why is it recomended against using two turbos that are similar in size? like a stock HX-35 and a 21cm upgraded H1C to a 60mm compressor wheel?

 

Because you need the larger one to be able to supply a MUCH GREATER volume of unheated air to the smaller one for it to be effective.

 

so with two similar turbos you will gain no advantage?

 

Its due to that the fact that you are compressing air into small volumes that the secondary is smaller than the primary. It would work, but wouldn't be very fun and rapidly run out of capacity and any benifit of twins would be offset by an extremely narrow operating window. You would though have very fast spool-ups. Happy building

 

yea i think im gonna build them. ill keep everyone posted and see how it turns out.... whats the worst that could happen... i dont like them? i got the H1C just laying around anyway.
i was thinking they would spool very quick and if i set the HX at a good wastegate point i could just run off the bigger H1C at top end. witha smarty/adrenaline stack, cam, and some small injectors(mach 1's maybe 1.6's) i would have a lowend monster... and if it doesnt work ill build some bigger twins. my goal would also be trying to get 25MPG on just fuel and i think this will help. call me krazy if you must but i dont have much use for a hot rod truck

 

my friend is running the exact same set up on his first gen.... spools very fast but around 2300rpm starts getting real hot and even with the waste gate blocked only makes about 38-40psi. but with very mild fuel it would be great fun on the streets.

 

what kind of boost does he see at low speeds, like 1500RPM? does he have surging problems? 24V's run a lil bit cooler but what are his pump mods? do you have a user name i can PM him by?

 

Just put the smaller turbo on the exhaust (secondary turbo) and the larger turbo afterwards. You could also increase the size of the wastegate and drill both sides of the turbine volute. I would put a larger turbo like a S366 on the bottom, for the amount of effort you doing on building twins, it would cool off the egt's more than using two small turbos. The smaller turbine housing will cause an increase in drive pressure and increase in egt's