Guest shifter51 Posted December 10, 2008 Share Posted December 10, 2008 I was hoping to get some input on this engine i built recently. It is a 383 small block chevy with flat top pistons, 5.7 eagle h beam rods , scat crank, it is overall a pretty heavy rotating assembly. The heads are sportsman 2 heads that have angled milled to 58 cc. The valves have been unshrouded and the chambers have cleaned up but the heads are unported otherwise. The heads have manley severe duty valves and comp cams pacaloy springs with titanium retainers, crane 1.5 roller rockers, stud girdle etc. Cam is a solid roller with 261 intake 270 exhaust duration at .050, lift is .625 on intake and exhaust. lobe center is 106 with a center line of 104. I am using a victor jr. that is port matched to 1205 gasket with a carb shop 750 cfm carb. The probelm is that engine completely falls on it face around 6000 rpm. It doesnt miss or any thing just acts like it ran out cam. Throughout the rest of the rpm range runs like one would expect with cam this size. I was wondering if the heads and or intake is to small for this application. I have had good luck with similar setups but on smaller cube engines (327, 350). Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted December 10, 2008 Share Posted December 10, 2008 From the very limited info, Id say ITS most likely related to EITHER valve springs and the valve train control issues OR the fuel supply pressure or volume, that cams certainly big enought in fact its a bit larger than Id suggest is ideal. If you suspect its the intake restricting flow add an open center 2" spacer under the carb, it will significantly boost the upper rpm flow rates if the plenums too small at minimal cost, but read the plugs, and verify the ignition advance, cam timing, ignition timing,and fuel flow rates, as they are suspect. You might also think about retarding the cam timing about 4 degrees that should move the tq curve about 200rpm high. BTW do you have a way to find the true fuel/air ratio, it should be at about 12.7:1 if its significantly leaner like 14:1 -15:1 or more that hurts power. http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG1409&N=700+115&autoview=sku personally I rarely use the vc jr intakes as Ive found these work noticably better http://store.summitracing.com/partdetail.asp?part=HLY%2D300%2D110&autoview=sku Quote Link to comment Share on other sites More sharing options...
Guest shifter51 Posted December 10, 2008 Share Posted December 10, 2008 Springs are comp cam # 944, 190# @1.950 and 747# @ 1.100. I don,t have a air fuel monitor on the car but the plugs look more to the 12.7:1 side. I have been lead to belive by others that intake is small, just wanting a second opinion thanks for the input. Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted December 10, 2008 Share Posted December 10, 2008 since the test with the 2" open spacer will tell you if the intakes too small and were talking $20 Id do that test. checking the cam install, (degreeing it in retarded 4 degrees ) is also cheap and it may solve your problem if you find the cams current indexing is off Quote Link to comment Share on other sites More sharing options...
HICKL Posted December 10, 2008 Share Posted December 10, 2008 What do you have your ignition timing set at? I had an issue with my balancer moving and thus I missed my timing (way too advanced) and my motor went very flat on top. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted December 10, 2008 Share Posted December 10, 2008 Incorrect valve lash will do the same thing. Aluminum heads you set at .006 tighter than spec when cold. Although you don't have aluminum heads the incorrect lash (too loose) will limit it to about 6500. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.