rougeherald Posted Tuesday at 20:35 Report Share Posted Tuesday at 20:35 Is there any information on the difference in performance of twin SUs vs a single stromberg carb, both on 1300 herald engine. The twin SUs are off mk4 spitfire. we are just wondering what the gain might be, fuel economy would be down I guess but would you see much gain in BHP? thanks in advance Aaron Link to comment Share on other sites More sharing options...
AndyTV8 Posted Tuesday at 23:00 Report Share Posted Tuesday at 23:00 i think switching to twin SU's (with the appropriate needles) and an extractor exhaust used to be expected to gain 10-12bhp in the SAH booklets - I'm sure someone with a better memory may be along shortly. .....Andy 1 Link to comment Share on other sites More sharing options...
sulzerman Posted Wednesday at 06:01 Report Share Posted Wednesday at 06:01 I had both on my herald. Acceleration was far better with the SU's and in theory economy should be about the same. Hope this helps. 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted Wednesday at 06:49 Report Share Posted Wednesday at 06:49 i would think you need to use a spitty cam to really gain from twin SU there were a lot of tests done years back (probably in the Kipping years ) and the outcome on a std 13/60 engine the big single strom was best all round Pete 1 Link to comment Share on other sites More sharing options...
Colin Lindsay Posted Wednesday at 07:58 Report Share Posted Wednesday at 07:58 8 hours ago, AndyTV8 said: i think switching to twin SU's (with the appropriate needles) and an extractor exhaust used to be expected to gain 10-12bhp in the SAH booklets - I'm sure someone with a better memory may be along shortly. .....Andy My SAH catalogue doesn't mention twin carbs, (probably an earlier version?) but it does have the Solex conversion with extractor manifold which gave a stated 11 bhp boost. I've actually just realised I have one of the shaped pancake filters for it, must try to dig it out. This is using their combined four branch inlet / exhaust manifold but no mention of any camshaft upgrade. It's been posted many times that you need the combination of camshaft and carbs to get the best out of twin carbs; I had an Alexander manifold on one of mine, plus I tried twin SUs on a Herald twin-carb manifold with no other alteration, but any increase in performance was negligible due to the camshaft being standard Herald. I reckon the best improvement I had on any basic 1200 was the single Stromberg conversion using an adaptor for the carb on the 1200 manifold. 1 Link to comment Share on other sites More sharing options...
rougeherald Posted Wednesday at 12:10 Author Report Share Posted Wednesday at 12:10 Thanks all I knew you would have pearls of wisdom on the topic, not sure camshaft change is on the cards so probably best sticking with the Stromberg instead, which after some tunning seems to be working well. Interesting you mention the alexander manifold @Colin Lindsay I know someone who has one, not in use. Thanks again Aaron Link to comment Share on other sites More sharing options...
Colin Lindsay Posted Wednesday at 12:32 Report Share Posted Wednesday at 12:32 Mine ran on twin Stromberg 125s, never really set up properly so it ran very rich. The original and not very sporty 1147 camshaft was probably the issue. It may have run better on the 1300 but I didn't have that manifold. Link to comment Share on other sites More sharing options...
ahebron Posted 18 hours ago Report Share Posted 18 hours ago I recall (and it might be wrong) hearing that twin carbs are best at wide open throttle, other than that the single is best. Link to comment Share on other sites More sharing options...
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