Hot Rod Forum banner

1.70 to 1.80 rockers

416 15
I have a BBC with 1.70 rockers? Jesel Sportsman. How much reliability am I going to sacrifice going to 1.80 ratio. I am running a hyd roller with I/E 242/249 @ .635//647

The reason for change is I increased displacement from 496 to 557 and believe it needs more cam to compensate for the increase in displacement. Due to wet boat exhaust I can't really replace cam with more duration as it would likely increase overlap and engine screwing exhaust reversion, currently at only 13 deg.
1 - 6 of 6 Posts

·
Registered
Joined
·
129 Posts
Discussion Starter · #7 ·
According to the flow bench

the baseline for the Dart iron heads shows: the intake flow increases with lift thru .700 and then drops off -4cfm @ .750 to [email protected]
the exhaust flow increases with lift thru .900

with slight port clean up: the intake flow increases about 12 %/0.1 step over raw thru .700 and then drops off -8cfm and is flat thru .900
the exhaust flow increases about 8-10%/0.1 step over raw thru .900

More port development to go after bronze guides installed - if they ever arrive!!!

My valvetrain is Lunati 74855 BH springs good for 0.700 180# seated, 408#/in. so I should be good. TS retainers, Manley extreme and marine exhaust not so light. I did what I could.
 

·
Registered
Joined
·
129 Posts
Discussion Starter · #9 ·
That doesn't really tell me much.
You're currently at .647, and talking about upping that .038.
The vague info you have, speaks of .700-.900 and is irrelevant. I'd rather see hard numbers.
If you have the .038 worth of room, it's probably fine. Check it anyway......
Might wanna check with the spring company about it and ask some questions about expected spring surge.
Yes that is what the rocker change would do. Im only considering it as the rockers are new and Jesel has been good about exchanging parts n\c in the past so why not. I will attempt to attach my spreadsheet with the initial and mild cleanup numbers, I think it shows promise.
 

Attachments

·
Registered
Joined
·
129 Posts
Discussion Starter · #14 ·
I'm dense...gurgle gurgle like it's sinking?

My heads are raw Dart Iron eagles for a Gen7 8.1L. not real common, there are only 3-4 head options for this marine/truck engine. Most 8.1s are not hot rodded, their pistons suck. Mine is an 8.8 stroker with non-oem everything. On my heads the intakes are at 378ish now with minimal re-work . The head porter I have is willing to help me with iron heads (lots won't) and confident of easily over 400 with a decent profiled valve job so I am down with that. If 1.8's help and low cost I will go with it as well.

My cam is a Raylar max effort unit made for wet exhaust inboards, in their 8.8 stroker kit, used on non-oem piston 496's, tried and true. They have other cams for stock blocks (trucks, motorhomes, etc) They have some for forced induction but are limited to dry exhaust where overlap is no issue.
 

·
Registered
Joined
·
129 Posts
Discussion Starter · #15 ·
I went ahead with the exchange of rockers to the 1.8 ratio.

I am looking to run mechanical roller lifters as its a toy not a DD

Currently my springs are about 180 seated/ 470 open

As an example

The spring specs for some solid rollers 7500rpm
Seat Pressure (Lbs):150-275
Open Pressure (Lbs):400-700

others (racier type) are 8000rpm
Seat Pressure (Lbs):250-350
Open Pressure (Lbs):600-850


As it could come down to price/avail....
Is it just the rpm rating that ups the spring pressure requirements. am I good with either since I am on the lower pressure end? or do the racier type need the higher pressure to run properly even if I remain well under the 7500rpm level.

Ideally I would like needless roller bearings with pressure oiled pins for endurance reasons.
 
1 - 6 of 6 Posts
Top