $1k race carb of the same size (apprx 800 cfm.) I'm pretty happy with that for the $250 bones I put into this carb.
The good carb however did hold rock solid on the egt's and my carb would vary a little at different rpm ranges. They told me it was due to the better metering blocks of the spendy carb.
100 LL avgas and 110 sunoco made no diff in egt's or hp for this 12.5:1 comp alum headed engine. We didn't try anything less as I can get avgas for the same price as super unleaded around here.
This motor apparrently likes more timing because 38 deg yielded 70 degree lower egt's than 34 deg timing. Kind of wierd but they said they had seen it before. Have any of you seen this before?
With the current jetting I had on the primary side (74's) and the 34 deg timing I had (thought I was being safe keeping timing on the lower side) we came to the conclusion that this was how I burnt the pistons last time. With the proform carb there was a rise in egt's at 3k-36k rpms, along with the slightly lean carb and the engine combo that didn't like less timing that all added up to too high egt's at cruise which is were I burnt the pistons at while cruising after I put the proform setup on.
We were able to get the egt's a little more consistant with some air bleed changes but still no where near as flat as the good carb. The final carb jets we stayed with were 80/84's on my proform main body 4150 holley carb. Almost where I started with (78's and 84's) when I put the proform on the previous engine but I was getting a rich looking condition when reading the plugs so I backed it down to 74's on the primary.
I was using autolite 3922's on the prev engine and we used ngk 7's on this dyno session and they looked good when all was said and done. I think I'll throw an autolite in one cylinder and see what it looks like now that I know the engine is tuned good.
Anyways it was cool for my first dyno session to see what all the little tweaks yielded and after 10 pulls I think they were ready to get rid of me but it was fun.
here (http://www2.***boat.com/forums/showthread.php?t=75223&highlight=caused) is the previous disscussion of my burnt pistions, looks like the pictures are gone though. We didn't run the n2o on the dyno cause of time and they said it was a little hard to control on there waterbrake dyno. I went with some custom JE pistions this time and now that the engine is tuned hopefully I'll keep it together better. The n2o system all checked out good with my pressure switch for the fuel and all, and they were pretty sure that it happenned when running n/a after seeing it this time on the dyno.
jd
The same combo with a different cam and big tube headers got over 600 hp at 6200 rpms but I don't wanna spend the extra dough for jacketed headers and run a smaller impeller to get those r's so I'll stick with mine. Plus with the n2o I can get all the hp this little jetboat wants.
Learnings,
The proform base plate and main body was able to get within 7 hp of peak when compared to a $1k race carb of the same size (apprx 800 cfm.) I'm pretty happy with that for the $250 bones I put into this carb.
The good carb however did hold rock solid on the egt's and my carb would vary a little at different rpm ranges. They told me it was due to the better metering blocks of the spendy carb.
100 LL avgas and 110 sunoco made no diff in egt's or hp for this 12.5:1 comp alum headed engine. We didn't try anything less as I can get avgas for the same price as super unleaded around here.
This motor apparrently likes more timing because 38 deg yielded 70 degree lower egt's than 34 deg timing. Kind of wierd but they said they had seen it before. Have any of you seen this before?
With the current jetting I had on the primary side (74's) and the 34 deg timing I had (thought I was being safe keeping timing on the lower side) we came to the conclusion that this was how I burnt the pistons last time. With the proform carb there was a rise in egt's at 3k-36k rpms, along with the slightly lean carb and the engine combo that didn't like less timing that all added up to too high egt's at cruise which is were I burnt the pistons at while cruising after I put the proform setup on.
We were able to get the egt's a little more consistant with some air bleed changes but still no where near as flat as the good carb. The final carb jets we stayed with were 80/84's on my proform main body 4150 holley carb. Almost where I started with (78's and 84's) when I put the proform on the previous engine but I was getting a rich looking condition when reading the plugs so I backed it down to 74's on the primary.
I was using autolite 3922's on the prev engine and we used ngk 7's on this dyno session and they looked good when all was said and done. I think I'll throw an autolite in one cylinder and see what it looks like now that I know the engine is tuned good.
Anyways it was cool for my first dyno session to see what all the little tweaks yielded and after 10 pulls I think they were ready to get rid of me but it was fun.
here (http://www2.***boat.com/forums/showthread.php?t=75223&highlight=caused) is the previous disscussion of my burnt pistions, looks like the pictures are gone though. We didn't run the n2o on the dyno cause of time and they said it was a little hard to control on there waterbrake dyno. I went with some custom JE pistions this time and now that the engine is tuned hopefully I'll keep it together better. The n2o system all checked out good with my pressure switch for the fuel and all, and they were pretty sure that it happenned when running n/a after seeing it this time on the dyno.
jd