Cam, webber, ratio and subframe mounting advice needed!

Message

itie jim · #1 Post by **itie jim** » Tue Apr 06, 2004 10:13 am

Hi, 
 
following my "new sprint" post a month or so ago I've finally managed to pick it up and put a few miles on it. 
 
Basically it goes very well indeed- it's running 45's, a stage three Triumphtune head, a piper cam and other goodies. I've checked ou the piper cam profile and it would seem to be a profile they no longer use, 28-64 64-28, nothing too wild. 45's are running with a 33mm choke. 
 
Anyway I reckon that I could get quite a lot more out of it by changing the cam and opening the chokes up a bit. I see Piper offer a 285 duration cam- does anyone have experience of using this or any other fast road profile? Also if so what are the webbers set up to. My car's running really nicely, it's just that I think I could get more!! I don't want to make the car undrivable but would just like to maximise it's potential! 
 
Perhaps Graham would have some ideas? 
 
Also the car has had poly bushes fitted some years ago, however with stiff suspension and wide yokohama tyres you can still really feel the subframe moving around, especially over crests or going hard into dips- does anyone have experience of using very hard poly bushes of even bolting the frame up solidly? 
 
Finally can anyone clarify the intermediate and final drive ratios used on the sprint? Surfing the net I find two possibilities of final drive- some say 3.45 other 3.64- my car's a 1980 with O/D. As for intermediate ratios my search revealsthe following: 
1st- 2.99 
2nd- 2.1 
3rd- 1.39 
4th- 1 
 
Seems a bit odd though as these ratios are wider than those used in the 1850. Any ideas or clarification would be most appreciated! Thanks<img src=http://www.ezboard.com/intl/aenglish/im ... s/roll.gif ALT=":rollin"> James.

SMIFTER · #2 Post by **SMIFTER** » Tue Apr 06, 2004 1:20 pm

The STR91/TT10106 profile is probably the next step up. Not a great profile for road use though as the power doesnt really come in below 3000rpm and it wont idle quite so nicely. Its not undrivable, just at low revs its no quicker than a standard sprint running SU's. 
 
Increasing the choke size will increase outright power but low speed torque will suffer as a result, you'll also need it to be rejetted if you change the chokes or the cam. Not really a DIY job. 
 
As for the subframe most of the racecars bolt it direct to the chassis - something I'm planning to do but probably not a good idea on the road unless you only drive on perfect roads as you could end up damaging the subframe or chassis. I havent got them but I'd imagine poly bushes are a good halfway house. 
 
The best diff ratio is probably 4:1 (standard 3.45) although they dont come cheap! The std gearbox ratios are not ideal for road use either as there is a big ratio gap between 2nd and 3rd - OK for a standard car but a high lift cam makes it a pain.

<a href="http://www.smifter1971.pwp.blueyonder.c ... >Smifter's Dolomite Sprint Website</a>

itie jim · #3 Post by **itie jim** » Tue Apr 06, 2004 3:43 pm

Thanks Graham, 
 
Do you use that cam? If so what chokes and jetting do you use? Also any idea if the intermediate ratios I quoted are correct? 
 
James.

SMIFTER · #4 Post by **SMIFTER** » Tue Apr 06, 2004 4:49 pm

Yes my car has the STR91 cam fitted was last running on 45 dellorto's with 36mm chokes. 
 
I could go to the trouble of taking the jets out and making a note of them but I cant be arsed! 
 
If I were you I'd save my pennies and get it rejetted on a rolling road by a pro. 
 
I cant remember what the gear ratios are - I'll check and let you know 
 
Graeme 

<a href="http://www.smifter1971.pwp.blueyonder.c ... >Smifter's Dolomite Sprint Website</a>

Carsreunited · #5 Post by **Carsreunited** » Tue Apr 06, 2004 7:55 pm

My car came with 45's and what I was told (also backed up by receipts) was a tuned head. Gas flowed, ported, STR139cam etc. 
 
Turns out that I had a standard head with a very mild cam. 
 
Obviously the 45's existed cos I could see them but it looks like the previous owner but one had removed the decent head before selling it on. I didn't care because it had a LSD which actually turned out to be a good un but being a complete muppet it could have been standard for all I knew at the time! 
 
Don't know your cars history but worth visually checking which I'm sure you will do at cam change time. 
 
Are you looking for power at the top end of the rev range or slightly more power across a broader rev range? Might also be worth visiting a rolling road just to see what you are getting at present but try and find one that would be prepared to do the rejetting at a later date. At least you should get a solid comparison of where it will have improved with the new cam and jetting. 
 
Scott

itie jim · #6 Post by **itie jim** » Wed Apr 07, 2004 9:05 am

Point taken! I've got receipts for all the bits, the last owner had the car for 8 years and bought it off his best mate who got all the work done. I did make a point of examining to see if it looked like the top end had been touched recently- spannered head nuts etc- but no sign of any movement. It's just fingers crossed really. The guy built the engine up from a new old stock lump he managed to get his hands on in the late 80's. He says it's not been touched since being built up and old MOTs show it to have done 30,000 miles. 
 
As for the cam, I dont want something totally intractable but I'd just like to get the most out of my (supposed) stage 3 head! Graham's suggestion seems like a good one. 
 
The car came with a mountain of bits (with receipts!)- competition radiator, high performance oil pump, height adjustable spax, stiff/short springs, rear roll cage, quick rack, poly bushes, straight through s/s exhaust, etc. 
 
One other question- can you buy 4 branch manifolds for sprints? I've more experience with spitfires/GT6s and I know with them if you want performance the 1st thing to do is junk the cast manifold- is that not the case with sprints? 
 
Cheers, James.<img src=http://www.ezboard.com/intl/aenglish/im ... /happy.gif ALT=":D">

MaddMart · #7 Post by **MaddMart** » Wed Apr 07, 2004 1:37 pm

Unfortunately there is not a lot of room on a Sprint for 4 branch manifolds. It can be done, but involves bending pipes everywhich way, removing heaters and maybe bits of the turret. Unless you're into a serious track car not worth the bother for the few bhp you would gain.

<a href="http://www.aqpd91.dsl.pipex.com/" target="top">Mad Mart's Website</a>

Carsreunited · #8 Post by **Carsreunited** » Wed Apr 07, 2004 10:15 pm

I've heard that a proper tubular manifold can release alot more power than a few bhp on the Sprint engine. The figure I was told was around 15bhp. But, as Mart says, the manifolds are to say the least custom built and look like Medusas head. I have a picture of Ken Clarkes manifold which I downloaded from this site somewhere. I can email it to you if you want james to give you some idea of the complexity. 
 
In the absence of that, have a look at the Group1 tuning manual that is on Sprintparts website. It shows you the sizes you can grind out the standard manifold outlets to. I think they have used this modification on their cars. I played around with a drill and some grinding stones on mine as well. 
 
<a href="http://www.sprintparts.triumphowners.co ... nID=480042" target="top">www.sprintparts.triumphowners.com/techt ...  
 
I should clarify that the 15bhp is on an already tuned engine with big carbs etc putting out around 200bhp. You wouldn't see nowhere near that on a standard setup. 
 
Scott

Edited by: <A HREF=http://pub52.ezboard.com/bthetriumphdol ... eunited</A> at: 9/4/04 5:58 pm

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