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MG MGA - MGA 1500 power, is it sufficient?

Hey guys,

Currently in the process of restoring an MGA 1500. Since 1998 we drive an MGA 1600, which in terms of performance is okay but not spectacular.

My question is, whether there is a noticable difference between the 1500 and 1600. If not I would prefer originality over performance.

Just wondering what your experiences are. I've driven various 1600 Mark 2s, which I found to be driving much smoother than Mark1s. But of course they have a different stroke as well.

And finally, would it be possible to rebore a 1489 to 1588?

Regards, Koen
Struijk Koen

Koen

I started with a 1500, and when I redid the engine, had it bored out to 1588 spec. Worked a treat till a con rod failed and the engine was scrap, but that was nothing to do with the overbore. The 1588 was a major performance improvement over the 1500.

Having failed to find another 1600 (or 1500) engine to replace the blown up unit, I fitted a 1622 engine. It again was a serious improvement over the 1600 - more power, smoother.

I have to add also that for all engines, a lightened flywheel is a major improvement. If you go too far though, the clutch gets a bit sharp (described on my car by one driver as being "giftig" (poisonous)!) The B clutch I have fitted is lighter to operate and stronger than the standard A one.

I would also recommend a Stage 2 head and a fast street cam. I have a 15/1600 Oselli Stage2 head for sale if you would like one. (It produces 13.5 bar compression on a 1622 engine with the flat top pistons, so I can't use it). Leadfree, stage 2, big valves, about 200km on it after Oselli's ministrations). I run a 1326 casting MGB head now, which gives about 9.5:1, which is on the limit for a SC.

Of course if you want REAL performance and originality, then the Judson is a great way to go. Then the Twin Cam boys can't keep up!
dominic clancy

Koen, I guess it is what you are looking for. I have a generally stock 1500. I really don't find it lacking. I must confess that I have never been a speed demon. What with Ownnign VW's Vegas, Pintos Spitfires instead of Mustangs and Camaros during my formative years. I have no problems running fully loaded at 75MPH down the highways. No matter what engine you go with, you will have problems beating the average low-priced import.

Chuck
Chuck Schaefer

My 1500 does fine. It wraps better than any of the MGB's I have owned and it is snapper than the 1980 MGB I had, even with a SU conversion (and that was a huge inprovement). You can go overbore and get 1600 displacement which is 100 cc's or about 6 ci's or 1.3 ci/cylinder more which in reality is pretty insignificant. A little head work would be more beneficial. Good luck with your project.
Bill Haglan

Make sure that you have everything balanced when rebuilding the engine if you want the car to be fun to drive. An unbalanced engine may not rev easily and may feel like it doesn't want to rev past 3500 rpm, but when balanced will be smooth to redline. I think that it is really worth doing.
Matt Dabney
M. H. Dabney

Dominic - I just bought a 1326 B head for my 1600. I haven't done the math yet to see what my actual comp. ratio would be before any head modifications, but how did you achieve 9.5:1 without so much milling of the head that you suffered valve-interference problems? I ask becuse I understand that the volume of the combustion chamber of the 1326 head is larger than the stock 1600 head, so any gains in power thru better breathing would be offset by a lower comp. ratio unless a lot of milling is done to the head, or differnt pistons are used.
thanks in advance.

Bryan
B Phillips

The early B 18 head works well on the 1500/1600 engines. The larger valves and better porting are very beneficial, in spite of lower compression.

It works even better if you get the compression ratio right. The original 15 head has 38cc combustion chamber volume. The 18 head has 43cc chamber volume. You can reduce the 43 to 38 by milling .047" from the bottom surface. This will not cause valve interference if you have not made any other changes.

Be careful not to mill off too much, as the head may have been previuously milled. Original head thickness is 3.187". Finished thickness needs to be 3.140" to bring the 18 head down to 38cc. If you mill farther for higher compression, or if you increase cam lift or rocker arm ratio, then you need to add eyeprows to the block to have sufficient running clearance for the valves.
Barney Gaylord

1600 has dished pistons, 1622 has flat pistons, which increases compression ratio because the head chamber is no longer augmented by the piston dish. With this compression I have to use 98 octane fuel to avoid predetonation.

I am going to install a copper gasket again to reduce the compression ratio to 8.5.
dominic clancy

1622 also uses the 16 head which has 43cc chamber similar to the 18 head. Flat top pistons in the 1622 only make 8.9 C/R as standard. If you can find low compression pistons for the 1622 they will have a very shallow dish to bring it down to 8.3 C/R.

To reduce C/R of the 1622 from 8.9 to 8.3 with a head gasket, you need to add about .035". Original gasket is abour .020" compressed, so you would be looking for about .055" finished thickness for the new head gasket.

If you have a 15 head (not shaved) on a 1622 engine, it would have about 9.75 C/R.

The 16 head was unique to the MGA 1622 engine (and a very few 1622 derivitives like Elva and TVR). Other 1622 engine applications commonly use the 15 head with deep dish pistons for a lower C/R.
Barney Gaylord

Using the large chamber head on a 1500 or 1588 will lose you significant power unless you also use flat top pistons. As Barney says, the larger valves are a definite plus, so it is worthwhile going for new pistons. You will end up with about 88 BHP without any other mods.
Bill Spohn

Koen,

Tell us what mods you already have?

I won't go back to flat-top pistons again. You need a very small dish to maintain the squish pattern. which can be machined back into the flat-tops though.

I have 35cc head... Barney is right on going for an 1800 head, but follow his instructions on fly cutting the block or the inlet valves will hit the bore as the valve guide centres are different. Late model MGB have bigger again valves... then your into the gas flow valves which I have and three angles cut into the seats.

Dominic, the amount of copper gaskets I've blown won't convince me to use them again. Dispite the composite ones being 1-2cc more.

I ran a 1500 for a while until I blew it up due to the head lifting and pumping all the water out on the way back from brands. ops. When you saw 801 at Silverstone in 2005 it still have a 1500.

If you chasing more power these mods are the way to go in my opinion and you can use them on any engine.

I order of power Gain and cost.

1) Extractors, covered in exhaust wrap. 3 into 1 does not go... hence the standard is rubbish.
2) 45 DCOE Weber don't get a 40 or 42 go straight for a 45 and down jet it... don't play with SU's they don't have a pump jet.
3) change the pushrods and cam followers to the 18v type... 500 extra RPM at the top end.
4) start playing with the head...
5) hot cams and vernier timing gear
6) roller rockers..... these are magic
7) distributor... not much gain here, optronic ignition not magnetic...as our distributors are 40 years old now.

then your into the full race stuff

All that stuff you can transplant onto an 1800 if you get to the limit of your 1500 later....
To be honest my 1500 was great and prob only had 10-15 BHP less than the 1800 I now have.

I never swapped the cam on my 1500 or did the head, it was just all bolt on stuff as I knew I was not going to keep that engine. I think it had about 15BHP more.... not allot, but it did rev much better

Throw some racing fuel (Avgas) in and give it a good long run to burn off the carbon on the pistons every now and then...

hope this helps.... email us if you want to know more.

One day I'll stick a page together on all this stuff.

Hope this helps..
Mark.
Mark Hester

Hey guys,

Thanks for your extensive comments.

At the moment I got a standard 1500 block. When I bought the car it had a 5-main MG B engine installed. Along with the car I got BP15GB 7510. The car being chassisnumber 65412 (from no. 61504 starter position changed to high) I started looking for a later engine, which I found in Norway (from Roar Nygard) 15GDUH 5065. (only 7715 GD engines were built by the way)In terms of performance there were no changes, only the blanking plate for the mechanical fuel pump was removed, as said the starter position changed and the propeller shaft changed.

See: http://www.mgcars.org.uk/mgarh/gd

So basically a standard 1500. I think I'll bore it to 1588 for a start. I am not sure about the head since I drove 2 or 3 cars with 18 heads which I found to run rough and less smooth than my 1600. However, this could be due to their tuning. What are your experiences?

I like the car to be as original as possible in terms of carbs, ignition and so on.

Thanks again for your comments!
Koen


Struijk Koen

Hey Mark -
We've been talking about building a 1800 with a cross flow head with a Weber. (cheater motor) Do you have a good resource for an original cross flow head?

thanks. Scott
MGA #41 (the Pile)

http://www.flickr.com/photos/43844271@N00/213273117/
skip

Koen,

OK I can see where you coming from now.
You want it to look stock from the outside, but more go on the inside.
From looking at that block you going to have to bore that allot to get rid of the rust so looks like you will end up with 1588 anyway, but your not going to know until they start.
If you want to stick with 1 1/2 carbs you can get them flowed on the insides, but who could still do that these days I have no idea.

Skip,
Nice racer...If your talking Derington heads then they turn up on eBay from time to time, but that's about it and the chances of getting one that has not been skimmed to death is slim.
If you talking Pierce MSX Cross flow Cylinder Head.

http://www.flowspeed.com/rates.htm#mgb-race

http://www.piercemanifolds.com/cylinderheads.htm

I've been toying with that idea too, but think now I might build a 5 bearing twin cam engine as I now have two. I think about 160-175 BHP could be possible.

Cheers
Mark.

Mark Hester

Never hurts to ask! I would kill for 160 hp. They would make us run in the big bore class for sure! Rumor has it some of the push rod guys from back east that run the Prather motors are getting close to 160hp.
skip (aka Scott)

This thread was discussed between 05/08/2006 and 13/08/2006

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