S4 SE engine mods

[nickspeed]

I run a restored S4 SE in completley original spec, and therefore on Strombergs. I would like to increase the power from the standard 125bhp to around 150/160, but retain the Strombergs, so that outwardly the engine appears unmodified. All thoughts and suggestions appreciated. Thanks, Nick

[Sadbrewer]

With all due respect Nick, I wouldn't want to restore a 50yr old car to anything other than original specification ( unless safety or practicality was an issue)?...and then modify it..the S4 goes like stink without pimping it up like on some of these TV programmes we see.
Apologies... I sincerely don't wish to appear rude but that is the kind of mod I would consider for a relatively modern, fun.. but otherwise worthless car. Just bask in it's originality and heritage and let her grow old with grace.

[rgh0]

Not much has been done or documented on modification of the Twincam Stromberg head for increased performance. Personally all my work has been on Weber heads

However a few general comments.

1. It going to be very hard to get over 150Hp in a Stromberg head 1600 cc road engine as your in the realm of "its not been done before"

2. Even in a Weber head over 150HP in a 1600 cc twincam takes a fair bit of detailed work to get right in a road engine. You may be able to get somewhere around 140 hp with a Stromberg

3. if i was attempting to maximise whats possible out of a Stromberg head for a road car i would do the following
a. Put in a short duration high lift cam and adjustable sprockets. The Newman Lot/280/443 looks like a good
candidate.
b. Put on a good exhuast system
c. Ensure everything matches up perfectly in the carbs and exhaust
d. Dyno the car to get the best ignition advance curve and Stromberg settings. Finding someone these days
who know how to tune Strombergs and has the parts will be a challenge.
e. Fitting larger inlet valves and doing some head porting may help but the effort and cost would be high for
uncertain returns
f. You could probably push the compression ratio to around 10.7 if you wanted to but that involves either
maching the head or a major bottom end rebuild with custom pistons

4. If you really want to spend time and money then investigate development of "Scatter Cams" for the head. I am not aware of anyone who has done it but its how the Mini and other A series racers get more out of their siamesed port heads

cheers
Rohan

[USA64]

A link to an explanation of "scatter cam".
https://mechanics.stackexchange.com/que ... i-want-one

[nickspeed]

Hi Rohan. Very useful, thank you. Will look at the cams and sprockets you suggest, and then match the carbs/head/exhaust as recommended. Will search for somebody with Stromberg experience and parts to set up. With thanks again. Nick

[The Veg]

My Plus 2 has Strombergs and a previous owner had the head modified to Dave Bean 'Stage II' specs which I understand is similar to 'big valve' specs but experts please correct me if that's not right. I've never driven a dead-stock Plus 2 or any other Twinc with Strombergs, so is it more powerful? I have no idea, let alone by how much if it is- but it does run nicely and is fun to drive.

[rgh0]

Accoding to the Dave Bean catalogue the stage 2 tune was the highest tune they recommended for a Stromberg and it gave 130 to 135 hp but they dont say if this is achieved on Stromberg or Weber or both.

it consisted of

10.3 compression ratio
The sprint cam or their 112 cam which is a low lift long duration (0.370 inch 300 degree) cam and there are better cams now but this cam could be used with standard valve gear.
A limited amount of porting in the area of the where the inlet turns the corner into the valve seat
Matching of inlet and outlet ports and carnbs and exhaust

They described it as "This is an economical hop-up job" I dont think the mods would give 130 to 135 hp with a sprint cam but would probably give it with the 112 cam at the cost of some low end torque.

cheers
Rohan

[The Veg]

I dont think the mods would give 130 to 135 hp with a sprint cam but would probably give it with the 112 cam at the cost of some low end torque.

Sounds about right- I have the 112 and it's definitely a little low on torque under about 2500-3000 but strong above. Not really an issue as long as I give it some beans from a standstill, but if I ever wanted to switch to a better cam for good fun street use without too much fuss for installation, what would you recommend?

[rgh0]

Something like the QED 420 Cam or equivalent with the Q55 springs with adjustable sprockets can fit normally with no fuss using all the other standard components for road use. This will give you above 140 hp at 6500 rpm and better torque than the 112 cams. There are better cams and springs but they require a bit more detailed work to set up and normally new longer valves and thinner steel followers are required.

cheers
Rohan

[nickspeed]

Thanks again Rohan. I was looking through the QED cams last night, and thought the 420 to be the one to go for. I had a Caterham HPC in the past and used QED cams and an Alpha Weber management system in that. Tractable, but with a little more at the top end. I run the standard ignition system in the Elan. Worth going to something like a 123 electronic distributor?

[Evante]

If you are in the US, the best person I know for Stromberg parts is Joe Curto, 718-762-7878, www.joecurto.com.

[nickspeed]

Thank you Jay, but sorry, I'm in Gloucestershire, UK

[rgh0]

The upside of 123 distributors is the lack of points and the ability to easily adjust the advance curve. The downside is the durability of the electronics packed into the distributor body exposed to all that heat and vibration.

cheers
Rohan

[DavidP]

Is there a reliability issue with the 123 distributors?

[rgh0]

I dont know of specific issues with the 123 distributor brand, its just a general concern about packing power electronics into a small distributor body with limited cooling and a lot of heat and vibration.

Group S historic racing regulations in Australia allow electronic triggered distributors provided it all fits into the distributor body and has no additonal functions. People have had problems with various brands under racing conditions so i have stuck with points on my Elan.

On my S1 Esprit and Plus 2 i have used Lumenition with the optical trigger and external control electronics box for 30 plus years without problems.

cheers
Rohan