I have a Seagull Decathlon 75-91. I was thinking about using a Saito 100 4 stroke and my fellow club members said I should switch to gas? I am confused as to what size gas engine to purchase. Am looking at an RCGF 15cc? Wingspan on Decathlon is 70.9 inches and weight is 7.5-8.4 lbs. Any suggestions?

I had that plane with an O.S. 91 four stroker in it, I would definetly go with a 20cc , The DLE20 would be a Nice Fit!!

Theres a newer EVO 15cc gasser out now, at Horizon. I just received mine and hope to power it up tomorrow. In a side by side size comparison with a OS.91fs (4-stroke), the mounts should be the same. Mines going in a TF corsair.
Edwin

The DLE20 - IMO, is a very compact little powerhouse that produces more power than most 1.20 size 4 stroke nitro's out there (if not all), and at it's cost point, is a very hard option to pass by.
Then there are the running costs - or lack of them when compared to nitro.

Definitely...

They may be on par with a two stroke 1.20 in terms of power.

We are running the DLE 20cc engines on Giant Big Stik planes used as trainers, swinging 17x6 props at well over 8300 RPM static.

The small engine has no trouble hauling around our heavily re-inforced trainers that weight in at 17lbs.

Somehow - once I finally get around to finishing it - I think my 10-11lb 65" P51 will not be lacking power with the DLE20 I have shoehorned into the cowl ..... though I'm going with the 'benchmark' Xoar 16x8.
That said, I'm aware of guys with that motor in the same size World Models P51 who are getting over 100mph in the top end (not that you want to fly that fast for long)

I really appreciate the insight offered on my engine question. I believe that I will probably go with the DLE20 for my Decathlon! Thanks much!!!

I have the larger Seagull decathlon with a DLE30 on it. I fly at 1/4 throttle and it runs great. But after talking to Valley View RC i would buy there VVRC20. I think it would be a perfect fit for a decath your size.

I have the seagull super decathlon 120 with a DLE 20 cc in it and I can tell you , it's a freakin rocket with unlimited vert. I take off at a really high angle of attack and climb out at only 1/4 throttle, so I think it may rip your firewall apart on the 90 size. But hey, if that's what your looking for, just sayin.post some vids if you do.