Its another LT1 383. Was a 355 used in road racing, 365rwhp with a custom cam, stock heads. Im turning it back to a street car, needed a new crank so what the hell going with a 383. Thought it would be simple, didnt plan on making any other changes but you know how that goes. Anyway 30 over factory block and deck height. Scat forged crank 3.75 and SRP forged pistons with 16c dish. Factory heads assuming 54cc. Cam is comp cams XFI 230/236. Using a .027/4.04 gasket im getting 10.77 static and 9.1 dynamic (assuming im calculating the IVC correctly). Im starting to feel like I didnt go big enough with the cam, but I already bought all this stuff. I have read a LOT of threads on this so forgive me but it sounds like a dynamic of 9 is about the limit for using pump 93. If so I suppose this is the best I can do with this combo unless I get a different cam? In that case any more power would have to be worth abandoning a brand new $400 camshaft. If she could tolerate a little more DCR then I suppose I could shave the deck a little. Thoughts? Also I dont know if the 1.6RR im using would change the DCR or IVC calculation and therefore the CR?

 

And the heads are still stock, not ported?

 

Stock other than the PAC springs. Interesting in specs at summit.com it says all the specs on the cam are based on the factory rocker ratio (1.5). But at the end of all the specs it says "Xtreme camshafts are engineered for 1.6 ratio rocker arms and beehive valve springs, which provide a dramatic increase in torque and horsepower."

 

The cam specs I saw on Comp Cams website show gross lift 0.576” intake / 0.570” exhaust. Dividing by the lobe lift they are basing that on 1.6X rockers. My thought on using that cam with totally stock head ports is not a good match. Stock LT1 heads generally peak flow a bit above 0.400” lift. Some tests show the flow stalls by 0.500” lift, and will start to drop above 0.500” lift due to turbulence(?).

https://web.archive.org/web/20081102...c/headflow.htm

In effect, putting all that lift on a stock/unported head can actually hurt performance. And, remember the 383ci wants almost 10% more flow than the stock 350ci at any given RPM. Seems like the stock heads would benefit greatly from at least a mild port job - e.g. LE1. Otherwise seems like the stock heads are going to struggle with that cam and the added displacement.

http://elliottsportworks.com/

I'm no engine builder, but just seems like an odd combination.

Might be worth asking Lloyd Elliott for a mild port, plus a custom cam to achieve the correct lift for the ported heads, and DCR for the 93-octane fuel.

 

send your heads to Lloyd Op. The XFI cam "may" be OK (read not optimal) so discuss with Lloyd. XFI series of cams IS based on 1:6 RR for lift #

I run the smaller, 466, XFI in my 383. More for emission compliance here in CA

 

Thanks for the advice. He said the combo should be fine on pump 93 with the LE1 port job. And since ive already got good hardware its only $750. Anyone know a good way to ship heads?

 

Nevermind my builder gave me a box just for shipping heads. Also they disassembled them so now the port job only costs $500. Of course Ill have to pay my guys to reassemble but thats not bad!