The Lotus Cars Community banner

1 - 3 of 3 Posts

·
Registered
Joined
·
153 Posts
Discussion Starter #1 (Edited)
Just to clarify this discussion it's intended for the 4cyl Turbo Esprit application.

I'm aware that there are 2 intake valves sizes avalaible for valve intake upgrades. The 36.83mm which is slightly bigger than the ones used in the S4s and the sport 300, and the 38mm used in the NA Sunbeam Lotus which will required bigger valve seats installed as well.

So far I've been told to go with a 104 intake cam (with 104 cam gear) and 36.8 intake valves, and leave the stock exhaust 107 cam (with 104cam gear), and stock exhaust valves alone. But I'm seriously considering to increase the exhaust valves for a better power upgrade. Perhaps to somewhere around ~34.82mm custome made Inconel exhaust valves if I get the 38mm installed in the intake side. Just to keep this ratio for max HP turbo performance of .89% intake to exhaust size.

I've done plenty of intake and exhaust head ports, matching and porting, and yes I'm aware that the valve springs will need to be upgrade.

So I'm just curious to see if anyone has gone with the 38mm intakes yet? Maybe the reason some people hasn't gone with these is because 38mm valve intake is an over kill for the 31mm exhaust valve... The answer it's all within the ratio!;)

JG
 

·
Cal H
Joined
·
982 Posts
I went with the 36.83mm on the intakes and the 107 cam with 104 pulley because that is were I want to play in the robust street in the mid to slightly upper rpm range. The main reason was I wanted the larger valves cut into the seats for a standard shim range without it getting too thin rather than having standard valves cut in deeper into the existing seats. Consulting with Tim if I were bouncing off the rev limiter a lot then go with the 104 cam and sacrifice the low end performance. We had many heads up car against car drives using larger valves and one with standard valves and the standard valves are quicker at lower speeds but once above hwy speeds and elevated rpm's the advantage shifts to the engine with the larger valves and the car will catch up on the top end to the car with smaller valves. I would say the difference would be even more exaggerated with the 38mm. I have been told the exhaust is just there and the stock exhaust valves are fine as people throw on all kinds of larger turbos and boost controllers. The difference in valves is much more important in a NA car vs a boosted car that rams A/F mix down the throat. The person you should be talking to is Gary Kemp. Be aware that he tends to prefer larger orders that catches his attention as I think it is a hassle with export paper work and the like for small parts order.
 

·
Registered
Joined
·
153 Posts
Discussion Starter #3
Thank you Cal for sharing your experience and point of view. Yes I have to agree that bigger valves will serve better on a high RPM (operation) engine. I might just go with the 36.83mm intake valves and make some custom 32 or ~32.5mm inconel exhaust valves... To not sacrifice much of neither the Top or the Bottom.

JG
 
1 - 3 of 3 Posts
Top